Method for manufacturing a medical bone connecting device

Abstract

A method for manufacturing a medical bone connecting device (10) is proposed that serves to connect two bones (V, H) or bone parts of a human or animal patient. The method comprises at least the following steps: a.) targeted deposition (80) in a common layer (17) of one or more strands (13) of reinforcing fibers (11) embedded in a matrix material (12), b.) repetition (81) of step a.) for a plurality of successive layers (17), in order to produce a preform (18) of the bone connecting device (10), and c.) compression (82) of the preform (18) in a mold (70) to form the bone connecting device (10). The strand or strands (13) are deposited in such a way in step a.) that they follow a multiple curved path (15) without crossing themselves or each other. Furthermore, a bone connecting device (10) manufactured according to this method is disclosed.

Description

[0001] TITLE

[0002] METHOD FOR MANUFACTURING A MEDICAL BONE CONNECTING DEVICE

[0003] TECHNICAL FIELD

[0004] The present invention relates to a method for manufacturing a medical bone connecting device that is configured to connect bones or bone parts of a human or animal patient. Such a connecting device can particularly be configured as a connecting rod for a pedicle system or configured as a vertebral connecting plate, such as e.g. a cervical plate, or configured as an end plate of a vertebral body replacement.

[0005] PRIOR ART

[0006] Bone connecting devices are frequently used in medicine to bring bones or bone parts into a desired position and hold them in this position, for example after a fracture, such as a traumatic fracture, or in the event of a malposition. In particular, bone connection devices are known in the form of spinal implant systems, which are used to connect and stabilize several vertebral bodies of the spine. These include pedicle systems in which several pedicle screws, each anchored in a vertebral body, are usually fixed to a common connecting rod and thereby connected to each other. Bone connecting devices in the form of vertebral connecting plate systems are also known, in which a connecting plate is fixed to several vertebrae of e.g. the cervical spine (in the case of a cervical plate) using screws in order to stabilize them. Another frequently used bone connecting device is the vertebral body replacement, which is used to replace one or more defective vertebral bodies. The vertebral body replacement, which is often used in combination with a pedicle system, is connected to adjacent vertebral bodies. To adapt to the space to be filled, the vertebral body replacement is often expandable.

[0007] Normally, bone connecting devices are made of metal, for example titanium and / or a titanium alloy. Such bone connecting devices are radio-opaque and allow the exact position of the implant (e.g. the pedicle screw) to be determined when the patient is examined using an imaging procedure such as computer tomography (CT). Despite this advantage, however, such metal implants obstruct the view of the bone connected to the implant and the surrounding tissue during fluoroscopy, as they are radio-opaque and also cause scattering effects during fluoroscopy, which in turn create artifacts in the area of the implant during visualization. Strong artifacts are also caused by such metallic bone connection devices in magnetic resonance imaging (MRI). Due to their radioopacity, metallic bone connection devices also impair the radiotherapy of cancer patients, as the relatively large metallic mass causes scattering phenomena that reduce the effectiveness of the radiation and therefore require a higher radiation dose, which in turn can cause side effects in the surrounding tissue.

[0008] In order to overcome the above-mentioned disadvantages of metallic bone connecting devices, bone connecting devices made of non-metallic composite materials have been developed. Although the production of three-dimensionally complex shapes from composite materials is challenging, it enables the production of radiotransparent components that do not have the above-mentioned disadvantages. In particular, bone connecting devices made of non-metallic composite materials based on carbon fiber-reinforced polyether ether ketone (PEEK) have established themselves on the market.

[0009] A pedicle system with components made from carbon fiber-reinforced PEEK is for example disclosed in EP 1 238 637 A1.

[0010] EP 1 236 451 A1 , WO 01 / 54629 A1 , WO 94 / 05235 A 1 and US 5,294,391 A disclose intervertebral cages that are made from a fiber-reinforced composite material.

[0011] A bone screw made from carbon fiber-reinforced PEEK is known from US 2004 / 0243129 A1.

[0012] A well-proven method for manufacturing carbon fiber-reinforced PEEK bone screws is disclosed in DE 44 45 305 C1 , where fiber-reinforced round rods made of a thermoplastic material are heated to forming temperature and then pressed into a negative mold by extrusion molding. The fibers, which can be long or continuous fibers in particular, are pressed in along the longitudinal direction of the screw. During extrusion molding, the outer fibers follow the inner surface of the mold so that they also enter the outer structures of the screw, thereby reinforcing the thread, for example. The mechanical properties and in particular the strength are important characteristics of bone connecting devices in general. In order to further improve the strength of bone connecting devices with more complicated 3D structures in particular, three-dimensional (3D) printing processes have recently been used that allow the targeted placement of reinforcing fibers. In this way, it is possible to deposit and arrange the fibers in accordance with the specific strength requirements of the device.

[0013] DE 101 50 256 A1 discloses the manufacture of bone implants in a 3D plotting process.

[0014] EP 1 243 231 A2 and WO 2004 / 037902 A1 both deal with the manufacture of dental implants from a polymeric material using 3D printing and also mention the use of fibers in this context.

[0015] WO 01 / 93786 A2 discloses spinal implants that are made from a polymer with fiber reinforcement and, among others, also mentions 3D printing as a possible fabrication method.

[0016] WO 2021 / 009414 A2 discloses a manufacturing method, in which an extruder produces a filament from a thermoplastic material and deposits it in parallel adjoining strips, in order to build up a 3D component layer-by-layer.

[0017] The placement of several straight strands next to each other to form a common layer and thus build up a 3D component layer by layer, is also disclosed by WO 2020 / 185106 A1.

[0018] WO 2019 / 025978 A1 discloses a method for the additive manufacture of medical devices. The additively manufactured structure comprises interstitial spaces, which are filled with a polymeric material. The interstitial spaces serve to customize the rigidity and flexibility of the component.

[0019] In the method disclosed by WO 2020 / 161239 A1, a medical implant is manufactured using a 3D printing process, in which a continuous fiber is deposited in a meandering shape to produce two-dimensional layers with alternating 0 / 90° lay-down patterns of parallel fibers.

[0020] US 2025 / 0017627 A1 discloses a medical bone implant which is manufactured from a thermoplastic composite material and comprises a passive magnetoelastic sensor for measuring data concerning the healing process and / or of a condition of the implant.

[0021] Further state-of-the-art documents that do not relate to the medical field but disclose 3D printing methods for manufacturing components made of a fiber-reinforced thermoplastic material are for example WO 2015 / 009938 A1 , WO 2021 / 176404 A1 and EP 3 272 488 A1.

[0022] The manufacturing of bone connecting devices made from fiber-reinforced plastic materials using 3D printing methods is, however, often complex and therefore cost-intensive. The manufacturing methods known to date are particularly complex and have particular limitations, if the component to be manufactured has a complex 3D structure and / or if the mechanical properties are to vary within the component.

[0023] SUMMARY OF THE INVENTION

[0024] It is an object of the present invention to provide a method for manufacturing a medical bone connecting device made of a fiber-reinforced composite material that is not only easy to perform but can also be adapted to different types of bone connecting devices having different configurations and mechanical properties.

[0025] The object is solved by a method as claimed in claim 1. A bone connecting device manufactured according to such a method is claimed in claim 20. Further embodiments of the invention are laid down in the dependent claims.

[0026] Thus, the present invention provides a method for manufacturing a medical bone connecting device that is configured to connect two bones or bone parts of a human or animal patient, comprising at least the following steps: a.) targeted deposition in a common layer of one or more strands of reinforcing fibers embedded in a matrix material, b.) repetition of step a.) for a plurality of successive layers, in order to produce a preform of the bone connecting device, and c.) compression of the preform in a mold to form the bone connecting device.

[0027] The strand or strands are deposited in such a way in step a.) that they follow a multiple curved path without crossing themselves or each other.

[0028] By depositing the strand or strands such in each layer that they follow a curved path without crossing themselves or each other, it is easily possible to ensure a desired level of strand filling for each layer and position within the device. The strands can be specifically deposited in each layer, e.g. by an extruder nozzle of a 3D printer, in such a way that not only the fiber extensions are in the direction of the expected load, but preferably also that no gaps or a minimum number of gaps are created. The division of the bone connecting device into layers enables the method to be easily applied to complex three-dimensional (3D) structures and to be easily adapted to different types and embodiments of bone connecting devices. It is also possible with the manufacturing method as described to adjust the mechanical strength of the bone connecting device or even of certain isolated regions of the bone connecting device in a targeted manner. This can be achieved by adjusting the strand fill level and / or the orientation of the strands in the device or in the respective region of the device. By following a multiple curved path, a certain strand can for example follow an outer and / or inner contour of the bone connecting device and, thus, optimally reinforce the device in these often particularly demanding regions. Moreover, if the strands follow a multiple curved path, it is also possible to maximize their length, e.g. to more than the maximum overall length of the bone connecting device, in order to further increase the strength of the device. By depositing the strands such that they do not cross themselves or each other, the layers usually have the same thickness everywhere, which means that preferably no gaps are created, when stacking the layers to build up the preform. In case that there are gaps in the preform, they are preferably such that they disappear or at least disappear for the most part during the compression of the preform in step c.).

