Osteochondral plug

Abstract

Described herein is an osteochondral plug and method of forming the osteochondral plug. The osteochondral plug has a plug cap with a porous structure for blood flow through the plug cap, the plug cap is made of a first polymer blend, the first polymer blend comprising 80 wt. % to 95 wt. % of ultra-high molecular weight polyethylene (UHMWPE); and 5 wt. % to 20 wt.% of a polymer of Formula 1; and a plug body with a second porous structure for blood flow through the plug body, the plug body is made of a second polymer blend, the second polymer blend comprising 80 wt. % to 95 wt. % of polycaprolactone; and 5 wt. % to 20 wt.% of a polymer of Formula 2, the plug cap is joined to the plug body.

Description

Osteochondral PlugREFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to Singapore patent application number 10202500370V with a filing date of 10 February 2025 and titled “3D Printed biphasic osteochondral plug for osteoarthritis treatment” and is incorporated herein by reference.FIELD OF THE INVENTION

[0002] The present disclosure relates to an osteochondral plug for osteoarthritis treatment, and a method of forming the osteochondral plug.BACKGROUND OF THE INVENTION

[0003] When patients suffer from pain from cartilage erosion or osteoarthritis (OA), a partial or total knee replacement surgery is necessary to relieve pain and restore mobility. This is a more invasive procedure and the lifespan of a knee arthroplasty implant is 15 - 20 years. Hence, it is important to delay this surgery as much as possible in young patients. Autografts harvested from non-weight bearing regions of a patient’s knee are ideal cartilage capped bone plugs but carry significant donor site morbidity. On the other hand, allografts are heavily processed to reduce infection risk. However, this processing results in loss of viable cells for cartilage regeneration. Another problem is varying cartilage defect size, which require surgeons to frequently either use multiple implants to fit a larger defect or modify implants to accommodate a smaller defect. Some orthopaedic surgeons have reported use of the Trufit plug for osteochondral repair with some success, but it is important to note that this is actually off-label usage of the Trufit plug. The Trufit plug is meant to be used as a gap filler after an autograft procedure and not to be used as an osteochondral plug and has a single layer structure. A table of comparison for existing technologies is given below.

[0004] Table 1. Comparison of existing technologies for treatment of osteoarthritis.&

[0005] The current gold standard for the treatment of early osteoarthritis with cartilage defects is microfracture surgery which does not restore native cartilage even with scaffolds and biologic augments. Further, microfracture causes underlying bone damage and has less than a 50% success rate. Metallic orthopaedic implants such as metal hemicap can treat the defect but result in erosion of existing healthy cartilage. Bone allografts can sometimes be used to fill the defect but these do not restore cartilage and their use in osteochondral defect filling is actually off-label. Hence, there is an unmet clinical need for early osteoarthritis treatment that can restore hyaline cartilage instead of damaging surrounding healthy cartilage.

[0006] CN105435311 describes a tissue engineering osteochondral composite support and a preparation method thereof, belonging to the technical field of biomaterials. The support is a multi-layer integrated structure, which is composed of a cartilage tissue support layer, a cartilage tissue calcification layer, a porous cell separation membrane and a bone tissue support layer. The cartilage tissue scaffold layer is inoculated with chondrocytes and introduced growth factors that promote chondrocyte formation to promote the growth of chondrocytes. The main rawmaterials such as heparan sulfate proteoglycan with good biocompatibility and degradability are selected.SUMMARY OF THE INVENTION

[0007] In a first aspect, there is provided an osteochondral plug comprising a plug cap with a porous structure for blood flow through the plug cap, the plug cap is made of a first polymer blend, the first polymer blend comprising 80 wt. % to 95 wt. % of ultra-high molecular weight polyethylene (UHMWPE); and 5 wt. % to 20 wt.% of a polymer of Formula 1; and a plug body with a second porous structure for blood flow through the plug body, the plug body is made of a second polymer blend, the second polymer blend comprising 80 wt. % to 95 wt. % of polycaprolactone; and 5 wt. % to 20 wt.% of a polymer of Formula 2, the plug cap is joined to the plug body.

[0008] The polymer of Formula 1 is:Li is selected from the group consisting of a substituted or unsubstituted divalent C10 to C24 aliphatic moiety, a substituted or unsubstituted divalent C10 to C24 aryl moiety, and combinations thereof, L2 is a substituted or unsubstituted divalent C2 to C6 aliphatic moiety, A1 is selected from the group consisting of RGD, hyaluronic acid, RLGYWS (SEQ ID NO: 1), and AGQWHRVSVRWG (SEQ ID NO: 2, A5G81), m is from 10 to 350, pi is 0.9 to 0.99, qi is 0.01 to 0.1 , pi + qi = 1.

[0009] The polymer of Formula 2 is:each of Ls and Le is a substituted or unsubstituted divalent C2 to C6 aliphatic moiety, n2 is from 30 to 100, A2 is selected from the group consisting of RGD, hyaluronic acid, RLGYWS (SEQ ID NO: 1), and AGQWHRVSVRWG (SEQ ID NO: 2, A5G81), P2 is 0.9 to 0.99, q2 is 0.01 to 0.1 , p2 + q2 = 1 , wherein m in Formula 1 and Formula2 is such thathas a number average molecular weight from 500 to 7000.

[0010] In an embodiment, A1 is RGD and is the polymer of Formula 1 a and / or A2 is RGD and is the polymer of Formula 2a.

[0011] In an embodiment,each independently selected from the group consisting of a substituted or unsubstituted divalent C2 to C10 aliphatic moiety.

[0012] In an embodiment, L3 is (CH2)ai, where ai is from 2 to 8, preferably ai is from 3 to 7, more preferably ai is from 4 to 6.

[0013] In an embodiment, l_4 is a substituted or unsubstituted divalent C2 to C4 aliphatic moiety, preferably l_4 is -CH2CH=CH-.

[0014] In an embodiment, ni is from 50 to 300, preferably m is from 150 to 250, more preferably m is from 170 to 200.

[0015] In an embodiment, wherein L2 is (CH2)a2, where a2 is from 2 to 6, preferably a2 is from 2 to 4, more preferably a2 is 2 or 3.

[0016] In an embodiment, m is such that the number average molecular weight is from 1000 to 5000, preferably m is such that the number average molecular weight is from 2000 to 4000, more preferably m is such that the number average molecular weight is from 3000 to 4000.

[0017] In an embodiment, the polymer blend consists essentially of 80 wt. % to 95 wt. % of UHMWPE; and 5 wt. % to 20 wt.% of the polymer of Formula 1. In an embodiment, the polymer blend consists of 80 wt. % to 95 wt. % of UHMWPE; and 5 wt. % to 20 wt.% of the polymer of Formula 1. In an embodiment, the polymerblend consists essentially of, or consists of, 90 wt. % of UHMWPE; and 10 wt.% of the polymer of Formula 1.

[0018] In an embodiment, the second polymer blend consists essentially of 80 wt. % to 95 wt. % of polycaprolactone; and 5 wt. % to 20 wt.% of the polymer of Formula 2. In an embodiment, the second polymer blend consists of 80 wt. % to 95 wt. % of polycaprolactone; and 5 wt. % to 20 wt.% of the polymer of Formula 2. In an embodiment, the second polymer blend consists essentially of, or consists of, 90 wt. % of polycaprolactone; and 10 wt. % of the polymer of Formula 2.

[0019] In an embodiment, the polymer of Formula 1 is a polymer of Formula 1b, wherein m is such that the polyethylene has a number average molecular weight of 5000,Formula 1b.

[0020] In an embodiment, the UHMWPE has a weight average molecular weight of 500 kDa.

[0021] In an embodiment, each of Ls and l_6 is a substituted or unsubstituted divalent C2 to C4 aliphatic moiety, preferably Ls is -(CH2)s and / or Le is -(CH2)2-.

