Implant fixation device

Abstract

An implant fixation device for an implant in a bone of a patient comprising at least one unit cell, each unit cell comprising: a top member; a base member longitudinally spaced apart from the top member about a longitudinal axis; at least one connection member connected to and extending between the top member and the base member, each connection member including a reentrant geometry such that the connection member includes a curved or angled configuration that extends inwardly towards the longitudinal axis from each of the top member and base member, the reentrant geometry changing lateral direction relative to the longitudinal axis at a reentrant apex; and at least one fixation arm which extends laterally outwardly from the connection member relative to the longitudinal axis, each fixation arm having a distal end spaced away from the connection member, each fixation arm includes at least one bracing member that extends from the fixation arm towards a bracing portion of the connection member, wherein the implant fixation device is configured to be moveable between: a compact configuration in which the top member and base member are longitudinally spaced apart a first distance which configures the connection member to locate the distal end of each fixation arm in a first lateral position relative to the longitudinal axis; and an expanded configuration in which the top member and base member are longitudinally spaced apart a second distance comprising a greater spaced apart distance to the first distance relative to the longitudinal axis, which configures the connection member to locate the distal end of each fixation arm in a second lateral position which is laterally further away from the longitudinal axis relative to the first lateral position.

Description

[0001] IMPLANT FIXATION DEVICE

[0002] PRIORITY CROSS-REFERENCE

[0003]

[0001] The present application claims priority from Australian Provisional Patent Application No. 2024902836 filed on 9 September 2024, the contents of which should be understood to be incorporated into this specification by this reference.

[0004] TECHNICAL FIELD

[0005]

[0002] An implant fixation device is disclosed that is configured for fixing (or alternatively affixing) an implant, such as an orthopaedic implant, within a bone. The implant fixation device is applicable for fixing an orthopaedic implant within a bone of a patient. However, it is to be appreciated that the disclosure should not limited to that application and may be used to fix (or affix) a number of types and configurations of implant devices in the bone of a patient, such as bone screws, plates, rods, cylinders, scaffolds (e.g. bone scaffolds), and / or other similar implant fixation arrangements and / or applications.

[0006] BACKGROUND

[0007]

[0003] The following discussion of the background is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[0008]

[0004] Bone implants may be used to treat orthopaedic trauma and disease around the body. Applications include (but are not limited to) bone fracture fixation plates, tendon repair anchors, and total joint replacement implants. Implant fixation is one important factor in the success of these procedures, with the loosening of an implant providing a primary reason for failure of joint replacement implants. In addition, where an implant loosens within a bone, bone recovery may not occur, or may result in slow bone recovery from the lack of compression stress at the interface between the implant and surrounding bone tissue.

[0005] Conventional bone implants typically rely on press-fit or screw fixation. Screws fixation may provide high levels of implant stability, with high pull-out loads (around 1000 N) and may be optimized for different bone densities through appropriate screw selection. However, because screws must be rotated about their own axis to achieve fixation, these can be difficult to use for non- axisymmetric / multiple fixation features. Such designs typically use press-fit fixation. Press-fit fixations enable non-axisymmetric / multiple fixation features and are frequently used for arthroplasty components. However, press-fit fixations provide lower initial fixation strength than screws, being typically being as low as 50 to 150 N of pull-out force in some applications. For example, the range of the peak pull-out force for the cementless tibial component of the knee implants can be between 170 to 380 N.

[0009]

[0006] Additionally, conventional screw and press fit bone implants may have a higher elastic modulus than the surrounding bone due to the implant comprising a solid material, typically metal. This mismatch of elastic modulus between the implant, the fixing arrangement and the bone can lead to a stress shielding effect, which then causes bone resorption, peri-prosthetic loosening and lateral bone fractures over time as a result.

[0010]

[0007] There may also be possible secondary bone tissue damaging due to high implant push-in force. For example, for cementless tibial component of the knee implants the push-in force can be from 1250 to 1450 N due to the need to form a tight fit, and the use of tools such as hammers to force the implant into the tight fitting bone cavity.

[0011]

[0008] It would therefore be desirable to provide a new and / or improved bone implant fixation device that may be configured to provide improved fixation strength compared to press-fit fixations.

[0012] SUMMARY

[0013]

[0009] A new and / or improved bone implant fixation device and related bone implant fixation method is disclosed. In embodiments, this bone implant fixation device and related method may provide an advantageous implant expanded configuration, that may be utilised to speed up the bone healing process.

[0014]

[0010] A first aspect provides an implant fixation device for an implant in a bone of a patient, the implant fixation device comprising at least one unit cell, each unit cell comprising: a top member; a base member longitudinally spaced apart from the top member about a longitudinal axis; at least one connection member connected to and extending between the top member and the base member, each connection member including a reentrant geometry such that the connection member includes a curved or angled configuration that extends inwardly towards the longitudinal axis from each of the top member and base member, the reentrant geometry changing lateral direction relative to the longitudinal axis at a reentrant apex; and at least one fixation arm which extends laterally outwardly from the connection member relative to the longitudinal axis, each fixation arm having a distal end spaced away from the connection member, each fixation arm includes at least one bracing member that extends from the fixation arm towards a bracing portion of the connection member, wherein the implant fixation device is configured to be moveable between: a compact configuration in which the top member and base member are longitudinally spaced apart a first distance which configures the connection member to locate the distal end of each fixation arm in a first lateral position relative to the longitudinal axis; and an expanded configuration in which the top member and base member are longitudinally spaced apart a second distance comprising a greater spaced apart distance to the first distance relative to the longitudinal axis, which configures the connection member to locate the distal end of each fixation arm in a second lateral position which is laterally further away from the longitudinal axis relative to the first lateral position..

[0015]

[0011] This first aspect provides a unit cell with reentrant geometry which also provides a negative Poisson ratio geometry (in other words is an auxetic structure) which can be utilised to position the distal ends of the fixation arms in two different positions, when the device is configured in the compact configuration or in the expanded configuration. In this sense, the negative Poisson's ratio geometric design may be aimed at addressing and / or ameliorating implant pulling by causing the connection members of the implant to expand (i.e. laterally move away from the longitudinal axis) when moving from the compact configuration to the expanded configuration.

[0016]

[0012] Movement between the compact and expanded configuration may be designed to utilise the distal end of the fixation arm as an anchoring member which can engage, and preferably fix the implant fixation device in place in a position within a surrounding cavity or enclosure in which the device is located, for example within a bone cavity of a bone of a patient.

[0017]

[0013] The compact configuration may be designed to recess the distal end of the fixation arm within the device to allow for easy insertion (with minimal push-in force) into the fixation location, for example in a bone cavity. In this regard, the distal end of the fixation arm is the point or points that may be designed where the implant device engages or otherwise is fixed into surrounding bone tissue. In the compact configuration, the position of the distal end is located level with or inwards of the outer ends of the top and base members, and in some embodiments may be parallel to the two ends of the top and base members of the unit cell. The position of the distal end may also be located further inwardly (i.e. move laterally towards the longitudinal axis) if necessary, through movement (for example compression or other movement) of the top member and base member towards each other relative to the longitudinal axis. This compact configuration may therefore advantageously reduce the lateral width of the implant fixation device. This reduced width may be utilised by sizing a bone cavity to match or be slightly larger than that width. Thus, when the implant fixation device is inserted into that cavity, little to no push in force (i.e. near-zero push-in force) is required to insert / implant the implant fixation device therein. This may assist in minimising damage resulting from inserting the implant fixation device into such a bone cavity when in use (see below).

[0014] In the expanded configuration, the distal end of at least one fixation arm may be positioned outwards of the outer ends of the top member and base member relative to the longitudinal axis (and outside of the unit cell). In this position, the distal end may be configured to abut, engage or otherwise fix or anchor into an adjoining wall of the surrounding cavity or enclosure, for example of a patient’s bone, in which the device is located. In embodiments, in the expanded configuration, the distal end of each fixation arm is configured to abut, preferably anchor the implant fixation device into an surface or wall of bone cavity into which the implant fixation device is located. This may provide immediate device fixation into the inserted location, for example a cavity in a bone (i.e. a bone cavity). This may also provide a high fixation force when inserted into the insertion location (as above). In addition, the implant device may also compress bone tissue to improve bone cell growth due to the initial pressure. In other words, this may provide implant-assisted osseointegration due to initial pressure provided by this fixation force from the distal ends of the fixation arm or arms of the device.

[0018]

[0015] It should be appreciated that the distal end of one or each fixation arm may have any suitable configuration. In embodiments, that distal end may comprise a single engagement point or engagement surface that is configured to engage or otherwise be fixed into surrounding bone tissue. In other embodiments, that distal end may include two or more engagement points or engagement surfaces configured to engage or otherwise be fixed into surrounding bone tissue. That surface may have a smooth configuration, or may be textured, contoured or otherwise shaped to engage or otherwise be fixed into surrounding bone tissue.

[0019]

[0016] The implant fixation device may be configured to be movable into a further configuration, for example a stretched configuration. In these embodiments, the connection members may further expand beyond the expanded configuration (i.e. laterally move away from the longitudinal axis) if the top member and base member are moved longitudinally further apart, and thus the implant fixation device may move from the expanded configuration to the stretched configuration. This may occur for example during a pulling process on the implant fixation device, particularly when insitu within a bone cavity. In this stretched configuration, the distal end of each fixation arm is located in or close to the second lateral position, the top member and base member are further spaced apart about the longitudinal axis relative to the second distance, and at least one portion of the bracing member is located in engagement with the bracing portion of the connection member thereby providing at least a longitudinal brace between the fixation arm and connection member. Movement between the expanded configuration to the stretched configuration (and beyond if the top member and the base member are moved longitudinally further apart) may be designed to utilise the distal end of the fixation arm as an anchoring member which can engage, and preferably fix the implant fixation device in place in a position within a surrounding cavity or enclosure in which the device is located. Thus, in this stretched configuration, the distal end of each fixation arm is again configured to abut, preferably anchor the implant fixation device into an surface or wall of bone cavity into which the implant fixation device is located.

[0020]

[0017] Advantageously, in the stretched configuration at least one portion of the bracing member may be located in engagement with the bracing portion of the connection member thereby providing at least a longitudinal brace between the fixation arm and connection member. In this configuration, the bracing member may form a force transferring brace between the fixation arm and connection member, forming a force bearing structure therebetween. In embodiments, the bracing member may form one side of a triangle between the fixation arm and connection member, thereby forming a load bearing structure which fixes the distal end of the fixation arm in or close to the second lateral position. This may advantageously lock the distal end into position in an adjoining wall of the surrounding cavity or enclosure in which the device is located, fixing the device into position therein. The bracing arrangement in this stretched configuration may result in a high fixation force and associated high pull-out force for the device when insitu, for example within a bone cavity. The device therefore may provide an advantageous negative Poisson's ratio geometric design that can function to address implant pulling by causing the implant to expand into this stretched configuration and beyond (see below) during the pulling process.

[0018] It should be appreciated that if the top member and base member are moved longitudinally further apart relative to the stretched configuration, the at least one connection member may be configured to laterally move further away from the longitudinal axis causing the distal end of at least one fixation arm to try to be positioned further outwards of the outer ends of the top and base members relative to the longitudinal axis (and outside of the unit cell). Where the distal end is engaged with, into or otherwise fixes into an adjoining wall of the surrounding cavity or enclosure in which the device is located, this may introduce a further fixing force between that distal end and the adjoining wall.

[0021]

[0019] This first aspect finds particular application in implant fixation devices for fixing an implant to a bone of a patient. Those implants may include bone screws, fixation screws (e.g. ligament fixation screws), plates, rods, cylinders, scaffolds (e.g. bone scaffolds), orthopaedic implants and other similar implant configurations. For example, this first aspect may be used as a fixation device for a tibial component of a knee implant; a femoral component of a hip implant; a humerus component of an elbow implant; a humerus component and / or scapula component of a shoulder implant; an ulna component of an elbow implant; a radial head component of an elbow implant; a tibia component of an ankle implant, or a dental implant fixture or screw. In other examples, the first aspect can be used as an implant fixation device for a bone fixation scaffold or a fixation screw, e.g. a ligament fixation screw. However, it should be appreciated that the methods and design are applicable to, a large variety of implant types and configurations.

[0022]

[0020] In some embodiments, movement between the compact configuration and the expanded configuration may comprise any suitable movement where the implant fixation device moves, recovers, expands or the like from the compact configuration to the expanded configuration. In embodiments, that movement may be facilitated by pre-stressing, compressing or the like the implant fixation device when in the expanded configuration (the normal unstressed configuration of the device) to move into the compact configuration, and the device having a resilient and / or elastic expansion from that compact / stressed configuration (when in the compact configuration) back to the expanded configuration. In this sense, the implant fixation device may undergo elastic deformation (resilient deformation) when moving from the expanded configuration to the compact configuration. Conversely, the device may undergo elastic recovery when moving from the compact configuration to the expanded configuration. In other words, the implant fixation device may then undergo resilient expansion when moving between the compact configuration to the expanded configuration. Similarly, the implant fixation device may be elastically stressed when moving from the expanded configuration to the compact configuration. Conversely, the elastic stress may be released when the implant fixation device moves from the compact configuration to the expanded configuration. In embodiments, the device therefore may provide an elastically pre-stressed negative Poisson's ratio structure that provides minimal push-in force by shrinking the size of the implant and high fixation force by expanding once fitted on-site.

[0023]

[0021] Similarly, for applicable embodiments, when and where possible, movement from the stretched configuration back to expanded configuration may comprise resilient recovery of the device. In embodiments, that movement may be facilitated by the implant fixation device being stressed or stretched when moved from the expanded configuration (the normal unstressed configuration of the device) into the stretched configuration, and the device having a resilient and / or elastic contraction from that stretched configuration back to the expanded configuration. In this sense, the implant fixation device may undergo elastic deformation (resilient deformation) when moving from the expanded configuration to the stretched configuration. Conversely, where possible (for example where the deformation force is released or abated) the device may undergo elastic recovery when moving from the stretched configuration to the expanded configuration. In other words, the implant fixation device may then undergo resilient contraction when moving between the stretched configuration to the expanded configuration. Similarly, the implant fixation device may be elastically stressed when moving from the expanded configuration to the stretched configuration. Conversely, the elastic stress may be released when the implant fixation device moves from the stretched configuration to the expanded configuration.

[0022] It should be appreciated that elastic recovery of the device may relate to the resilience of the material. This resilience may ensure that that the device resiliently recovers into the normal configuration, after being moved into the compact configuration (when allowed to expand). Similarly, this resilience may ensure that that the device resiliently recovers into the normal configuration, after being moved into the stretched configuration. In many embodiments, that normal configuration corresponds with the expanded configuration. In this sense, the implant fixation device may be formed from a resilient material (see below). Where the expanded configuration is the natural or normal position for the device, the device can be moved into the compact configuration, typically by moving the top member and the base member together along the longitudinal axis, resiliently deforming the connection member or members. This may elastically pre-stress the connection members. When the compression or other holding force is released, the implant fixation device resiliently expands back to the expanded configuration. In this movement, the position of the distal end of the fixation arm or arms may laterally move relative to the longitudinal axis as described above.

[0024]

[0023] In other embodiments, the implant fixation device may comprise a shape memory material, having a remembered shape comprising the expanded configuration. Shape memory materials (SMPs) are a class of smart materials capable of responding to external stimuli with a shape change. This response encompasses shape fixity (deformation followed by fixation into a temporary shape), and shape recovery (a return to the original, remembered, permanent shape). It should be appreciated that shape-memory materials (SMM)s are materials that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. For the present invention, the predeformed ("remembered") shape may comprise the expanded configuration of the implant fixation device, and the deformed configuration (in which it is deformed when cold) may comprise the compact configuration. Accordingly, in embodiments, the implant fixation device may move from the compact configuration to the expanded configuration by changing the temperature of the implant fixation device, for example by raising the temperature of the implant fixation device.

[0024] In some embodiments, the shape memory material may comprise a thermoresponsive shape memory material, that has a shape that is modulated by temperature, for example the application of heat. In these embodiments, there is a thermal transition temperature (Ttrans) which separates the two different states - i.e. shape fixity (deformation followed by fixation into a temporary shape), and shape recovery (a return to the original, remembered, permanent shape). Thus, a temporary shape formed by deformation at T > Ttrans can be fixed by cooling to T < Ttrans and can also be subsequently recovered by heating to T > Ttrans again. In embodiments, the shape fixity (deformation followed by fixation into a temporary shape) is set at a lower temperature T2 than the shape recovery (a return to the original, remembered, permanent shape) state T1 , where T2 < T1. For example, T2 may be a freezing temperature, for example from -10 to 5 °C, preferably from -10 to 0 °C, and T2 may be around body temperature, for example from 35 to 39 °C, preferably 36 to 38 °C, more preferably from 36 to 37 °C. However, it should be appreciated that other temperature ranges are possible.

[0025]

[0025] In embodiments, the implant fixation device may be configured with a shape memory material that is biased to expand from the compact configuration to the expanded configuration when at or above a phase transformation temperature. That phase transformational temperature is preferably is less than or at about human body temperature, for example, the phase transformation temperature may be less than about 36°C. By providing a transformation temperature less than or at about human body temperature, the implantable object may be advantageously biased to expand to the expanded configuration when implanted within a living human being.

[0026]

[0026] The phase transformation temperature will be material dependent. For example, for shape memory alloys, the phase transformation temperature may correspond to a finish temperature, Af, for transformation from martensite to austenite. The transformation temperature being the finish temperature from martensite to austenite may advantageously enable the implantable object to exhibit superelastic and / or shape memory effects at or above the transformation temperature. In other forms, for example for shape memory polymers, the phase transformation temperature may correspond with a thermal transition temperature (Ttrans) associated with SMP switching segments may either be a glass transition temperature (Tg) or a melting transition temperature (Tm).

[0027]

[0027] The implant fixation device may be superelastic when above the transformation temperature. A superelastic implantable object may advantageously be compressed to the compact configuration and resiliently biased to expand to the expanded configuration without excessive damage to the implantable object. In some embodiments, the implant fixation device may be formed from a shape memory alloy. Forming the implantable object from shape memory alloy advantageously enables the implantable object to exhibit superelastic and / or shape memory effects when above the transformation temperature.

[0028]

[0028] A variety of shape memory alloys or materials can be used for these embodiments of the implant fixation device. The implant fixation device can be made from shape memory materials. In embodiments, the shape memory material (SMM) comprises a shape memory alloy, or a shape memory polymer. SMM include shape memory polymers or shape memory alloys. Commonly used shape memory alloys include nickel-titanium (NiTi - also known as Nitinol), copper-aluminium-nickel, copper-based SMAs, such as Cu-Zn-AI and Cu-AI-Ni, or iron based SMAs such as Fe-Mn-Si. However, it should be appreciated that SMAs can also be created by alloying zinc, copper, gold and iron. Other shape memory materials include shape memory polymers include PEEK based polymers or those listed in J Mater Chem B. 2021 June 03; 9(21 ): 4287-4297, the contents of which should be considered to be incorporated into this specification by this reference. In addition, other shape memory materials include:

[0029] • Polyurethane-Based Shape Memory Polymers;

[0030] • Polycaprolactone (PCL) Shape Memory Polymers;

[0031] • Zirconia;

[0032] • Poly(N-isopropylacrylamide) (PNIPAAm) Hydrogel; and

[0033] • Poly(ethylene glycol) (PEG)-Based Hydrogels.