[0029] The bone connecting device serves to connect two bones or bone parts either directly or indirectly, i.e. via a further other device. A connection to a bone or bone part means that a corresponding device or component is attached to the bone or bone part in such a way that it cannot change its position relative to the bone or bone part, even if the patient moves. The device or component can be anchored, in particular screwed, into the bone or bone part for this purpose. Alternatively, however, it can simply rest against the outside of the bone, in which case it is secured, for example via other components and / or via the surrounding tissue, such that the device cannot move relative to the bone. Bonding the device to the bone or bone part, e.g. using bone cement, is also conceivable if so desired. It is to be understood that, in most embodiments, a device that is connected to a bone or bone part cannot usually be removed from and / or moved relative to the bone without the help of a tool.

[0030] According to a first particularly preferred embodiment, the medical bone connecting device is a component of a pedicle screw system for spinal stabilization, such as a pedicle screw or, what is particularly preferred, a connecting rod that serves to connect two or more pedicle screws with each other. Other components of a pedicle system that might be manufactured according to the method as described are, for example, a tulip head that serves to attach the connecting rod to a pedicle screw, a washer that is adapted to be arranged within the tulip head between the connecting rod and the head of the pedicle screw, or a threaded nut that is configured to be screwed into the tulip head, in order to firmly secure the connecting rod in the tulip head. Alternatively, the bone connecting device can also be e.g. a connector system, such as in particular an axial or parallel connector system that serves to connect two or more connecting rods of e.g. a pedicle system with each other, either axially one behind the other or in parallel to each other.

[0031] According to a second particularly preferred embodiment, the bone connecting device has the shape of a plate, in order to for example form a bone plate that is configured to connect two or more bones or bone parts for example after a fracture, such as a traumatic fracture, or after the treatment of a tumor or an infection or in the case of a malposition. If the bone connecting device is a bone plate, it can particularly be configured to connect two or more vertebrae with each other, as in the case of a cervical or lumbar plate. Particularly preferred is an embodiment in which the bone connecting device is configured as a cervical plate. It is also conceivable for the bone connecting device to be a bone screw that is adapted to be used in combination with a bone plate as described.

[0032] According to a third particularly preferred embodiment, the bone connecting device manufactured according to the method as described is configured as a component of a vertebral body replacement (VBR). In particular the end plates of the VBR, which serve to contact the adjacent vertebrae, are well suited to be manufactured in accordance with the method as described above. However, it is generally also conceivable that the bone connecting device is e.g. a main or base body of the VBR. If the VBR is expandable, the connecting device as described can also be formed by an expansion slide and / or an expandible body of the VBR.

[0033] In yet another embodiment, the method as described can be used to manufacture a bone connecting device configured as an intervertebral disc cage or as one or several components thereof, if it is e.g. an expandable intervertebral disc cage.

[0034] As understood, what is meant by a targeted deposition of a strand is a deposition in which the location of where the strand comes to lie is clearly (pre-)defined, i.e. it is not left to random chance. In a particular embodiment, the strand or strands are deposited by a nozzle through which it / they are preferably extruded. Usually, only a single strand is deposited at a time. By depositing the strand or strands in a targeted way in step a.), the positions and orientations of the reinforcement fibers in the bone connecting device can precisely be defined and e.g. be specifically adjusted to the strength requirements of the device.

[0035] The deposition in a common layer in step a.) means that all strands which are deposited in the same step a.) together form a layer, which is defined by the volume of the sum of all of these strands. Thus, each layer of the preform is usually associated with one step a.), i.e. with the deposition of one or more strands in a common step a.). In the preform, the layers and / or the connecting surfaces arranged between them are usually still recognizable as such, i.e. for example when the preform is cut up and examined (depending on the case with a certain, possibly even microscopic magnification). After completion of the compression, i.e. in the finished bone connection device, the layers can be so strongly interlinked that the connecting surfaces arranged between them are not discernible anymore, even if the device is cut up and examined under magnification. However, the regular arrangement of the layers with the strands is usually still recognizable. Since the strands of a common layer do not cross themselves or each other, the layer usually has a thickness that corresponds to the strand with the largest diameter deposited in the respective step a.).

[0036] The one or more strands are preferably deposited in such a way that each of the strands extends within a single layer only. Thus, the preform preferably comprises strands that reside within a single layer and no strands that extend from one layer to another. This greatly simplifies the manufacture of the preform, both in planning and in production. Due to the same reasons, the preform advantageously also comprises reinforcing fibers that reside within a single layer and no reinforcing fibers that extend from one layer to another. Thus, the preform preferably does not comprise any three-dimensional interlocking by means of strands and / or fibers.

[0037] If more than one strand is deposited in step a.), then the multiple strands are preferably deposited sequentially one after the other. Thus, only a single strand is preferably deposited in step a.) at a time. A more precise deposition is possible in this way. In certain embodiments, however, it is also conceivable that in step a.) multiple strands are deposited in parallel, i.e. at the same time, in order to e.g. achieve a faster production. In an embodiment of the method, where more than one strand is deposited in step a.), the multiple strands preferably extend non-parallel to each other at least over a certain portion of their length.

[0038] While a deposition of strands with differing diameters can be achieved, it is preferred that all strands deposited in a same step a.) have the same diameter. It is even preferred that all strands used for producing the preform in steps a.) and b.) have the same diameter. The production can greatly be facilitated in this way. For example, it is possible that the same fiber-reinforced material is extruded through the same nozzle for several or all strands. Separation of the strands can then be achieved by simply cutting the extruded strand e.g. at the nozzle and moving the nozzle to the deposit starting point of the next strand, in order to continue with the extrusion and deposition of the next strand.

[0039] The preferred strand diameter is in a range between 0.1 to 2 mm, more preferably in a range of 0.3 to 1 mm and particularly preferably in a range of 0.4 to 0.6 mm. It has been recognized that a high internal strength of the finished bone connecting device combined with a good processability of the fiber-reinforced material can be achieved with strands having these diameters.

[0040] The layers produced by the targeted deposition of strands in step a.) are preferably flat layers. Thus, each layer preferably extends two-dimensionally in a plane and advantageously has a constant thickness. The different layers produced in step a.) are preferably arranged parallel to each other in the preform.

[0041] A strand comprises one or more fibers and the matrix material. The matrix material is preferably a plastic, in particular a thermoplastic. The fibers are preferably carbon fibers. The one or more fibers of a common strand usually all have the same length as the respective strand, meaning that each fiber extends along the entire length of the strand. The fibers of a strand are preferably at least partly entangled or intertwined with each other. The strength of the strand is improved in this way. The fiber or the fibers are embedded in the matrix material, meaning that the matrix material surrounds the fiber(s). In a preferred embodiment, each fiber is completely surrounded by the matrix material, which means that the matrix material covers the entire surface of the fiber. In an even more preferred embodiment, the fibers are not only embedded in the matrix material, but also impregnated by the matrix material, meaning that the matrix material is not only present at the surface of the fibers, but also between them. In this way, bone connecting devices of particularly high strength can be manufactured.

[0042] The strands deposited in step a.) can generally have any arbitrary shape in cross-section. Preferred, however, is a circular cross-sectional shape, because the strands are then easier to process. A rectangular or square cross-sectional shape of the strand would for example also be conceivable.

[0043] If more than one strand is deposited in each step a.), they can have different or the same lengths. In particular, if the bone connecting device comprises a complex 3D structure, deposition of more than one strand with different lengths is usually preferred, because this allows filling out a respective layer of the device in a particularly simple way. Deposition of more than one strand per layer with all strands having the same length can, however, be advantageous in some embodiments, in order to e.g. improve the strength of the manufactured device.

[0044] In step a.), the strand or the strands are preferably deposited in such a way that each of them follows a multiple curved path. In some embodiments, in particular if the bone connection device is a connecting rod of a pedicle system, the multiple curved path is regularly curved, i.e. ornamental-like. In a preferred embodiment, each of the deposited strands is curved more than 5 times, and preferably more than 8 times, most preferably more than 12 times, by at least 20°, preferably by more than 40°, more preferably by more than 60°, most preferably by more than 90°, meaning that the strand changes its direction of longitudinal extension by a respective angel due to the curve.