[0022] In an embodiment, n2 is from 30 to 50, m is from 60 to 80.

[0023] In an embodiment, the polymer of Formula 2 is Formula 2b,Formula 2b, wherein n2 is such that a macromonomer containing the polycaprolactone has a number average molecular weight of 5000 to 6000.

[0024] In an embodiment, the plug cap and the plug body each has a first end and a second end opposite to the first end, the second end of the plug cap is joined to the first end of the plug body, the porous structure of the plug cap and the plug body allows for blood flow from the second end of the plug body to the first end of the plug cap.

[0025] In an embodiment, the plug cap is joined to the plug body by an interlocking mechanism.

[0026] In an embodiment, a protrusion extends out from the second end of the plug cap to mate with a notch in the first end of the plug body.

[0027] In an embodiment, the protrusion has a frustoconical shape or a partial frustoconical shape.In a second aspect, there is provided a method of forming an osteochondral plug, the method comprising providing a film, wherein the film is a polyester based film or a polypropylene based film; melting a first polymer blend comprising 80 wt. % to 95wt. % of ultra-high molecular weight polyethylene (UHMWPE); and 5 wt. % to 20 wt.% of a polymer of Formula 1; melting a second polymer blend, the second polymer blend comprising 80 wt. % to 95 wt. % of polycaprolactone; and 5 wt. % to 20 wt.% of a polymer of Formula 2; three dimensionally printing with the first polymer blend on the film a plug cap with a porous structure for blood flow through the plug cap; three dimensionally printing with the second polymer blend a plug body with a porous structure for blood flow through the plug body, wherein the plug cap is joined to the plug body; and cooling the printed plug cap and plug body to form the osteochondral plug.

[0028] The polymer of Formula 1 and Formula 2 is as described above.

[0029] Advantageously, the use of the polymers of Formula 1 and Formula 2 provides an osteochondral plug composed of a cap and body made of different materials that provided different unique properties including both cartilage regeneration and osteointegration while allowing the body 15 to be biodegradable. This is not possible with using either material alone.BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure (FIG.) 1 shows in panel (a) a biphasic osteochondral plug material composition where the plug cap or surface layer is made of ultra-high molecular weight polyethylene (UHMWPE) and the plug body is made of polycaprolactone (PCL) and panel (b) shows the plug implementation concept.

[0031] FIG. 2A to FIG. 2F shows the osteochondral plug design. FIG. 2A, FIG.2B and FIG. 2C respectively show a side view, a perspective view and a bottom view of the cap. FIG. 2D, FIG. 2E, and FIG. 2F respective show a perspective view, a side view, and a top view of the plug body. FIG. 2Gshows the three dimensional (3D) printed OC plug prototype test fitted into a hole created in the porcine femoral condyle.

[0032] FIG. 3 shows the in vitro chondrocyte proliferation test on UHMWPE, PE-RGD at 5, 10 and 20 wt.% in UHMWPE at 48hrs.

[0033] FIG. 4 shows on the left a perspective view of the plug body and on the right a top view of the plug body.

[0034] FIG, 5 shows in panel (a) osteochondral plugs implanted in defects created in both the medial and lateral knee compartment of the femoral condyl, withthe porous polyethylene surface showing. Panel (b) shows the microfracture in the femoral condyl of the other leg as positive control.

[0035] FIG. 6 panel (a) shows a knee joint implanted with the plug at day 0 (left) and week (wk) 24 (right). The plug surface can be seen clearly on day 0. On week 24, cartilage has been regenerated over one plug with cartilage similar to native cartilage and partial regeneration in the other implant. FIG. 6 panel (b) shows the partial regeneration of the cartilage still has greater than 50% closure. FIG. 6 panel (c) showed no cartilage regeneration in the microfracture control (left image) and no bone growth over microfracture holes drilled into bone (right image).

[0036] FIG. 7 shows (from left to right) bone growth in the plug cross section, inside knee joint, and blood vessels growing in plug body.

[0037] FIG. 8 shows only a small fragment of the plug body left (PCL component). The remaining PCL has osteointegrated and is no longer detachable or identifiable. The pore design from the residual plug body can be seen.DETAILED DESCRIPTION OF THE INVENTION

[0038] In the following description, numerous specific details are set forth in order to provide a thorough understanding of various illustrative embodiments of the invention. It will be understood, however, to one skilled in the art, that embodiments of the invention may be practiced without some or all of these specific details. Embodiments described in the context of one of the methods or products are analogously valid for the other methods or products. Similarly, embodiments described in the context of a method are analogously valid for a product, and vice versa.

[0039] Where a combination is disclosed, each subcombination of the elements of that combination is also specifically disclosed and is within the scope of the invention. Conversely, where different elements or groups of elements are disclosed, combinations thereof are also disclosed. Where any element of an invention is disclosed as having a plurality of alternatives, examples of that invention in which each alternative is excluded singly or in any combination with the other alternatives are also hereby disclosed; more than one element of an invention can have such exclusions, and all combinations of elements having such exclusions are hereby disclosed.

[0040] Where a range of values is recited, it is to be understood that each intervening integer value, and each fraction thereof, between the recited upper and lower limits of that range is also specifically disclosed, along with each subrange between such values. The upper and lower limits of any range can independently be included in or excluded from the range, and each range where either, neither or both limits are included is also encompassed within the invention. Where a value being discussed has inherent limits, for example where a component can be present at a concentration of from 0 to 100%, or where the pH of an aqueous solution can range from 1 to 14, those inherent limits are specifically disclosed. Where a value is explicitly recited, it is to be understood that values which are about the same quantity or amount as the recited value are also within the scope of the invention, as are ranges based thereon.

[0041] The term “aliphatic group” or “aliphatic” refers to a moiety that may be saturated (e.g. single bond) or contain one or more units of unsaturation, e.g., double and / or triple bonds, and in particular refers to the carbon atom forming the bond and may be monovalent or divalent as understood by the structure and context. An aliphatic group may be straight chained, branched or cyclic, contain carbon, hydrogen or, optionally, one or more heteroatoms and may be substituted or unsubstituted. Non-limiting examples of substituents include a halogen, a hydroxyl, an ether, an amine, a carbamate, a carbonate ester, a urea, an aryl group (e.g. benzyl, phenyl ethyl and the like), a carbonyl, a carboxylic acid, an ester, an amide, a cyano, a nitro, a thiol, a sulfoxide, and a sulfone. It is understood that the substituent may be further substituted.

[0042] The term "alkyl" as used herein is a branched or unbranched saturated monovalent hydrocarbon radical of 1 to 24 carbon atoms (C1-C24), such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, f-butyl, n-pentyl, isopentyl, s-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, eicosyl, tetracosyl, and the like. The alkyl group can be cyclic or acyclic. The alkyl group can be branched or unbranched. The alkyl group can also be substituted or unsubstituted. For example, the alkyl group can be substituted with one or more groups including, but not limited to, alkyl, cycloalkyl, alkoxy, amino, ether, halide, hydroxy, nitro, silyl, sulfo-oxo, or thiol, as described herein.

[0043] The term “aryl group” refers to a monovalent aromatic radical which includes carbocyclic aromatic rings and heteroaryl rings (nitrogen, oxygen, and sulphur and the like), and in particular refers to the atom forming the bond being part of the ring structure. The term “aromatic group" may be used interchangeably with the terms “aryl”, “aryl ring” “aromatic ring”, “aryl group” and “aromatic group”. The aryl group may be substituted at any one or more substitutable ring atom. Nonlimiting examples of substituents include a halogen, a hydroxyl, an ether, an amine, a carbamate, a carbonate ester, a urea, an aliphatic group (e.g. tolyl, mesityl) an aryl group (e.g. biphenyl), a carbonyl, a carboxylic acid, an ester, an amide, a cyano, a nitro, a thiol, a sulfoxide, and a sulfone. It is understood that the substituent may be further substituted.