[0029] One of the important advantages of embodiments of this implant fixation configuration is that the fixation arm may be braced when a pulling force is applied to the top member or base member, for example when stresses are applied by a connected implant. This pulling force may be resisted through movement, deformation and the like of the fixation arm being resisted through force transfer from that fixation arm through the bracing member, through to the bracing portion of the connection member. Engagement of the bracing member with the connection member braces the fixation arm against movement and deformation. This may be configured to allow the distal end of each fixation arm to stay in position, for example in place fixed into the wall of the surrounding bone cavity. In this sense, the distal end of each fixation arm may stay located at the second lateral position, or where it may have marginally or slightly moved, it will still be close or proximate to that second lateral position. In embodiments, the intent may be to keep the distal end of each fixation arm in place to function to fix the implant fixation device in place within the implanted location, for example in a bone cavity. Thus in embodiments, the distal end of each fixation arm may be located in or close to the second lateral position in the stretched configuration through engagement with a wall or other surface of a bone cavity.

[0034]

[0030] In some embodiments, the at least one bracing member may be connected or otherwise fixed to the bracing portion of the connection member. In these embodiments, the bracing member may be permanently connected with the bracing portion of the connection member thereby providing at least a longitudinal brace between the fixation arm and connection member in the compact and expanded configuration, in addition to the stretched configuration (in applicable embodiments). That connection may comprise a permanent connection for example being affixed, fused or integrally formed together. However, it should be appreciated that the connection may be designed to be releasably connected, such that the bracing member may be released from being connected to the bracing portion of the connection member where or when desired. In some embodiments, the possible elastic nature of the material may be used to allow the bracing member to flex during movement between the compact, expanded and stretched configurations. Again, when in the stretched configuration, the bracing member may be configured to form a force transferring brace between the fixation arm and connection member, forming a force bearing structure therebetween. In embodiments, the bracing member may form one side of a triangle between the fixation arm and connection member, thereby forming a load bearing structure which fixes the distal end of the fixation arm in or close to the second lateral position. This may advantageously lock the distal end into position in an adjoining wall of the surrounding cavity or enclosure in which the device is located, fixing the device into position therein.

[0035]

[0031] Any suitable portion of the bracing member may engage with the bracing portion of the connection member to form a brace between the fixation arm and the connection member, for example when in the stretched configuration. For example, the bracing member may comprise a curved or hooped member, and a portion of the curved or hooped body may contact the bracing portion of the connection member. In other embodiments, the bracing member may include a contact member having a surface that is complementary or similar in configuration to the bracing portion of the connection member. That contact member may engage with the bracing portion of the connection member to form said brace between the fixation arm and the connection member. In embodiments, a distal end of the bracing member may engage with the bracing portion of the connection member in the stretched configuration to form said brace between the fixation arm and the connection member. It should be appreciated that this distal end of the bracing member may comprise any suitable form. In embodiments, the distal end may comprise a further elongate member, a shaped body, for example a spherical end piece or plate, or a suitable configured surface. In other embodiments, that distal end may comprise an end member, thus forming an angled member. For example, each bracing member may comprise an L-shaped member. However, other it should be appreciated that other configurations may also be used, for example L, b, o, d, T, Y or J shaped members.

[0036]

[0032] That bracing member may have any suitable configuration. For example, in embodiments each bracing member that extends at an acute angle longitudinally away from the fixation arm towards the bracing portion of the connection member to provide a longitudinal and lateral brace between the fixation arm and connection member. The angle can be selected to suit the geometric design of the connection member. In some embodiments, the acute angle may be from 10 to 89 degrees, such as from 10 to 80 degrees, 10 to 60 degrees, 10 to 50 degrees, 10 to 30 degrees, 20 to 80 degrees, 20 to 60 degrees, 20 to 50 degrees, 20 to 45 degrees, 30 to 80 degrees, 30 to 60 degrees, 30 to 45 degrees, 45 to 80 degrees, 45 to 60 degrees. That member may have any suitable configuration. In embodiments, each bracing member may comprise an elongate member which extends at that acute angle longitudinally away from the fixation arm in a lateral direction towards the longitudinal axis. In embodiments, each bracing member may extend from or proximate the distal end of said fixation arm.

[0037]

[0033] Each bracing member may be configured to engage with the bracing portion of the connection member to limit relative longitudinal movement between the top member and base member towards each other when the implant fixation device is moved into the compact configuration. In this regard, the bracing member may be configured to be spaced apart from the bracing portion of the connection member in the expanded configuration. Similarly, the bracing member may be configured engage with the bracing portion of the connection member in the compact configuration. The spacing between each bracing member and the related bracing portion of the connection member in the expanded configuration may then be selected to provide a limited longitudinal movement between the between the top member and base member towards each other when the implant fixation device is moved into the compact configuration from that expanded configuration. That spacing or gap may be preferably configured to comprise a small longitudinal distance, such that the top member only moves a short distance towards the base member when moving between the expanded configuration and compact configuration. For example, that spacing may be typically less than 1 mm, preferably less than 0.5 mm. In some embodiments, the bracing member may be configured such that the spacing or gap between a distal end of the bracing member and said portion of the connection member matches the movement between the expansion and compact configurations which facilitates a full elastic deformation of the reentrant unit cell. Thus, when moving from the expanded configuration to the compact configuration (which may be a compression deformation process as described above), the distal end of the bracing member may come into contact with the lower section of the reentrant unit cell. The gap between the distal end of the bracing member and the reentrant unit cell may be sufficient to facilitate a full elastic deformation of the reentrant unit cell.

[0038]

[0034] In some embodiments, the spacing between each bracing member and the related bracing portion of the connection member in the expanded configuration may close to, or equal to zero. In these embodiments, the distal end of the bracing member may be touching or otherwise engaged with the related bracing portion of the connection member in the expanded configuration. As noted above, in some embodiments the bracing member and the related bracing portion may be connected together, for example affixed, releasably connected or integrally formed together. In this way, the fixation arm may be connected directly to the base member (via the connection between the bracing member and the related bracing portion of the connection member) while still maintaining the locking mechanism. In these embodiments, the bracing member may be permanently connected with the bracing portion of the connection member thereby providing at least a longitudinal brace between the fixation arm and connection member in the compact and expanded configuration, for example, in addition to the stretched configuration.

[0039]

[0035] The bracing portion of the connection member may comprise any suitable section of the connection member which a portion of the bearing member may engage to transfer load from the fixation arm through to the respective top member and / or base member. In embodiments, that bracing portion may comprise a section of the connection member that is closer to the respective top member and / or base member than the reentrant apex. The bracing portion may therefore be advantageously located close to the respective top member and / or base member to assist with force transfer thereto, and thus enhance the bracing function of the bracing member engaging with the connection member. In embodiments, the bracing portion of the connection member may comprise a section of the connection member proximate or closely connected to the respective top member or base member.

[0036] Operation of the implant fixation device may be assisted by configuring the length of the fixation arm or arms to position the distal end thereof within the lateral lengths of the top member and base member. For example, in embodiments, in the compact configuration, the distal end of each fixation arm may be configured to not extend laterally past the ends of each of the top member and base member, and in the expanded configuration at least one fixation arm is configured to extend laterally past the ends of each of the top member and base member. The length of each fixation arm may be configured at any desired length to meet those requirements. In some examples, the perpendicular length of each fixation arm may be equal to or greater than half the length of the maximum width of the top member and the base member.

[0040]

[0037] In some embodiments, at least one fixation arm may extend substantially laterally from the respective connection member, preferably in a perpendicular or in a substantially perpendicular orientation to the longitudinal axis. However, it should be appreciated that the fixation arm may be configured at any suitable angle relative to the longitudinal axis. For example, in some embodiments, the fixation arm or arms may be angled downwardly towards the base member. In some embodiments, the fixation arm or arms may be angled downwardly towards the base member at an angle from greater than 0 to 30 degrees, preferably from 1 to 20 degrees, more preferably from 2 to 15 degrees, more preferably from 3 to 10 degrees. In other examples, the fixation arm or arms may be angled downwardly towards the base member. In some embodiments, the fixation arm or arms may be angled upwardly towards the top member at an angle from greater than 0 to 12 degrees, preferably from 1 to 10 degrees, more preferably from 2 to 7 degrees, more preferably from 3 to 5 degrees.

[0041]

[0038] Similarly, each fixation arm may be connected to the connection member at any suitable point. However, in many embodiments the maximum lateral movement of the connection member relative to the longitudinal axis may occur at the reentrant apex. It may therefore be advantageous for the at least one fixation arm to extend from at or proximate the reentrant apex thereof. In addition, in many embodiments the reentrant apex may be located at or proximate a mid- section of the connection member. However, it should be appreciated that the location of the reentrant apex may depend on the particular reentrant configuration of the connection member.

[0042]

[0039] In embodiments, each fixation arm may extend from the relevant connection member in a perpendicular or substantially perpendicular orientation to the longitudinal axis. In these embodiments, the length of each fixation arm (a horizontal arm relative to the longitudinal axis) may be configured to exceed half the greatest length of the top member and / or and base member.

[0043]

[0040] The implant fixation device may have any suitable configuration. Similarly, the comprising unit cell may have any suitable negative Poisson ratio geometry. In embodiments, the unit cell comprises a planar or two dimensional structure. In these embodiments, the unit cell configuration may be formed from any number of elongate members. For example, the top member, the base member and the connection member may all comprise elongate members laid out in two- dimensional plane. Examples of suitable elongate members for the unit cell may include a configuration wherein the top member, base member and connection member comprise a rod, bar, wire, shaft, tube or strut. However, it should be appreciated that any suitable member configuration may be used. In embodiments, the top member, base member and connection member may comprise bars or struts having a thickness of at least 0.8 mm, preferably 0.8 to 5 mm, more preferably from 0.8 to 3 mm, more preferably from 0.8 to 2 mm. In embodiments, the top member, base member and connection member comprise bars or struts having a thickness of at least 1 mm, preferably 1 to 5 mm, more preferably from 1 to 3 mm, more preferably from 1 to 2 mm. In embodiments, the top member, base member and connection member comprise bars or struts having a thickness of at least 2 mm, preferably 2 to 5 mm, more preferably from 2 to 4 mm, more preferably from 2 to 3 mm. In embodiments, the top member and / or base members may be formed as a rigid body, and may, in embodiments be integrated / connected to an section of an implant or other part of the body of an implant.

[0041] As noted previously, the implant fixation device may be formed from any suitable material. In embodiments, the implant fixation device may comprise a shape memory material, such as a shape memory alloy or shape memory polymer or the like, as previously described. In other embodiments, fixation device may be comprised of a resilient material, for example a metallic, polymeric, ceramic material or combinations thereof. Examples of suitable metallic materials include gold, silver, platinum, Co-Cr alloys, a stainless steel, niobium, tantalum, titanium, a titanium alloy, nickel and combinations thereof. For example, Stainless steel 316L, Ti-6AI-4V, Ti-8Mn, Ti-6AI-7Nb, Ti-3AI-2.5 V, Ti-13Nb-13Zr, Ti- 12Mo-6Zr-2Fe, Ti-15Mo, titanium-zirconium alloys, Co-Cr-Mo, Co-20Cr- 15 W-10Ni, Co-35Ni-20, Cr-10Mo, Co-28Cr-6Mo. Examples of suitable polymeric materials include polyethylene (PE), polyurethane (PU), polyamide (PA), polytetrafluoroethylene (PTFE), polymethylmethacrylate (PMMA), polyethylene terephthalate (PET), synthetic rubber (SR), polystyrene (PS), polyetheretherketone (PEEK), polylactic acid (PLA), and polyglycolide (PGA), and combinations thereof. Examples of suitable ceramic materials include aluminium oxide, zirconium oxide, zirconium dioxide. Examples of other materials that may be used include carbon, graphene or the like. It should be appreciated that combinations of the above listed materials could also be used, including for example use in or as part of a composite material. In addition, it should be appreciated, that in those embodiments in which the implant fixation device includes a ceramic component, the device is at least partially ceramic, in some case comprising a composite material i.e. a ceramic composite material. The Implant fixation device preferably comprises a biocompatible material. Depending on the application requirements, the implant fixation device may comprise a biodegradable material. This may be used to provide a patient with a full recovery for temporary fixation. Where applicable the implant may be made by biodegradable material, which can bring the original structure back for the patient.

[0044]

[0042] The connection member may be advantageously configured with a reentrant geometry providing a curved or angled member, preferably curved or angle strut between the top member and base member. As can be appreciated, a reentrant geometry comprises a reentrant angle in which the curved or angled configuration defines an interior angle greater than 180°, with its point turning back into the figure rather than out from it. That reentrant angle is typically between 180° and 360° depending on the configuration of the connection member. In this configuration, the reentrant apex defines the turning point i.e. where the reentrant geometry of the connection member turns back (changes lateral direction) relative to the longitudinal axis.

[0045]

[0043] That reentrant geometry of each connection member may take any number of forms. In some embodiments, each connection member may comprise at least two curved or angled sections, having at least one curved or angled section extending from the top member and at least one curved or angled section extending from the base member, with the curved or angled sections meeting at the reentrant apex. Various curves or angles may be suitable. However, it should be appreciated that the use of curved sections in the connection member may provide a more even distribution of force and stress through the length of the connection member between the top member and base member. Sharp angles, for example where the reentrant angle comprise a sharp bend or point bend, may create stress raising points in the connection member. The inclusion or curves in the reentrant geometry advantageous may be used to avoid these stress raising geometries. Thus, in embodiments, the curved or angled sections may comprise at least one curve extending from the respective top member or base member to the reentrant apex. For example in some embodiments, the curved section of each connection member may comprise a sigmoid curve which extends between the respective top member or base member and reentrant apex. In this form, the curves of the sigmoid curve may comprise a radius R = 1 / 4 longitudinal distance between the top member and base member when in the expanded configuration. This advantageously provides a continuous radius curve through the reentrant geometry.

[0046]

[0044] Those curved or angled sections may extend from any suitable part or section of the top or base member. For example, the curved or angled section may extend inwardly from or proximate an outer edge of the top member or base member towards the longitudinal axis meeting at a reentrant apex. However, it should be appreciated that the curved or angled section may equally be configured to extend inwardly from an interior section of the top member or base member (i.e. away from the edge of those members) and towards the longitudinal axis meeting at a reentrant apex.

[0047]

[0045] The connection member may have any suitable configuration that includes a reentrant geometry. In embodiments, each connection member may have a longitudinally symmetrical configuration about the reentrant apex. A longitudinally symmetrical configuration may provide the advantage of having a similar compression and expansion properties along the longitudinal length of the unit cell.

[0048]

[0046] Each unit cell may comprise any number of connection members. In some embodiments, a single connection member may be provided. In some embodiments, two or more connection members may be provided. In some embodiments, two connection members may be provided. Where the device includes two symmetrical connection members, movement from the expanded configuration to the compact configuration causes lateral contraction of the spacing between the adjoining reentrant apex about the longitudinal axis. Moreover, in these embodiments, each connection member may be configured to comprise a symmetrical mirror of the other connection member about the longitudinal axis. This symmetrical configuration again may assist in providing similar compression and expansion properties along the longitudinal length of the unit cell.

[0049]

[0047] As previously noted, the implant fixation device may comprise at least one planar unit cell. In this respect, the top member, the base member and the connection member of each unit cell may all comprise elongate members laid out in a two-dimensional plane. The final structure of the implant fixation device may form an assembly of the multiplied unit cells achieved by circumferentially spacing multiple unit cells (for example 2D unit cells) about a central axis. In embodiments, that central axis may comprise the longitudinal axis of the unit cell. However, it should be appreciated that in some embodiments a different axis which is centrally located relative to each unit cell may be used about with the multiple unit cells are circumferentially spaced about and / or around. A larger form (in many cases a 3D form) of the implant fixation device may then be created by including at least two, preferably at least five, for example between two to ten (or more) of the unit cell circumferentially spaced apart about the longitudinal axis. In embodiments, the implant fixation device may then be created by including more than seven, for example 7 to 20 or more of the unit cell circumferentially spaced apart about the longitudinal axis. Thus, the implant fixation device may comprise at least two unit cells circumferentially spaced apart about a central axis, for example the longitudinal axis. In embodiments, fixation device may comprise from two to seven unit cells circumferentially spaced apart about the longitudinal axis. In embodiments, the implant fixation device may comprise one of two, three, four, five, six or seven unit cells circumferentially spaced apart about the longitudinal axis. It should be appreciated that multiple, typically a larger number of unit cells is preferred to maximise the potential locking force.

[0050]

[0048] Using multiple unit cells in this manner may multiply the achievable pullout strength of the device corresponding with the number of unit cells in the structure. Theoretically, the peak pull-out force can reach to M * N (M: peak pull out force for a single cell; N: number of the unit cell) with near zero push-in force (minimal damage to the bone). However, it should be appreciated that the peak pull-out force of a particular unit cell design may be dependent on a number of factors, including material, geometric configuration, dimensions and the like.

[0051]

[0049] Movement from the expansion position to the compact configuration may require a further element or tool to hold the implant fixation device in that prestressed position. The Implant fixation device may therefore further include at least one deformation tool configured to hold the implant fixation device in the compact configuration. The deformation tool may have any suitable configuration, for example a clip, clasp, bolt and nut / threaded aperture, screw and nut / threaded aperture arrangement. In some embodiments, the deformation tool comprises a threaded bolt and aperture located in the top member and base members.

[0052]

[0050] Nevertheless, it should be appreciated that in embodiments where the implant fixation device is formed from a shape memory material (as described previously), such as a shape memory alloy, a further element or tool to hold the implant fixation device in that pre-stressed position may not be required as the shape change is achieved using changes in temperature.

[0053]

[0051] Fixation results of the implant fixation device may be enhanced through the use of a porous structure added to or used in conjunction with the bone implant fixation device. This porous structure may also improve the mechanical properties of the overall implant fixation device. In embodiments, the implant fixation device may further include a porous structure, preferably a lattice structure, configured to at least partially enclose the implant fixation device therein. The porous structure may be preferably configured to extend between adjacent faces of unit cells about longitudinal axis. The porous structure may also be configured to provide a scaffold for bone in-growth. In this sense, a porous / lattice structure of this type may be added to facilitate bone cell growth, thereby aiding in the bone healing process. The porous structure may be preferably configured to provide mechanical properties similar to those of bone, for example having a similar yield strength and / or Young’s modulus. The porous structure may therefore provide the desired mechanical properties when implanted in a bone cavity and also serve as a scaffold for bone cell growth if necessary. Any suitable lattice structure may be used. In some embodiments, the porous lattice structure may comprise a cubic lattice. However, it should be appreciated that other lattice structures may be used, such as tetragonal, orthorhombic, monoclinic, triclinic, hexagonal, rhombohedral or the like. Similarly, it should be appreciated that the porous structure may have any suitable porosity, for example between 20 to 80 percent porosity, preferably between 30 and 70 percent porosity, more preferably between 40 and 60 percent porosity, or alternatively between 20 and 70 percent porosity. In embodiments, the porosity may be between 45 and 55 percent, for example around or about 50 percent. Similarly, the porous structure may comprise any suitable pore size, for example between 200 and 1000 pm, preferably between 300 and 900 pm, more preferably between 400 and 800 pm, and yet more preferably between 500 and 700 pm, for example from 550 to 650 pm. It should be appreciated that the particular porosity and pore size may be selected and designed to suit the particular lattice structure, material and lattice configuration. In embodiments, the porous structure may be configured to mimic the natural porous structure of bone, for example human bone.

