CA2689725A1 - Polyol based-bioceramic composites - Google Patents

Abstract

Crosslinked polyol based-bioceramic composites are prepared by the reaction of a polyol and polycarboxylic acid in the presence of a bioceramic. Implantable medical devices fabricated at least in part with the crosslink'ed polyol-bioceramic composite materials are useful in a wide variety of applications.

Description

POLYOL BASED - BIOCERAMIC COMPOSITES
FIELD OF THE INVENTION
The present invention relates to polyol based composite materials. In particular, the present invention relates to polyol-bioceramic based composite materials useful in tissue engineering.
BACKGROUND OF THE INVENTION
Replacement of damaged or diseased body parts is an increasingly important part of medicine. For example, over 8 million surgical procedures are performed in the United States each year to treat the millions of Americans experiencing organ failure or tissue loss. Although procedures for organ transplantation and reconstructive surgery have the potential to dramatically improve quality of life, and in some cases save life, there are problems associated with them. These procedures often require either transplantation from a second surgical site, for example a skin and bone grafts, or organ donation from a healthy donor individual. Major problems with organ transplantation include the shortage of donor organs and the need for life-long administration of anti-rejection drugs. The problem with second site surgeries is that these procedures are associated with pain and in some cases, morbidity. Consequently, the science of tissue engineering has emerged with the goal of developing organs, tissues, and synthetic biomaterials which can be used to augment and/or replace traditional transplant technologies.
Collagen is the structural protein of connective tissues, such as skin (soft tissue) and bone (hard tissue). Although it has been described to be inelastic in contrast to elastin, another structural protein in connective tissue, collagen is actually elastic with elastic strain being 10-15 % and the coefficient of restitution (resilience) being 90 %, the same as that of elastin. A muscle fibre, i.e. muscle cell, is composed of three structural proteins: myosin, actin and titin. The reshaping ability of muscle fibre is provided by titin, a giant elastic protein with elastic strain being 150 %.
The biocompatible and flexible polymers have been developed as an artificial substitute for collagen in connective tissue and muscular fibres in muscular tissue. To date, the biocompatible polymers most often utilised are thermoplastic polyesters, including poly(lactide acid) (PLA) and poly(glycolic acid) (PGA), as well as their copolymers (PLGA) or blends. To engineer connective and muscular tissues, which mostly work under dynamic loading conditions, such as in bone (constant and cyclic compression), heart and skeletal muscle (contraction and relaxation), the biomaterial should show long-term elasticity. These mechanical characteristics are impossible with thermoplastic polymers, because they undergo plastic (i.e. permanent) deformation almost immediately when loaded and their elongation at break is rather short, smaller than 3 %.
Poly(polyol sebacate) (PPS) is a family of crosslinked elastomers recently developed for the applications of soft tissue engineering. Polyols are alcohols containing multiple hydroxyl groups. Glycerol, maltitol, sorbitol, xylitol and isomalt are some of the more common types. These types of polymers break down by simple hydrolysis to natural metabolisable by-products, and are therefore considered highly biocompatible. In vitro studies have indicated that degradation of poly(glycerol sebacate) (PGS) results in an acidic micro-environment. The acidic degradation products of other polymers, such as polyesters, lead to an inflammatory response and thus limit their ability to serve as a vehicle for cellular transplantation in most organ systems. It is envisaged that similar issues will occur during the degradation of PPS
polymer systems.
The mechanical properties of PPS polymers may also change during in vivo degradation which can lead to a reduction in their mechanical properties.
Hence, there is a need for improved bioengineering materials which are more chemically and mechanically stable under in vivo conditions. It is desirable that the new family of composites will be biocompatible, elastic and tough, and will have a potential of wide applications in tissue engineering.

SUMMARY OF THE INVENTION
In work leading up to the present invention, the inventors sought to develop improved biocompatible polyol composite systems which have broad applicability to tissue engineering.
In one aspect, the present invention provides a crosslinked polyol-bioceramic composite which comprises:
(A) a polymer matrix formed from the condensation reaction between (I) a polyol component containing at least three hydroxyl groups; (II) a polycarboxylic acid component containing at least two carboxylic groups; and (B) at least one bioceramic material phase substantially homogeneously distributed throughout the polymer matrix;
wherein the amount bioceramic material in the composite being at least about 0.5 % to about 20% by weight of the total weight of the composite.
In another aspect, the present invention provides a method of preparing a crosslinked polyol-bioceramic composite comprising the steps of.