[0044] The term “araliphatic” refers to a monovalent aliphatic radical as described above that is substituted with one or more aryl groups. The term “aralkyl” or “arylalkyl” refers to a monovalent alkyl radical substituted with one or more aryl groups. In certain embodiments, the aralkyl has from 7 to 30 (C7-30), from 7 to 20 (C7-20), or from 7 to 16 (C7-16) carbon atoms. Examples of aralkyl groups include, but are not limited to, benzyl, 2-phenylethyl, and 3-phenylpropyl. In certain embodiments, aralkyl are optionally substituted with one or more substituents.

[0045] The term “linker” or “crosslinker” joins two or more different components of a molecule and is necessary divalent or more to join the components to form the molecule. Thus, when the aliphatic, alkyl, aryl, araliphatic, and aralkyl terms are used in the context of a linker, these terms may be divalent or more as understood by the structure and context.

[0046] The term “substituted" shall mean the replacement of one or more hydrogen atoms in a given structure with a substituent including, but not limited to, halo, alkyl, alkenyl, alkynyl, aryl, heterocyclyl, thiol, alkylthio, arylthio, alkylthioalkyl, arylthioalkyl, alkylsulfonyl, alkylsulfonylalkyl, arylsulfonylalkyl, alkoxy, aryloxy, aralkoxy, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, alkoxycarbonyl, aryloxycarbonyl, haloalkyl, amino, trifluoromethyl, cyano, nitro, alkylamino, arylamino, alkylaminoalkyl, arylaminoalkyl, aminoalkylamino, hydroxy, alkoxyalkyl, carboxyalkyl, alkoxycarbonylalkyl, aminocarbonylalkyl, acyl, aralkoxycarbonyl, carboxylic acid, sulfonic acid, sulfonyl, phosphonic acid, aryl, heteroaryl,heterocyclic, or aliphatic. It is understood that the substituent may be further substituted.

[0047] As used herein the term “CX” refers to the number of carbons in the recited moiety or group, and can be a single number or range. The moiety or group may be further substituted or functionalised.

[0048] Described herein is a biphasic osteochondral plug 5 for cartilage regeneration and bone regeneration using bioactive ultra-high molecular weight polyethylene (UHMWPE) and bioactive polycaprolactone (PCL) and three dimensional (3D) printing by fused filament fabrication (FFF) method. A unique pin and socket design was created to lock the plug surface made of UHMWPE and plug body made of bioactive PCL, together, without causing inter-component rotation.

[0049] To address the unmet clinical need of cartilage repair in early osteoarthritis patients or young patients with cartilage defects, a biphasic osteochondral plug 5 (OC plug) was developed that contains a cartilage-regenerating surface component 10 and a bone-regenerating stem 15 for osteointegration. As the joint surface undergoes significant abrasion, wear and tear due to repeated joint movements, a mechanically tough material such as ultra-high molecular weight polyethylene (UHMWPE), is required. UHMWPE is currently used in articulating surfaces of hip joint implants and tibial spacers of knee joint implants. The use of non-biodegradable bioactive polyethylene (PE) in a UHMWPE base polymer, enables regeneration of cartilage through chondrocyte binding and proliferation, in the plug surface. On the other hand, to improve osteointegration of the plug body, biodegradable bioactive polycaprolactone (PCL) may be used to facilitate bone regeneration through binding of a5|31 integrin for osteogenesis, osteodifferentiation and osteoinduction. Three dimensional (3D) printing may be used to create unique pores in the plug to facilitate blood flow to the plug surface for chondrogenesis which is important for cartilage regeneration, as well as for creating customised plugs for uneven defects. A sketch of the plug design concept is given in FIG. 1 panel (a).

[0050] The osteochondral plug 5 comprises two components, an UHMWPE surface component or cap 10 for chondrocyte binding and a PCL body 15 for osteointegration. The plug cap 10 and plug body 15 are joined together. Bioactive UHMWPE and bioactive PCL are used respectively in the cap 10 and body 15. The plug cap 10 has a diameter (d) and a height (hi) while the plug body 15 has adiameter (d) and a height (hs). In an example, the plug cap 10 and body has a diameter of 1 cm. The height (hi) of the plug cap 10 is 0.2 cm and the height (h2) of the plug body 15 is 1.3 cm. The dimensions of the plug 5 including the plug cap 10 and plug body 15 may be manufactured as required. Plugs 5 with fixed dimensions may be manufactured and / or custom made according to the patient’s requirements. In an embodiment, the plug cap 10 and plug body 15 each have a cylindrical shape.

[0051] Both components are designed to be porous to allow stem cell-carrying blood to penetrate the plug 5 and reach the top of the plug 5 or chondrogenesis to occur. The plug body 15 may also have bone regeneration throughout the entire plug 5 due to its internal porosity when it is filled with blood. An interlocking design is used to prevent interlayer rotation due to material delamination. A socket and pin design is created to lock the two components together and prevent intercomponent rotation. The plug body 15 has a lattice design for blood flow to enhance osteointegration. The plug cap 10 is porous to allow blood flow to the top surface of the plug 5 for chondrogenesis. An example of the porous structure in the plug body 15 is a triangular infill pattern as shown in FIG. 4. The left image in FIG. 4 is a perspective view of the plug body 15 with the triangular infill pattern and the right image is a top view of the plug body 15 with the triangular infill pattern in the cross section of the plug body 15. The triangular pores create channels for blood to flow from the subchondral bone upwards to the cartilage to supply nutrients for regeneration which a solid plug would not allow. Furthermore, the channels introduce more surface area for blood and cells to interact with the material to encourage growth from within. As an example, the pore area is measured to be at 1 ,2mm2with a circumscribed diameter of 1 ,2mm.

[0052] The plug cap 10 has a first end (or a top end) and a second end (bottom end) opposite the first end. The first end of the cap 10 is the top end of the plug 5 as a whole. The plug body 15 has a first end (or a top end) and a second end (bottom end) opposite the first end. The second end of the plug body 15 is the bottom end of the plug 5 as a whole. The second end of the cap 10 is joined to the first end of the plug body 15. Both the cap 10 and body 15 are porous to allow the flow of blood from the second of the plug body 15 to the first end of the plug cap 10 (i.e. from one end of the plug 5 to the opposite end).

[0053] Panel (b) of FIG. 1 shows a schematic of the implantation of the plug 5. The first image in panel (b) shows the knee joint with cartilage defect. The second image shows the femoral condyle with the plug 5 inserted into the knee joint with cartilage defect. The third image shows that over time only the non-biodegradable bioactive PE cap 10 is left after the biodegradable bioactive PCL body 10 biodegrades within an expected time of two years and new bone grows into space formerly occupied by the plug body 10.

[0054] Examples of the bioactive PE that may be used for the plug cap 10 are described in WQ2022093107A1. The plug cap 10 is made from a polymer blend of polyethylene and a polymer with a norbornene backbone with pendants containing polyethylene and a PEG linker joined to a short peptide of Arginine-Glycine-Aspartic acid (with one of the carboxylic acid as a methyl ester) (RGD) (SEQ ID NO: 3), RLGYWS (SEQ ID NO: 1), AGQWHRVSVRWG (SEQ ID NO: 2, A5G81) or hyaluronic acid. An embodiment of the bioactive PE is Formula 1.Li is selected from the group consisting of a substituted or unsubstituted divalent C10 to C24 aliphatic moiety, a substituted or unsubstituted divalent C10 to C24 aryl moiety, and combinations thereof, L2 is a substituted or unsubstituted divalent C2 to C6 aliphatic moiety, A1 is selected from the group consisting of RGD, hyaluronic acid, RLGYWS (SEQ ID NO: 1), and AGQWHRVSVRWG (SEQ ID NO: 2, A5G81),n is from 10 to 350, m is such thathas a number average molecular weight from 500 to 7000, pi is 0.9 to 0.99, qi is 0.01 to 0.1 , pi + qi = 1.