[0054]

[0052] It should be appreciated, that the implant fixation device may also be designed or configured to a patient-specific customised implant design in embodiments.

[0055]

[0053] A second aspect of the present invention provides an orthopaedic implant that comprises: a connector configured to couple with or comprises a section of an articulation element of the orthopaedic implant; and an implant fixation device extending from the base side of the connector according to the first aspect of the present invention.

[0056]

[0054] This second aspect provides an orthopaedic implant that includes the implant fixation device of the first aspect. As above, that orthopaedic implant may comprise a variety of implants for knee, elbow, back, leg, arm, neck or similar surgeries. In embodiments, the articulation element of the orthopaedic implant may comprise at least one of: a tibial component of a knee implant; a femoral component of a hip implant; a humerus component of an elbow implant; a humerus component and / or scapula component of a shoulder implant; an ulna component of an elbow implant; a radial head component of an elbow implant; a tibia component of an ankle implant, or a dental implant fixture or screw.

[0057]

[0055] In some embodiments, the implant fixation device may be connected to or incorporated with the connector, for example, the stem part of a knee implant could be largely formed by an implant fixation device. In other embodiments, the implant fixation device may form part of or extend from another component of the implant. For example, the orthopaedic implant of this second aspect may further comprise: a plate including a top side and a base side opposite to the top side; wherein the connector is located in or extends from the top side of the plate; and the implant fixation device extends from the base side of the plate.

[0056] Thus in some embodiments, the orthopaedic implant comprises: a plate including a top side and a base side opposite to the top side; a connector that is located in or extends from the top side of the plate, the connector configured to couple with an articulation element of the orthopaedic implant; and an implant fixation device extending from the base side of the plate according to the first aspect.

[0058]

[0057] The orthopaedic implant may include any number of additional elements. In embodiments, the orthopaedic implant further comprises a tooling tunnel configured to enclose the implant fixation device within a cavity or enclosure formed in a bone. The tooling tunnel may be configured to provide a path for accessing the implant fixation device for delivering and releasing compression stress, for example providing access to manipulate a deformation tool that may be located or engaged in or with the implant fixation device.

[0059]

[0058] As mentioned in the first aspect, bone regrowth can be enhanced through the inclusion of a bone scaffold around the implant fixation device. The orthopaedic implant may therefore further include a porous structure, preferably a lattice structure, configured to at least partially enclose the implant fixation device therein, which may also be configured to provide a scaffold for bone ingrowth. Similarly, in some embodiments, at least one section of the plate may include a porous structure, preferably a lattice structure, configured to at least partially enclose the implant fixation device therein configured to provide a scaffold for bone in-growth. These porous sections of the plate may be located in any suitable location. For example, the porous structure may be located in those locations in the implant may be considered to induce a stress-shielding effect. These locations may include distal edge regions of the plate, the underside or bone facing side of the plate and the like.

[0060]

[0059] A third aspect provides a bone fixation scaffold comprising: a connector scaffold having a first end and second end, spaced apart from the first end; and at least one implant fixation device according to the first aspect extending from at least one of the first end or second end.

[0061]

[0060] This third aspect provides a bone fixation scaffold that may be located or otherwise held in place in the adjoining bone sections using one or more implant fixation devices described above for the first aspect. That connector scaffold may be used in any suitable bone of a patient that has a gap, cavity, hold, break or similar which needs to be filled or reconnected. This may reestablish the structure of that bone, and may fill in missing pieces of that bone structure or similar. Applications include bone fixation scaffold for finger bones, arm bones, leg bones or similar. The type of connector scaffold may depend on the application. For example, the connector scaffold may comprise a cage, wire, staple, plate, screw, rod, tubular structure, external fixation device, or a combination thereof. Additionally, at least one section of the connector scaffold may include a porous structure, preferably a lattice structure, configured to provide a scaffold for bone in-growth. Similarly, the implant fixation device may include a porous structure, preferably a lattice structure, configured to at least partially enclose the implant fixation device therein, which may also be configured to provide a scaffold for bone in-growth.

[0062]

[0061] In some applications, only one implant fixation device may be required. However, in other applications, two or more implant fixation devices may be used. For example, the bone fixation scaffold may include at least one implant fixation device extending each of the first end and second end thereof.

[0063]

[0062] A fourth aspect provides a fixation screw, preferably a ligament fixation screw, comprising: an elongate threaded shaft, and at least one implant fixation device according to the first aspect located within the threaded shaft, said threaded shaft including at least one aperture through which the distal end of the fixation arm extends.

[0064]

[0063] This fourth aspect provides a fixation screw that may be inserted to fix an implant, part of an implant, prothesis or body part into position in or on that bone. For example, the fixation screw of this aspect may be used in ligament surgery, such as an anterior cruciate ligament (ACL) graft, where one or more fixation screws may be used to fix the ACL graft into position using one or more implant fixation devices located in proximal bone sections.

[0065]

[0064] In these embodiments, the implant fixation device may be located within the screw structure with the distal ends of the fixation arms extended through a threaded section of the threaded shaft to enable those distal ends of the fixation arms to interact and fix the screw in place when fully inserted into a threaded bone cavity. In this respect, the distal ends of the fixation arms thereof may be designed to follow the shape of the pitch of the thread of the elongate threaded shaft (screw). A single fixation device may be included in the threaded shaft. However, it may be advantageous to include multiple fixation devices therein. In such embodiments, the threaded shaft may include at least two implant fixation devices longitudinally arranged, preferably longitudinally stacked, along a longitudinal axis of the threaded shaft. In embodiments, the implant fixation device may be configured with two bracing members which extend outwardly of the respective fixation arm in opposite longitudinal directions in order to provide bi-direction fixation - i.e. resist movement of the screw in both longitudinal directions when in the insertion location, for example a bone cavity.

[0066]

[0065] A fifth aspect provides a method of fixing an implant within a cavity formed in a bone, each cavity having at least one sidewall, the method comprising: inserting an implant fixation device according to the first aspect into a bone cavity when configured in the compact configuration; and moving the implant fixation device into the expanded configuration, such that each fixation arm moves laterally away from the longitudinal axis, perpendicularly past the ends of each of the top member and base member and contacts the sidewalls of the surrounding bone cavity.

[0067]

[0066] This fifth aspect provides a new bone implant fixation method that may also speed up the bone healing process. It involves an elastically pre-stressed porous negative Poisson's ratio structure that, in embodiments, may be configured to provide minimal push-in force by shrinking the size of the implant and high fixation force by expanding once fitted on-site. The implant fixation device may therefore advantageously enable the implant to be immediately fixed into position by this method, and may provide near-zero push-in force required for implantation by shrinking of the implant before the implantation process. Implant-assisted osseointegration due to initial pressure - in this sense the implant may also compress bone tissue in embodiments which assists to improve bone cell growth due to the initial pressure. Again, this provides a negative Poisson's ratio geometric design and method which may be configured to address and / or ameliorating implant pulling by causing the implant to expand during the pulling process.

[0068]

[0067] As explained for the first aspect, the expanded configuration may be the natural or normal position for the device, with the device being configured to be moved into the compact configuration, typically by moving the top member and the base member together along the longitudinal axis, resiliently deforming the connection member or members. In these embodiments, prior to implantation into a bone cavity, the implant fixation device may therefore be moved from an expanded configuration to the compact configuration by moving the top plate and bottom plate together along the longitudinal axis and fixing the device in the compact configuration. In these embodiments, the device is elastically prestressed. In this sense, the implant fixation device may be in the expanded configuration (i.e. undeformed) as its natural state. Prior to insertion into the bone cavity, the device may be elastically deformed and placed into the compact configuration, and lateral contraction occurs bringing the distal ends of each fixation arm laterally within the unit cell (i.e. not extending perpendicularly past the ends of each of the top member and base member). The deformed device may be maintained in the compact configuration and inserted into a prepared bone cavity. The device may then be released from the compact configuration, and elastically / resiliently moves back into the expanded configuration, where each fixation arm moves laterally away from the longitudinal axis, perpendicularly past the ends of each of the top member and base member, and contacts the sides of the surrounding bone cavity.

[0068] Similarly, as explained for the first aspect, in applicable embodiments, when and where possible (for example where the deformation force is released or abated) movement from the stretched configuration back to expanded configuration may comprise resilient recovery of the implant fixation device. In embodiments, that movement may be facilitated by the implant fixation device being stressed or stretched when moved from the expanded configuration (the normal unstressed configuration of the device) into the stretched configuration, and the device having a resilient and / or elastic contraction from that stretched configuration back to the expanded configuration.

[0069]

[0069] As explained for the first aspect, in other embodiments, the implant fixation device may comprise a shape memory material, having a remembered shape comprising the expanded configuration. Shape memory materials (SMPs) are a class of smart materials capable of responding to external stimuli with a shape change. This response encompasses shape fixity (deformation followed by fixation into a temporary shape), and shape recovery (a return to the original, remembered, permanent shape). It should be appreciated that shape-memory materials (SMM)s are materials that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. For the present invention, the pre-deformed ("remembered") shape may comprise the expanded configuration of the implant fixation device, and the deformed configuration (in which it is deformed when cold) may comprise the compact configuration. Accordingly, in embodiments, the implant fixation device may move from the compact configuration to the expanded configuration by changing the temperature of the implant fixation device, for example by raising the temperature of the implant fixation device.

[0070]

[0070] In some embodiments, the shape memory material may comprise a thermoresponsive shape memory material, that has a shape that is modulated by temperature, for example the application of heat. In these embodiments, there is a thermal transition temperature (Ttrans) which separates the two different states - i.e. shape fixity (deformation followed by fixation into a temporary shape), and shape recovery (a return to the original, remembered, permanent shape). Thus, a temporary shape formed by deformation at T > Ttrans can be fixed by cooling to T < Ttrans and can also be subsequently recovered by heating to T > Ttrans again. In embodiments, the shape fixity (deformation followed by fixation into a temporary shape) is set at a lower temperature T2 than the shape recovery (a return to the original, remembered, permanent shape) state T1 , where T2 < T1. For example, T2 may be a freezing temperature, for example from -10 to 5 °C, preferably from -10 to 0 °C, and T2 may be around body temperature, for example from 35 to 39 °C, preferably 36 to 38 °C, more preferably from 36 to 37 °C. However, it should be appreciated that other temperature ranges are possible.

[0071]

[0071] Again, an embodiments, the implant fixation device may be configured with a shape memory material that is biased to expand from the compact configuration to the expanded configuration when at or above a phase transformation temperature. That phase transformational temperature is preferably is less than or at about human body temperature, for example, the phase transformation temperature may be less than about 36°C. By providing a transformation temperature less than or at about human body temperature, the implantable object may be advantageously biased to expand to the expanded configuration when implanted within a living human being.

[0072]

[0072] The phase transformation temperature will be material dependent. For example, for shape memory alloys, the phase transformation temperature may correspond to a finish temperature, Af, for transformation from martensite to austenite. The transformation temperature being the finish temperature from martensite to austenite may advantageously enable the implantable object to exhibit superelastic and / or shape memory effects at or above the transformation temperature. In other forms, for example for shape memory polymers, the phase transformation temperature may correspond with a thermal transition temperature (Ttrans) associated with SMP switching segments may either be a glass transition temperature (Tg) or a melting transition temperature (Tm).

[0073]

[0073] The implant fixation device may be superelastic when above the transformation temperature. A superelastic implantable object may advantageously be compressed to the compact configuration and resiliently biased to expand to the expanded configuration without excessive damage to the implantable object. In some embodiments, the implant fixation device may be formed from a shape memory alloy. Forming the implantable object from shape memory alloy advantageously enables the implantable object to exhibit superelastic and / or shape memory effects when above the transformation temperature.

[0074]

[0074] As previously described, a variety of shape memory alloys or materials can be used for these embodiments of the implant fixation device. The implant fixation device can be made from shape memory materials (SMM). SMM include shape memory polymers or shape memory alloys. Commonly used shape memory alloys include nickel-titanium (NiTi - also known as Nitinol), copper- aluminium-nickel, copper-based SMAs, such as Cu-Zn-AI and Cu-AI-Ni, or iron based SMAs such as Fe-Mn-Si. However, it should be appreciated that SMAs can also be created by alloying zinc, copper, gold and iron. Other shape memory materials include shape memory polymers include PEEK based polymers or those listed in J Mater Chem B. 2021 June 03; 9(21 ): 4287-4297, the contents of which should be considered to be incorporated into this specification by this reference. In addition, other shape memory materials include:

[0075] • Polyurethane-Based Shape Memory Polymers;

[0076] • Polycaprolactone (PCL) Shape Memory Polymers;

[0077] • Zirconia;

[0078] • Poly(N-isopropylacrylamide) (PNIPAAm) Hydrogel; and

[0079] • Poly(ethylene glycol) (PEG)-Based Hydrogels.

[0080]

[0075] Similar to the first aspect, the method of this fifth aspect may apply to a variety of implants fixing an implant within a cavity formed in a bone of a patient. Those implants may include bone screws, fixation screws, plates, rods, cylinders, scaffolds (e.g. bone scaffolds), orthopaedic implants and other similar implant configurations. In some embodiments, the implant comprises an orthopaedic implant, a bone fixation scaffold or a fixation screw, for example as discussed above. For example, the method of this fifth aspect may be used to insert a fixation device for a tibial component of a knee implant; a femoral component of a hip implant; a humerus component of an elbow implant; a humerus component and / or scapula component of a shoulder implant; an ulna component of an elbow implant; a radial head component of an elbow implant; a tibia component of an ankle implant, or a dental implant fixture or screw. In other examples, the method of this fifth aspect can be used as an implant fixation device for a bone fixation scaffold or a fixation screw, e.g. a ligament fixation screw. However, it should be appreciated that the methods and design are applicable to, a large variety of implant types and configurations.

[0081]

[0076] The configuration of the implant fixation device and related method described above may provide the following advantages over conventional fixation devices and arrangements:

[0082] 1. Easy-fit and fit-retaining: Unlike conventional fixed implants that have a static shape, the disclosed implant fixation device may exhibit improved stability and retention properties through two combined features: the above described implant locking mechanism when in the stretched configuration; and bone cell growth over time within the porous structure (where utilised).

[0083] 2. Shorter surgical time and better bone recovery: Compared to the conventional fixed-shape implant surgical process, the total surgical duration using the disclosed implant fixation device may be shortened. This may be achieved by making the implant fixation device smaller before the implantation process, and then releasing the implant to let it expand in the prepared bone cavity without external push-in force required. The shorter the surgical time, the faster healing will be achieved, and the risk of infection may be reduced.

[0084] 3. Less damage to the surrounding bone tissue: In contrast to the high push-in force resulting in secondary bone tissue damage, the disclosed implant fixation device may assist in ameliorating secondary bone tissue damage. During the implantation process, the pre-deformed structure (i.e. when in the compact configuration) minimises contact between the implant fixation device and bone tissue before release, thereby reducing the risk of secondary damage during implantation. 4. Faster healing: Compared to conventional implants, the bone healing and recovery process may be promoted by the applied pressure from the disclosed implant fixation device to the contacting bone tissue surface through the release of the pre-compacted structure. Bone cell growth may also be facilitated by the porous structure (where utilised), which may be configured to mimic the natural porous bone structure, for example human bone structure.

[0085] 5. Fully patient-specific and customise for better match with anatomic feature: In comparison to off-shelf products, the disclosed implant fixation device may be highly customisable, with features conforming to the local anatomical geometry and structural properties of the patient, for example bone density, Young’s modulus, strength and the like.

[0086] 6. Full recovery for temporary fixation: Where applicable the disclosed implant fixation device may be made by biodegradable material, which can bring the original structure back for the patient.

[0087] BRIEF DESCRIPTION OF THE DRAWINGS

[0088]

[0077] Examples of the present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular embodiments, wherein:

[0089]

[0078] Figure 1 illustrates (a) an example of an unit cell design for an implant fixation device according to an embodiment; and (b) a simulated process of lateral contraction of the unit cell under compression.

[0090]

[0079] Figure 1 A, 1 B and 1 C illustrates further example of an unit cell design for the implant fixation device according to embodiments.

[0091]

[0080] Figure 1 D illustrates further example of an unit cell design for the implant fixation device having different bracing member designs according to embodiments.

[0081] Figure 2 (a) to (d) illustrates four steps of the simulated pull-out performance of the unit cell of the device illustrated in Figure 1 .

[0092]

[0082] Figure 2A (a) to (d) illustrates four steps of the simulated pull-out performance of the unit cell of the device illustrated in Figure 1 D(a).

[0093]

[0083] Figure 2B (a) to (c) illustrates an example of an unit cell design for an implant fixation device in which the fixation arms are connected to the base member which still retains auxetic behaviour and locking effect, showing the unit cell in (a) expanded configuration; (b) compact configuration; and (c) stretched configuration.

[0094]

[0084] Figure 2C (a) to (c) illustrates an example of an unit cell 105F for an implant fixation device 100F in which the fixation arms 120F are angled downwardly towards the base member 112F which still retains auxetic behaviour and locking effect.

[0095]

[0085] Figures 2D(a) to (o) illustrates a series unit cells 105H for an implant fixation device 10OH in which the fixation arms 120H are angled upwardly towards the top member 11 OH by different tilt-up angles (I3> = 1 ° to 15°).

[0096]

[0086] Figure 2E which provides a plot of pulling force versus time when a pulling force is applied to the top member of the devices shown in Figures 2D, illustrating (a) the full plot; and (b) a segment providing a comparative segment of the full plot.

[0097]

[0087] Figure 2F provides a plot of the maximum pull out force versus the tilt-up angle of the fixation arms for the devices shown in Figure 2D.

[0098]

[0088] Figure 3 provides a plot of the pull-out force of a single unit cell of the device illustrated in (a) Figure 1 and 2; and (b) Figure 1 D(a) and 2A.

[0099]

[0089] Figure 4 provides an illustration of the 3D form of the bone implant fixation device, created by multiplying of the unit cell from two (X2) to seven (X7) unit cells circumferentially spaced apart around the central longitudinal axis.

[0090] Figure 4A provides an illustration of the 3D form of the bone implant fixation device, created by multiplying of the unit cell from two (X2) to seven (X7) unit cells circumferentially spaced apart around the central longitudinal axis where the bone implant fixation devices include tooling access similar to the configuration illustrated in Figure 10.

[0100]

[0091] Figures 5 to 8 provide deformation, stress, strain and yielding comparison between two unit cell configurations, namely (a) angular unit cell; and (b) sigmoidal curved unit cell.

[0101]

[0092] Figure 9 illustrates one example of a porous lattice structure that may be added to the bone implant fixation device illustrated in Figures 1 and 4.

[0102]

[0093] Figure 9A illustrates another example of a porous lattice structure that may be added to the bone implant fixation device illustrated in Figures 1 and 4 including a tooling access similar to the configuration illustrated in Figure 10.

[0103]

[0094] Figure 10 provides a schematic illustration of one example implant fixation device (unit cell multiplied x2) and an example of tooling that may be used to deform the device into the compact configuration.

[0104]

[0095] Figure 11 provides a schematic illustration of one insertion process of the implant fixation device in a 2D form into a bone cavity.

[0105]

[0096] Figure 12 provides a schematic illustration of one example application of the implant fixation device when used as an implant fixation device within a tibial plate of a knee implant.