[0045] For forming the preform of the bone connecting device, it is generally possible to produce all layers in steps a.) and b.) in a first step and then to stack the layers in a subsequent second step. In a more preferred embodiment, however, each new layer that is produced in step a.) is directly deposited on a previously produced layer, such that the preform is directly built up layer-by-layer. Thus, in the latter case, the strand or strands are directly deposited onto a previously produced layer in step a.). This has the advantage that the matrix material is still warm in the deposition and preferably bonds with the adjacent, previously produced layer. Of course, it is also possible that e.g. an adhesive is used to bond the layers, independently of whether the strands are deposited directly on a previously produced layer or not. In a further alternative, it is also possible that the layers are not bonded to each other, but only get connected by compression in step c.). The deposition of the strands in steps a.) and b.) can be carried out outside of the mold. After completion of steps a.) and b.), the preform can then be transferred e.g. by hand or by a robot into the mold, in order to carry out step c.). In another embodiment, it is also conceivable to deposit the strands directly into the mold in steps a.) and b.), such that a transfer of the preform is not necessary with regard to step c.).

[0046] When the layers produced in step a.) are transferred into the mold or manufactured by means of direct deposition directly in the mold, the mold preferably has a temperature that is well below the melting point of the matrix material. The temperature of the mold can for example be less than 150 °C, in particular in a range of between 25 °C and 150 °C. The mold is then preferably closed and heated, in order to carry out step c.). The compression in step c.) can thus be a thermal compression or a mechanical compression under elevated temperature. For this purpose, the mold is preferably heated up to a temperature that is higher than the melting point of the matrix material. Advantageously, however, the temperature is kept below the melting point of the fibers during the entire step c.).

[0047] After heating up the preform in the mold to higher than the melting point of the matrix material in step c.), an active cooling is preferably carried out, in order to cool down the composite material and in particular the matrix material. The compression is preferably increased and is advantageously at its highest during the active cooling phase. The temperature of the composite material, in particular of the matrix material, is preferably lowered below the solidification point of the matrix material, more preferably by at least 100 °C below the solidification point of the matrix material, during the active cooling phase. In the case of PEEK, the temperature is preferably lowered to less than 220 °C, more preferably to 150 - 220 °C. This process of the compression combined with active cooling preferably lasts for 4 to 10 minutes.

[0048] The compression of the preform in a mold in step c.) is preferably carried out with a completely closed mold. Thus, there is no possibility for the strands and in particular the matrix material to escape from the mold during compression. Bone connecting devices with particularly high strength can be achieved in this way. The mold is usually made of two parts or more for this purpose, such that it can be opened and closed. If the mold can completely be closed, it can preferably be closed such that its interior is completely sealed to the outside with regard to the matrix material.

[0049] During the compression of the preform in a mold in step c.), preferably this step is carried out with no injection of any further material. In a particularly preferred embodiment, the finished product, i.e. the finished bone connection device that is fully manufactured and ready for use without any further processing steps, does not comprise any additional material compared to the preform. This makes the manufacture of the bone connection device particularly simple.

[0050] In step c.), the preform can be compressed in such a way that a certain shape is given to the bone connecting device. Thus, the shape of the bone connecting device does not necessarily have to be the same as the shape of the preform. In most embodiments, however, the general shape of the preform is still recognizable in the finished bone connecting device, because the compression in step c.) does not cause any change in shape at all, or because the change in shape is so slight that the original basic shape is still recognizable.

[0051] After completion of step c.), the mold is preferably opened and the bone connecting device is removed from the mold.

[0052] With the manufacturing method as described, bone connecting devices can be produced that have a particularly high surface quality and geometric accuracy. Preferably, no shaping and / or surface treatment, in particular no further processing steps at all, are carried out, after removing the bone connecting device from the mold.

[0053] While it is preferred that no further processing steps are carried out after removal of the bone connecting device from the mold, it is nevertheless generally possible that the device removed from the mold for example serves as a green body, in order to be pyrolized by a liquid carbide forming substance and, thereafter, to be infiltrated by a liquid carbide forming substance. In this way, it would be possible to produce a ceramic matrix composite (CMC)- component configured as a bone connecting device with particular properties, such as high- temperature stability, high thermal shock resistance, high hardness, high corrosion resistance, lightweight and versatility in providing unique engineering solutions.

[0054] The strand or the strands deposited in step a.) preferably have a length which is equal to or greater than the maximum overall length of the bone connecting device. By the use of strands of such lengths, a bone connecting device with a particular strength can be manufactured. The shortest strand per layer is preferably longer, more preferably by a multiple longer, than the smallest width of the preform at the level of the respective layer. In some embodiments, the shortest strand per layer can even be longer than the maximum overall length of the bone connecting device, i.e. the length measured along the maximum extension of the device. In order to e.g. achieve a good strength of the bone connecting device, it can be preferred that the lengths of the strands of a same layer differ by less 50%, more preferably by less than 30%, even more preferably by less than 10%, in each case. In a preferred embodiment, more than 40%, more preferably more than 60% and most preferably more than 80% of the strands deposited in the repeated applications of step a.) are longer than the maximum overall length of the bone connecting device. Particularly preferred are embodiments in which 100% of the strands deposited in the repeated applications of step a.) are longer than the maximum overall length of the bone connecting device.

[0055] In a particularly preferred embodiment of the method, the strand or strands are deposited in such a way in step a.) that any internal cavities are removed in the compression of step c.). In order to achieve this, the strand or strands are preferably deposited such in step a.) that the area inside the outer contour of the respective layer is completely filled up in each case or at least filled up such, that possibly remaining gaps are closed during the compression in step c.). For example, the strands can be deposited in such a way that during the subsequent compressing process the strands flow laterally to the fiber direction (perpendicular to the fiber direction) under pressure and thus the gaps created by the strand deposition are closed. By a "lateral flowing of the strands" what is meant is that the matrix material is in a flowable state when compressed in step c.), thereby filling any gaps that may still be present in the preform. In this way, it is possible to manufacture a bone connecting device from a fiber-reinforced plastic material without having any gaps or pores. For this purpose, it is preferably not necessary to impregnate the layers or the preform with any additional filler material before, during, between or after steps a.) and c.). Thus, the finished bone connecting device is preferably exclusively made from the fiber-reinforced matrix material used in the deposition of step a.) and does not comprise any further materials or fillers or any gaps or pores with air inclusions or the like.

[0056] While it is generally possible that each strand comprises one fiber only, according to a preferred embodiment each strand comprises 1'000 to 24'000 fibers, preferably 3'000 to 6'000 fibers, in particular if the strands are made of carbon. With these amounts of fibers per strand, the strands are still flexible enough on one hand, in order to be deposited along a multiple curved path in most embodiments, and also effect a good strength of the finished bone connecting device on the other hand. In step a.), preferably less than 30, more preferably less than 20, in particular less than 10 strands are deposited per layer. With such small numbers of strands per layer, a particularly good internal strength of the bone connecting device can be achieved.

[0057] In certain embodiments and particularly if the bone connecting device is a connecting rod of a pedicle system, only one single strand is deposited in each step a.). Thus, each layer of the preform is defined by one single strand in this case. Using only a single strand per layer not only facilitates the manufacturing process, but also results in a bone connecting device having a particularly good inner strength.

[0058] The volume content of the reinforcing fibers in the bone connecting device is preferably in a range between 20% and 80%, more preferably between 35% and 70%, particularly preferably between 45% and 60%. With volume contents in these ranges, high internal strength of the finished bone connecting device combined with good processability of the fiber-reinforced material could be achieved.

[0059] The reinforcing fibers are preferably made of carbon and the matrix material is advantageously a plastic, in particular a high-temperature thermoplastic with a temperature resistance of up to 250°. Advantageous for use as the matrix material are particularly the material groups of polyaryletherketones, polyimides and polysulphones. In a particularly preferred embodiment, the fiber-reinforced plastic material used in the strand deposition of step a.) is carbon fiber-reinforced polyether ether ketone (PEEK).