[0055] An example of a specific polymer of Formula 1 , is the polymer of Formula 1 a (where A1 is RGD) and Formula 1 b (which further defines the Li and L2 moieties) shown below.

[0056] Examples of the bioactive polycaprolactone (PCL) that may be used in the plug body 15 are described in W02022093106 and W02023033730A2, The plug body 15 is made from a polymer blend of PCL and a polymer with a norbornene backbone with pendants containing PCL and a PEG linker joined to a short peptideof Arginine-Glycine-Aspartic acid (with one of the carboxylic acid as a methyl ester) (RGD) (SEQ ID NO: 3), RLGYWS (SEQ ID NO: 1), AGQWHRVSVRWG (SEQ ID NO: 2, A5G81 ) or hyaluronic acid. An embodiment of the bioactive PCL is Formulaeach of Ls and Le is a substituted or unsubstituted divalent C2 to C6 aliphatic moiety,n2 is from 30 to 100, m is such thathas a number average molecular weight from 500 to 7000.

[0057] An example of a specific polymer of Formula 2, is the polymer of Formula 2a (where A2 is RGD) and Formula 2b (which further defines :the Ls and Le moieties) shown below., is such that a macromonomer containing the polycaprolactone has a number average molecular weight of 5000 to 6000.

[0058] An embodiment of the OC plug 5 is shown in FIG. 2A to 2F and may contain a few key features to account for various factors such as translational and rotational separation, material thermal expansion / contraction, oversized first layer, fluid flow capability and surface alignment. The OC plug 5 has two parts which maybe termed as “surface” layer 10 and “body” 15. The surface layer 10 may also be termed a cap or a head (of the plug 5) herein. FIG. 2Ato 2C show the plug cap 10 and FIG. 2D to FIG. 2F shows the plug body 15.

[0059] In an embodiment, the cap 10 may have a generally cylindrical shape. In an embodiment, each of the top and bottom regions of the cap 10 may be curved at the edges while top surface 22 and bottom surface 32 are flat and faces outwards. Hence, each of the top and bottom region may be like a frusto-hemispherical shape, in other words the top and bottom region may be like a hemisphere or ellipsoid with a plane cutting of the rounded part of the hemisphere such that the top and bottom outward facing surfaces 22, 32 of the cap 10 are flat. Advantageously, a flat top surface 22 provides more surface area that interacts with the build plate during printing compared to a rounded top surface. Due to the nature of the UHMWPE material used for the cap 10, the surface area interfacing with the build plate should be maximised to prevent any print failure due to part delamination.

[0060] The cap 10 may be viewed as having three layers as shown in FIG. 2A. The topmost (or first) layer 20 which is also the top layer of the entire plug 5 and top layer 22 faces outward when the plug 5 is implanted as shown in FIG. 2G. The cap 10 has a middle layer 25 and a bottom layer 30. As UHMWPE contracts substantially, the trailing edge 40 of the cap 10 was curved with a radius of 0.3mm to prevent any irregularity arising from the contraction which will affect the subsequent layers and result in poor part finishing. Hence, the trailing edge 40 has a fillet (curved) edge with a radius curvature of 0.3mm. Similarly, the leading edge 45 of the plug cap 10 was curved to a radius of 0.7mm to ensure that no oversized first layer occurs which will lead to dimensional inaccuracy of the top surface of the head 10. The leading edge 45 has a fillet (curved) edge with a radius curvature of 0.7mm. The outward facing surfaces of the top layer 20 and bottom layer 30 are flat except at the respective curved edges 40, 45. Hence, as may be seen in FIG. 2, the middle layer 25 of the cap 5 has the widest diameter with the top layer 20 and bottom layer 30 of the cap 5 curving inwards. The diameter of the cap 10 may be measured with respect to the middle layer 25. Thus, the three layers of the cap 10 may be viewed as having a generally cylindrical shape with surfaces of either end of the cylinder having curved edges.

[0061] The plug body 10 has a general cylindrical shape (FIG. 2D and 2E) with a notch 55 on one end surface 52 to accommodate the protrusion 35 of the cap 5. The notch 55 may be shaped to fit the shape of the protrusion 35. In an example, the notch 55 is three quarters of a frustoconical shape to match the protrusion 35 (FIG. 2F).

[0062] For translation and rotation separation, a mating mechanism may be provided between the plug cap 10 and plug body 15. Apin / cone mechanism (male) was created on the plug cap component 10 while a socket mechanism (female) was created on the plug body 15. In an embodiment, the plug surface 10 is provided with a frustoconical shaped protrusion 35 that is received within a notch 55 in the plug body 15. This allows suppression on the existing two degrees of freedom which prevents a total separation of both components during application. In an embodiment, the plug 5 may be three dimensionally printed with the plug surface 10 and plug body 15 joined together.

[0063] A protrusion 35 is attached to the bottom layer 30 of the cap 5 and protrudes outwards from the bottom layer 30 (FIG. 2A to FIG. 2C). The protrusion 35 may have a tapered side profile as seen in FIG. 2Aand FIG. 2B. The protrusion 35 may be shaped as a frustocone. This allows for engagement with the notch 55 in the plug body 15. Advantageously, a frustocone (i.e. a frustoconical shaped object) or a partial frustocone shaped protrusion limits translational motion and may be produced using a three dimensional printing process (for example fused filament fabrication (FFF) and fused deposition modelling (FDM)) with good print fidelity. Current limitations with the FFF and FDM printing devices limit how small the protrusion 35 may be printed where if the cone becomes too small a blob of material would just be created. Furthermore, there is a need to Io limit the amount of the bioactive polyethylene within the plug body 15 made of the bioactive polycaprolactone as the plug body 15 is inside the subchondral bone region and to avoid excessive heat exposure to the bioactive polycaprolactone. The portion where the protrusion 35 and notch 45 joins involves printing with two different materials with different printing temperatures where the printing temperature of the bioactive polyethylene may cause problem for the printed bioactive polycaprolactone layers. Hence, there is a need to limit the height of the protrusion 35 which correlates to the exposure time.

[0064] In an embodiment, the protrusion 35 may be a portion of a frustoconical shaped protrusion 35, for example from half (1 / 2) to seventh-eighth (7 / 8) of the frustocone. In an example, the screw may be three quarters of a frustoconical shape to engage the cap 5 with the plug body 10 and prevent total separation. The three quarters of the frustocone may be seen in the bottom view of the cap 10 in FIG. 2 panel (a). A three quarter frustoconical shaped protrusion 35 provides a balance of size and material as a smaller protrusion may be insufficient to resist rotational motion while a larger protrusion 35 means less material connects the protrusion 35 to the cap 10 which may result in the part being less resilient.

[0065] Fluid flow capability was enabled by incorporating a porous structure within the plug 5 with exposed ends of the head 10 and stem 15. This was achieved using infill density and infill pattern settings in Ultimaker Cura. By creating a porous plug 5, stem cell carrying blood from the subchondral bone is able to penetrate the entire plug 5 and reach the top surface 20 of the plug 5, allowing for chondrogenesis to occur on the plug surface 20. At the same time, osteogenesis can occur within the plug body 10 with this same blood penetration. With enhanced osteointegration of plug 5, the plug 5 may also be secured within the void, decreasing the risk of plug 5 loosening.

[0066] The top plug surface 20 may have a chamfered edge tapered slightly at 30 degrees over 0.7mm to reduce any surface misalignment between the surface and surrounding cartilage due to the curved nature of the articulating surface. This feature was determined to be crucial in preventing any plug protrusion from introducing abrasion to the cartilage on the opposite articulating surface.