[0106]

[0097] Figure 13 provides a schematic illustration of one example application of the implant fixation device when used as an implant fixation device within a femoral component of a hip implant.

[0098] Figure 14 provides a schematic illustration of one example application of the implant fixation device when used as an implant fixation device within ligament fixing screws, for example an ACL graft.

[0107]

[0099] Figure 15 provides a schematic illustration of one example application of the implant fixation device when used as an bone fixation scaffold for joining two sections of a bone together, for example a finger bone.

[0108]

[0100] Figure 16 provides a schematic illustration of another example application of the implant fixation device when used as an bone fixation scaffold for joining two sections of a bone together, for example a finger bone, showing (a) half unit cell configuration used in the device; (b) to (i) various forms of the half unit cell configuration used for joining two sections of a bone together, for example a finger bone.

[0109] DETAILED DESCRIPTION

[0110]

[0101] Examples of a new and / or improved bone implant fixation device, examples of implants that include the bone implant fixation device and related bone implant fixation methods will now be described. In embodiments, the bone implant fixation device and method may assist in speeding up bone healing processes. The bone implant fixation, related methods and design may be applicable to, but not limited to, bone screws, fixation screws (e.g. ligament fixation screws), plates, rods, cylinders, scaffolds (e.g. bone scaffolds), and implant fixation devices.

[0111]

[0102] Figures 1 and 2 illustrates an example of an implant fixation device according to an embodiment of the present invention. The illustrated fixation device 100 comprises a two dimensional unit cell which is configured to be implanted into a bone, typically a bone cavity, of a patient (which will for example be described in more detail below in relation to Figures 11 to 15). Figure 1 (a) illustrates the implant fixation device in its normal and expanded configuration. The illustrated unit cell 105 comprises a series of interconnected members, which in the illustrated case comprise elongate members or shafts, integrally connected to form the two dimensional geometric shape.

[0103] The interconnected members of this unit cell 105 include: a top member 110 and a base member 112 which are longitudinally spaced apart from the top member 110 about a longitudinal axis X; and two curved connection members 114 which extend therebetween and interconnect the top member 110 and the base member 112. The illustrated top member 110 and base member 112 comprise straight elongate members that are perpendicularly arranged relative to the longitudinal axis X. However, it should be appreciated that the top member 110 and the base member 112 may have any suitable configuration, for example curved or other geometric shape. The curved connection members 114 extend longitudinally (relative to longitudinal axis X) between the top member 110 and the base member 112. The shape of each connection member 114 is configured to provide the unit cell 105 with a negative Poisson behaviour by having a reentrant geometry where each connection member 113 includes a curved (or in other embodiments angled - see below) configuration that extends inwardly towards the longitudinal axis X from each of the top member 110 and base member 112 and changing lateral direction relative to the longitudinal axis at a reentrant apex 116. This reentrant geometry provides the connection members 114 with the unique property of lateral contraction L (Figure 1 (b)) when the connection members 114 are subjected to longitudinal movement, for example compression - typically by moving (e.g. compressing) the top member 110 and base member 112 together along the longitudinal axis X. This will be explained in more detail below.

[0112]

[0104] The unit cell 105 also includes two fixation arms 120 which extend laterally outwardly from each connection member 114 relative to the longitudinal axis X. In the illustrated embodiment each fixation arm 120 is connected to the connection member 114 at or about the reentrant apex 116 as this mid-section of the unit cell 105 experiences the most significant contraction in the transverse direction for that particular geometry. However, it should be appreciated that each fixation arm may be connected at any suitable point on the connection member 114. Each fixation arm 120 has a distal end 122 that is spaced away from the connection member 114. That distal end 122 is configured to move laterally relative to the longitudinal axis when the connection members 114 are subjected to longitudinal compression.

[0113]

[0105] Each fixation arm 120 also includes a bracing member 130 that extends from the respective fixation arm 120 towards a bracing portion 132 of the proximate connection member 114. In the illustrated embodiment, the bracing member 130 extends at an angle 6 from the fixation arm 120. That angle 6 may be any suitable angle from the fixation arm 120, for example an acute angle longitudinally away from the fixation arm towards the bracing portion of the connection. In the illustrated embodiment, 6 is 60 degrees. However it should be appreciated that this angle 6 can be selected to suit the geometric design of the connection member 114. In some embodiments, 6 may be from 10 to 89 degrees, such as from 10 to 80 degrees, 10 to 60 degrees, 10 to 50 degrees, 10 to 30 degrees, 20 to 80 degrees, 20 to 60 degrees, 20 to 50 degrees, 20 to 45 degrees, 30 to 80 degrees, 30 to 60 degrees, 30 to 45 degrees, 45 to 80 degrees, 45 to 60 degrees.

[0114]

[0106] Each bracing portion 132 includes an engagement section 135. In the illustrated embodiment the engagement section 135 comprises a flange or extension member of an L-shaped bracing member 130, which is spaced apart from the bracing portion 132 of the proximate connection member 114 when in this normal / expanded configuration (Figure 1 (a)). However, it should be appreciated that the bracing member 130, bracing portion 132 and engagement section 135 can have any suitable configuration (see further examples described below for example).

[0115]

[0107] In the illustrated embodiment, each fixation arm 120 extends substantially laterally from the respective connection member 114, preferably in a perpendicular or in a substantially perpendicular orientation to the longitudinal axis X. However, it should be appreciated that the fixation arm 120 can be configured to extend at any suitable angle relative to the longitudinal axis X. Similarly, each fixation arm 120 may be connected to the connection member 114 at any suitable point. However, it should be appreciated that the maximum lateral movement of the connection member 114 relative to the longitudinal axis X occurs at the reentrant apex 116. It can therefore be advantageous for each fixation arm 120 to extend from at or proximate the reentrant apex 116, as in the illustrated embodiment.

[0116]

[0108] For this embodiment, the unit cell 105 is symmetrically shaped about the longitudinal axis X, with the shape of the connectors also being symmetrically shaped about the reentrant apex. However, it should be appreciated in other embodiments those shape of the unit cell 105 may not necessarily have this symmetry.

[0117]

[0109] The unit cell 105 therefore has a reentrant geometry which exhibits negative Poisson’s ratio behaviour. This unique lateral contraction properties of this geometry can be utilised for the purpose of bone implant fixation. The process of lateral contraction of the unit cell 105 is simulated and illustrated in Figure 1 b. In this figure, the original shape (termed the “expanded configuration”) is indicated by the thin grey line marked “original”, and the compact configuration is represented by the thinker grey line marked “deformed”. As evident, the lateral contraction of the fixation arms on both sides is equal and uniform as a result of the symmetry in that unit cell - as indicated above.

[0118]

[0110] As illustrated in Figures 1 (a) and 1 (b), the implant fixation device 200 may be configured to be moveable between the following functional positions:

[0119] 1. A compact configuration (Figure 1 (b)) in which the top member 110 and base member 112 are longitudinally spaced apart a first distance S1 . This configures the connection member 114 to locate the distal end 122 of each fixation arm 120 in a first lateral position (corresponding to distance P2) relative to the longitudinal axis X.

[0120] 2. An expanded configuration (Figure 1 (a)), which is the normal uncompact configuration of the illustrated unit cell 105 / fixation device 100. In the expanded configuration, the top member 110 and base member 112 are longitudinally spaced apart a second distance S1. Distance S1 is greater than distance D2 relative to the longitudinal axis X. This configures the connection member 114 to locate the distal end 122 of each fixation arm 120 in a second lateral position (corresponding to distance P2) which is laterally further away from the longitudinal axis X relative to the first lateral position - i.e. distance P2 is greater than distance P1 .

[0121]

[0111] In this way, movement between the compact and expanded configuration, is designed to utilise the distal end 122 of the fixation arm 120 as an anchoring member which can engage, and preferably fix the implant fixation device 100 in place in a position within a surrounding bone cavity or enclosure in which the device 100 is located.

[0122]

[0112] The compact configuration may be designed to recess the distal end 122 of the fixation arms 120 within the device 100 to allow for easy insertion (with minimal push-in force) into a fixation location, for example in a bone cavity. The fixation arm 120 length may be selected to enable the unit cell 105 to position the distal end 122 of the fixation arm in two positions relative to the outer edge of the top member 110 and base member 112 of the unit cell 105. In the compact configuration, the position of the distal end 122 of the fixation arms 120 shifts inwardly (as a result of lateral movement of the connection members 114) and becomes parallel and / or position laterally inwardly of the outer edge of the top member 110 and base member 112 of the unit cell 105. This compact configuration may therefore advantageously reduce the lateral width of the fixation arms of the implant fixation device 100 to match or be slightly larger than the width / diameter of a bone cavity in which it is to be inserted. Thus, when the implant fixation device 100 is inserted into that cavity, little to no push in force (i.e. near-zero push-in force) may be required to insert / implant the implant fixation device 100 therein.

[0123]

[0113] In the expanded configuration, the distal end 122 of the fixation arm 120 may be positioned outside of the unit cell (i.e. extends laterally beyond the outer edge of the top member 110 and base member 112 of the unit cell 105) due to the horizontal arm's length being greater than that half of the top 110 and bottom 112 members. In this position, the distal end 122 may be configured to engage or otherwise fix into an adjoining wall of the surrounding bone cavity or enclosure. This may provide immediate device fixation into the inserted location, for example a cavity in a bone (i.e. a bone cavity). This may also provide a high fixation force when inserted into the insertion location (as above). In addition, the implant device may also compress bone tissue to improve bone cell growth due to the initial pressure. In other words, this may provide implant-assisted osseointegration due to initial pressure provided by this fixation force from the distal ends of the fixation arm or arms of the device.

[0124]

[0114] It should be appreciated that the distal end 122 of one or each fixation arm 120 may have any suitable configuration. In Figures 1 and 2, that distal end 122 comprises a single engagement point or engagement surface that is configured to engage or otherwise be fixed into surrounding bone tissue (not illustrated in Figures 1 and 20. However, other and / or alternate configurations are possible. For example, that distal end 122 may include two or more engagement points or engagement surfaces configured to engage or otherwise be fixed into surrounding bone tissue. In this respect, the use and configuration of engagement points or engagement surfaces can be designed to provide a surface determined by local bone's properties, i.e. contact pressure does not exceed bone strength. Additionally, the engagement point, points, surface or surfaces of that distal end 122 may have a smooth configuration, or may be textured, contoured or otherwise shaped to engage or otherwise be fixed into surrounding bone tissue. For example, in some embodiments, that engagement surface or surfaces may be curved.

[0125]

[0115] The length of the fixation arm 120 can have any suitable length to provide the above movement. In the implant fixation device 100 illustrated in Figures 1 (a), 1 (b) and 2, each fixation arm 120 extends from the mid-section of the reentrant geometry of the respective connection member 114. The length of each fixation arm 120 may be configured to exceed half the length of the top member 110 and base member 112, with the length of each fixation arm 120 being configured at any desired length to meet those requirements. Additionally, the length of each top member 110 and base member 112 are the same in the illustrated embodiment. However, it should be appreciated that those lengths may differ in other embodiments.

[0126]

[0116] Movement between the compact configuration and the expanded configuration may comprise any suitable movement where the implant fixation device moves, recovers, expands or the like from the compact configuration to the expanded configuration. In the illustrated embodiment, the implant fixation device 100 may be configured to undergo elastic deformation (resilient deformation) when moving from the expanded configuration (Figure 1 (a)) to the compact configuration (Figure 1 (b)) - typically by moving (e.g. compressing) the top member 110 and the base member 112 together. Conversely, the device 100 may be configured to undergo elastic recovery when moving from the compact configuration (Figure 1 (b)) to the expanded configuration (Figure 1 (a)) - which typically comprises the implant fixation device 100 resiliently expanding into the expanded configuration. The implant fixation device 100 may therefore be elastically stressed when moving from the expanded configuration to the compact configuration. That elastic deformation and recovery relates to the resilience of the material - which will be discussed in more detail below.

[0127]

[0117] The configuration change of the device can also be achieved through phase transformation, not just by elastic deformation. In some embodiments, the implant fixation device may comprise a shape memory material, having a remembered shape comprising the expanded configuration. Shape memory materials (SMPs) are a class of smart materials capable of responding to external stimuli with a shape change. This response encompasses shape fixity (deformation followed by fixation into a temporary shape), and shape recovery (a return to the original, remembered, permanent shape). It should be appreciated that shape-memory materials (SMM)s are materials that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. For the present invention, the pre-deformed ("remembered") shape comprises the expanded configuration of the implant fixation device, and the deformed configuration in which it is deformed when cold comprises the compact configuration. Accordingly, in embodiments the implant fixation device moves from the compact configuration to the expanded configuration by changing the temperature of the implant fixation device, preferably raising the temperature of the device.

[0128]

[0118] In some embodiments, the shape memory material may comprise a thermoresponsive shape memory material, that has a shape that is modulated by temperature, for example the application of heat. In these embodiments, there is a thermal transition temperature (Ttrans) which separates the two different states - i.e. shape fixity (deformation followed by fixation into a temporary shape), and shape recovery (a return to the original, remembered, permanent shape). Thus, a temporary shape formed by deformation at T > Ttrans can be fixed by cooling to T < Ttrans and can also be subsequently recovered by heating to T > Ttrans again. In embodiments, the shape fixity (deformation followed by fixation into a temporary shape) is set at a lower temperature T2 than the shape recovery (a return to the original, remembered, permanent shape) state T1 , where T2 < T1. For example, T2 may be a freezing temperature, for example from -10 to 5 °C, preferably from -10 to 0 °C, and T2 may be around body temperature, for example from 35 to 39 °C, preferably 36 to 38 °C, more preferably from 36 to 37 °C. However, it should be appreciated that other temperature ranges are possible.

[0129]

[0119] In embodiments, the implant fixation device may be configured with a shape memory material that is biased to expand from the compact configuration to the expanded configuration when at or above a phase transformation temperature. That phase transformational temperature is preferably is less than or at about human body temperature, for example, the phase transformation temperature may be less than about 36°C. By providing a transformation temperature less than or at about human body temperature, the implantable object may be advantageously biased to expand to the expanded configuration when implanted within a living human being.

[0130]

[0120] The phase transformation temperature will be material dependent. For example, for shape memory alloys, the phase transformation temperature may correspond to a finish temperature, Af, for transformation from martensite to austenite. The transformation temperature being the finish temperature from martensite to austenite may advantageously enable the implantable object to exhibit superelastic and / or shape memory effects at or above the transformation temperature. In other forms, for example for shape memory polymers, the phase transformation temperature may correspond with a thermal transition temperature (Ttrans) associated with SMP switching segments may either be a glass transition temperature (Tg) or a melting transition temperature (Tm). The implant fixation device may be superelastic when above the transformation temperature. A superelastic implantable object may advantageously be compressed to the compact configuration and resiliently biased to expand to the expanded configuration without excessive damage to the implantable object. In some embodiments, the implant fixation device may be formed from a shape memory alloy. Forming the implantable object from shape memory alloy advantageously enables the implantable object to exhibit superelastic and / or shape memory effects when above the transformation temperature.

[0131]

[0121] For example, in shape memory alloys like Nitinol (Ni-Ti alloy), the shapechanging mechanism relies on a reversible phase transformation between the austenite (high-temperature) and martensite (low-temperature) phases. This phase transformation enables the material to "remember" its original shape and return to it when the temperature changes. The implant fixation device may be designed to change its configuration in response to changes in temperature, from a cold temperature (Temperature B - preferably lower than body temperature, for example freezing - close to zero degrees Celsius) when configured in the compact configuration, and a higher temperature than temperature B (temperature A, for example body temperature - 36 to 37 degrees Celsius) where the device can recover or move into its remembered configuration, in this case corresponding to the expanded configuration. In this sense, a shape memory material can be used, and be "trained" to have a compact configuration at low temperatures and then transition to an expanded configuration at human body temperature (for example from 36 to 37 degrees Celsius).

[0132]

[0122] For, shape memory polymers (SMPs) that shape change may result from “Netpoints” which are chemical or physical crosslinks that set the permanent (remembered) shape whereas “switching segments” allow for fixation into a temporary shape and for recovery back to the permanent (remembered) shape. Thermoresponsive SMPs have a shape that is modulated by application of heat. Thermal transition temperature (Ttrans) associated with SMP switching segments may either be a glass transition temperature (Tg) or a melting transition temperature (Tm). Thus, a temporary shape formed by deformation at T > Ttrans can be fixed by cooling to T < Ttrans and can also be subsequently recovered by heating to T > Ttrans again. For SMPs, the shape memory effect may be entropically driven.

[0133]

[0123] As previously described, a variety of shape memory alloys or materials can be used for these embodiments of the implant fixation device. The implant fixation device can be made from shape memory materials (SMM). SMM include shape memory polymers or shape memory alloys. Commonly used shape memory alloys include nickel-titanium (NiTi - also known as Nitinol), copper- aluminium-nickel, copper-based SMAs, such as Cu-Zn-AI and Cu-AI-Ni, or iron based SMAs such as Fe-Mn-Si. However, it should be appreciated that SMAs can also be created by alloying zinc, copper, gold and iron. Other shape memory materials include shape memory polymers include PEEK based polymers or those listed in J Mater Chem B. 2021 June 03; 9(21 ): 4287-4297, the contents of which should be considered to be incorporated into this specification by this reference. In addition, other shape memory materials include:

[0134] • Polyurethane-Based Shape Memory Polymers;

[0135] • Polycaprolactone (PCL) Shape Memory Polymers;

[0136] • Zirconia;

[0137] • Poly(N-isopropylacrylamide) (PNIPAAm) Hydrogel; and

[0138] • Poly(ethylene glycol) (PEG)-Based Hydrogels.

[0139]

[0124] As illustrated in Figures 2, the implant fixation device 200 may also be configured to be moveable into the following additional functional position from and back to (where applicable) the expanded configuration:

[0140] 3. A stretched configuration (illustrated in Figures 2(b), (c) and (d)) in which the distal end 22 of each fixation arm 22 is located in or close to the second lateral position (corresponding to distance P2), the top member 110 and base member 112 are further spaced apart (at distance S3, S4, S5 and greater) relative to the second distance S2 through a pulling force P being exerted on at least the top member 110. This deforms the unit cell 105 and connection members 114 in a manner that locates the engagement section 135 of each bracing member 130 in engagement with the bracing portion 132 of the proximate connection member 114 thereby forming a longitudinal brace between the fixation arm 120 and connection member 114.

[0141]

[0125] In this way, movement from the expanded configuration to the stretched configuration (and beyond if the top member 110 and base member 112 are moved longitudinally further apart) is also designed to utilise the distal end 122 of the fixation arm 120 as an anchoring member which can engage, and preferably fix the implant fixation device 100 in place in a position within a surrounding bone cavity or enclosure in which the device 100 is located.

[0142]

[0126] The stretched configuration (Figure 2) may be reached when the connection members 114 are caused to further expand (i.e. laterally move away from the longitudinal axis) when the top member 110 and base member 112 are moved longitudinally further apart when moving from the expanded configuration to the stretched configuration. This may occur for example during a pulling process on the implant fixation device 100, particularly when insitu within a bone cavity. This pulling force P (Figure 2) may be resisted through movement, deformation and the like of the fixation arm 122 being resisted through force transfer from that fixation arm 122 through the bracing member 130, through to the bracing portion 132 of the connection member 114 thereby bracing the fixation arm 114 against movement and deformation. In the illustrated embodiments, the bracing member 130 forms one side of a triangle between the fixation arm 120 and connection member 114, thereby forming a load bearing structure which fixes the distal end of the fixation arm in or close to the second lateral position. The distal end 122 of each fixation arm 120 is braced to stay located at the second lateral position P2, or where it may have marginally or slightly moved, it will still be close or proximate to that second lateral position P2, anchoring the implant fixation device in place within the implanted location. The bracing arrangement in this stretched configuration may (Figure 2) result in a high fixation force and associated high pull-out force for the device when insitu, for example within a bone cavity.