[0060] As already mentioned, according to a particularly preferred embodiment, the bone connecting device is a connecting rod for a pedicle system. In this case, in step a.), the strand or the strands are preferably deposited in a regular wave-pattern over at least a portion of the overall main length of the connecting rod. The wave-pattern formed by the strand preferably fills out the entire width of the preform and, advantageously, of the connecting rod. The deposition of the strand or strands, preferably of one strand only per layer, in a regular wave-pattern over at least a portion of the connecting rod brings about the advantage that the flexibility of the connecting rod can be precisely adjusted and defined over a large range. The possibility to manufacture connecting rods for a pedicle system having different, well-defined flexibilities over a large range enables the pedicle system to be manufactured to the specific needs of its application, i.e. to the patient and / or to the position and the intended used of the pedicle system in the patient. The flexibility of the connecting rod can particularly well be adjusted by defining the spatial frequency of the waves along the longitudinal extension of the rod and / or, which is more preferred, by the angular orientation in which curves formed by the wave-pattern are bent relative to the longitudinal direction of the rod.

[0061] The strands preferably all extend over the entire main length of the connecting rod. In this way, a continuous and good internal strength can be achieved over the entire length of the rod.

[0062] In certain embodiments, it is also possible that the wave-pattern formed by the strands of the connecting rod only extends over a portion of the entire main length of the connecting rod. This allows to e.g. effect a higher flexibility over only the respective portion of the rod, while the other portion(s) of the rod have a lower flexibility. In the portion(s) without the wave-pattern, the same strands can in this case for example run straight along the longitudinal extension of the rod.

[0063] If there is a wave-pattern, the fiber or fibers are preferably deposited such in step a.), that they describe a curve of at least 90°, more preferably of at least 135° in each wave of the wave-pattern. In a particularly preferred embodiment, the strand or strands are deposited such that they describe a curve of at least 180° in each wave of the wave-pattern. It could be established in tests, that by providing curves of 180° or more in the wave-pattern, not only a sufficient filling of each layer can be achieved with regard to the avoidance of gaps or pores in the finished connecting rod, but also that a connecting rod with a high internal strength and a particularly well adjustable flexibility can be manufactured.

[0064] According to a preferred embodiment, in step a.), the strand or strands are deposited such that the waves formed by the wave-pattern are bent in an absolute value range between 85° and 20°, preferably between 75° and 30°, particularly preferably between 55° and 35°, in relation to the main longitudinal direction of the connecting rod. With waves that are bent in a range between 55° and 35°, an optimal flexibility of the connecting rod can be achieved for many applications of a pedicle system, in particular if the rod is made of a carbon- reinforced thermoplastic. By bending the waves at a greater angle than 55° relative to the longitudinal direction, i.e. by up to 85°, the flexibility of the rod can be increased, in order to e.g. increase the range of movement of the two bones or bone parts connected to the rod.

[0065] In step a.) of the manufacturing of a connecting rod, the fiber or fibers are preferably deposited such that the waves of successive layers are bent in alternating directions in each case in relation to the main longitudinal direction of the connecting rod. A connecting rod with a good internal strength and well adjustable flexibility can be manufactured in this way. It has also surprisingly been found out that by depositing the strands in wave-patterns and in particular with alternatingly bent wave-patterns, the flexibility of the final connecting rod is independent to a large extent on the direction in which it is flexed perpendicularly to the longitudinal direction. Thus, the flexibility is largely the same, no matter whether the rod is flexed in the layer direction or perpendicularly thereto.

[0066] In order to achieve a good filling level without gaps or pores, the waves formed by each strand are all bent in the same parallel directions.

[0067] In order to give the connecting rod a changing stiffness along its main longitudinal direction, the waves formed by each strand can be bent in varying angles along the main longitudinal direction of the connecting rod. Thus, the angle of bending of the waves can in this case particularly be in accordance with the desired flexibility of the connecting rod at the respective longitudinal position.

[0068] In order to make the bone connecting device and in particular the connecting rod visible in medical imaging procedures, a wire, preferably a radio-opaque wire, such as for example a metal wire, can additionally be deposited e.g. in one of steps a.) or in-between, in order to be arranged between the layers of strands and to serve as a marker, e.g. visual or fiducial marker, in medical imaging procedures. The wire, which is advantageously made of a biocompatible material, preferably has the same length as the bone connecting device, in particular the connecting rod. Thus, the wire preferably extends over the entire main length of the bone connecting device. The provision of a marker, in particular of a wire, such as a metal wire, in order to make the device visible in medical imaging procedures, can also be preferred if the bone connecting device is e.g. a bone plate, such as a cervical plate, or an end plate of a VBR. The marker can in these cases have a different form than a wire and be specifically configured to the form of the device.

[0069] In some embodiments, one or several passive and / or active sensors can be placed within or on the medical bone connecting device, in order to e.g. measure one or more parameter(s) of the healing process and / or of a condition of the implant, such as stress or movement. The one or several passive and / or active sensors can particularly be deposited e.g. in one of steps a.) or in-between, in order to be arranged between the layers of strands. In the case of one or several passive sensors, at least one of the passive sensors is preferably a passive magnetoelastic sensor. The measurement carried out by a magnetoelastic sensor is based on a change of the magnetic characteristics of a material of the sensor. In order to enable a measurement based on the magnetoelastic effect, the at least one passive magnetoelastic sensor usually comprises a sensor material in the form of a ferromagnetic material, preferably a ferromagnetic alloy, with an inverted magnetostriction. The ferromagnetic material changes its magnetic characteristics under mechanical or thermal stress, respectively, and especially its magnetic permeability, which can be detected and measured by means of a suitable measuring instrument or reading device, respectively. In one particular embodiment, the passive magnetoelastic sensor can be in the form of a micro wire.

[0070] According to a further particularly preferred embodiment, the bone connecting device has a plate-like overall shape and is in particular a bone plate including, for example, a vertebral connecting plate, such as a cervical or lumbar plate, or an end plate of a vertebral body replacement. In this case, the bone connecting device preferably has one or several apertures extending through the device, each of which is laterally delimited by less than 5 strands per layer, preferably by less than 3 strands per layer, in particular by only a single strand per layer. In some embodiments, all the apertures extending therethrough the device are laterally delimited by less than 5 strands per layer, preferably by less than 3 strands per layer, in particular by only a single strand per layer.

[0071] For the manufacturing of the bone connecting devices with plate-like overall shapes as mentioned, but also for the manufacturing of other bone connecting devices, it can be preferable, if in step a.), a major part of the main longitudinal extension of each strand is deposited in such a way that it either follows an inner and / or an outer contour of the bone connection device or that it fills an inner part of the respective layer in a meandering, circular and / or spiral shape. It has been realized that for strands which do not follow an inner or outer contour, a deposition along a meandering, circular and / or spiral path is particularly well suited to fill up the areas distant from the contours without leaving any gaps or pores.

[0072] The present invention also refers to a bone connecting device manufactured as indicated above. The bone connecting device can particularly be a connecting rod for a pedicle system or a bone plate including a vertebral connecting plate, such as a cervical plate, or an end plate of a vertebral body replacement. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings,

[0074] Fig. 1 shows a schematic side view of a pedicle system in situ relative to the spine of a patient, with a connecting rod manufactured according to the invention;

[0075] Fig. 2 shows a 3D printer during the targeted deposition of a strand;

[0076] Fig. 3 shows a flowchart of a preferred embodiment of the method according to the invention for manufacturing a medical bone connecting device;

[0077] Fig. 4a schematically shows a side view of the connecting rod of Fig. 1 in isolated position;

[0078] Fig. 4b shows a central cross-sectional longitudinal view of the preform used for manufacturing the connecting rod of Fig. 1 ;

[0079] Fig. 4c shows an enlarged partial view of a central layer of the preform used for manufacturing the connecting rod of Fig. 1 ;

[0080] Fig. 4d shows an enlarged detail view of the rectangular area marked by a dashed line in Fig. 4c;

[0081] Fig. 4e shows an enlarged partial view of two adjacent central layers of the preform used for manufacturing the connecting rod of Fig. 1 ;

[0082] Fig. 5 shows an enlarged partial view of a central layer of the preform used for manufacturing a connecting rod according to another embodiment;

[0083] Fig. 6 shows an enlarged partial view of a central layer of the preform used for manufacturing a connecting rod according to yet another embodiment;

[0084] Fig. 7 shows an enlarged partial view of a central layer of the preform used for manufacturing a connecting rod according to yet another embodiment;

[0085] Fig. 8 shows a graph for visualizing the dependencies of the relative rigidity and strength on the bending angle of the waves formed by the wave-pattern in relation to the main longitudinal direction of the connecting rod;

[0086] Fig. 9a shows a schematic cross-sectional view of a mold with inserted preform immediately before thermal compression during the manufacturing of a connecting rod of a pedicle system according to the inventive method;

[0087] Fig. 9b shows the mold of Fig. 9a during thermal compression of the preform in order to form the connecting rod; Fig. 10 shows a side view of another embodiment of a connecting rod of a pedicle system manufactured according to the inventive method;