(i) providing at least one polyol component containing at least three hydroxyl groups;
(ii) providing at least one polycarboxylic acid component containing at least two carboxylic acid;
(iii) partially reacting the polyol with the polycarboxylic acid to form a prepolymer solution;
(iv) substantially homogeneously distributing at least one bioceramic material throughout the prepolymer solution; and (v) subjecting the prepolymer solution of step (iv) to further reaction conditions to introduce further crosslinking to form the crosslinked polyol-bioceramic composite.
In another aspect, the present invention provides a crosslinked polyol-bioceramic scaffold composite comprising (A) a porous bioceramic foam formed from at least one bioceramic material;
and (B) a polyol polymer matrix wherein the polyol polymer matrix is formed in situ in the foam by the condensation reaction of (I) a polyol component containing at least three hydroxyl groups; (II) a polycarboxylic acid component containing at least two carboxylic groups;
wherein the amount bioceramic material in the polyol-bioceramic scaffold composite being at least about 50 % to about 70% by weight of the total weight of the polyol-bioceramic scaffold composite.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Illustrates the pH values of culture medium after incubation with PGS
and Poly-DL-lactic acid (PDLLA).
Figure 2: Illustrates the pH values of culture medium after incubation with PGS-BG composites.
Figure 3: Illustrates cell numbers after cultured with extracts of materials for 2 days.
Figure 4: Illustrates the dead cells during the 2-day culturing in extracts of materials. The differences of PGS-15%BG vs other samples are significant (p <
0.01).
No significant differences in cell death were revealed among other samples.
Figure 5: Illustrates the percentage dead/live cells during the 2-day culturing in extracts of materials. The differences of PGS-15 wt% BG vs other samples are significant (p < 0.01). No significant differences in cell death were revealed among other samples.
Figure 6: Illustrates Young's modulus of PGS-BG composite materials vs weight percentage of BG.
Figure 7: Illustrates Ultimate tensile strength of PGS-BG composite materials vs weight percentage of BG.
Figure 8: Illustrates the Elongation at rupture of PGS-BG composite materials vs percentage of BG
Figure 9: Illustrates (a) Plot of Stress (MPa) vs Strain for pure poly(glycerol sebacate) (PGS); (b) Plot of Stress (MPa) vs Strain with PGS-10 wt% BG
composite Figure 10: Illustrates plot of ultimate tensile strength (UTS, MPa) for pure PGS, PGS-5% HA and PGS-10% HA.
Figure 11: Illustrates Young's modulus (MPa) for pure PGS, PGS-5 wt% HA
and PGS-10 wt% HA.
Figure 12: Strain at break for pure PGS, PGS-5 wt% HA and PGS-10 wt% HA.
Figure 13: Illustrates pH measurement of medium soaked with PXS, and PXS-BG composite at 2%, 5% and 10% wt% BG.
Figure 14: Illustrates elongation at rupture for PXS and PXS-BG at 2%, 5% and 10% wt% BG.
Figure 15: Ultimate tensile strength (UTS, MPa) of PXS and PXS-BG at 2%, 5% and 10% wt% BG.
Figure 16: Young's modulus of PXS and PXS-BG at 2%, 5% and 10% wt%
BG.
Figure 17: (a)-(b) Porous structure of Bioglass-derived ceramic scaffolds before and after being coated with poly(glycerol sebacate), respectively. (c)-(d) Microstructure of the struts before and after coating of poly(glycerol sebacate), respectively.
Figure 18: Illustrates the compressive mechanical strengths of porous network with or without PGS coatings (coating of PGS was followed by a crosslink treatment).
Figure 19: Illustrates the FTIR spectrum of Bioglass , pure poly(glycerol sebacate) (PGS) and Bioglass network coated with PGS and treated for crosslink. The peak at 1573 cm-1 in the spectrum of Bioglass -PGS is the vibration band of sodium carboxylate group.
Figure 20: Illustrates the XRD spectra of 45S5 Bioglass -ceramic foams (a) sintered at 1000 C for 1 hr and (b) coated with poly(glycerol sebacate); which were immersed in simulated body fluid for 3, 7 and 30 days. All spectra were obtained using 0.1 g powder. The major peaks of Na2Ca2Si3O9 phase and hydroxyapatite are marked by V and =, respectively.
Figure 21: Hydroxyapatite formed on a Bioglass scaffold strut (a) without and (b) with PGS coating, after soaking in simulated body fluid for 14 days.
5 Figure 22: Illustrates the compressive strength values of Bioglass -ceramic scaffolds coated with PGS and treated for crosslink, which was followed by soaking a simulated body fluid for up to 2 months. The inset is a degradation kinetics indicated by the data.
Figure 23: Illustrates the schematic growth kinetics of bone (blue curve), degradation kinetics of an ideal scaffold (red curve) and typical degradation kinetics of most scaffolds in reality (black curve).
Figure 24: Illustrates the SNL cell proliferation kinetics measured by the AlamarBlueTM technique. The initial plating density was 5000 cells / ml each well in a 48-well plate (n = 3). Overall, the differences between any two of the three groups were not significant (p > 0.05).