[0127] In the illustrated embodiment, the implant fixation device 100 may be configured to undergo elastic deformation (resilient deformation) when moving from the expanded configuration to the stretched configuration (Figure 2). Movement from the stretched configuration back to expanded configuration (if possible, for example where the deformation force is released or abated) may thus comprise elastic recovery (resilient recovery) of the device 100. This movement may be facilitated by the implant fixation device 100 being stressed or stretched when moved from the expanded configuration (the normal unstressed configuration of the device) into the stretched configuration, and the device 100 having a resilient and / or elastic contraction from that stretched configuration back to the expanded configuration. Again, that elastic deformation and recovery relates to the resilience of the material - which will be discussed in more detail below.

[0143]

[0128] Again, the configuration change of the device can also be achieved through phase transformation, not just by elastic deformation. In some embodiments, the implant fixation device may comprise a shape memory material, having a remembered shape comprising the expanded configuration as described previously, and below in relation to one embodiment described for Figure 11 .

[0144]

[0129] A simulation of the pull-out performance of one unit cell 105 of the device 100 is shown in Figure 2. The outer sides 150 of a bone cavity 152 are illustrated in contact with the distal ends 122 of the fixation arms 120. The simulated pullout process represents a simplified model of human cancellous bone, with the mechanical properties of the materials obtained from reported literature, and the device simulated with mechanical properties of an additive manufactured Ti-6AI- 4V alloy. The following describes the implant locking mechanism of the stretched configuration in four steps:

[0145] • Step 1 (Figure 2(a)): The implant device 100 is the expanded configuration inserted into the bone cavity 152, with the distal end 122 of each fixation arm 120 contacting and exerting pressure on the surrounding bone sidewalls 150 of bone cavity 152. • Step 2 (Figure 2(b)): A pulling force P is exerted on the top member 110 of the unit cell 105. The longitudinal distance between the top member 110 and base member 112 expands to distance S3 (which is greater than distance S2, shown in Figure 2(a)). This deforms the connection member 112, pushing the reentrant apex 116 laterally outwardly, and thus exerting further lateral pressure between the distal ends 122 of the fixation arms 122 and the surrounding bone sidewalls 150 of bone cavity 152. This also locates the engagement section 135 of each bracing member 130 in engagement with the bracing portion 132 of the proximate connection member 114 thereby forming a longitudinal brace between the fixation arm 120 and connection member 114.

[0146] • Step 3 (Figure 2(c)): As the pulling process progresses, the longitudinal distance between the top member 110 and base member 112 expands to distance S4 (which is greater than distance S3, shown in Figure 2(b)) and the distal end 122 of each fixation arm is continuously being pushed into the surrounding bone tissue of the bone sidewalls 150. The entire bracing assembly of the fixation arm 120, bracing member 130 and connection member 114 acts as a stopper, assisting the lower part of the main unit cell 105 body to resist moving in the pulling direction of pulling force P. This forms the basis of the implant locking mechanism.

[0147] • Step 4 (Figure 2(d)): This is an extreme case of the pulling process to exaggerate the locking mechanism, in which the unit cell main 105 body is severely deformed with the longitudinal distance between the top member 110 and base member 112 expanding to distance S5 (which is greater than distance S4, shown in Figure 2(c)). However, due to the locking mechanism described in step 3, the entire unit cell 105 remains locked in its original position.

[0148]

[0130] The pull-out force evolution obtained from the simulation results for device configuration 100 (and also device configuration 100E) corresponding with the positions shown in Figure 2 is provided in Figure 3. The simulation shows that this locking mechanism from the bracing member 130 significantly increases pullout force, with the pull out force increasing immediately at the onset of pulling as a result of the bracing member 130 forming a brace between the fixation arm 120 and engaged connection member 114. This enables this particular unit cell 105 configuration to have a pull-out force which peaked at 130 N. In comparison, Figure 3 also shows that a unit cell 105E (device configuration 100E) where the formation of a brace takes further deformation of the unit cell 105E and fixation arms 120E for the bracing member 130 to form a brace between the fixation arm 120 and engaged connection member 114. The pulling mechanism and results therefore show a very low initial bracing force until the bracing member 130 contacts the connection member 114, and there is an change (increase) in the pull out force. The pull-out performance of this unit cell 105A of the device 100A will be described in more detail below in relation to Figure 2A.

[0149]

[0131] The reentrant geometry of the connection member 114 can have any suitable configuration to provide a suitable negative Poisson ratio behaviour. The reentrant geometry may comprise a curved or angled member. In embodiments, the connection member 114 may comprise at least one curve extending from the respective top member 110 or base member 112 to the reentrant apex 116. For example, the implant fixation device 100 shown in Figures 1 and 2 has a curved configuration comprising a sigmoid curve which extends between the respective top member 110 or base member 112 and reentrant apex 116. In the illustrated example, the sigmoid curve has a radius R = 1 / 4 longitudinal distance S1 between the top member 110 and base member 112 when in the expanded configuration. This advantageously provides a continuous radius curve through the reentrant geometry. However, it should be appreciated that other radii may be used, including different radii for the two curves making up the sigmoid curve where appropriate. As noted above, each connection member 114 in this embodiment has a longitudinally symmetrical configuration about the reentrant apex 116, providing the advantage of having a similar compression and expansion properties along the longitudinal length of the unit cell 105.

[0150]

[0132] Other reentrant geometries are possible for the connection members 114. For example, Figure 1A(a) illustrates an implant fixation device 100A with a unit cell 105A having an angled reentrant geometry. In this embodiment, each connection member 114A comprises an angled strut that extends from the top edge of the top member 110A or base member 112A towards the longitudinal axis X to the reentrant apex 116A. Like the first embodiment, a fixation arm 114A extends longitudinally outward from the reentrant apex 116A. A bracing member 130A extends from the fixation arm 114A to function as a brace when in a stretched configuration. It should be appreciated that this device 100A moves between a compact configuration, expanded configuration and stretched configuration in a similar manner as described in relation to the device 100 embodiment described in relation to Figures 1 and 2.

[0151]

[0133] Another reentrant geometry is illustrated in Figure 1A(b) which shows an implant fixation device 100B with a unit cell 105B having connection members 114B including a single concave curve reentrant geometry. In this embodiment, each connection member 114B comprises concave curve that curves from the top edge of the top member 110B or base member 112B the reentrant apex 116A which forms the apex of that curve. Again, like the first embodiment (Figure 1 and 2), a fixation arm 114B extends longitudinally outward from the reentrant apex 116B. A bracing member 130B extends from the fixation arm 114B to function as a brace when in a stretched configuration. It should be appreciated that this device 100B also moves between a compact configuration, expanded configuration and stretched configuration in a similar manner as described in relation to the device 100 embodiment described in relation to Figures 1 and 2.

[0152]

[0134] It should be appreciated that the use of curved sections in the connection member provides a more even distribution of force and stress through the length of the connection member between the top member and base member. Sharp angles, for example where the reentrant angle comprises a sharp bend or point bend create stress raising points in the connection member. The inclusion or curves in the reentrant geometry advantageous avoids these stress raising geometries. This difference is shown in Figures 5 to 8 which illustrate the difference in deformation, stress, strain and yielding comparison between (a) an angular unit cell 105A similar to that shown in device configuration illustrated in Figure 1 B(a); and (b) sigmoidal curved unit cell 105 as included in the device 100 shown is illustrated in Figures 1 and 2.

[0135] Figure 5 illustrates the geometry of two reentrant unit cells, 105A and 105, both featuring a reentrant angle of 45 degrees, a reentrant height H, and a reentrant strut length L. Reentrant unit cell 105 is a modified version of 105A, where the straight reentrant strut L is replaced by two curves with a radius R=H / 4. This modification to form reentrant unit cell 105 was made with the aim to reduce stress concentration effects on the reentrant structure of reentrant cell 105A under loading.

[0153]

[0136] Figure 6 shows the elastic deformation properties along the longitudinal direction (Y-axis) of the two reentrant unit cells, 105A and 105, as obtained from finite element analysis using the commercial software Marc Mentat 2021.1. The material properties used in this simulation for both unit cells are those of Ti-6AI- 4V. Longitudinal displacement was induced by applying compression to the top surface of the reentrant unit cells. Due to the inclusion of the curved radius in unit cell 105, it exhibited greater longitudinal elastic deformation capacity compared to unit cell 105A, which lacked the curved design. This enhancement allows the reentrant unit cell 105 to withstand greater deformation under loading without experiencing plastic damage, and it also enables higher pressure to be exerted by the distal end 122 on the bone cavity 150.

[0154]

[0137] Figures 7(a) and 7(b) compare the locations where plastic deformation first occurs at the onset of yielding, as indicated by the plastic strain values from the same finite element analysis (refer to Figure 6). The curved reentrant unit cell 105 showed plastic deformation (yielding location) at the top and bottom sharp corner but not at the centre curved region. Figures 7(c) and 7(d) compare the equivalent Von Mises stress values of the two unit cells under the same amount of compression that stopped at the onset of yielding of reentrant unit cell 105A. A high stress concentration of 807 MPa was observed at the sharp bend in reentrant unit cell 105A, whereas unit cell 105, with its curved design, exhibited a much more uniform stress distribution with a maximum stress of only 348 MPa.

[0155]

[0138] These finite element analysis results demonstrate that the curved reentrant unit cell 105 possesses improved elastic deformation properties due to the curved design, which effectively reduces stress concentration effects.

[0139] Each unit cell may comprise any number of connection members. The embodiments illustrated in Figures 1 , 1A, 1 C and 1 D include two connection members. Moreover, in these embodiments, each connection member is configured to comprise a symmetrical mirror of the other connection member about the longitudinal axis. Again, this symmetrical configuration assists in providing similar compression and expansion properties along the longitudinal length of the unit cell.

[0156]

[0140] In some embodiments, for example, as illustrated in Figure 1 B, the unit cell 105C may comprise a single connection member 114C. This unit cell 105C is effectively half the unit cell 105 illustrated in Figures 1 and 2, having all the same geometric features and function. It should be appreciated that due to this similarity that the description of the device 100 and unit cell 105 for the unit cell 105 illustrated in Figures 1 and 2 equally applies to this half-cell embodiment, including movement between and configurational properties of the compact configuration, the expanded configuration and the stretched configuration, but relating to half of that described configuration. This unit cell 105 provides a more compact configuration which may be configured to be installed in more compact environments compared to the full two connection member configuration (Figures 1 and 2). For example, where two fixation arms 114C are required to secure the device 100C in opposing walls of a bone cavity (or other installation location), each unit cell 105C may be symmetrically aligned I mirrored about a central axis Y so that each fixation arm 120C projects outwardly in opposite directions, as shown in Figure 1 B(b). That mirrored configuration may be formed into a device 101 A or 101 B shown in Figures 1 B(c) and 1 B(d) having a shared top member 110C and base member 112C, in those cases having a cylindrical (Figure 1 B(c)) or cuboid (Figure 1 B(d)) configuration respectively, which can assist with connection to an appropriate implant or scaffold geometry, depending on the particular application.

[0157]

[0141] The bracing member of the illustrated devices 100, 100A to 10OH may be adapted or designed with any suitable configuration. As previously discussed, any suitable portion of the bracing member may engage with the bracing portion of the connection member in the stretched configuration to form said brace between the fixation arm and the connection member. That contact member may engage with the bracing portion of the connection member to form said brace between the fixation arm and the connection member. In embodiments, a distal end of the bracing member may engage with the bracing portion of the connection member in the stretched configuration to form said brace between the fixation arm and the connection member. Similarly, be appreciated that this distal end of the bracing member may comprise any suitable form.

[0158]

[0142] Figures 1 C and 1 D provide different device configurations which illustrate different bracing member configurations that may be used to engage with the bracing portion of the connection member in the stretched configuration to form said brace between the fixation arm and the connection member. Each of these configurations comprise the same auxetic unit cell 105 geometry as illustrated and described in relation to the device 100 illustrated in Figures 1 and 2, with the connector member 114 in each device 100D to 100H having a curved (sigmoid) reentrant geometry as described for device 100 (Figures 1 and 2). It should be appreciated that the description of like parts in for device 100 (Figures 1 and 2) equally applies to these devices 100D to 100H. The difference in each device relates to the configuration of the bracing member 130D to 130H, including differences in engagement sections 135E to 135H.

[0159]

[0143] Firstly, Figure 1 C provides an example of a device 1 C which includes bracing members 130D extending in each longitudinal direction (i.e. directed longitudinally towards the top member 110D and base member 112D). Each bracing member 130D has an L-shaped configuration which extends towards a bracing portion 132D of the proximate connection member 114. The bracing functionality operates as previously described for device 100 (Figures 1 and 2). However, this configuration provides a brace and locking function for pulling forces in each longitudinal direction, i.e. arrows P1 and P2 in Figure 1 C. This configuration can be advantageous for implant fixation where the implant may experience multidirectional forces.

[0144] Figures 1 D(a) to (d) illustrate various bracing member 130E to 130H configurations that may be used in the device 100E to 100H.

[0160]

[0145] Figures 1 D(b) and (c) illustrate different engagement section 135E to 135H configurations that can be used for the bracing member 130F and 130G. For example, the engagement section 135F of bracing member 130F in Figure 1 D(b) comprises the distal end of the bracing member 130F. This may simply be the planar end of the bracing member 130F, as shown in Figure 1 D(b), or may have a shaped end, for example as shown in Figures 1 D(c) and 1 D(d). In this regard, the engagement section 135G of bracing member 130G in Figure 1 D(c) comprises a spherical distal end. Similarly, the engagement section 135H of bracing member 130H in Figure 1 D(d) comprises the top end of an inverted T shaped member. Nevertheless, it should be appreciated that any suitable shape could be used, for example L, b, o, d, T, Y or J shaped members.

[0161]

[0146] Furthermore, it should again be appreciated that whilst not illustrated, each bracing member may extend at any suitable angle from the fixation arm, for example an acute angle longitudinally away from the fixation arm towards the bracing portion of the connection as discussed previous. That angle may be selected to suit the geometric design of the connection member. Similarly, as previously described, the bracing portion of the connection member may comprise any suitable section of the connection member which a portion of the bearing member may engage to transfer load from the fixation arm through to the respective top member and / or base member.

[0162]

[0147] Figure 1 D(d) also illustrates an embodiment where the bracing member 130H is connected to each fixation arm at a location spaced away from the distal end 122H of the fixation arm 120H. As noted above, each bracing member 130H comprises an inverted T shaped member which extends perpendicularly away from the fixation arm 120 about 1 / 3 the length of the fixation arm 130H. It should be appreciated that this configuration still braces movement of the fixation arm 120H in a similar manner as taught for device 100 (Figures 1 and 2).

[0163]

[0148] Finally, Figure 1 (a) shows a simple perpendicular bracing member 130E which extends perpendicularly from the distal end 122E of each fixation arm 120E. It should be noted that in this configuration, the gap G between the distal end of bracing member 130E and the bracing portion 132E of the proximate connection member 114 in the expanded configuration is much larger relative to the equivalent gap in device 100 (Figure 1 ). This means that when the device 100E is subjected to a pulling force, when deformed in the stretched configuration, each fixation arm 120E must be bent or deformed to a greater extent before that the distal end of bracing member 130E engages with the bracing portion 132E of the proximate connection member 114 to form the bracing configuration which resists the pulling force. This can be seen more clearly in Figure 2A which provides snap-shot steps of a simulation of the pull-out performance of a device 100E comprising one unit cell 105E when a pulling force P1 is applied to the top member 110E. As with Figure 2, the outer sides 150 of a bone cavity 152 are illustrated in contact with the distal ends 122E of the fixation arms 120E. The simulated pull-out process represents a simplified model of human cancellous bone, with the mechanical properties of the materials obtained from reported literature, and the device simulated with mechanical properties of an additive manufactured Ti-6AI-4V alloy. The following describes the implant locking mechanism of the stretched configuration in four steps:

[0164] • Step 1 (Figure 2A(a)): The unit cell 105E of the device 100E is the expanded configuration inserted into the bone cavity 152, with the distal end 122E of each fixation arm 120E contacting and exerting pressure on the surrounding bone sidewalls 150 of bone cavity 152.

[0165] • Step 2 (Figure 2A(b)): A pulling force P is exerted on the top member 110E of the unit cell 105E. The longitudinal distance between the top member 110E and base member 112E expands to distance S3 (which is greater than distance S2, shown in Figure 2A(a)). This deforms the connection member 112, pushing the reentrant apex laterally outwardly, and thus exerting further lateral pressure between the distal ends 122E of the fixation arms 122E and the surrounding bone sidewalls 150 of bone cavity 152. Each fixation arm 120E bends, but not sufficiently for the distal end (engagement section 135E) of each bracing member 130E to be located in engagement with the bracing portion 132E of the proximate connection member 114E. The pulling force is therefore not yet resisted. • Step 3 (Figure 2A(c)): As the pulling process progresses, the longitudinal distance between the top member 110E and base member 112E expands to distance S4 (which is greater than distance S3, shown in Figure 2A(b)) and the distal end 122E of each fixation arm 120E is continuously being pushed into the surrounding bone tissue of the bone sidewalls 150. Each fixation arm 120E bends further, but not sufficiently for the distal end (engagement section 135E) of each bracing member 130E to be located in engagement with the bracing portion 132E of the proximate connection member 114E. The pulling force is therefore not yet resisted, and as illustrated the implant device 100E moved longitudinally upwardly by the pulling force due to bending of the fixation arms 120E. However, the distal ends 122E of each fixation arm 120E stay affixed into bone sidewalls 150.

[0166] • Step 4 (Figure 2A(d)): As the pulling process progresses, the longitudinal distance between the top member 110E and base member 112E expands to distance S5 (which is greater than distance S4, shown in Figure 2A(c)) and the distal end 122E of each fixation arm 120E is continuously being pushed into the surrounding bone tissue of the bone sidewalls 150. Each fixation arm 120E bends further, but this time sufficiently to locates the distal end (engagement section 135E) of each bracing member 130E in engagement with the bracing portion 132E of the proximate connection member 114E thereby forming a longitudinal brace between the fixation arm 120E and connection member 114E. At this point, the entire bracing assembly of the fixation arm 120E, bracing member 130E and connection member 114E acts as a stopper, assisting the lower part of the main unit cell 105E body to resist moving further in the pulling direction of pulling force P.

[0167]

[0149] As noted previously, the pull-out force evolution obtained from the simulation results, corresponding with the positions shown in Figure 2A is provided in Figure 3 for device configuration 100E. The simulation shows that for device configuration 100E has a very low initial bracing force until the bracing member 130E contacts the connection member 114E, and there is an immediate change (increase) in the pull out force. The locking mechanism from the bracing member 130E significantly increases pull-out force when finally engaged, with the pull out force increasing immediately once the bracing member 130E forms a brace between the fixation arm 120E and engaged connection member 114E.