[0067] The plug 5 may be 3D printed via FFF. The plug 5 was used for a test fitting on a porcine femoral condyle as shown in FIG. 1 panel (b). This test fitting allows a better understanding of the form and fit of the plug 5 with respect to the host tissue and enables further refinement in terms of the plug overall diameter before the actual in vivo porcine study.

[0068] It was determined that the plug diameter (“d”) needs to be the same as the hole diameter with a maximum tolerance of +0.5mm. This ensures a tight fit between the implant and the hole, preventing any implant loosening and subsequent implant failure.

[0069] In an embodiment, bioactive UHMWPE (PE-RGD) was used for the plug surface layer 10 as it was demonstrated to be able to enhance chondrocyte proliferation over bioactive PCL (FIG 3). Various amounts of PE-RGD was blended with Lubmer L3000 UHMWPE (weight average molecular weight (Mw) of 500 kDa) from Mitsui Chemicals to obtain a formulation for creating the plug surface. UHMWPE was selected as the base polymer as it is a biocompatible material commonly used in articulating surfaces of joint implants due to its mechanical toughness and inertness. However, it is well-known that PE causes foreign body reaction in the human body. From chondrocyte testing assays, PE-RGD was used to create chondrocyte binding property in UHMWPE and also to reduce inflammation due to UHMWPE.

[0070] As shown in FIG. 3, relative to the pure UHMWPE, PEsooo-RGD 5% and PEs.ooo-RGD 10% revealed an increase of 18% and 40% in chondrocytes proliferation respectively. It is notable that, an increasing dose of bioaddtive (PEs ooo-RGD 20%) not only shows no cell improvement but regression to a same level as PEs.ooo-RGD 5% (18%) was observed. These findings demonstrated that the optimum formulation for chondrocyte proliferation is PE5,000-RGD 10% in UHMWPE. It is noteworthy that chondrocytes produce collagen which forms hyaline cartilage. Hence, it demonstrates the capability of the bioactive PE in cartilage regeneration, and it was determined that PE-RGD 10 % was most effective in chondrocyte proliferation.

[0071] On the other hand, bioactive PCL was used for the plug body 15 as it needs to be able to enhance osteointegration. 5 to 20 wt. % of PCL-RGD may be blended with medical grade PCL to make up to 100 wt. % (Evonik Resomer C212, with an inherent viscosity of 1.13 - 1.38 dL / g) to create a formulation for creating the plug body 15. In an example, 10 wt. % of PCL-RGD was blended with 90 wt. % PCL to make the plug body 15. Using either the bioactive PE or bioactive PCL alone would not provide both chondrocyte proliferation and osteointegration as the plug 5.

[0072] As UHMWPE is a non-polar material with low surface energy, it results in poor adhesion property which poses a challenge for fused deposition modelling (FDM) printing technology which is also known as fused filament fabrication (FFF). Build plate adhesion and layer adhesion with bioactive PCL are the main issuesfaced in printing the plug 5. However, a specific methodology was developed to itigate these issues.

[0073] Table 2 below highlights the printing parameters used. Build plate adhesion was improved by utilising a polyester based film which enables bioactive UHMWPE to adhere well on it throughout the printing process and is left after removal of the printed part. A polypropylene based film may also be used. Moreover, this was further improved using brim with a width of 7mm to prevent any warpage from occurring.

[0074] Layer adhesion with bioactive PCL was enhanced through the use of printing temperature parameter for print core 2. As bioactive UHMWPE melts between 130 to 140°C, print core 2 loaded with bioactive PCL was set between 120 to 140°C. This ensures both materials are in molten state where they will adhere to each other as they cool down concurrently during the printing process. Cooling was set according to the shrinkage of each material where it was disabled for print core 1 while moderate cooling was applied for print core 2.

[0075] Table 2. FDM / FFF printing parameters

[0076] The final implant was placed in porcine knee joints in vivo for safety and efficacy studies. The lateral and medial compartment of the knee joint was each drilled with 1 hole, in both hind legs of the pig (six pigs, 12 legs, 24 defects). One leg was used as control where microfracture was done on both holes as positive control whilst OC plugs 5 were inserted in each of two holes in the other leg as the test group.

[0077] The plugs 5 were fitted exactly into the defects created and hammered slightly to ensure that they are flushed with the surrounding cartilage surface so that there would be no implant sticking out of the cartilage (FIG. 5). Panel (a) of FIG. 5 shows the OC plugs 5 implanted in the defects in both the medial and later knee compartment of the femoral condyl with the top surface 20 of the plug 5 showing. Panel (b) of FIG. 5 shows the microfracture in the femoral condyl of the other leg of the pig as a positive control. The pigs were monitored for 6 months to determine the extent of cartilage and bone growth at end point.

[0078] FIG. 6, FIG. 7, and FIG. 8 show various pictures of the results of the implanted plugs 5 in the pigs after 24 weeks (approximately 6 months). FIG. 6 panel (a) shows the implanted plants in the knee joint at day 0 (left image) and week (wk) 24 (right image). On week 24, cartilage has been regenerated over one plug withcartilage similar to native cartilage. Partial regeneration of cartilage was observed in the other implant with greater than 50% closure (FIG. 6 panel (b)). In contrast, no cartilage regeneration in the microfracture control (left image) and no bone growth over microfracture holes drilled into bone (right image) was observed as shown in FIG. 6 panel (c). FIG. 7 shows bone growth in the plug cross section (left image) and inside the knee joint (centre image). Blood vessels growing in the plug body is shown in the right image of FIG. 7. FIG. 8 shows only a small fragment of the OC plug body 15 was left (PCL component). The remaining plug body 15 has osteointegrated and was no longer detachable or identifiable. The pore design from the residual plug body 15 can be seen in FiG. 8.

[0079] It has been successfully demonstrated that the plugs 5 are able to osteointegrate as well as regenerate cartilage in vivo using porcine knee joint defect models. The unique pore design to allow blood flow from the bone to the plug surface, without being interfered by the locking mechanism, allowed for successful blood flow through. This is critical for cartilage regeneration. Further, UHMWPE is notoriously challenging to be printed three dimensionally, especially in objects with fine details, such as the fine pores in the plug. However, a good printing method has been described herein to print the pores effectively without loss in pore size or shape.

[0080] In vitro chondrocyte studies show the bioactive PCL cannot encourage chondrocyte growth and the bioactive PE is needed for the plug 5. Yet, if the entire plug 5 were made of bioactive PE, then it is fully non-biodegradable.

[0081] The bioactive materials used in the implant 5 allowed for both cartilage regeneration and osteointegration. In contract, the microfracture control showed no bone growth over the 1 mm holes created even after 6 months. Yet, there is complete osteointegration of the implant 5 in the pig’s femur. This clearly showed the efficacy of the plug 5 both in terms of material design and material choice. Vascularization of the plug 5 in the plug body 15 was observed where blood vessels were observed. Revascularisation in synthetic bone grafts in very challenging and no synthetic graft has been able to achieve that. Yet, successful blood vessel growth into the bone graft component (PCL part 15) of the plug 5 was achieved and shown, further demonstrating the prowess of this technology. The pores designed in theplug and the material used, allowed for this challenging tissue growth to be achieved.

[0082] The dual layer structure of the plug 10 made of the different bioactive polyethylene and bioactive polycaprolactone provides the plug 10 with different properties including both cartilage regeneration and osteointegration while allowing the plug body 15 to be biodegradable to reduce the size of the plug 10 over time. This is not possible with using either material alone.

[0083] A comparison of the plug 5 described herein and existing products are compared in Table 3.

[0084] Table 3. Comparison of osteochondral plug 5 and existing products>

[0085] Experimental

[0086] Materials

[0087] The bioactive polymers used herein comprises of a synthetic polymer blended with the respective bioadditive.