DETAILED DESCRIPTION OF THE INVENTION
The new composites possess several advantages over thermoplastics and pure PPS. The PPS-based bioceramics-reinforced composites can buffer microanatomic environment and maintain its pH value close to the normal physiological condition.
The composites have a more predictable biocompatibility than pure PPS, and their biocompatibility is comparable to the clinically applied polymer Poly-DL-lactic acid (PDLLA) in terms of cytotoxicity and cell proliferation. The PPS-10 wt% BG
composites are tougher than thermoplastics/related composites and pure PPS.
Depending on the formulation used to prepare the composite, the composites may be made to be as soft and flexible as soft tissues. The composites could provide a stable and reliable mechanical function over the initial period of implantation.
The amount of bioceramic material used in the preparation of the composites of the present invention may be at least about 5 % to about 15% by weight of the total weight of the composite. Preferably, at least about 10% by weight of the total weight of the composite.
The polyol component used to prepare the inventive composites may be selected from the group comprising glycerol, erythritol, threitol, ribitol, arabinitol, xylitol, allitol, alritol, galactitol, sorbitol, mannitol, iditol and malitol.
Preferably the polyol used is glycerol, maltitol, sorbitol, xylitol or isomalt. More preferably, the polyol component is glycerol.

The polycarboxylic acid component may be selected from the group comprising a metabolite, an aldaric acid, an alkanedioic acid, an alkenedioic acid, or an amino acid, or a derivative or salt thereof.
In one embodiment, the polycarboxylic acid component is an aldaric acid selected from the group comprising 2-hydroxy- malonic acid, tartaric acid, ribaric acid, arabanaric acid, xylaric acid, allaric acid, altraric acid, galacteric acid, glucaric acid, or mannaric acid, or a derivative or salt thereof.
In another embodiment, the polycarboxylic acid component is a metabolite selected from the group comprising succinic acid, fumaric acid, a-ketoglutaric acid, oxaloacetic acid, malic acid, oxalosuccinic acid, isocitric acid, cis-aconitic acid, or citric acid, or a derivative or salt thereof.
In another embodiment, the polycarboxylic acid component is an alkanedioic acid selected from the group comprising dimercaptosuccinic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, or sebacic acid, or a derivative or salt thereof. Preferably, the alkanedioic acid is sebacic acid, or a derivative or salt thereof.
In another embodiment, the polycarboxylic acid component is an alkenedioic acid selected from the group comprising fumaric acid, maleic acid, glutaconic acid, itaconic acid, mesaconic acid, or traumatic acid, or a derivative or salt thereof.
In another embodiment, the polycarboxylic acid component is an amino acid selected from the group comprising aspartic acid or glutamic acid, or a derivative or salt thereof.
The bioceramic used in the preparation of the composites of the present invention may be selected from the group comprising alumina, zirconia, apatites, calcium phosphates, silica based glasses, and bioactive glass ceramics and combinations and modified forms.
In one embodiment, the bioceramic is an apatite. The apatite may be selected from the group comprising hydroxyapatite (Cayo(PO4)6(OH)2), floroapatite (Caio(PO4)6F2), chlorapatite (Ca5Cl(P04)3), carbonate apatide (CaioH2(P04)6-5H20)) and combinations and modified forms. Preferably the apatite is hydroxyapatite.
In another embodiment, the bioceramic may be a bioactive glass. With this embodiment, the bioactive glass may be selected from the group comprising 45S5, 58S, S53P4, S70C30 and combinations and modified forms. Preferably, the bioactive glass is 45S5, which is commonly referred to as Bioglass .
The polyol-bioceramic composite of the present invention may be used to treat a disease, condition, or disorder from which a subject is suffering.