[0168]

[0150] Figure 2B (a) to (c) illustrates an example of an unit cell 105F for an implant fixation device 100F in which the fixation arms 120F are connected to the base member 112F which still retains auxetic behaviour and locking effect. Again, this configuration comprises the same auxetic unit cell 105 geometry as illustrated and described in relation to the device 100 illustrated in Figures 1 and 2, with the connector member 114F in each device 100D to 100H having a curved (sigmoid) reentrant geometry as described for device 100 (Figures 1 and 2). It should be appreciated that the description of like parts in for device 100 (Figures 1 and 2) equally applies to this devices 100F. The difference in this device embodiment relates to the bracing member 130F being connected to, preferably integrally connected to, the bracing portion 132F of the respective connection member 114F thereby providing at least a longitudinal brace between the fixation arm and connection member in the stretched configuration (Figure 2B(c)), as well as in the compact configuration (Figure 2B(b)) and expanded configuration (Figure 2B(a)). That connection may comprise a permanent connection for example being affixed, fused or integrally formed or may be designed to be releasably connected, such that the bracing member may be released from being connected to the bracing portion of the connection member where or when desired.

[0169]

[0151] Figure 2C (a) to (c) illustrates an example of an unit cell 105G for an implant fixation device 100G in which the fixation arms 120G are angled downwardly towards the base member 112G. Again, this configuration comprises the same auxetic unit cell 105 geometry as illustrated and described in relation to the device 100 illustrated in Figures 1 and 2, with the connector member 114G in each device 100D to 100H having a curved (sigmoid) reentrant geometry as described for device 100 (Figures 1 and 2). It should be appreciated that the description of like parts in for device 100 (Figures 1 and 2) equally applies to this devices 100G. The difference in each device relates to the fixation arms 120G being angled downwardly towards the base member 112G at an angle of around (3> = 25 degrees. This embodiment still retains auxetic behaviour (see for example movement of the distal ends 122G of the fixation arms 120G between the expanded configuration (Figure 2C(a)) and the compact configuration (Figure 2C(b)), and also retains the locking effect of the distal ends 122 in the surrounding bone sidewalls 150 of bone cavity 152 resulting from engagement of the bracing member 130F with the bracing portion 132F of the respective connection member 114F when in the expanded configuration and stretched configuration. Whilst one embodiment is illustrated, it should be appreciated that the fixation arm or arms may be angled downwardly towards the base member at various different angles. For example, in some embodiments the fixation arm or arms may be angled downwardly towards the base member at an angle from greater than 0 to 30 degrees, such as from 1 to 20 degrees, or from 2 to 15 degrees, or from 3 to 10 degrees.

[0170]

[0152] Figures 2D(a) to (o) illustrates a series variants of a unit cell 105H for an implant fixation device 100H in which the fixation arms 120H are angled upwardly towards the top member 110H by different tilt-up angles (B = 10to 15°). The pullout performance of this series of tilt up fixation arms was considered. It should be noted that these unit cells 105H with different tilt-up angles (B = 1 ° to 15°) have the same projection width Wfor engagement section 135H of each bracing member 130H, and have the same gap G between the engagement section 135H and bracing portion 132H of the respective connection member 114H.

[0171]

[0153] As with the embodiments described above, when a pulling force is exerted, the fixation arms 120H flex downwards until the engagement section 135H of each bracing member 130H, engages with the bracing portion 132H of the respective connection member 114H. This provides the maximum arm length perpendicularly against an engagement surface such as a bone wall, that can be achieved. This configures each of the unit cells 105H with different tilt-up angles (I3> = 1 ° to 15°) into a configuration having an optimal locking effect and the providing maximum pressure to the engagement surface through the distal end of the fixation arm 120H.

[0172]

[0154] As shown in Figure 2E which provides a plot of pulling force versus time when a pulling force is applied to the top member 110H. This plot shows that the best locking effect may be achieved by using slightly up-tilted fixation arms 120H. In this respect, the fixation arms 120H with 5, 4, and 3 degree up-tilting showed the highest pulling resistance. The fixation arms 120H with 12 to 15 degree up tilting showed significantly lower pulling force resistance, with 14 and 15 degree up tilting eventually moving within a bone cavity 152 in which the device is contained within when placed in extreme stretched configuration by the pulling force. Here the distal ends of the fixation arms 120H detach from the surrounding bone sidewalls 150 of bone cavity 152 (similar to as shown in Figure 2G(b)). This can be seen for example in the results plotted in Figure 2E(a) where the 14 and 15 degree up tilting configurations peak and / or taper between 0.25 and 0.3 seconds.

[0173]

[0155] In addition, as shown in Figure 2F, which provides a plot of the maximum pull out force versus the tilt-up angle of the fixation arms 120H, the maximum pullout force remains reasonably constant for tilt up angle fixation arms of 1 to 10 degrees, and then decreases. Again, fixation arms with 12 to 15 degree up tilting were found to have a much lower maximum pull out force, with 14 and 15 degree up tilting having the lowest maximum pullout force.

[0174]

[0156] Finally, Figures 2G (a) and (b) illustrates the extreme case of a unit cell 105I of a fixation device 100I with up-tilted fixation arms 120I where angle I3> is 30 degrees. In this case, the distal ends 122 of the fixation arms 1201 are not locked into position in the stretched configuration as shown in Figure 2g(b) - thus have no locking effect.

[0175]

[0157] Referring now back to the device configurations shown in Figures 1 and 2, it should be appreciated that each bracing member 130 may be configured to engage with the bracing portion 132 of the connection member 114 to limit relative longitudinal movement between the top member 110 and base member 112 towards each other when the implant fixation device 100 is moved into the compact configuration (Figure 1 (b)). As shown in Figure 1 (a), the bracing member 130 may be configured to be spaced apart from the bracing portion 132 of connection member 114 by a gap G when in the expanded configuration. This gap G may be selected to provide a limited longitudinal movement between the between the top member 110 and base member 112 towards each other when the implant fixation device 100 is moved into the compact configuration from that expanded configuration. That spacing or gap may be configured to comprise a small longitudinal distance, such that the top member only moves a short distance for example, less than 1 mm, or less than 0.5 mm. Nevertheless, that gap G may be configured to match the movement between the expansion and compact configurations which facilitates a full elastic deformation of the reentrant unit cell.

[0176]

[0158] The device 100 and unit cell 105 illustrated in Figures 1 , 1A to 1 D, 2 and 2A comprise a planar or two dimensional structure formed from elongate members laid out in 2-dimensional plane. These elongate members may be a rod, bar, wire, shaft, tube or strut, or any suitable member configuration. For example, these members may comprise bars or struts having a thickness of at least 0.8 mm, preferably 0.8 to 5 mm, more preferably from 0.8 to 3 mm, more preferably from 0.8 to 2 mm. In embodiments, these members may comprise bars or struts having a thickness of at least 1 mm, preferably 1 to 5 mm, more preferably from 1 to 3 mm, more preferably from 1 to 2 mm. In embodiments, these members may comprise bars or struts having a thickness of at least 2 mm, preferably 2 to 5 mm, more preferably from 2 to 4 mm, more preferably from 2 to 3 mm. In embodiments, the top member 110 and / or base member 112 may be formed as a rigid body, and may, in embodiments be integrated / connected to an section of an implant or other part of the body of an implant.

[0177]

[0159] As noted previously, the implant fixation device 100 (and any one of 100A to 100H and 200A to 200F and other embodiments described herein) may be formed from any suitable material. In embodiments, the implant fixation device fixation device 100 (and any one of 100A to 10OH and 200A to 200F and other embodiments described herein) may comprise a shape memory material, such as a shape memory alloy or shape memory polymer or the like, as previously described. In other embodiments, the implant fixation device 100 (and any one of 100A to 100H and 200A to 200F and other embodiments described herein) may be comprised of a resilient material, for example a metallic, polymeric, ceramic material or combinations thereof. Examples of suitable metallic materials include: gold, silver, platinum, Co-Cr alloys, a stainless steel, niobium, tantalum, titanium, a titanium alloy, nickel, and combinations thereof. For example, Stainless steel 316L, Ti-6AI-4V, Ti-8Mn, Ti-6AI-7Nb, Ti-3AI-2.5V, Ti-13Nb- 13Zr, Ti-12Mo-6Zr-2Fe, Ti-15Mo, titanium-zirconium alloys, Co-Cr-Mo, Co- 20Cr-15 W-10Ni, Co-35Ni-20, Cr-10Mo, Co-28Cr-6Mo. Examples of suitable polymeric materials include: polyethylene (PE), polyurethane (PU), polyamide (PA), polytetrafluoroethylene (PTFE), polymethylmethacrylate (PMMA), polyethylene terephthalate (PET), synthetic rubber (SR), polystyrene (PS), polyetheretherketone (PEEK), polylactic acid (PLA), and polyglycolide (PGA), and combinations thereof. Examples of suitable ceramic materials include: aluminium oxide, zirconium oxide, zirconium dioxide. Examples of other materials that could be used include carbon, graphene, or the like. It should be appreciated that combinations of the above listed materials could also be used, including for example use in or as part of a composite material. In addition, it should be appreciated, that in those embodiments in which the implant fixation device includes a ceramic component, the device will likely be at least partially ceramic, in some case comprising a composite material i.e. a ceramic composite material. The Implant fixation device 100 (and any one of 100A to 100H and 200A to 200F and other embodiments described herein) preferably comprises a biocompatible material. Depending on the application requirements, the implant fixation device (and any one of 100A to 100H and 200A to 200F and other embodiments described herein) may comprise a biodegradable material. This can be used to provide a patient with a full recovery for temporary fixation.

[0178]

[0160] In particular embodiments, the implant fixation device 100 (and any one of 100A to 100H and 200A to 200F and other embodiments described herein) is formed from titanium or a titanium alloy. As noted above, titanium and its alloys have long been used in orthopedic and dental fields because of their outstanding characteristics such as excellent biocompatibility, osseointegration, high corrosion resistance, high fatigue strength, good strength to weight ratio and fracture toughness.

[0179]

[0161] The implant fixation device 100 (and any one of 100A to 100H and 200A to 200F and other embodiments described herein) can be manufactured by any suitable method. As can be appreciated, that method may be material specific. Suitable methods include additive manufacturing, moulding or the like. In advantageous embodiments, the implant fixation device is made using an additive manufacturing process. For example, where the implant fixation device is produced using a metal or metal alloy such as titanium or a titanium alloy, the implant fixation device can be formed using Electron Beam Melting (EBM) or Selective Laser Melting (SLM) techniques which may utilise powder bed fusion techniques. Alternatively, a cold spray or thermal spray additive manufacturing technique could be utilised. Where the implant fixation device is formed from a polymer a powder bed fusion technique such as selective laser sintering, multijet fusion or the like. However, any number of other of additive manufacturing or product manufacturing techniques could be used. It should be appreciated that a skilled person would be able to select the appropriate additive manufacturing technology for the given implant fixation design and material composition.

[0180]

[0162] As illustrated in Figure 4, the final structure of the implant fixation device 100 may form an assembly of the multiplied unit cells 100 achieved by circumferentially spacing multiple two-dimensional unit cells 100 about the longitudinal axis X (for example rotating and copying those unit cells 100). These figures may for example illustrate configurations of the implant fixation devices formed from a shape memory material, as described above. This figure illustrates examples of three-dimensional (3D) forms of the bone implant fixation device, created by multiplying of the unit cell from two to seven times. A 3D form of the implant fixation device may then be created by including at least two (200A - Figure 4(a)), three (200B - Figure 4(b)), four (200C - Figure 4(c)), five (200D - Figure 4(d)), six (200E - Figure 4(e)), or seven (200F - Figure 4(f)). However, it should be appreciated that some embodiments of the implant fixation device may then be created by including more than seven unit cells, for example 7 to 20 or more of the unit cell circumferentially spaced apart about the longitudinal axis. As previously noted, using multiple unit cells in this manner may multiply the achievable pull-out strength of the device corresponding with the number of unit cells in the structure. Theoretically, the peak pull-out force can reach to M * N (M: peak pull out force for a single cell; N: number of the unit cell) with near zero push-in force (minimal damage to the bone). For example, for a titanium based unit cell with a strut thickness of 0.8 mm, the peak pull-out force M has been found to be 130 N. Moreover, for an implant fixation device with a strut thickness of 0.8 mm (the minimal feature to be produced by electron beam melting), the maximum number of unit cells that may be used is 7. Therefore, theoretically, the maximum achievable pull-out strength of the implant fixation device (having seven unit cells - such as shown in Figure 4(f)) is 130 N x 7 = 910 N. In comparison, for a conventional press-fit implant, such as a knee implant, the range of peak pull-out force for the cementless tibial component is 170 to 380 N. However, it should be appreciated that the peak pull-out force of a particular unit cell design will be dependent on a number of factors, including material, geometric configuration, dimensions and the like.

[0181]

[0163] Figure 4A provides an illustration of the 3D form of the bone implant fixation device, created by multiplying of the unit cell from two (X2) to seven (X7) unit cells circumferentially spaced apart around the central longitudinal axis where the bone implant fixation devices include tooling access similar to the configuration illustrated and described below in relation to Figure 10. As described below in relation to Figure 10, a deformation tool 400 (illustrated in Figure 10) can be inserted through the tooling apertures which can be used to hold the implant fixation device in the compact configuration.

[0182]

[0164] Embodiments of the bone implant device may further include additional components that can assist in strengthening the device, as well as assist in holding the device in the compact configuration ready for insertion into an implant location such as a bone cavity.

[0183]

[0165] Figure 9 illustrates one example of a strengthening arrangement comprising a porous lattice structure 300 that can be added to the bone implant fixation device 200A. These figures may for example illustrate configurations of bone implant fixation devices 200A formed from a shape memory material, as described above. It should be appreciated that a porous lattice structure of this type comprises a three dimensional lattice that is formed with three dimensional porous structure running therein. The three dimensional lattice can be formed in any suitable form, for example through interconnecting nodes with lattice struts or members to form the desired geometric lattice structure, for example a cubic lattice structure. The porous lattice structure 300 assists in achieving the best fixation results and improves the mechanical properties of the implant fixation device 200A. This porous lattice structure 300 may be configured to at least partially enclose the implant fixation device 300 therein. For example, the illustrated device 200A comprises two unit cells spaced apart evenly about longitudinal axis X. The porous lattice 300 illustrated in Figure 9 therefore comprises a segment configured to extend between adjacent faces of unit cells 105 about longitudinal axis X. When assembled, four segments of the porous lattice structure 300 are used to enclose the unit cells 105 of the device 200A as shown in Figure 9(c). Whilst a two unit cell embodiment is illustrated, it should be appreciated that the configuration and segment size of the porous lattice 300 segments will match the configuration of the device. Thus, for an implant fixation device that includes six sides, the segment will be around 360 / n degrees where n=6 in segment angle.

[0184]

[0166] As illustrated in Figure 9A, the device 200A2 may have the configuration shown and described in relation to Figure 10, having a porous lattice 300 configured to accommodate that configuration, for example including a central groove or chamfer 320A providing a tool access tunnel through the assembled porous / lattice structure. The central groove or chamfer 320A accommodating the tooling sections of this embodiment. As described below in relation to Figure 10, a deformation tool 400 (illustrated in Figure 10) can be inserted through the tooling apertures 405 and 407 which can be used to hold the implant fixation device 200A2 in the compact configuration.

[0185]

[0167] The porous lattice structure 300 may also be configured to provide a scaffold for bone in-growth. In this sense, a porous / lattice structure of this type may be added to facilitate bone cell growth, thereby aiding in the bone healing process. The porous lattice structure 300 may be configured to provide mechanical properties similar to those of bone, particularly the yield strength and the Young’s modulus. The porous structure may therefore provide the desired mechanical properties when implanted in a bone cavity and also serve as a scaffold for bone cell growth if necessary.

[0168] Any suitable lattice structure may be used. The illustrated porous lattice 300 comprises a cubic lattice. However, it should be appreciated that other lattice structures could be used, such as tetragonal, orthorhombic, monoclinic, triclinic, hexagonal, rhombohedral or the like. For example, one example of a porous lattice 300 comprises a lattice structure that consists of cubic units having a porosity of 50 percent with pore size of 600 pm, which is a pore size that is reportedly favourable for bone ingrowth. However, it should be appreciated that any suitable porosity may be used, for example between 20 to 80 percent porosity, preferably between 30 and 70 percent porosity, more preferably between 40 and 60 percent porosity, or alternatively between 20 and 70 percent porosity. In embodiments, the porosity may be between 45 and 55 percent, for example around or about 50 percent. Similarly, any suitable pore size may be used, for example between 200 and 1000 pm, preferably between 300 and 900 pm, more preferably between 400 and 800 pm, and yet more preferably between 500 and 700 pm, for example from 550 to 650 pm. Again, it should be appreciated that the particular porosity and pore size may be selected and designed to suit the particular lattice structure, material and lattice configuration.

[0186]

[0169] The porous lattice structure 300 may be comprised of any suitable material, preferably a biocompatible material. That material may comprise for example a metallic, polymeric, ceramic material or combinations thereof. Examples of suitable metallic materials include: gold, silver, platinum, Co-Cr alloys, a stainless steel, niobium, tantalum, titanium, a titanium alloy, nickel, and combinations thereof. For example, Stainless steel 316L, Ti-6AI-4V, Ti-8Mn, Ti- 6AI-7Nb, Ti-3AI-2.5 V, Ti-13Nb-13Zr, Ti-12Mo-6Zr-2Fe, Ti-15Mo, titaniumzirconium alloys, Co-Cr-Mo, Co-20Cr-15 W-10Ni, Co-35Ni-20, Cr-10Mo, Co- 28Cr-6Mo. Examples of suitable polymeric materials include: polyethylene (PE), polyurethane (PU), polyamide (PA), polytetrafluoroethylene (PTFE), polymethylmethacrylate (PMMA), polyethylene terephthalate (PET), synthetic rubber (SR), polystyrene (PS), polyetheretherketone (PEEK), polylactic acid (PLA), and polyglycolide (PGA), and combinations thereof. Examples of suitable ceramic materials include: aluminium oxide, zirconium oxide, zirconium dioxide. Examples of other materials that could be used include carbon, graphene or the like. It should be appreciated that combinations of the above listed materials could also be used. In particular embodiments, the porous lattice structure is formed from titanium or a titanium alloy. As noted above, titanium and its alloys have long been used in orthopedic and dental fields because of their outstanding characteristics such as excellent biocompatibility, osseointegration, high corrosion resistance, high fatigue strength, good strength to weight ratio and fracture toughness.

[0187]

[0170] The porous lattice structure 300 may be formed by any suitable process. In embodiments, the porous lattice structure 300 may formed using an additive manufacturing process, for example Electron Beam Melting (ELM) or Selective Laser Melting (SLM) techniques which may utilise powder bed fusion techniques. In some embodiments, a powder bed fusion process may be used, and the porous lattice structure 300 may be designed to be formed without complex support structures.

[0188]

[0171] Movement from the expansion position to the compact configuration may require a further element or tool to hold the implant fixation device 100 in that prestressed position. Figure 10 illustrates one example of deformation tool 400 configured to hold the implant fixation device 200A2 in the compact configuration. This deformation tool 400 comprises a threaded bolt 403 which is configured to pass through top aperture 405 in the top of device 200A2, and screw into a threaded aperture 407 in the base of device 200A2. The length of the shaft of threaded bolt 403 is sized to locate the device in the compact configuration. However, whilst not illustrated, it should be appreciated that other deformation tool configurations are possible, for example a clip, clasp, bolt and nut / threaded aperture, screw and nut / threaded aperture arrangements. It should be noted that additional ribs 420 were added to the top member 110K and base member 112K device to facilitate its uniform deformation during the application of force using the deformation tool 400.