[0088] Fig. 11 shows a side view of yet another embodiment of a connecting rod of a pedicle system manufactured according to the inventive method;

[0089] Fig. 12 shows a side view of yet another embodiment of a connecting rod of a pedicle system manufactured according to the inventive method;

[0090] Fig. 13 shows a side view of yet another embodiment of a connecting rod of a pedicle system manufactured according to the inventive method;

[0091] Fig. 14 shows a side view of yet another embodiment of a connecting rod of a pedicle system manufactured according to the inventive method;

[0092] Fig. 15 shows a schematic side view of a bone plate manufactured according to the invention and anchored in the humerus of a patient by means of bone screws;

[0093] Fig. 16 shows a schematic side view of a bone plate manufactured according to the invention and anchored in the cervical spine of a patient by means of bone screws;

[0094] Fig. 17a shows the top view of an example of a cervical plate manufactured according to the invention;

[0095] Fig. 17b schematically shows a central layer of the preform used for manufacturing the cervical plate of Fig. 17a, with marked ends of individual strands;

[0096] Fig. 17c shows an overlay of Figs. 17a and 17b;

[0097] Fig. 18a shows the top view of an example of a bone plate manufactured according to the invention;

[0098] Fig. 18b schematically shows a central layer of the preform used for manufacturing the bone plate of Fig. 18a, with marked ends of individual strands;

[0099] Fig. 18c shows an overlay of Figs. 18a and 18b;

[0100] Fig. 19a shows a schematic cross-sectional view of a mold with inserted preform immediately before thermal compression during the manufacturing of a bone plate according to the inventive method;

[0101] Fig. 19b shows the mold of Fig. 19a during thermal compression of the preform in order to form the bone plate;

[0102] Fig. 20 shows a schematic side view of a vertebral body replacement (VBR) in situ relative to the spine of a patient and comprising end plates manufactured according to the invention, and used in combination with a pedicle system;

[0103] Fig. 21a shows the side facing away from the vertebral body of one of the end plates of the VBR of Fig. 20;

[0104] Fig. 21b schematically shows a central layer of the preform used for manufacturing the end plate of Fig. 21a, with marked ends of individual strands;

[0105] Fig. 21c shows the side facing towards the vertebral body of the end plate of Fig. 21a;

[0106] Fig. 22a shows a schematic cross-sectional view of a mold with inserted preform immediately before thermal compression during the manufacturing of an end plate for a VBR according to the inventive method; and

[0107] Fig. 22b shows the mold of Fig. 22a during thermal compression of the preform in order to form the end plate.

[0108] DESCRIPTION OF PREFERRED EMBODIMENTS

[0109] In Figures 1 to 22b, different embodiments of bone connecting devices manufactured according to the inventive method and method steps as well as devices for carrying out the inventive method or at least steps thereof are shown. Elements of different embodiments, having the same or a similar function are marked with the same reference sign in each case.

[0110] Fig. 1 shows a particularly preferred embodiment of a bone connecting device configured as a connecting rod 23 of a pedicle system 20. The pedicle system 20 has a plurality of pedicle screws 21 , which are each screwed into a vertebral body V of a patient's spine S. Each of the pedicle screws 21 is attached to the connecting rod 23 by means of a tulip head 22. The connecting rod 23 thus connects the pedicle screws 21 to each other and thereby locks the vertebral bodies V. By connecting the pedicle screws 21 and therewith the vertebral bodies V, the connecting rod 23 thus forms a bone connecting device. Due to the elongated shape of the connecting rod 23, a main longitudinal direction L is defined. The pedicle system 20 can be effectively used for spinal stabilization by enabling rigid fixation of the vertebral bodies V relative to one another. In addition, the pedicle system 20 can be used, for example, to relieve the intervertebral discs I arranged between the vertebral bodies V in each case.

[0111] Figure 3 shows the preferred steps applied by the inventive method, in order to manufacture a bone connecting device 10, such as e.g. the connecting rod 23 of Fig. 1. As starting materials for carrying out the manufacturing method, reinforcement fibers 11 and a matrix material 12 are used. The reinforcement fibers 11 are preferably carbon fibers. The matrix material 12 is preferably from the material groups of polyaryletherketones, polyimides and polysulphones. In particular polyether ether ketone (PEEK) can be used as the matrix material, which is then preferably combined with a plurality of fibers 11 made of carbon, in order to form a composite strand 13. For example and according to a preferred embodiment, 3'000 to 6'000 carbon fibers 11 can be embedded in the matrix material 12, in order to form the composite strand 13.

[0112] In order to form a preferably continuous composite strand 13, the fibers 11 are preferably embedded side by side lengthwise as continuous fibers in the matrix material 12. In order to obtain a strand 13 with particular high strength, it is preferred that the fibers 11 of the strand 13 are at least partly entangled or intertwined with each other. A particularly good connection to the matrix material 12 is achieved, if the fibers 11 are not only embedded in (i.e. surrounded by) the matrix material 12, but also impregnated by the matrix material 12. For embedding and, preferably, impregnating the fibers 11 , the matrix material 12 is usually heated up to above its melting point, in order to adopt a liquid state.

[0113] The such produced continuous composite strand 13 is then used to build a preform 18 of the bone connecting device 10. For this purpose, a 3D printer 60 is used, as it is shown in Fig. 2. In the 3D printer 60, which is adapted for additive manufacturing processes, the composite strand 13 is stored on a storage wheel 61. From the storage wheel 61 , the continuous strand 13 is unwound by means of two or more opposing feed wheels 62, which guide the composite strand 13 to a heater 63. In the heater 63, the strand 13 is heated up, in order to be better processable and to be pressed through a nozzle 64. The nozzle 64 serves to deposit the strand 13 in a targeted manner onto a worktable 65 of the 3D printer 60. The nozzle 64 is movable relative to the worktable 65, in order to deposit the strand 13 in a targeted way along a predetermined path of a layer 17. The path along which the strand 13 is deposited on the worktable 65 by the nozzle 64 is specified by control data previously given to a controller of the 3D printer, e.g. manually by an operator via a user interface on a computer, or via a storage element, or via a data stream from a network. The control of the movements of the nozzle 64 relative to the worktable 65 during the deposition of the strand 13 is preferably carried out automatically by means of a controller based on the control data. Thus, by means of the 3D printer shown in Fig. 2, a method step 80 as described in Fig. 3, i.e. a targeted deposition of a strand 13 in a layer 17 is carried out.

[0114] As can be seen in Fig. 2, if the targeted deposition of the strand 13 in a first layer 17 is completed, the strand 13 is cut before, after or at the nozzle 64 by means of a cutting device not shown in the figures and a new layer 17 is produced on top of the previous layer 17 by means of another targeted deposition of the strand 13. The cutting of the strand 13 becomes visible by the ends of the strand 14. Of course, a cutting of a strand 13 can also be carried out during the production of a layer 17, in order to continue the deposition at another location of the same layer 17. Thus, a plurality of layers 17 are produced by means of repeatedly carrying out step 80, i.e. the targeted deposition of the strand 13 in layer 17, as it is described by repetition loop 81 in Fig. 3.

[0115] The targeted deposition 80 in repetition loop 81 is continued layer-by-layer until a preform 18 of the bone connecting device 10 is completed, meaning that all layers 17 as required to form the preform 18 have been produced using the 3D printer. The preform 18 thus has a layer structure, with each layer 17 being formed by one or multiple parts of the strand 13. The strands 13 of each of the layers 17 in each case follow a multiple curved path and are arranged such that they do not cross themselves or each other. Moreover, they are preferably arranged such in each layer 17 that there are no large gaps or pores, except of course for the ones (if needed in some embodiments) which later on should also be present to form large apertures in the finished bone connecting device 10.

[0116] The preform 18 usually has a shape that is identical or closely corresponds or is at least similar to the shape of the finished bone connecting device 10. The strands 13 of the preform 18 and in particular the fibers 11 contained therein are usually arranged and oriented the same as in the finished bone connecting device 10 later on. Thus, by the targeted deposition in step 80 using the 3D printer 60, the precise arrangement and orientation of the reinforcement fibers 11 can be defined not only with regard to the preform 18, but also with regard to the finished bone connecting device 10.