The crosslinked polyol-bioceramic composite of the present invention may be adapted and constructed to have a shape selected from particles, tube, sphere, strand, coilend strand, capillary network, film, fibre, mesh and sheet.
The crosslinked polyol-bioceramic composite of the present invention may be used as a tissue engineering construct, as a nerve conduit, as a mesh to be used in surgical abdominal hernia repair, or in intervertebrate disc repair.
Polyol based polymer systems Polyol-based polymers useful in the preparation of the inventive composite materials are described in, for example, WO 2008/144514 Entitled "Polyol-based polymers", the contents of which are hereinbefore incorporated by reference.
Other examples of suitable polyol polymer systems are described, in for example, Biomaterials 29 (2008) 4726-4735 Entitled" Biodegradable poly(polyol sebacate polymers), the contents of which are hereinbefore incorporated by reference.
Bioceramics can include any ceramic material that is compatible with the human body with reactive hydroxyl or amine groups. More generally, bioceramic materials can include any type of compatible inorganic material or inorganic/organic hybrid material with reactive hydroxyl or amine groups. Bioceramic materials can include, but are not limited to, alumina, zirconia, apatites, calcium phosphates, silica based glasses, or glass ceramics, and pyrolytic carbons. Bioceramic materials can be bioabsorbable and/or active. A bioceramic is active if it actively takes part in physiological processes. A bioceramic material can also be "inert," meaning that the material does not absorb or degrade under physiological conditions of the human body and does not actively take part in physiological processes.
Illustrative examples of apatites and other calcium phosphates, include, but are not limited hydroxyapatite (Caj0(PO4)6(OH)2), floroapatite (Ca10(PO4)6F2), carbonate apatide (Ca10H2(PO4)6-5H2O)), calcium phosphate , Mg-substituted tricalcium phosphate, dicalcium phosphate, tricalcium phosphate (Ca3(PO4)2), octacalcium phosphate (Ca8H2(PO4)6-5H2O), amorphous calcium phosphate, calcium pyrophosphate (Ca2P2O7-2H2O), tetracalcium phosphate (Ca4P2O9), carbonate hydroxyapatite and dicalcium phosphate dehydrate (CaHPO4-2H2O).
The calcium phosphate may be selected from the group comprising Cerap Atite , Synatite , Biosorb , Calciresorb , Chronos , Biosel , Ceraform , Eurocer , Mbcp , Hatric , Tribone 80 , Triosite , Tricos and mixtures thereof The term bioceramics can also include bioactive glasses that are bioactive glass ceramics composed of compounds such as SiO2, Na2O, CaO, and P2O5. For example, a commercially available bioactive glass, Bioglass , is derived from certain compositions of SiO2-Na2O-K2O-CaO-MgO-P2O5 systems. Some commercially available bioactive glasses include, but are not limited to:
45S5: 46.1 mol% SiO2, 26.9 mol% CaO, 24.4 mol% Na2O and 2.5 MOM P205;
58S: 60 mol% SiO2, 36 mol% CaO, and 4 mol% P2O5; and S70C30: 70 mol% SiO2, 30 mol% CaO.
A common characteristic of bioactive glasses and ceramics is a time-dependent kinetic modification of the surface that occurs upon implantation. The surface forms a biologically active hydroxyl carbonate apatite (HCA) layer which provides the bonding interface with tissues. The HCA phase that forms on bioactive implants is chemically and structurally equivalent to the mineral phase in bone providing interfacial bonding.
An overview of different bioactive glass compositions and their corresponding bioactivities is given in, for example, Hench, LL., "Bioceramics: from concept to clinic", J. Am. Ceram. Soc, 1991, 74, 1487-510, the contents of which are hereinbefore incorporated by reference. .
Various sizes of the bioceramic particles may be used in the composite. For example, the bioceramic particles can include, but are not limited to, nanoparticles and/or micro particles. A nanoparticle refers to a particle with a characteristic length (e.g., diameter) in the range of about 1 nm to about 1,000 nm. A micro particle refers to a particle with a characteristic length in the range of greater than 1,000 nm and less than about 10 micrometers. Additionally, bioceramic particles can be of various shapes, including but not limited to, spheres and fibers.
Polyol composite materials with high levels of bioceramic An alternative embodiment of the present invention allows the fabrication of biocomposites with high levels of bioceramic. A new composite scaffold has been engineered from an elastomer poly(glycerol sebacate) (PGS) and BG. In addition to a bone-bonding ability and excellent biocompatibility, the new composite scaffold exhibits unique mechanical properties that have never been reported for any existing scaffolds. First, it possesses a predictable mechanical strength that is close to the theoretical strength limit. Second it has a mechanically steady state over a period of degradation in a physiological environment while the structure of composite material is disrupted. The second feature is of great importance to tissue engineering that requires a mechanically steady state post implantation before the onset of rapid degradation kinetics.