[0088] PCT / SG2020 / 050621 (published as WO 2022 / 093106) describes the preparation of bioactive polycaprolactone. PCL-RGD x % refers to a blend of pure PCL at (100-x) % with PCL-RGD copolymer at x %.

[0089] Synthesis of (H2IMes)(pyr)2(CI)2RuCHPh

[0090] Pyridine (2 mL) was added to Grubbs second generation catalyst (0.5 g, 0.59 mmol) in a 20 mL vial with a screw cap. The reaction was stirred at room temperature for 15 minutes during which a colour change from red to green was observed. Hexanes (16 mL) was added to the green solution and a green solid began to precipitate. The green precipitate was vacuum-filtered, washed with hexanes (4 x 10 mL), and dried under vacuum to afford the catalyst as a green powder.

[0091] Synthesis of NBPEGs,4ooRGD

[0092] RGD (with 1 carboxylic acid on aspartic acid protected with OMe) (0.0937 g, 0.26 mmol), was dissolved in MeOH (2.5 ml) in a 4 ml vial, in the glovebox. iPr2EtN (91 pl, 0.52 mmol) was added to form the solution (A). HOBt (0.0353 g, 0.26 mmol) and HBTU (0.0992 g, 0.26 mmol) were dissolved in MeOH (12.5 ml) in a20 ml vial at 40°C, followed by addition of the RGD solution (A), to give the mixture (B). The mixture (B) is then added to NBPEG3,400NH2 (0.77g, 0.218 mmol) in a 40 ml vial and stirred at room temperature (r.t.) for 24h. The resultant mixture was then evaporated to dryness and was added to Et20 (50 ml). The Et20 solution was chilled in a freezer for 48 h and decanted. MeOH (5 ml) was added to the residue and filtration was performed. The filtrate was evaporated to dryness followed by dialysis against deionized water and lyophilization to give a pale yellow solid as the product NBPEG OORGD (0.8g, yield 95%).1H NMR (D2O, 500 MHz, 25°C): 5 = 6.37 (s, 2H, NB), 4.04 (m, RGD), 3.85 (m, RGD), 3.71 (m, PEG), 3.64 (d, 4H, J=2.5Hz, NB), 3.23 (m, RGD), 3.00 (m, RGD), 2.86 (d, 2H, J=1.5Hz), 1.92 (m, RGD), 1.70 (m, RGD), 1.52 (d, 1H, J=10Hz, NB), 1.32 (d, 1H, J=10Hz. NB). ESI-MS (M4-H4-Na)2+: calculated: 1716.99; found: 1716.0 (n=65).

[0093] Synthesis of N-(Hydroxypropyl)-cis-5-norbomene-exo-2,3-dicarboximide (NPH)

[0094] A round-bottom flask was charged with c / s-5-norbornene-exo-2,3-dicarboxylic anhydride (0.985 g, 6.0 mmol) and 3-amino-1 -propanol (0.473 g, 6.3mmol). To the flask was added 30 mL toluene, followed by triethylamine (84 pL, 0.60 mmol). A Dean-Stark trap was attached to the flask, and the reaction mixture was heated at reflux (135 °C) for 4 h. The reaction mixture was then cooled and concentrated in vacuo to yield a pale yellow oil. This residue was diluted with 30 mL of dichloromethane and washed with 0.2 M HCI (20 mL) and saturated NaCI (20 mL). The organic layer was dried over Na2SO4, concentrated in vacuo, and dried overnight in a vacuum oven to yield 1 .22 g of white solid.1H NMR (500 MHz, CDCIs): 66.27 (t, J = 2.0 Hz, 2H), 3.64 (t, J = 6.4 Hz, 2H), 3.53 (q, J = 6.1 Hz, 2H), 3.26 (s, 2H), 2.71 (m, 2H), 2.60 (m, 1 H), 1.84-1.70 (m, 2H), 1.55 (m, 1 H), 1.24 (d, 1 H).

[0095] Synthesis of NPH-PCL macromonomer by ring opening polymerisation (ROP)

[0096] NPH-PCL macromonomers with different degree of polymerization (DP) were prepared by ROP. As an example, s-caprolactone (6-Hexanolactone) (0.5 ml, 0.52 mol) was added to a 20 ml scintillation vial containing NPH initiator (0.05 g, 0.23 mmol), dissolved in toluene (1 ml). A standard solution of Sn(Oct)2 of concentration 91 pmol / ml, was prepared and used for ROP reactions. Sn(Oct)2 (0.0037g, 9.1 pmol) was added to the mixture and the resultant solution was stirred at 110 °C for 90 min and precipitated into methanol. The methanolic solution was then placed in the freezer overnight to result in white precipitate which was filtered and washed with methanol. The residue is then dried under vacuum overnight. GPC analysis (THF): Mri= 5,613, PDI = 1.08, yield 0.4478 g.

[0097] Typical procedure for ROMP of NPH-PCL macromonomer and NBPEG3400RGD macromonomer as representative prep for PCL-peptide type copolymers

[0098] NBPEG3400RGD macromonomer (0.2 eq.) was weighed into a 4 ml scintillation vial followed by addition of NPH-PCL (0.05 g). THF (0.021 M with respect to NPH-PCL) was added and the mixture stirred at room temperature till a clear solution was obtained. A solution of Grubbs second generation catalyst or (H2lMes)(pyr)2(CI)2RuCHPh in THF (1.25 mol %, 0.05 M) was added to the solution and the reaction is stirred for 2 hour (h) at 30 °C. Ethyl vinyl ether was added to the reaction mixture followed by MeOH (3 ml) and the mixture was placed in the freezer for 1 h to give a white ppt. The mixture was centrifuged and mother liquor was decanted. The residue was resuspended in methanol, centrifuge followed by decanting mother liquor again, to wash the residue. The washing with MeOH was carried out 3 times before the final residue was dried overnight in a vacuum oven. The amount of the NBPEG3400RGD macromonomer is from 1 to 10% of the monomers, in other words q is from 0.01 to 0.1 , and p is from 0.9 to 0.99 where p + q is 1.

[0099] For the PCL-RGD copolymer, gel permeation chromatography (GPC) analysis (THF): M„ = 140,000, PDI = 1.21.

[0100] PCT / SG2020 / 050622 (published as WO 2022 / 093107) describes the preparation of the bioactive polyethylene. PE-RGD x % refers to a blend of pure UHMWPE at (100-x) % with PE-RGD copolymer at x %.

[0101] Synthesis of NB-SA-t PEs.ooo

[0102] Succinic acid-terminated polyethylene (MW 5000) (SA-t PEs.ooo) (10 g, 2 mmol) was weighed into a 250 ml round bottom flask (rbf) followed by addition of toluene (120 ml). Hexamethylenediamine (HMDA) (0.2784 g, 2.4 mmol) and triethylamine (0.28 ml, 2 mmol) were added. The mixture was stirred under reflux overnight connected with a Dean Stark trap for water removal. The resultant suspension was cooled and concentrated, followed by addition of MeOH, to give a beige precipitate. The mixture was filtered and the residue was washed with MeOH before dryness, to give SA-t PEs.ooo-HMDA quantitatively.

[0103] SA-t PEs.ooo-HMDA (10.2 g, 2 mmol) was added to a 250 ml rbf followed by addition of cisnorbornene-exo-2,3-dicarboxylic anhydride (0.366 g, 2.2 mmol), toluene (120 ml) and triethylamine (0.28 ml, 2 mmol). The mixture was refluxed overnight with a connected Dean Stark trap for water removal. The resultant suspension was cooled and concentrated, followed by addition of MeOH, to give a beige precipitate. The mixture was filtered and the residue was washed with MeOH before dryness, to give NB-SA-t PEs.ooo macromonomer (9.4g, yield 90%). 1 H NMR (1 ,2-C6D4CI2, 400 MHz, 120oC): 5 = 6.03 (m, 2H, NB), 5.44 (m, 1H, -CH=CH-), 5.24 (m, 1H, -CH=CH-), 3.39 (m, 6H, -CH2- on HMDA), 3.05 (s, 3H, -CH2- on HMDA), 2.41 (m, 5H), 1.95 (m, 3H), 1.22 (m, PE), 0.84 (M, -CH3).