[0189]

[0172] The deformation tool 400 can be formed from any suitable material. Examples include a metallic, polymeric material or combinations thereof. Examples of suitable metallic materials include: gold, silver, platinum, Co-Cr alloys, a stainless steel, niobium, tantalum, titanium, a titanium alloy, nickel, and combinations thereof. For example, Stainless steel 316L, Ti-6AI-4V, Ti-8Mn, Ti- 6AI-7Nb, Ti-3AI-2.5 V, Ti-13Nb-13Zr, Ti-12Mo-6Zr-2Fe, Ti-15Mo, titaniumzirconium alloys, Co-Cr-Mo, Co-20Cr-15 W-10Ni, Co-35Ni-20, Cr-10Mo, Co- 28Cr-6Mo. Examples of suitable polymeric materials include: polyethylene (PE), polyurethane (PU), polyamide (PA), polytetrafluoroethylene (PTFE), polymethylmethacrylate (PMMA), polyethylene terephthalate (PET), synthetic rubber (SR), polystyrene (PS), polyetheretherketone (PEEK), polylactic acid (PLA), and polyglycolide (PGA), and combinations thereof. It should be appreciated that other materials could also be used, and that the material selection is at least partially dependent on the configuration of the specific deformation tool.

[0190]

[0173] Figure 11 illustrates one example of inserting the implant fixation device 100 into a prepared bone cavity 450. The schematic uses a single unit cell of the implant fixation device 100 as illustrated and described in relation to Figures 1 and 2 to illustrate implantation in a two dimensional format. The method essentially comprises:

[0191] • inserting the implant fixation device 100 into a preformed bone cavity 450 when configured in the compact configuration; and

[0192] • moving the implant fixation device 100 into the expanded configuration, such that each fixation arm 114 moves laterally away from the longitudinal axis X, perpendicularly past the ends of each of the top member 110 and base member 112 and contacts the sidewalls 460 of the surrounding bone cavity 450.

[0193]

[0174] As illustrated in Figure 11 , the steps in this implantation process shown are:

[0194] 1 ). Figure 11 (a): The implant fixation device 100 is undeformed - i.e. in the expanded configuration.

[0195] 2). Figure 11 (b): The implant fixation device 100 is elastically deformed by moving (e.g. compressing) the top member 110 and base member 112 together to be placed in the compact configuration. This results in lateral contraction of the distal ends 122 of the fixation arms 120 (as previously described) to bring these ends within the width of the top member 110 and base member 112.

[0196] 3). Figure 11 (c): The compact device (i.e. device in the compact configuration) is maintained in that compact configuration (for example using deformation tool 400) and inserted into a prepared bone cavity 450.

[0197] 4). Figure 11 (d): The compact device is fully inserted into the bone cavity 450.

[0198] 5). Figure 11 (e): The force used to hold the device in the compact configuration is released (for example removing the deformation tool 400), and the fixation arms 120 and distal ends 122 move laterally outwardly of the longitudinal axis X, and contacts the surrounding bone in the walls 460 of the bone cavity 450.

[0199]

[0175] In an alternative embodiment, the implant fixation device 100 may be constructed from a shape-memory material, such as shape memory alloys or other materials (as discussed previously), which provides for a temperature induced shaped changing between the expanded configuration and compact configuration. Referring again to Figure 11 , this shape memory material embodiment can be explained in relation to inserting the implant fixation device 100 into a prepared bone cavity 450. Again, the schematic uses a single unit cell of the implant fixation device 100 as illustrated and described in relation to Figures 1 and 2 to illustrate implantation in a two dimensional format. The method again essentially comprises:

[0200] • inserting the implant fixation device 100 into a preformed bone cavity 450 when configured in the compact configuration. In this case, the shape memory material can be deformed and held in this configuration at a selected temperature, for example to a freezing temperature (Temperature B); and

[0201] • warming the implant fixation device 100 to cause it to move into the expanded configuration (the memory or remembered position / configuration), such that each fixation arm 114 moves laterally away from the longitudinal axis X, perpendicularly past the ends of each of the top member 110 and base member 112 and contacts the sidewalls 460 of the surrounding bone cavity 450. The expanded condition of the shape memory material, the normal configuration, corresponds with a different temperature, for example human body temperature (Temperature A - (for example from 36 to 37 degrees Celsius). Temperature A is preferably higher than Temperature B.

[0202]

[0176] As previously described, shape-memory materials (SMM)s are materials that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. For the present invention, the pre-deformed ("remembered") shape comprises the expanded configuration of implant fixation device, and the deformed configuration in which it is deformed when cold comprises the compact configuration. In this respect, the implant fixation device may be configured with a shape memory material that is biased to expand from the compact configuration to the expanded configuration when at or above a phase transformation temperature. That phase transformational temperature is preferably is less than or at about human body temperature, for example, the phase transformation temperature may be less than about 36°C as noted above.

[0203]

[0177] As illustrated in Figure 11 , the steps in this implantation process shown are:

[0204] 1 ). Figure 11 (a): The implant fixation device 100 is undeformed - i.e. in the expanded configuration, at Temperature A, preferably human body temperature (for example from 36 to 37 degrees Celsius).

[0205] 2). Figure 11 (b): The temperature of the implant fixation device 100 is move to the compact configuration, where the top member 110 and base member 112 move together and held in that configuration by lowering the temperature of the device to Temperature B (freezing temperature). This results in lateral contraction of the distal ends 122 of the fixation arms 120 (as previously described) to bring these ends within the width of the top member 110 and base member 112.

[0206] 3). Figure 11 (c): The compact device (i.e. device in the compact configuration) is maintained at temperature B so that it remains in that compact configuration and is inserted into a prepared bone cavity 450.

[0207] 4). Figure 11 (d): The compact device is fully inserted into the bone cavity 450.

[0208] 5). Figure 11 (e): The implant fixation device 100 is warmed up to temperature A in the bone cavity, for example to human body temperature (typically from 36 to 37 degrees Celsius). This causes the shape memory material to move to its remembered shape / configuration, i.e. the stretched configuration. Here the implant fixation device may be at least partially restoring to its shape at temperature A. In this configuration the fixation arms 120 and distal ends 122 move laterally outwardly of the longitudinal axis X, and contacts the surrounding bone in the walls 460 of the bone cavity 450.

[0209]

[0178] The implant fixation device 100 advantageously enables the implant to be immediately fixed into position by this method, and may provide near-zero pushin force required for implantation by shrinking of the implant before the implantation process.

[0210]

[0179] Figures 12 to 15 illustrate various implant configurations that embodiments of the implant fixation device of the present invention may be used to assist in fixing the connected implant into position in a preformed bone cavity.

[0211] Application Example 1: Knee implant

[0212]

[0180] The disclosed fixation device can be used to fix an orthopaedic implant in place. One example is shown in Figure 12 which illustrates an example of using the implant fixation device 500 to fix the tibial component of a conventional knee implant for insertion into the tibia bone 550. In this embodiment, the arrangement comprises:

[0213] • a tibial plate 510 including a top side 512 onto which the tibial component (not illustrated) is attached and a base side 514 opposite to the top side 512. The tibial plate 510 includes pegs 515 that can be used for positioning the tibial plate 510 during the surgical procedure.

[0214] • a stem 520 which extends from the base side 514 of the tibial plate 510 and has a base 525 on which the implant fixation device 500 is connected.

[0215] • a connector (not illustrated, but usually a threaded aperture or threaded pin or rod that is located in or extends from the top side 510 of the tibial plate 510, the connector configured to couple with an articulation element of the tibial implant. • an implant fixation device 500. Each fixation device 500 can have any suitable configuration. The illustrated fixation device 500 is shown as having a configuration as described in relation to Figures 1 , 2, 4(a), 9 and 10.

[0216] • an optional porous lattice structure 300.

[0217]

[0181] The implant fixation device 500 is positioned at the end of the stem 520. A tooling tunnel 530 may be provided through the stem 520 to provide a path for accessing the implant fixation device 500 for manipulating a deformation tool (for example as previously described) that is holding the device 500 in the compact configuration. However, it should be appreciated that where the implant fixation device 500 is formed from a shape memory material, such as a shape memory alloy, the tooling tunnel and associated feature may not be required as the shape change is achieved using changes in temperature.

[0218]

[0182] It should be appreciated that this configuration can be adapted for a variety of orthopaedic implants, for example for knee, elbow, back, leg, arm, neck or similar surgeries. Examples include a tibial component of a knee implant (as described above); a femoral component of a hip implant; a humerus component of an elbow implant; a humerus component and / or scapula component of a shoulder implant an ulna component of an elbow implant; a radial head component of an elbow implant; a tibia component of an ankle implant, or a dental implant fixture or screw.

[0219]

[0183] Bone regrowth can be enhanced through the inclusion of a bone scaffold around the implant fixation device. A porous lattice structure 300 can be added to the stem and the underneath part of the tibial plate to facilitate bone cell growth, thereby aiding in the bone healing process. Similarly, whilst not illustrated, at least one section of the tibial plate 510 may include a porous lattice structure, configured to at least partially enclose the implant fixation device therein configured to provide a scaffold for bone in-growth. For example, the porous structure may be located in distal edge regions of the plate and / or those locations in the implant may be considered to induce a stress-shielding effect.

[0184] It should be appreciated, that whilst the above example illustrates the implant fixation device to extend from tibial plate 510, in other the implant fixation device may be configured to extend from, and / or be incorporated with the connector that is configured to couple with an articulation element of the implant. For example, the stem part of the knee implant may also be fully replaced by the implant fixation device in some embodiments.

[0220] Application Example 2: Hip implant

[0221]

[0185] A further example of use of the disclosed fixation device to fix an orthopaedic implant in place is shown in Figure 13. This Figure illustrates an example of using the implant fixation device 600 to fix femoral component 645 of a hip implant in the femoral bone 650. In this embodiment, the arrangement comprises:

[0222] • a plate 610 including a top side 612 onto which the femoral component 645 is attached and a base side 614 opposite to the top side 612. The plate 610 includes pegs 615 that can be used for positioning the plate 510 during the surgical procedure.

[0223] • a stem 520 which extends from the base side 614 of the plate 610 and has a base 625 on which the implant fixation device 600 is connected.

[0224] • a connector 640 that extends from the top side 610 of the plate 610, the connector 640 configured to couple with articulated femoral component 645.

[0225] • an implant fixation device 600. Each fixation device 600 can have any suitable configuration. The illustrated fixation device 600 is shown as having a configuration as described in relation to Figures 1 , 2, 4(a), 9 and 10.

[0226] • an optional porous lattice (not illustrated - but similar in configuration to porous lattice structure 300 shown in Figure 12).

[0227]

[0186] Again, the implant fixation device 600 is positioned at the end of the stem 620. A tooling tunnel 630 may be provided through the stem 620 to provide a path for accessing the implant fixation device 600 for manipulating a deformation tool (for example as previously described) that is holding the device in the compact configuration. A section of the tooling tunnel 630A may also extend through the connector 640. Application Example 3: Ligament Screw

[0228]

[0187] Figure 14 illustrates an implant arrangement where the disclosed implant fixation device is included in a fixation screw 710, for example a ligament fixation screw. As shown in Figure 14, the fixation screw 710 comprises:

[0229] • an elongate threaded shaft 712 (only a section of which is illustrated in Figure 14(b), which includes a series of apertures 715 longitudinally arranged and included in that shaft 712.

[0230] • at least one implant fixation device 700 located within the threaded shaft 712, with the distal ends 722 of the fixation arms 720 extending out of the apertures 712 in a position that can contact the walls of a cavity (threaded cavity or the like) that the screw is inserted within when the implant fixation device 700 is in the expanded configuration. In this respect, the distal ends 722 may be designed to follow the shape of the pitch of the thread of the elongate threaded shaft 712 (screw). Each fixation device 700 can have any suitable configuration. The illustrated fixation device 700 has a similar configuration as described in relation to Figures 1 , 2, 4(a), 9 and 10. In embodiments, the implant fixation device 700 is configured with two bracing members (as described above in relation to Figure 1 C) in order to provide bi-direction fixation - i.e. resist movement of the screw in both longitudinal directions when in the bone cavity 752 (for example as shown in Figure 14(d)).

[0231] • The illustrated fixation device 700 has a configuration shown and described in relation to Figure 10, and includes a tooling access aperture 730 at the top of the fixation screw 710. However, it should be appreciated that where the implant fixation device 700 is formed from a shape memory material, such as a shape memory alloy, the tooling access aperture 730 and associated feature may not be required as the shape change is achieved using changes in temperature.

[0232]

[0188] The fixation screw 710 may be inserted to fix an implant, part of an implant, prothesis or body part into position in or on that bone. For example, as shown in Figure 14(d) the fixation screw may be used in an anterior cruciate ligament (ACL) graft, where two fixation screws 710 may be used to fix the ACL graft into position. Application Example 4: Bone fixation scaffold

[0233]

[0189] Figure 15 illustrates an example application, where embodiments of the disclosed implant fixation device 800 is used to hold a bone fixation scaffold in place for example a finger bone 850. That connector scaffold may be used in any suitable bone of a patient that has a gap, cavity, hold, break or similar which needs to be filled or reconnected. This may reestablish the structure of that bone, and may fill in missing pieces of that bone structure or similar. Applications include bone fixation scaffold for finger bones, arm bones, leg bones or similar.

[0234]

[0190] The illustrated example of a bone scaffold arrangement comprises:

[0235] • a connector scaffold 810 having a first end 812 and second end 814 which is spaced apart from the first end 814; and

[0236] • two implant fixation devices 800, with an implant fixation device 800 attached to the first end 812 and second end 814 of the connector scaffold. Each fixation device 800 can have any suitable configuration. The illustrated fixation device 800 is illustrated as having a configuration as described in relation to Figures 1 , 2, 4(a), 9 and 10.

[0237]

[0191] The type of connector scaffold 814 will depend on the application. The illustrated connector scaffold 810 is a solid connector bar comprising two crossbars. However, other configurations are possible. For example, the connector scaffold 810 may comprise a cage, wire, staple, plate, screw, rod, tubular structure, external fixation device, or a combination thereof. Additionally, whilst not illustrated, it should be appreciated that at least one section of the connector scaffold 810 may include a porous lattice structure, similar to those arrangements described previously, which is configured to provide a scaffold for bone in-growth.

[0238]

[0192] Similarly, the implant fixation device 800 may include a porous lattice structure 300, configured to at least partially enclose the implant fixation device therein, which may also be configured to provide a scaffold for bone in-growth as shown and described in relation to Figure 9.

[0193] Figure 16 provides a schematic illustration of another example application of the implant fixation device 910, 912, 914, 916 when used as an bone fixation scaffold for joining two sections of a bone together, for example a finger bone 950. As shown in Figure 16(a), this embodiment uses a unit cell 900 comprising the mirrored half unit cell described and illustrated in relation to Figure 1 B above. The description of the half unit cell from Figure 1 B equally applies to the unit cell 900 illustrated in Figure 16.

[0239]

[0194] Figures 16(b) to (i) illustrate various example embodiments of the half unit cell configurations forming bone scaffold arrangements that are used for joining two sections of a bone together, for example a finger bone 950.

[0240]

[0195] Figure 16 (b) illustrates an implant fixation device 910 in which the two half unit cells 900 have been joined longitudinally to form the implant. The connector scaffold in this embodiment comprises the two half unit cells 900. The implant fixation device 910 can be implanted in a bone, for example sections of a finger bone 950 as shown in Figure 16(c).

[0241]

[0196] Figure 16 (d) illustrates an implant fixation device 912 in which the two half unit cells 900 have also been joined longitudinally to form the implant. The connector scaffold in this embodiment comprises the two half unit cells 900. However, in this embodiment a porous lattice 900A has been added to portions of the half unit cells 900. As above, the porous lattice 900A may be configured to provide a scaffold for bone in-growth. In this sense, a porous / lattice structure of this type may be added to facilitate bone cell growth, thereby aiding in the bone healing process. As previously discussed above, it should be appreciated that a porous lattice structure of this type comprises a three dimensional lattice that is formed with three dimensional porous structure running therein. The three dimensional lattice can be formed in any suitable form, for example through interconnecting nodes with lattice struts or members to form the desired geometric lattice structure, for example a cubic lattice structure. The porous lattice structure 900A may assists in achieving the best fixation results and improves the mechanical properties of the implant fixation device 900. The implant fixation device 910 can be implanted in a bone, for example sections of a finger bone 950 as shown in Figure 16(c).

[0242]

[0197] Figures 16 (f) illustrates an implant fixation device 914, 916 in which one half unit cell 900 has been joined to a fixation screw 920. That fixation screw 920 may be a porous screw. The connector scaffold in this embodiment comprises the fixation screw 920 in conjunction with the half unit cells 900. The implant fixation device 914, 916 can be implanted in a bone, for example sections of a finger bone 950 as shown in Figure 16(c). In Figure 16(h), the half unit cell 900 of implant fixation device 914 is bridging the gap between the bones 950. In Figure 16(i), the fixation screw 920 of implant fixation device 916 is bridging the gap between the bones 950.

[0243]

[0198] The above described fixation devices have been applied by way of embodiment to an orthopedic implant, fixation screw and connector scaffold. However, it should be understood that it is intended that the implant fixation device may be applied to any type of implant to be inserted into the bone of a patient.

[0244]

[0199] Finally it should be appreciated that the disclosed implant fixation device and associated methods may be applied to a variety of bone and bone structures including in embodiments human patients, animals or the like. In embodiments, the disclosed implant fixation device and associated methods may be applied to a variety of bone and bone structures to non-human patients for example animals or the like. In embodiments, the disclosed implant fixation device and associated methods may be applied to a variety of human bone and bone structures. In some embodiments, the disclosed implant fixation device and associated methods may be used applied to a variety of non-patient bone and bone structures, for example in non-surgical testing or demonstration applications.

[0245]

[0200] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[0201] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.

[0246]

[0202] It is to be understood that the following clauses are provided by way of example only, and are not intended to limit the scope of what may be claimed in the following claim set the present or any such future application. Features may be added to, modified or omitted from the clauses so as to further define or redefine the invention or inventions.

[0247] CLAUSE 1 . An implant fixation device for an implant in a bone of a patient, the implant fixation device comprising at least one unit cell, each unit cell comprising: a top member; a base member longitudinally spaced apart from the top member about a longitudinal axis; at least one connection member connected to and extending between the top member and the base member, each connection member including a reentrant geometry such that the connection member includes a curved or angled configuration that extends inwardly towards the longitudinal axis from each of the top member and base member, the reentrant geometry changing lateral direction relative to the longitudinal axis at a reentrant apex; and at least one fixation arm which extends laterally outwardly from the connection member relative to the longitudinal axis, each fixation arm having a distal end spaced away from the connection member, each fixation arm includes at least one bracing member that extends from the fixation arm towards a bracing portion of the connection member, wherein the implant fixation device is configured to be moveable between: a compact configuration in which the top member and base member are longitudinally spaced apart a first distance which configures the connection member to locate the distal end of each fixation arm in a first lateral position relative to the longitudinal axis; and an expanded configuration in which the top member and base member are longitudinally spaced apart a second distance comprising a greater spaced apart distance to the first distance relative to the longitudinal axis, which configures the connection member to locate the distal end of each fixation arm in a second lateral position which is laterally further away from the longitudinal axis relative to the first lateral position.