In certain embodiments, the inventive polyol-bioceramic composite is a component of a biomedical device or implant. In certain embodiments, the inventive polyol-bioceramic is a polymer film or coating on an implant. In certain embodiments, the inventive polymer is an implant. In certain embodiments, the inventive polymer implant is a polymer matrix.
In one embodiment, the inventive polyol-bioceramic composite is surgically implanted or injected into a subject on or near diseased or damaged tissue. In certain embodiments, the inventive polymer implant aids in the in-growth of surrounding healthy tissue to the diseased area.
The polyol-bioceramic composite may be produced in different forms, depending upon the intended use and purpose. Suitable forms include solid, putty, and paste, depending on the degree of crosslinking of the polyol. If the polyol-bioceramic composite is in solid form, it may be, for example, a shaped or unshaped solid, it may be a pre-formed solid, it may be a frame or a lattice, or another solid form.
The solid form may be very stiff, stiff, slightly flexible, soft, rubbery, or other. The polyol-bioceramic composite may be a putty. If in putty form, it may be anywhere from a dense or thin putty. The polyol-bioceramic composite may be a paste. If a paste, it may be anywhere from a thick to a thin paste.
In one embodiment, the bioceramic may be formed into a porous scaffold prior to the addition of the polyol components and then crosslinked to form a polyol-bioceramic composite. This type of preparation is particularly suitable for producing composites with high bioceramic loading.
The present invention provides a method of making an inventive polymer composite comprising the steps of-(i) providing a polyol;
(ii) providing a polycarboxylic acid, or derivative thereof;
(iii) providing a bioceramic and (iv) reacting the polyol with the polycarboxylic acid in the presence of the biocermaic to form a polymer composite.
A person skilled in the art will appreciate that a wide variety of reaction conditions may be employed to promote the above transformation, therefore, a wide variety of reaction conditions are envisioned; see generally, March 's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, M. B. Smith and J.
March, 5th Edition, John Wiley & Sons, 2001, and Comprehensive Organic Transformations, R.C. Larock, 2nd Edition, John Wiley & Sons, 1999, the entirety of both of which are incorporated herein by reference.
In certain embodiments, the reaction of step (iv) is a condensation reaction {e.g., reaction between a carboxylic acid or derivative thereof and an alcohol, with the extrusion of water, an alcohol by-product, or a suitable leaving group). In certain embodiments, the reaction of step (iv) further comprises the application of heat. In certain embodiments, the reaction of step (iii) comprises heating the polyol and the polycarboxylic acid to a temperature of at least 50 C. In certain embodiments, the reaction is heated to a temperature of at least 60 C, 70 C, 80 C, 90 C, 100 C, 110 C, 5 120 C, 125 C, 130 C, 135 C, 140 C, 145 C, 150 C, 155 C, 160 C, 165 C, or 170 C.
In certain embodiments, the reaction of step (iii) further comprises conducting the reaction under reduced pressure.
Optionally, other components or additives may be added to the polyol-bioceramic composite. These additives may be added for various reasons. For 10 example, additives may be added to increase biocompatibility, to decrease the possibility of rejection, to decrease the risk of infection, to increase the rate of natural bone growth in the bioceramic, or to increase the rate of natural cell growth near the implant. Additives may also be added to change or enhance some of the properties of the bioceramic. For example, the bioceramic may include growth factors, cells, other materials and elements, curing or hardening components, and other possible additives.
In a particular embodiment, the present invention provides a poly(glycerol sebacate)-bioglass composite which comprises:
(A) a polymer matrix formed from the condensation reaction between (I) glycerol; (II) sebacic acid; and (B) Bioglass substantially homogeneously distributed throughout the polymer matrix;
wherein the amount Bioglass in the composite being at least about 0.5 %
to about 20% by weight of the total weight of the composite.
The invention is illustrated by the following non-limiting examples.
Materials and Methods Bioglass powder was purchased from NovaBonewith particle size being <5 m. Unless stated otherwise, all other materials were obtained from Sigma.
Example 1: Synthesis of poly(glycerol sebacate) (PGS) prepolymer PGS prepolymer was synthesized by polycondensation of 1 mole each of glycerol and sebacic acid at 120-130 C under argon for 12-24 hr. The prepolymer was then dissolved in tetrahydrofuran (THF) to produce a 50 wt/v % solution, as illustrates in Scheme 1.