[0104] Each of the macromonomers were prepared separately and copolymerised in a random manner using a second generation Grubbs’ catalyst (Gll-catalyst). The NB-PEG macromonomer was weighed into a 20 ml vial followed by addition of NB-SA-t PEs.ooo (5 equivalents). 1 ,2-diclorobenzene (2.4 ml) was added and the mixture stirred at 75 °C till a brown solution was obtained. A solutionof the 2rdgeneration Grubbs’ catalyst in 1,2-diclorobenzene (1.25 mol %, 0.05 M) was added and the mixture was stirred for 24 h at 75 °C. Ethyl vinyl ether was added to the mixture followed by MeOH (15 ml) to give a beige precipitate. The mixture was filtered and the residue was washed with water / acetone before dryness. All copolymers were obtained with the isolated yield over 90%. NB-SA-t PE conversion and NB-PEG-peptide incorporation varied, but the amount of the NB-PEG-peptide in the polymer is from 1 to 10% of the monomers, in other words q is from 0.01 to 0.1 , and p is from 0.9 to 0.99 where p + q is 1.< <

[0105] PEs.ooo-RGD copolymer1H NMR (1 ,2-C6D4CI2, 400 MHz, 120°C): 5 = 6.06 (s, unreacted NB-SA-t PEs.ooo), 5.48 (m, vinyl proton on SA-t PEs.ooo), 5.30 (m, vinyl protons on SA-t PEs.ooo), 3.55 (s, PEG), 3.41 (m), 3.27 (s), 3.09 (s), 2.44 (m), 1.93 (m), 1.28 (s, PE), 0.84 (m, 3H, -CH3 on SA-t PEs.ooo).

[0106] FFF 3D Printing

[0107] Osteochondral plugs 5 were produced using an Ultimaker S5 dual material 3D printer. The 3D printer utilises FFF printing technology where heated nozzle deposits on a heated buildplate along the toolpath based on the G-code of the printfile. G-code file was created using Ultimaker Cura software where printing parameters (Table 2) were set for the printing process. Bioactive polymer filaments with a diameter of 2.85mm were used with the 3D printer. These filaments were produced as described in PCT / SG2022 / 050620 (published as WO 2023 / 033730).

[0108] Briefly, base polymer pellets were cryogenically grinded to powder form that is less than 1 mm in particle size using a SPEX 6770 Freezer / Miller or a SPEX 6875 Freezer / Miller. Subsequently, the base polymer and bioadditive were mixed using a ThinkyMixer ARE-250 or SPEX 8000D Mixer / Mill for at least 10 to 12 minutes and this mixture is referred to as the “formulation”. Filament extrusion was performed using ThermoScientific Process 1 1 Twin-Screw Extruder (TSE) which comprises extruder, melt pump with a nozzle of 03 mm, water bath, and haul unit. The filament diameter needs to range between 2.5 mm to 3.1 mm as the FFF printer is configured for a 2.85mm filament diameter. It is also able to manufacture filament suitable for a FFF printer with a 1.75mm filament diameter configuration. The polyester film (UltiMaker Adhesion Sheet) is applied on the existing glass buildplate to provide a layer of adhesion for the UHMWPE during the printing. The OC plug 5 is printed in such a way that the cap 10 made of the UHMWPE blend gets printed first followed by the plug body 15 made of the PCL blend.

[0109] In vitro test

[0110] The chondrocyte proliferation in vitro test was conducted on bioactive UHMWPE 5, 10 and 20 wt. % over a 96 hours period. Human chondrocyte cell line (CHON-001) was used and maintained in complete Dulbecco's Modified Eagle Medium (DMEM) (G418, 10% fetal bovine serum). A total of 4 samples were prepared into a U-shaped design to acquire tight fit dimensions with respect to the 24-well tissue culture plate used. 50,000 chondrocytes were seeded into the wells with bioactive UHMWPE in 500pL complete DMEM. The cells were grown for 96 hours in 37°C incubator at 5% CO2. Cells were harvested by detachment with 0.05% Trypsin and cell proliferation was assessed with CyQUANT™ Cell Proliferation Assay kit (Invitrogen, Waltham Massuchusetts) after 96 hours. Cell proliferation was measured using a microplate reader with excitation at 485 nm and emission detection at 530 nm (Tecan, Mannedorf, Switzerland).

[0111] In vivo test

[0112] An in vivo animal study was conducted to analyse bone regeneration using 6 New Zealand white rabbits of weight ranging between 3.0 to 3.8kg and 4 sample groups over a period of 3 months. Zoletil50, Xylazine Hydrochloride was used to anesthetise the rabbits in 1:1 ratio at 0.4 ml_ dosage. After the rabbits were anesthetised and fixed, fur was removed in the leg, the skin disinfected and covered. The skin was cut longitudinally along the medial side of femoral condyle after the rabbits have been anesthetised and skin disinfected. Soft tissues were separated layer by layer until the femoral condyle was exposed. A pilot hole was drilled using a smaller drill bit and the drill bit size was increased gradually to obtain the required hole size of 6mm diameter at 8 mm depth in the femoral condyle of each of the rabbit’s two hind legs. The wounds were cleaned with saline and the sample was implanted into it according to the groupings provided in Table 4 below. Surgical sites were sutured back after implantation is completed. The sample groups were pure PCL, PCL-RGD 5 %, PCL-RGD 10 % and chronOS® Bone (Depuy Synthes). CT scans were taken on day 0, week 6 and week 12 post-surgery.

[0113] Table 4. Sample groupings

[0114] In vivo porcine study

[0115] 6 Yorkshire pigs of weight between 41 - 49 kg were used in this study. The implants and microfracture sites were randomly distributed on different legs of the pigs. The pigs were anesthetised and placed in supine position with hind legs secured to the operating table. After the legs were disinfected with iodine solution, an incision at the knee joint was made from the top of the patella to the medial edge of the tibial tubercle. Meticulous haemostatic was performed throughout the procedure as no tourniquet was used. A medial parapatellar arthrotomy was carried out, taking care not to damage the underlying cartilage or internal structures of the knee joint (e g. meniscus, cruciate ligaments). The patella was subluxed laterally, providing exposure to the knee joint. The ligamentum mucosum was released inorder to visualize the lateral femoral condyle of the pig, exposing the underlying anterior cruciate ligament and lateral meniscus. A Hohmann retractor was inserted at the level of the joint line to visualise the medial and lateral femoral condyles sequentially. A crosshair was marked on the most distal and central portion of the femoral condyle cartilage.

[0116] For the microfracture procedure, an 8 mm biopsy punch was used to cut out a disc of cartilage to simulate cartilage loss in early osteoarthritis. Three microfractures were created using a 2mm drill bit (FIG. 5 panel (b)). For the OC plug 5, a pilot drill hole was performed with the 2mm drill bit. This was enlarged with a 10mm drill bit to a depth of 10mm (the dimensions of the OC plug 5). Excess cartilage flaps around the newly created bony defect were excised. The OC plug was inserted by hand, coaxially to the bone defect and impacted till the surface was flush with the native cartilage.

[0117] The arthrotomy closure was performed using Vicryl 1 and 2 / 0 sutures in a continuous fashion. The skin was closed using Vicryl 2 / 0 sutures. Dermabond skin glue and antibacterial cream was used prior to reversal of anesthesia. Postoperative care of the animal was in accordance to institutional guidelines according to approved Institutional Animal Care and Use Committee (IACUC) protocol 2023 / SHS / 1812.