[0117] Due to the increased temperature of the strand 13 after passing through the heater 63, the matrix material 12 of the strand is softened and thus preferably bonds, at least to a certain extent, with the matrix material 12 of the already deposited strands 13 in the lower layer 17 during the deposition. As a result, the preform 18 advantageously has a certain internal cohesion, what facilitates the further handling of the preform 18. In other cases, the layers 17 are not bonded to each other or are even produced separately from each other. It is conceivable for example in a mass production to produce several copies of the same layer 17 at the same time in parallel, and only then to produce the other layers 17, again several in parallel, in order to assemble a plurality of preform 18 only after all layers 17 of all preforms have been produced. In these cases, where the layers 17 of a preform 18 are not bonded together, it is also possible to insert the layers 17 individually into the mold. Less preferred, but generally possible is to provide an adhesive between the layers 17, in order to at least partially bond the layers 17 and forming a preform 18 before or during the insertion of the preform 18 into the mold.

[0118] The preform 18 is thus inserted into a mold 70 (see e.g. Figures 9a, 19a and 22a), in order to undergo thermal compression in step 82 of Fig. 3. The mold preferably has the negative shape of the bone connecting device 10. The insertion of the preform 18 into the mold 70 can be done manually by an operator or automatically, e.g. by means of a robot arm. When inserting the preform 18, the temperature of the mold 70 is far below the melting point of the matrix material 12. The mold temperature is for example between 25 °C and 150 °C.

[0119] For the thermal compression 82, the mold 70 is first closed under slight pressure effected by a press and heating plates are brought into contact with the mold 70 (press and heating plates not shown in the Figures). The mold 70 is then heated to the processing temperature of approximately 400 - 420 °C (note: melt temperature of the matrix material 12 made of PEEK is 343 °C). Depending on the weight of the mold 70, this process usually takes approximately 5 - 15 minutes.

[0120] After a mold temperature of approximately 400 - 420 °C has been reached, the press is opened and the heating plates are moved away from the mold 70 and the mold 70 is held in a closed state with a special holder (carrier frame or carrier plates). Two cooling plates (not shown in the Figures) are then inserted and positioned laterally at the top and bottom between the heating plates and the mold 70. This exchange of the heating plates with the cooling plates is an intermediate step of the thermal compression 82. In other embodiments, it would of course also be possible to integrate the heating and the cooling units in the mold 70.

[0121] As the next substep of the thermal compression 82, the press is closed and the pressure force on the still hot mold 70 is substantially increased, in order to compress and consolidate the preform 18 inserted in the mold 70. At the same time, the cooling process becomes effective, which cools the mold 70 down to approximately 150 - 220 °C when PEEK is used as the matrix material 12. Depending on the weight of the mold 70, this process takes approximately 4 - 10 minutes.

[0122] As the last step of the manufacturing process, after completion of the thermal compression 82, the mold 70 is opened and the bone connecting device 10 is removed from the mold 70 in a mold removal step 83. For this purpose, the press is first opened, the cooling plates are then retracted sideways and the “cold” mold 70 is opened. The consolidated bone connecting device 10 can then be removed.

[0123] During the thermal compression 82, the fibers 11 generally retain their original stretched direction. Bone connecting devices 10 produced using the manufacturing process as described have a particularly high mechanical strength and rigidity. According to a preferred embodiment of the manufacturing process, no further processing steps are carried out after removal of the bone connecting device 10 from the mold 70.

[0124] Figures 4a - 4e illustrate a particularly preferred embodiment of a bone connecting device 10 configured as a connecting rod 23 of a pedicle system 20 as shown in Figure 1. The connecting rod 23 has an elongated shape, by which a main longitudinal direction L is defined, as it is depicted by the dashed line in Figure 4a. Usually, the connecting rod 23 has one or more bends, which can vary depending on the application. The connecting rod 23 shown in Figure 4a is only slightly bent. Other examples will be described further below in relation to Figures 10 to 14.

[0125] Figures 4b - 4e show cross sectional views of the preform 18 used for manufacturing the connecting rod 23 of Figure 4a. In particular, the strand arrangement within the preform 18 is visible. Figure 4b and in particular the enlarged partial view of Figure 4c show, by means of an exemplary layer 17, how a single strand 13 is deposited in each layer 17 along a multiple curved path 15 with a plurality of successive curves 16 at regular intervals. As can be seen, the strand 13 has been deposited such in a targeted manner by means of a 3D printer 60, that it not only extends over the entire longitudinal length of the connecting rod 23, but also fills out the entire width of the connecting rod 23. Moreover, the strand 13 is arranged such, that in the thermal compression 82, the matrix material 12 fills all gaps in the respective layer. As a result, a connecting rod 23 is obtained, which does not have any air inclusions, internal gaps or pores.

[0126] The regular geometrical pattern of the strand 13 as shown in Figure 4c is shown in more detail in Figure 4d. It is to be noted that the strands 13 of all layers 17 are deposited according to an identical wave-pattern as the one shown in Figures 4c and 4d, with the exception of the wave bents in alternating directions, as described further below with respect to Figure 4e. As can be clearly seen from Figure 4d, the strand 13 describes a curve 16 of more than 180° in each wave of the wave-pattern. Furthermore, it can be recognized that the waves of the wave-pattern formed by the strand 13 are bent in relation to the longitudinal direction L of the connecting rod 23. In the present embodiment, the waves have a bending angle a of 45° relative to the main longitudinal direction L. The waves or curves 16 formed by the strand 13 are all bent in the same, parallel directions.

[0127] In the present embodiment, the strand 13, which has a diameter in a range of 0.4 mm to 0.6 mm, forms a partial circle in each curve 16 with a diameter d of 1.5 mm (see Figure 4e). The width Wthat is covered by the strand 13 due to its deposition in a wave-pattern amounts to 5.1 mm. The periodic distance D between of the wave- pattern along the main longitudinal direction L is 2.5 mm. The peak distance D' measured from one curve 16 of the strand 13 to the next curve 16 oriented in the opposite direction amounts to 4.3 mm.

[0128] As can be seen from Figure 4e, the strand 13 is deposited in each case (i.e. in each layer 17) such that the waves of successive layers 17 are bent in alternating directions in relation to the main longitudinal direction L of the connecting rod 23. Thus, if the waves of the layer 17 as shown in Figure 4c are bent with a bending angle a of +45° relative to the main longitudinal direction L, the waves formed by the strand 13 in the directly adjacent layer 17 are bent with a bending angle a of -45°. It was found that in this way a flexibility of the connecting rod 23 can be obtained that is largely independent of the direction in which the connecting rod 23 is flexed perpendicularly to the main longitudinal direction L.

[0129] Figure 4e also shows the provision of a metal wire 24 that extends centrally within the connecting rod 23 along of its entire longitudinal extension. In the manufacturing, the metal wire 24 is placed in the preform 18 between two layers 17, i.e. between the deposition of two strands 13. The metal wire 24 serves as a marker to make the connecting rod 23 visible in medical imaging procedures, such as e.g. computer tomography or magnetic resonance imaging.

[0130] In a concrete example of a produced connecting rod 23 for a pedicle system 20, a total of 26 layers 17 were stacked up, as in Figure 4e with alternatingly bent wave-patterns. The preform 18 produced in this way was inserted into a corresponding mold 70, compressed and demolded as described above. A connecting rod 23 having final diameter of 6 mm could be produced in this way. The strands 13 for the manufacturing of this connecting rod 23 were based on continuous carbon fiber-reinforced PEEK with a strand diameter of 0.5 mm. The fiber volume content in the strand 13 and, thus, in the preform 18 and in the connecting rod 23 was 58 %. An additional titanium wire was inserted between the 13thand 14thlayer 17 as a marker and compressed as part of the preform 18. The resulting connecting rod 23 had a low stiffness of approximately 20 - 25 GPa in a direction perpendicular to the main longitudinal direction L.

[0131] Figure 5 shows an embodiment, in which the wave-pattern described by the multiple curved path 15 (along which the strand 13 has been deposited) only extends over a part of the length of the preform 18 used for manufacturing the connecting rod 23. In the other part of the preform, a plurality of strands 13 are arranged in such a way that they extend in parallel along the main longitudinal direction L of the preform 18. By means of such a strand arrangement, a connecting rod 23 can be manufactured that has different flexibilities along of its main longitudinal direction L.

[0132] Figures 6 and 7 show embodiments which differ from the one in Figures 4a - 4e only by the bending angle a, by which the waves formed by the wave-pattern are bent in relation to the main longitudinal direction L. In Figure 6, a bending angle a of 80° has been applied and in Figure 7 a bending angle a of 30°.

[0133] Figure 8 shows a graph that illustrates the non-linear dependencies of the relative rigidity and strength on the bending angle a of the waves formed by the wave-pattern in relation to the main longitudinal direction L of the connecting rod 23. It can be observed that the rigidity and the strength of the connecting rod 23 can particularly well be adjusted in a targeted manner for practical applications, if the bending angle a is in an absolute value range between 85° and 20°, preferably between 75° and 30°, particularly preferably between 55° and 35°. The provision of a connecting rod 23 having a certain flexibility brings about the advantage that the patient still has a certain degree of mobility, which has a particularly positive effect in the long term.