[0248] CLAUSE 2. An implant fixation device according to clause 1 , wherein the implant fixation device undergoes elastic deformation when moving from the expanded configuration to the compact configuration, and undergoes elastic recovery when moving from the compact configuration to the expanded configuration.

[0249] CLAUSE 3. An implant fixation device according to clause 1 , wherein the implant fixation device is further configured to be moveable into a stretched configuration from the expanded configuration, in which the distal end of each fixation arm is located in or close to the second lateral position, the top member and base member are further spaced apart about the longitudinal axis relative to the second distance, and at least one portion of the bracing member is located in engagement with the bracing portion of the connection member thereby providing at least a longitudinal brace between the fixation arm and connection member.

[0250] CLAUSE 4. An implant fixation device according to clause 3, wherein the implant fixation device undergoes elastic deformation when moving from the expanded configuration to the stretched configuration, and undergoes elastic recovery when moving from the stretched configuration to the expanded configuration.

[0251] CLAUSE 5. An implant fixation device according to clause 1 or 3, wherein the implant fixation device comprises a shape memory material, having a remembered shape comprising the expanded configuration. CLAUSE 6. An implant fixation device according to clause 5, wherein the implant fixation device moves from the compact configuration to the expanded configuration by changing the temperature of implant fixation device, preferably raising the temperature of the implant fixation device.

[0252] CLAUSE 7. An implant fixation device according to clause 5 or 6, wherein the shape memory material comprises a shape memory alloy, or a shape memory polymer.

[0253] CLAUSE 8. An implant fixation device according to clause 3, wherein in the stretched configuration, a distal end of the bracing member engages with the bracing portion of the connection member to form said brace between the fixation arm and the connection member.

[0254] CLAUSE 9. An implant fixation device according to any preceding clause, wherein each bracing member comprises an L-shaped member.

[0255] CLAUSE 10. An implant fixation device according to any preceding clause, wherein each bracing member extends from or proximate the distal end of said fixation arm.

[0256] CLAUSE 11 . An implant fixation device according to any preceding clause, wherein each bracing member that extends at an acute angle longitudinally away from the fixation arm towards the bracing portion of the connection member to provide a longitudinal and lateral brace between the fixation arm and connection member, preferably from 10 to 80 degrees, more preferably from 10 to 60 degrees.

[0257] CLAUSE 12. An implant fixation device according to clause 11 , wherein each bracing member comprises an elongate member which extends at an acute angle longitudinally away from the fixation arm in a lateral direction towards the longitudinal axis. CLAUSE 13. An implant fixation device according to any preceding clause, wherein the bracing member is configured to be spaced apart from the bracing portion of the connection member in the expanded configuration.

[0258] CLAUSE 14. An implant fixation device according to any preceding clause, wherein the bracing member is configured engage with the bracing portion of the connection member in the compact configuration.

[0259] CLAUSE 15. An implant fixation device according to any preceding clause, wherein the spacing between each bracing member and the related bracing portion of the connection member in the expanded configuration is selected to provide a limited longitudinal movement between the between the top member and base member towards each other when the implant fixation device is moved into the compact configuration from that expanded configuration.

[0260] CLAUSE 16. An implant fixation device according to any preceding clause, wherein the bracing portion of the connection member comprises a section of the connection member proximate or closely connected to the respective top member or base member.

[0261] CLAUSE 17. An implant fixation device according to any preceding clause, wherein the at least one bracing member is connected or otherwise fixed to the bracing portion of the connection member.

[0262] CLAUSE 18. An implant fixation device according to any preceding clause when dependent through clause 3, wherein the distal end of each fixation arm is located in or close to the second lateral position in the stretched configuration through engagement with a wall or other surface of a bone cavity.

[0263] CLAUSE 19. An implant fixation device according to any preceding clause, wherein in the compact configuration, the distal end of each fixation arm is configured to not extend laterally past the ends of each of the top member and base member, and in the expanded configuration at least one fixation arm is configured to extend laterally past the ends of each of the top member and base member.

[0264] CLAUSE 20. An implant fixation device according to any preceding clause, wherein the perpendicular length of each fixation arm is equal to or greater than half the length of the maximum width of the top member and the base member.

[0265] CLAUSE 21. An implant fixation device according to any preceding clause, wherein in the expanded configuration, the distal end of each fixation arm is configured to abut, preferably anchor the implant fixation device into an surface or wall of bone cavity into which the implant fixation device is located.

[0266] CLAUSE 22. An implant fixation device according to any preceding clause, wherein the at least one fixation arm extends substantially laterally from the respective connection member, preferably in a perpendicular or in a substantially perpendicular orientation to the longitudinal axis.

[0267] CLAUSE 23. An implant fixation device according to any preceding clause, wherein the at least one fixation arm extends from at or proximate the reentrant apex thereof, and preferably the reentrant apex is located at or proximate a midsection of the connection member.

[0268] CLAUSE 24. An implant fixation device according to any preceding clause, wherein each connection member comprises at least two curved or angled sections, having at least one curved or angled section extending from the top member and at least one curved or angled section extending from the base member, with the curved or angled sections meeting at the reentrant apex.

[0269] CLAUSE 25. An implant fixation device according to clause 24, wherein the curved or angled sections comprise at least one curve extending from the respective top member or base member to the reentrant apex.

[0270] CLAUSE 26. An implant fixation device according to clause 25, wherein the curved section of each connection member comprises a sigmoid curve which extends between the respective top member or base member and reentrant apex. CLAUSE 27. An implant fixation device according to clause 26, wherein the curves of the sigmoid curve comprise a radius R = 1 / 4 longitudinal distance between the top member and base member when in the expanded configuration.

[0271] CLAUSE 28. An implant fixation device according to any preceding clause, wherein each connection member has a longitudinally symmetrical configuration about the reentrant apex.

[0272] CLAUSE 29. An implant fixation device according to any preceding clause, comprising two connection members, each connection member comprising a symmetrical mirror of the other connection member about the longitudinal axis.

[0273] CLAUSE 30. An implant fixation device according to any preceding clause, further comprising at least two unit cells circumferentially spaced apart about a central axis, preferably circumferentially spaced apart about the longitudinal axis.

[0274] CLAUSE 31. An implant fixation device according to clause 30, comprising at least five, preferably from two to ten unit cells circumferentially spaced apart about the longitudinal axis.

[0275] CLAUSE 32. An implant fixation device according to any preceding clause, further including at least one deformation tool configured to hold the implant fixation device in the compact configuration.

[0276] CLAUSE 33. An implant fixation device according to clause 32, wherein the deformation tool comprises a threaded bolt and aperture located in the top member and base members.

[0277] CLAUSE 34. An implant fixation device according to any preceding clause, further includes a porous structure, preferably a lattice structure, configured to at least partially enclose the implant fixation device therein.

[0278] CLAUSE 35. An implant fixation device according to clause 34, wherein the porous structure is configured to provide a scaffold for bone in-growth. CLAUSE 36. An implant fixation device according to clause 34 or 35, wherein the porous structure is configured to extend between adjacent faces of unit cells about longitudinal axis.

[0279] CLAUSE 37. An implant fixation device according to any preceding clause, wherein the top member, base member and connection member comprise a rod, bar, wire, shaft, tube or strut.

[0280] CLAUSE 38. An implant fixation device according to any preceding clause, wherein fixation device is comprised of a resilient material, preferably comprising a metallic, polymeric, ceramic material or combinations thereof.

[0281] CLAUSE 39. An implant fixation device according to any preceding clause, wherein fixation device is comprised of: gold, silver, platinum, Co-Cr alloys, a stainless steel, niobium, tantalum, titanium, a titanium alloy, nickel, polyethylene (PE), polyurethane (PU), polyamide (PA), polytetrafluoroethylene (PTFE), polymethylmethacrylate (PMMA), polyethylene terephthalate (PET), synthetic rubber (SR), polystyrene (PS), polyetheretherketone (PEEK), polylactic acid (PLA), and polyglycolide (PGA), aluminium oxide, zirconium oxide, zirconium dioxide, carbon, graphene, or combinations thereof.

[0282] CLAUSE 40. An implant fixation device according to any preceding clause, wherein the implant fixation device comprises a biocompatible material, and / or optionally a biodegradable material.

[0283] CLAUSE 41 . An orthopaedic implant comprising: a connector configured to couple with or comprises a section of an articulation element of the orthopaedic implant; and an implant fixation device extending from the base side of the connector according to any one of clauses 1 to 40.

[0284] CLAUSE 42. An orthopaedic implant according to clause 41 , further comprising: a plate including a top side and a base side opposite to the top side; wherein the connector is located in or extends from the top side of the plate; and the implant fixation device extends from the base side of the plate.

[0285] CLAUSE 43. An orthopaedic implant according to clause 41 or 42, further comprising a tooling tunnel configured to enclose the implant fixation device within a cavity or enclosure formed in a bone.

[0286] CLAUSE 44. An orthopaedic implant according to clause 41 , 42 or 43, further includes a porous structure, preferably a lattice structure, configured to at least partially enclose the implant fixation device therein, which is also configured to provide a scaffold for bone in-growth.

[0287] CLAUSE 45. An orthopaedic implant according to any one of clauses 41 to 44, wherein at least one section of the plate includes a porous structure, preferably a lattice structure, configured to provide a scaffold for bone in-growth.

[0288] CLAUSE 46. An orthopaedic implant according to any one of clauses 41 to 45, wherein the articulation element of the orthopaedic implant comprises at least one of: a tibial component of a knee implant; a femoral component of a hip implant; a humerus component of an elbow implant; a humerus component and / or scapula component of a shoulder implant; an ulna component of an elbow implant; a radial head component of an elbow implant; a tibia component of an ankle implant, or a dental implant fixture or screw.

[0289] CLAUSE 47. A bone fixation scaffold comprising: a connector scaffold having a first end and second end, spaced apart from the first end; and at least one implant fixation device according to any one of clauses 1 to 40 extending from at least one of the first end or second end.

[0290] CLAUSE 48. A bone fixation scaffold according to clause 47, wherein the bone fixation scaffold includes at least one implant fixation device extending each of the first end and second end thereof. CLAUSE 49. A bone fixation scaffold according to clause 47 or 48, wherein the connector scaffold comprises a cage, wire, staple, plate, screw, rod, tubular structure, external fixation device, or a combination thereof.

[0291] CLAUSE 50. A bone fixation scaffold according to clause 47, 48 or 49, wherein at least one section of the connector scaffold includes a porous structure, preferably a lattice structure configured to provide a scaffold for bone in-growth.

[0292] CLAUSE 51 . A bone fixation scaffold according to any one of clauses 47 to 50, further includes a porous structure, preferably a lattice structure, configured to at least partially enclose the implant fixation device therein, which is also configured to provide a scaffold for bone in-growth.

[0293] CLAUSE 52. A fixation screw, preferably a ligament fixation screw, comprising: an elongate threaded shaft, and at least one implant fixation device according to any one of clauses 1 to 40 located within the threaded shaft, said threaded shaft including at least one aperture through which the distal end of the fixation arm extends.

[0294] CLAUSE 53. A fixation screw according to clause 52, wherein the threaded shaft includes at least two implant fixation devices longitudinally arranged, preferably longitudinally stacked, along a longitudinal axis of the threaded shaft.

[0295] CLAUSE 54. A method of fixing an implant within a cavity formed in a bone, each cavity having at least one sidewall, the method comprising: inserting an implant fixation device according to any one of clauses 1 to 40 into a bone cavity when configured in the compact configuration; and moving the implant fixation device into the expanded configuration, such that each fixation arm moves laterally away from the longitudinal axis, perpendicularly past the ends of each of the top member and base member and contacts the sidewalls of the surrounding bone cavity.

[0296] CLAUSE 55. A method according to clause 54, wherein prior to implantation into a bone cavity, the implant fixation device is moved from an expanded configuration to the compact configuration by moving the top plate and bottom plate together along the longitudinal axis and fixing the device in the compact configuration.

[0297] CLAUSE 56. A method according to clause 54, wherein implant fixation device comprises a shape memory material, having a remembered shape comprising the expanded configuration, and the implant fixation device is moved from the compact configuration to the expanded configuration by changing the temperature of the implant fixation device, preferably raising the temperature of the implant fixation device.

[0298] CLAUSE 57. A method according to clause 54, 55 or 56, wherein the implant comprises an orthopaedic implant, a bone fixation scaffold or a fixation screw.

Claims

CLAIMS1 . An implant fixation device for an implant in a bone of a patient, the implant fixation device comprising at least one unit cell, each unit cell comprising: a top member; a base member longitudinally spaced apart from the top member about a longitudinal axis; at least one connection member connected to and extending between the top member and the base member, each connection member including a reentrant geometry such that the connection member includes a curved or angled configuration that extends inwardly towards the longitudinal axis from each of the top member and base member, the reentrant geometry changing lateral direction relative to the longitudinal axis at a reentrant apex; and at least one fixation arm which extends laterally outwardly from the connection member relative to the longitudinal axis, each fixation arm having a distal end spaced away from the connection member, each fixation arm includes at least one bracing member that extends from the fixation arm towards a bracing portion of the connection member, wherein the implant fixation device is configured to be moveable between: a compact configuration in which the top member and base member are longitudinally spaced apart a first distance which configures the connection member to locate the distal end of each fixation arm in a first lateral position relative to the longitudinal axis; and an expanded configuration in which the top member and base member are longitudinally spaced apart a second distance comprising a greater spaced apart distance to the first distance relative to the longitudinal axis, which configures the connection member to locate the distal end of each fixation arm in a second lateral position which is laterally further away from the longitudinal axis relative to the first lateral position.

2. The implant fixation device according to claim 1 , wherein the implant fixation device undergoes elastic deformation when moving from the expanded configuration to the compact configuration, and undergoes elastic recovery when moving from the compact configuration to the expanded configuration.

3. The implant fixation device according to claim 1 , wherein the implant fixation device is further configured to be moveable into a stretched configuration from the expanded configuration, in which the distal end of each fixation arm is located in or close to the second lateral position, the top member and base member are further spaced apart about the longitudinal axis relative to the second distance, and at least one portion of the bracing member is located in engagement with the bracing portion of the connection member thereby providing at least a longitudinal brace between the fixation arm and connection member, and optionally wherein the implant fixation device undergoes elastic deformation when moving from the expanded configuration to the stretched configuration, and undergoes elastic recovery when moving from the stretched configuration to the expanded configuration.

4. The implant fixation device according to claim 3, wherein the implant fixation device undergoes elastic deformation when moving from the expanded configuration to the stretched configuration, and undergoes elastic recovery when moving from the stretched configuration to the expanded configuration.

5. The implant fixation device according to claim 1 or 3, wherein the implant fixation device comprises a shape memory material, having a remembered shape comprising the expanded configuration.

6. The implant fixation device according to claim 5, wherein the implant fixation device moves from the compact configuration to the expanded configuration by changing the temperature of implant fixation device, preferably raising the temperature of the implant fixation device, and optionally wherein the shape memory material comprises a shape memory alloy, or a shape memory polymer.

7. The implant fixation device according to any one of claims 1 to 6 when dependent through claim 3, wherein in the stretched configuration, a distal end of the bracing member engages with the bracing portion of the connection member to form said brace between the fixation arm and the connection member.

8. The implant fixation device according to any preceding claim, wherein each bracing member comprises at least one of: comprises an L-shaped member; each bracing member extends from or proximate the distal end of said fixation arm; or each bracing member that extends at an acute angle longitudinally away from the fixation arm towards the bracing portion of the connection member to provide a longitudinal and lateral brace between the fixation arm and connection member, preferably from 10 to 80 degrees, more preferably from 10 to 60 degrees, and optionally wherein each bracing member comprises an elongate member which extends at an acute angle longitudinally away from the fixation arm in a lateral direction towards the longitudinal axis.

9. The implant fixation device according to any preceding claim, wherein the bracing member is configured to be spaced apart from the bracing portion of the connection member in the expanded configuration, and optionally wherein the bracing member is configured engage with the bracing portion of the connection member in the compact configuration.

10. The implant fixation device according to any preceding claim, wherein the spacing between each bracing member and the related bracing portion of the connection member in the expanded configuration is selected to provide a limited longitudinal movement between the between the top member and base member towards each other when the implant fixation device is moved into the compact configuration from that expanded configuration.11 . The implant fixation device according to any preceding claim, wherein the bracing portion of the connection member comprises a section of the connection member proximate or closely connected to the respective top member or base member, and optionally wherein the at least one bracing member is connected or otherwise fixed to the bracing portion of the connection member.

12. The implant fixation device according to any preceding claim, wherein the perpendicular length of each fixation arm is equal to or greater than half the length of the maximum width of the top member and the base member.

13. The implant fixation device according to any preceding claim, wherein in the expanded configuration, the distal end of each fixation arm is configured to abut, preferably anchor the implant fixation device into an surface or wall of bone cavity into which the implant fixation device is located.

14. The implant fixation device according to any preceding claim, wherein the at least one fixation arm comprises at least one of: the at least one fixation arm extends substantially laterally from the respective connection member, preferably in a perpendicular or in a substantially perpendicular orientation to the longitudinal axis; or the at least one fixation arm extends from at or proximate the reentrant apex thereof, and preferably the reentrant apex is located at or proximate a midsection of the connection member.

15. The implant fixation device according to any preceding claim, wherein each connection member comprises at least two curved or angled sections, having at least one curved or angled section extending from the top member and at least one curved or angled section extending from the base member, with the curved or angled sections meeting at the reentrant apex, and optionally wherein each connection member has a longitudinally symmetrical configuration about the reentrant apex.

16. The implant fixation device according to any preceding claim, comprising two connection members, each connection member comprising a symmetrical mirror of the other connection member about the longitudinal axis.

17. The implant fixation device according to any preceding claim, further comprising at least two unit cells circumferentially spaced apart about a central axis, preferably circumferentially spaced apart about the longitudinal axis, and optionally comprising at least five, preferably from two to ten unit cells circumferentially spaced apart about the longitudinal axis.

18. The implant fixation device according to any preceding claim, further includes a porous structure, preferably a lattice structure, configured to at least partially enclose the implant fixation device therein, and optionally wherein the porous structure is configured to provide a scaffold for bone in-growth.

19. An orthopaedic implant comprising: a connector configured to couple with or comprises a section of an articulation element of the orthopaedic implant; and the implant fixation device extending from the base side of the connector according to any one of claims 1 to 18.

20. A bone fixation scaffold comprising: a connector scaffold having a first end and second end, spaced apart from the first end; and at least one implant fixation device according to any one of claims 1 to 18 extending from at least one of the first end or second end.21 . A fixation screw, preferably a ligament fixation screw, comprising: an elongate threaded shaft, and at least one implant fixation device according to any one of claims 1 to 18 located within the threaded shaft, said threaded shaft including at least one aperture through which the distal end of the fixation arm extends.

22. A method of fixing an implant within a cavity formed in a bone, each cavity having at least one sidewall, the method comprising: inserting an implant fixation device according to any one of claims 1 to 18 into a bone cavity when configured in the compact configuration; and moving the implant fixation device into the expanded configuration, such that each fixation arm moves laterally away from the longitudinal axis, perpendicularly past the ends of each of the top member and base member and contacts the sidewalls of the surrounding bone cavity.

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