Claims

Claims1. An osteochondral plug comprisinga plug cap with a porous structure for blood flow through the plug cap, the plug cap is made of a first polymer blend, the first polymer blend comprising 80 wt. % to 95 wt. % of ultra-high molecular weight polyethylene (UHMWPE); and 5 wt. % to 20 wt.% of a polymer of Formula 1 ,Li is selected from the group consisting of a substituted or unsubstituted divalent C10 to C24 aliphatic moiety, a substituted or unsubstituted divalent C10 to C24 aryl moiety, and combinations thereof,L2 is a substituted or unsubstituted divalent C2 to C6 aliphatic moiety, Ai is selected from the group consisting of RGD, hyaluronic acid, RLGYWS (SEQ ID NO: 1), and AGQWHRVSVRWG (SEQ ID NO: 2, A5G81),m is from 10 to 350,pi is 0.9 to 0.99, qi is 0.01 to 0.1 , pi + qi = 1 ; anda plug body with a second porous structure for blood flow through the plug body, the plug body is made of a second polymer blend, the second polymer blend comprising 80 wt. % to 95 wt. % of polycaprolactone; and 5 wt. % to 20 wt.% of a polymer of Formula 2,each of Ls and l_6 is a substituted or unsubstituted divalent C2 to C6 aliphatic moiety,n2 is from 30 to 100,A2 is selected from the group consisting of RGD, hyaluronic acid, RLGYWS (SEQ ID NO: 1), and AGQWHRVSVRWG (SEQ ID NO: 2, A5G81), P2 is 0.9 to 0.99, q2 is 0.01 to 0.1 , p2 + q2 = 1 ,wherein m in Formula 1 and Formula 2 is such thathas a number average molecular weight from 500 to 7000,the plug cap is joined to the plug body.

2. The osteochondral plug according to claim 1 , wherein Ai is RGD and is the polymer of Formula 1 a and / or A2 is RGD and is the polymer of Formula 2a.

3. The osteochondral plug according to claim 1 or claim 2, wherein Li iseach independently selected from the group consisting of a substituted or unsubstituted divalent C2 to C10 aliphatic moiety.

4. The osteochondral plug according to claim 3, wherein L3 is (CH2)ai, where ai is from 2 to 8, preferably ai is from 3 to 7, more preferably ai is from 4 to 6.

5. The osteochondral plug according to claim 3 or claim 4, wherein L4 is a substituted or unsubstituted divalent C2 to C4 aliphatic moiety, preferably l_4 is -CH2CH=CH-6. The osteochondral plug according to any one of claims 1 to 5, wherein m is from 50 to 300, preferably m is from 150 to 250, more preferably m is from 170 to 200.

7. The osteochondral plug according to any one of claims 1 to 6, wherein L2 is (CH2)a2, where a2is from 2 to 6, preferably a2is from 2 to 4, more preferably a2is 2 or 3.

8. The osteochondral plug according to any one of claims 1 to 7, wherein m is such that the number average molecular weight is from 1000 to 5000, preferably m is such that the number average molecular weight is from 2000 to 4000, more preferably m is such that the number average molecular weight is from 3000 to 4000.

9. The osteochondral plug according to any one of claims 1 to 8, wherein the polymer blend consists essentially of 80 wt. % to 95 wt. % of UHMWPE; and 5 wt. % to 20 wt.% of the polymer of Formula 1 , preferably the polymer blend consists of 80 wt. % to 95 wt. % of UHMWPE; and 5 wt. % to 20 wt.% of the polymer of Formula 1.

10. The osteochondral plug according to claim 9, wherein the polymer blend consists essentially of, or consists of, 90 wt. % of UHMWPE; and 10 wt.% of the polymer of Formula 1.

11. The osteochondral plug according to any one of claims 1 to 10, wherein the second polymer blend consists essentially of 80 wt. % to 95 wt. % of polycaprolactone; and 5 wt. % to 20 wt.% of the polymer of Formula 2, preferably the second polymer blend consists of 80 wt. % to 95 wt. % of polycaprolactone; and 5 wt. % to 20 wt.% of the polymer of Formula 2.

12. The osteochondral plug according to claim 11, wherein the second polymer blend consists essentially of, or consists of, 90 wt. % of polycaprolactone; and 10 wt. % of the polymer of Formula 2.

13. The osteochondral plug according to any one of claims 1 to 12, wherein the polymer of Formula 1 is a polymer of Formula 1 b, wherein ni is such that the polyethylene has a number average molecular weight of 5000,Formula 1b.

14. The osteochondral plug according to any one of claims 1 to 13, wherein the UHMWPE has a weight average molecular weight of 500 kDa.

15. The osteochondral plug according to any one of claims 1 to 14, wherein each of Ls and l_6 is a substituted or unsubstituted divalent C2 to C4 aliphatic moiety, preferably Ls is -(CH2)s and / or Le is -(CH2)2-.

16. The osteochondral plug according to any one of claims 1 to 15, wherein n2 is from 30 to 50, m is from 60 to 80.

17. The osteochondral plug according to any one of claims 1 to 16, wherein the polymer of Formula 2 is Formula 2b,Formula 2b, wherein n2 is such that a macromonomer containing the polycaprolactone has a number average molecular weight of 5000 to 6000.

18. The osteochondral plug according to any one of claims 1 to 17, wherein the plug cap and the plug body each has a first end and a second end opposite to the first end, the second end of the plug cap is joined to the first end of the plug body, the porous structure of the plug cap and the plug body allows forblood flow from the second end of the plug body to the first end of the plug cap.

19. The osteochondral plug according to claim 18, wherein the plug cap is joined to the plug body by an interlocking mechanism.

20. The osteochondral plug according to claim 19, wherein a protrusion extends out from the second end of the plug cap to mate with a notch in the first end of the plug body.

21. The osteochondral plug according to claim 20, wherein the protrusion has a frustoconical shape or a partial frustoconical shape.

22. A method of forming an osteochondral plug, the method comprising providing a film, wherein the film is a polyester based film or a polypropylene based film;melting a first polymer blend comprising 80 wt. % to 95 wt. % of ultra- high molecular weight polyethylene (UHMWPE); and 5 wt. % to 20 wt.% of a polymer of Formula 1 ,Formula 1,Li is selected from the group consisting of a substituted or unsubstituted divalent C10 to C24 aliphatic moiety, a substituted or unsubstituted divalent C10 to C24 aryl moiety, and combinations thereof,L2 is a substituted or unsubstituted divalent C2 to C6 aliphatic moiety, A1 is selected from the group consisting of RGD, hyaluronic acid, RLGYWS (SEQ ID NO: 1), and AGQWHRVSVRWG (SEQ ID NO: 3, A5G81),m is from 10 to 350, m is such thathas a number average molecular weight from 500 to 7000, pi is 0.9 to 0.99, qi is 0.01 to 0.1, pi + qi = 1;melting a second polymer blend, the second polymer blend comprising 80 wt. % to 95 wt. % of polycaprolactone; and 5 wt. % to 20 wt.% of a polymer of Formula 2,Formula 2, each of Ls and Le is a substituted or unsubstituted divalent C2 to C6 aliphatic moiety,n2 is from 30 to 100, m is such thathas a number average molecular weight from 500 to 7000, A2 is selected from the group consisting of RGD, hyaluronic acid, RLGYWS (SEQ ID NO: 1), and AGQWHRVSVRWG (SEQ ID NO: 3, A5G81),P2 is 0.9 to 0.99, q2 is 0.01 to 0.1 , p2 + q2 = 1 ;three dimensionally printing with the first polymer blend on the film a plug cap with a porous structure for blood flow through the plug cap;three dimensionally printing with the second polymer blend a plug body with a porous structure for blood flow through the plug body, wherein the plug cap is joined to the plug body; andcooling the printed plug cap and plug body to form the osteochondral plug.

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