[0134] The step of the thermal compression 82 of a preform 18 for manufacturing the connecting rod 23 is shown in Figures 9a and 9b. As can be seen from Figure 9a, the preform 18 has a rectangular cross-section with a plurality of layers 17 which are each formed by a single strand 13. Due to the deposition of the strands 13 along a multiple curved path 15 in each layer 17, the (single) strand 13 appears several times in each layer 17 in the cross-sectional view. Also shown in Figure 9a is, how the plurality of fibers 11 of each strand 13 are embedded in the matrix material 12.

[0135] Due to the internal shape of the mold 70 with its mold receptacle 71 and the mold stamp 72, the rectangular cross-sectional shape of the preform 18 becomes circular during compression (Figure 9b). Also, the strands 13 merge together during the thermal compression 82 so that their separating surfaces become difficult or even impossible to recognize. All gaps that might have been present in the preform 18 between the strands 13, are closed during the thermal compression 82. The orientation of the fibers 11 withing the preform 18 is not changed due the thermal compression 82.

[0136] During the thermal compression 82, usually the final shape and in particular the bending of the connecting rod 23 is defined by the application of a respectively shaped mold 70. As it is shown in Figures 10 to 14, connecting rods 23 having a plurality of different shapes can be manufactured. Most of the connecting rods 23 of pedicle systems 20 are slightly bent one or two times along their longitudinal extension, in order to be adapted for being positioned at a respective part of a patient's spine.

[0137] Figures 15 and 16 show other, but also particularly preferred embodiments of a bone connection device 10 manufactured according to the inventive method configured as bone plates. The bone connecting device 10 of Figure 15 is a bone plate 30 which may be, for example, a trauma plate, for connecting two or more bones or bone parts, such as the humerus H as illustrated in this example. The bone connecting device 10 of Figure 16 is a vertebral connecting plate configured as a cervical plate 40 that serves to connect and rigidly fix two or more vertebral bodies V of the cervical spine S relative to one another. While the bone plate 30 is anchored within the humerus H by means of a plurality of bone screws 32, the cervical plate 40 is fixedly attached to the vertebral bodies V by means of bone screws 42. For the bone screws 32, 42, a plurality of apertures 31 or 41 extending therethrough the plates are provided within the bone plate 30 and the cervical plate 40, respectively (see Figures 18a and 17a).

[0138] The deposition of the strands 13 in an exemplary layer 17 of the preform 18 for manufacturing the cervical plate 40 is shown in Figures 17b and 17c. As can be seen from these Figures, the strands 13 are deposited in such a way that they completely fill out the layer 17 within its outer and inner contours, or at least in such a way that all gaps are closed during the thermal compression 82. In the present embodiment, seven strands 13 are deposited, in order to fill up the layer 17. The ends of strands 14 are marked in Figure 17b. As can be seen in Figures 17b and 17c, the seven strands 13 have been deposited such by the 3D Printer 60 in step 80 that they do not cross themselves or each other. Each of the apertures 41 is laterally delimited by a single strand 13 only, which gives the component a particularly good strength in the relevant areas. Furthermore, the outer contour of the layer 17 is formed by a single strand 13 which extends along the entire circumference of the layer 17, thereby giving it a particular good strength. The further layers 17 of the same preform

[0139] 18 are not shown in the Figures, but have an identical or similar arrangement of strands 13 as the one shown in Figures 17b and 17c.

[0140] The deposition of the strands 13 in an exemplary layer 17 of the preform 18 for manufacturing the bone plate 30 is shown in Figures 18b and 18c. As can be seen from these Figures, the strands 13 are deposited in such a way that they completely fill out the layer 17 within its outer and inner contours, or at least in such a way that all gaps are closed during the thermal compression 82. In the present embodiment, only two strands 13 are deposited, in order to fill up the layer 17. The ends of strands 14 are marked in Figure 18. As can be seen in Figures 18b and 18c, the two strands 13 have been deposited such by the 3D Printer 60 in step 80 that they do not cross themselves or each other. The inner parts of the layer 17 are filled by the strands 13 in a meandering or spiral shape, as it is shown by the arrows in Figure 18b. Each of the apertures 31 is laterally delimited by no more than two strands 13 only. Furthermore, the outer contour of the layer 17 is formed by a single strand 13 which extends along the entire circumference of the layer 17. Thus, the strands 13 follow the inner and outer contours of the preform 18 and, as a result, the bone plate 30 possesses particularly good strength. The further layers 17 of the same preform 18 are not shown in the Figures, but have an identical or similar arrangement of strands 13 as the one shown in Figures 18b and 18c.

[0141] Figures 19a and 19b show the thermal compression 82 of the preform 18 in a mold 70, in order to manufacture the cervical plate 40 of Figure 16. As can be seen from Figure 19b, the final arched cross-sectional shape of the cervical plate 40 is defined by the application of a respectively shaped mold 70. The plurality of layers 17 of the preform 18 are each formed by a plurality of strands 13, each of which comprises a plurality of fibers 11 embedded in the matrix material 12. Upon the thermal compression 82 (Figure 19b), the strands 13 merge together so that their separating surfaces become difficult or even impossible to recognize. All gaps that might have been present in the preform 18 between the strands 13 are closed during the thermal compression 82. The orientation of the fibers 11 withing the preform 18 is, however, not changed due the thermal compression 82.

[0142] Figure 20 shows a further particularly preferred embodiment of a bone connecting device according to the invention configured as a vertebral body replacement (VBR) 50. The VBR 50 has an expansion slide 51 , a main or expansion body 52 and two end plates 53 at opposed ends of the expansion body 52. Both end plates 53 are manufactured in accordance with the invention of a fiber-reinforced plastic material. Just like the bone connecting devices 10 of all other embodiments shown in the Figures, each of the end plates 53 is preferably formed as a whole in a single piece.

[0143] The expansion slide 51 has an overall cylindrical shape, with an outer thread that allows the expansion slide 51 to be screwed into the expansion body 52 and, thus, to adjust the length of the VBR 50. A connecting structure is formed on each of the upper side of the expansion slide 51 and the under side of the expansion body 52, which enables one of the end plates 53 to be attached and fastened to a respective complementary connection structure 56 provided on the end plate (see Figure 21a).

[0144] The end plates 53 are both formed as a substantially flat base body, on one side of which the connecting structure 56 is formed, which serves to attach and fasten the end plate 53 to a respective connecting structure of the expansion slide 51 or of the expansion body 52. A bone contacting surface with a bonding structure 57 is formed on the side opposite to the connecting structure 56 of the end plate 53. The bonding structure 57 is designed for contact with a bone, in particular with a vertebral body V of the patient and has a corresponding surface structure which favors a close bonding and, in particular, promotes ingrowth of the bone.

[0145] The connection structure 56 is formed to have a plurality of radial indentations 55 that are arranged within a central cylindrical elevation 58 of the end plate 53, as shown in Figure 21a. Apertures 54 are provided which can extend therethrough, in order to for example lower the weight of the end plate 53 and / or provide engaging structures to enable attachment of an instrument with which the physician can handle and e.g. expand the endplate 53 and / or the VBR 50.

[0146] The VBR 50 is inserted into the free space or void caused by a missing vertebral body between two adjacent vertebral bodies V of a patient in a non-expanded state, and then expanded by the physician in order to fill the space between the two adjacent vertebral bodies V and to fit closely to the vertebral bodies V with the bonding structure 57 of each end plate 53. The expanded state of the VBR 50 is shown in Figure 20. The physician performs the expansion by means of partially unscrewing the expansion slide 51 from the expansion body 52 with a tool or instrument not shown in the Figures, until the endplates 53 engage the vertebral bodies V and the proper height is restored to the patient’s spine at that spine level. As shown, the VBR may also be used in combination with a pedicle system 20. Figure 20 shows a pedicle system 20 present and anchored in the same spine S and in adjacent vertebral bodies V as the VBR 50, in order to stabilize the spine S in the region of the VBR 50. Some or all components of the pedicle system 20, in particular the connecting rod 32, can be manufactured by the method according to the invention.