O O
HO OH + O O ~ OO OR

~OH

Scheme 1: Reaction of glycerol and sebacic acid to produce poly(glycerol sebacate) Example 2: PGS- Bioglass (BG) composite A series of PGS-bioceramic composites were prepared by mixing Bioglass powder into the PGS prepolymer solution prepared in Example 1 to produce 1, 5, and 15 wt % percentage PGS-BG composite. As a reference, a PGS polymer was prepared which contained 0% wt% BG. The slurries were then vigorously stirred for at least 1 hour and the resulting solution cast onto glass slides to produce sheet materials.
The cast slurry was then dried at ambient condition for 24 hours and under vacuum in oven for another 24 hours. Finally, the materials were then treated at 120-130 C for 2-5 days to crosslink the PGS. After soaking in deionizer water for 5 hours, the sheets could be easily peeled off.
Example 3: Acidity testing of PGS- Bioglass composite Acidity testing was carried out by utilizing a small piece of the polymer samples, weighing approximately 0.4 g. These miniature pieces were sterilized in a 70% alcohol/deionised water solution. After allowing the samples to dry for 2 hours, each sample was then soaked in 4 mL of Dulbecco's Modified Eagle's Medium (DMEM) tissue culture medium and placed in a sterilised 15 mL centrifuge tubes.
These tubes were then placed in an incubator at 37 C under 5% CO2 atmosphere in order to simulate similar conditions that you would find in the human body.
The acidity measurements were carried out by using a pH meter while the samples were still inside the incubator at the prescribed environmental conditions. On day 0, the first acidity measurement was made after incubation of the samples had preceded for 4 hours when the conditions in the incubator matched 37 C and 5% CO2 atmosphere. These measurements were repeated 24 and 48 hours later on day 1 and day 2 respectively to determine the pH levels over the testing period.
Figure 1 demonstrates the comparative pH values of the culture environment, PDLLA and PGS polymer samples. Compared with clinically applied degradable polyester PDLLA, PGS crosslinked at 130 C did not introduce considerable acidity during its degradation, whereas PGS crosslinked at 120 and 110 C caused significant decreases in the pH values of the culture medium after one-day incubation.