[0147] Figure 21b shows the arrangement of the strands 13 within an exemplary layer 17 of one of the end plates 53, with the ends of the strands 14 being marked. The strands 13 have been deposited in step 80 such that they completely fill the layer 17 without crossing themselves or each other, i.e. no overlapping or intersecting of strands 13. Since the inner parts of the layer 17 are filled by the strands 13 in circular and spiral paths, an effective filling of the layer 17 could be achieved that does not lead to any air inclusions, gaps or pores in the thermal compression 82. It is also noted that all apertures 54 are laterally delimited by only a small number of strands 13, which at least partially follow the respective inner contour of the end plate 53 and thereby increase its strength in the respective regions. The outer contour of the layer 17 is completely formed by a single strand 13 that extends along the entire circumference of the layer 17. As a result, an end plate 53 with a particularly good strength at its inner and outer contours is obtained.

[0148] Figures 22a and 22b show the thermal compression 82 of the preform 18 in a mold 70, in order to manufacture one of the end plates 53 of the VBR 50 of Figure 20. As can be seen from Figure 22b, the final cross-sectional shape of the end plate 53 with its distinct elevation 58 is not yet present in the preform 18, but only defined during the thermal compression 82 by the application of a respectively shaped mold 70. The plurality of layers 17 of the preform 18 are each formed by a plurality of strands 13, each of which comprises a plurality of fibers 11 embedded in the matrix material 12. Upon thermal compression 82 (Figure 22b), the strands 13 merge together so that their separating surfaces become difficult or even impossible to recognize. All gaps that might have been present in the preform 18 between the strands 13, are closed during the thermal compression 82. The orientation of the fibers 11 withing the preform 18 is, however, not changed due the thermal compression 82.

[0149] The present invention is not limited to the embodiments as described and shown. Instead, a large variety of modifications is possible. The strands for example do not need to have a length which is greater than the maximum overall length of the bone connecting device. Instead, while this is rather not preferred for most embodiments, it could, however, nevertheless be advantageous for some embodiments to carry out the inventive method using a large number of short strands. Conversely, while it has been mentioned that each layer can be made from one single strand only, it is not even necessary that the strands be cut during the manufacturing process from one layer to another. Instead, it would also be conceivable to continue the production of a subsequent layer using the same strand as in the previous layer, which would even improve the mutual connection of the layers. The bone connecting device manufactured from the inventive method does not necessarily be a connecting rod of a pedicle system, a bone plate or an end plate of a VBR. It is also conceivable to manufacture for example a pedicle screw or a bone screw, a tulip head of a pedicle system, an expansion slide or an expansion body of a VBR by means of the inventive method. Further examples of bone connecting elements that could basically be manufactured according to the inventive method are for example interbody cages used in spine fusion or any components, such as e.g. parallel or serial connectors, of external or internal fixation systems, such as pedicle systems. A large variety of further modifications is possible.

[0150] LIST OF REFERENCE SIGNS

[0151] 10 Bone connecting device

[0152] 11 Fibers

[0153] 12 Matrix material

[0154] 13 Strand

[0155] 14 End of strand

[0156] 15 Multiple curved path

[0157] 16 Curve

[0158] 17 Layer

[0159] 18 Preform

[0160] 20 Pedicle system

[0161] 21 Pedicle screw

[0162] 22 Tulip head

[0163] 23 Connecting rod

[0164] 24 Wire

[0165] 30 Bone plate

[0166] 31 Aperture

[0167] 32 Bone screw

[0168] 40 Cervical plate

[0169] 41 Aperture

[0170] 42 Bone screw

[0171] 50 VBR

[0172] 51 Expansion slide

[0173] 52 Expansion body

[0174] 53 End plate

[0175] 54 Aperture

[0176] 55 Indentation

[0177] 56 Connection structure

[0178] 57 Bonding structure

[0179] 58 Elevation 60 3D printer

[0180] 61 Storage wheel

[0181] 62 Feed wheel

[0182] 63 Heater

[0183] 64 Nozzle

[0184] 65 Worktable

[0185] 70 Mold 71 Mold receptacle 72 Mold stamp

[0186] 80 Targeted deposition

[0187] 81 Repetition loop

[0188] 82 Thermal compression

[0189] 83 Mold removal

[0190] L Main longitudinal direction d Diameter a Bending angle

[0191] W Width

[0192] D Periodic distance

[0193] D' Peak distance

[0194] S Spine

[0195] V Vertebral body I Intervertebral disc

[0196] H Humerus

Claims

CLAIMS1. A method for manufacturing a medical bone connecting device (10) that serves to connect two bones (V, H) or bone parts of a human or animal patient, comprising at least the following steps: a.) targeted deposition (80) in a common layer (17) of one or more strands (13) of reinforcing fibers (11) embedded in a matrix material (12), b.) repetition (81) of step a.) for a plurality of successive layers (17), in order to produce a preform (18) of the bone connecting device (10), and c.) compression (82) of the preform (18) in a mold (70) to form the bone connecting device (10), characterized in that the strand or strands (13) are deposited in such a way in step a.) that they follow a multiple curved path (15) without crossing themselves or each other.

2. The method of claim 1 , wherein the strand or strands (13) have a length which is equal to or greater than the maximum overall length of the bone connecting device (10).

3. The method as claimed in claim 1 or 2, wherein in step a.), the strand or strands (13) are deposited in such a way that any internal cavities are removed in the compression (82) of step c.).

4. The method as claimed in one of the preceding claims, wherein each strand (13) comprises 1'000 to 24'000 fibers (11), preferably 3'000 to 6'000 fibers (11).

5. The method as claimed in one of the preceding claims, wherein in step a.), less than 30, preferably less than 20, in particular less than 10 strands (13) are deposited.

6. The method as claimed in one of claims 1 to 4, wherein one single strand (13) is deposited in step a.).

7. The method as claimed in any of the preceding claims, wherein the volume content of the reinforcing fibers (11) in the bone connecting device (10) is in a range between 20% and 80%, preferably between 35% and 70%, particularly preferably between 45% and 60%.

8. The method as claimed in any of the preceding claims, wherein the reinforcing fibers (11) are made of carbon and the matrix material (12) is a plastic, in particular a high-temperature thermoplastic with a temperature resistance of up to 250°, such as from the material groups of polyaryletherketones, polyimides and polysulphones.

9. The method as claimed in any of the preceding claims, wherein the bone connecting device (10) is a connecting rod (23) for a pedicle system (20).

10. The method of claim 9, wherein in step a.), the strand or the strands (13) are deposited in a regular wave-pattern over at least a portion of the overall main length of the connecting rod (23).

11. The method of claim 10, wherein in step a.), the strand or strands (13) are deposited such that they describe a curve (16) of at least 180° in each wave of the wave-pattern.

12. The method of claim 10 or 11 , wherein in step a.), the strand or strands (13) are deposited such that the waves formed by the wave-pattern are bent in an absolute value range between 85° and 20°, preferably between 75° and 30°, particularly preferably between 55° and 35°, in relation to the main longitudinal direction (L) of the connecting rod (23).

13. The method as claimed in claim 12, wherein in step a.), the strand or strands (13) are deposited such that the waves of the strands (13) of successive layers (17) are bent in alternating directions in each case in relation to the main longitudinal direction (L) of the connecting rod (23).

14. The method as claimed in claim 12 or 13, wherein the waves formed by each strand (13) are all bent in parallel directions.

15. The method as claimed in claim 12 or 13, wherein the waves formed by each strand (13) are bent in varying angles (a) along the main longitudinal direction (L) of the connecting rod (23), in order to give the connecting rod (23) a changing stiffness along its main longitudinal direction (L).

16. The method as claimed in any of the preceding claims, wherein a wire (24), in particular a metal wire, is additionally deposited, in order to be arranged between the layers (17) of strands (13) and to serve as a marker in medical imaging procedures.

17. The method as claimed in any of the preceding claims, wherein the bone connecting device (10) has a plate-like overall shape and is in particular a bone plate (30), a vertebral connecting plate (40) or an end plate (53) of a vertebral body replacement (50).

18. The method as claimed in claim 17, wherein the bone connecting device (10) has one or several through-going apertures (31 , 41 , 54), each of which is laterally delimited by less than 5 strands (13) per layer (17), preferably by less than 3 strands (13) per layer (17), in particular by only a single strand (13) per layer (17).

19. The method as claimed in claims 17 or 18, wherein in step a.), a major part of the main longitudinal extension of each strand (13) is deposited in such a way that it either follows an inner and / or an outer contour of the bone connection device (10) or that it fills an inner part of the respective layer (17) in a meandering, circular and / or spiral shape.

20. A bone connecting device (10), in particular a connecting rod (23) for a pedicle system (20) or a vertebral connecting plate (40) or an end plate (53) of a vertebral body replacement (50), manufactured according to one of the preceding claims.

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