Unfortunately, the PGS synthesised at 130 C were fully crosslinked and brittle and have little potential to produce tough (strong and elastic) composites.
Figure 2 illustrates the pH values of culture medium when incubated with PGS-BG composite samples. It was revealed that the pH value of the culture microenvironment could be maintained at the normal (nearly neutral) level of the body with 5 and 10 wt% BG-PGS composites, and shows an improvement in pH stability compared to even for the PGS-1 wt% BG composite.
Example 4: Cell Proliferation and cytotoxicity In vitro assessment was carried out following the elution test method provided by ISO 10993. The extracts were obtained by placing the test (PGS and PGS-BG
composites) and control (PDLLA) materials in separate cell culture media under standard conditions (0.2 g/ml of culture medium for 24 hours at 37 C). Each fluid extract obtained was then applied to a cultured-cell monolayer, replacing the medium.
In this way, cells were supplied with a fresh nutrient medium containing extractables derived from the test or control materials. The cultures were then returned to the 37 C
incubator for 2 days. The culture media were collected for the measurement of dead cells and the living cells were then lysed and collected.
Finally, the cell numbers were measured using the lactate dehydrogenase (LDH) technique. Figure 3 shows the number of living cells after cultured with extracts of materials for 2 days for blank, PDLLA, PGS, PGS-5 wt% BG, PGS-10 wt% BG. It was observed that cells proliferated well on all materials (test and control), with no significant difference in cell numbers (p > 0.05). Compared with tissue culture plate (i.e. no test and control materials), the cell numbers were significantly reduced when cultured with extracts of PDLLA and PGS-5 wt% BG samples.
No Material vs PDLLA (p < 0.05), No Material vs PGS-5 wt% BG (p < 0.01).
Differences between any other two groups were not significant (p > 0.05).
Figures 4 and 5 illustrate the number of dead cells and the percentages of dead/live cells. PGS-15 wt% BG samples showed significant cytotoxicity, probably because of the overshoot of pH. Too alkaline environment could be the reason.
Although pure PGS did not show significant difference statistically, it must be mentioned that there was a large variation from one sample to another, and this indicated the inhomogeneity of this material, whereas PGS-BG materials are much more predictable with small variations. In conclusion, PGS doped with 5-10 wt%
BG
showed the best biocompatibility, compared with pure PGS and PGS-15 wt% BG
materials.
Example 5: Mechanical Properties of PGS-BG composites Mechanical properties for each of the composites were determined including ultimate tensile strength (UTS), Young's modulus and strain at rupture, as shown in Figures 6 to 8. The UTS and young's modulus increased with the percentage of added BG. The strain at rupture decreased first with the increasing of BG
concentration.
However, it increased significantly in PGS -10 wt% BG, changing from less than 300%
in pure PGS to larger than 600% in PGS -10 wt% BG.
The observed increase in strength is surprising as it is far and beyond what you would expect from merely the introduction of 10 wt% BG.
Example 6: Degradation of PGS-BG composites The mechanical properties of these materials during degrading were determined in vitro. Figures 9a and 9b demonstrate the change of stress-strain curves of pure PGS
and PGS-BG composite over incubation time. It can be seen that after one day soaking the mechanical strength of the composites immediately dropped to the level of pure PGS, and then remain relative stable. This is a very useful mechanical behaviour. In many applications to soft tissue engineering, the addition of BG is expected to buffer the pH of a physiological environment and provide a stable mechanical support over the initial implantation period. An implant that is mechanically too strong to match soft tissue could cause significant pain for the patients.
Conclusion The results for the strain experienced by the samples are surprising. The common belief is that mixing a polymer with a ceramic is that the composite would have properties that lie between the two materials. The polymer component allows for large amount of elongation as the chains stretch when the material is under tension.
However, the ceramic Bioglass component does not have the same ability to extend when under tension. Thus, one would assume that the overall elongation of the test samples would decrease as more Bioglass is added. This theory does prove accurate for the first three polymer mixes. As demonstrated, the elongation decreases when more Bioglass is added. However, when 10 weight percent of Bioglass is added, this theory becomes in consistent with the observed results. The IOwt% samples have a far larger ability to strain that the polymer alone. This seems to indicate that there is some new form of interaction between the two materials that takes place in the microstructure when the weight percentage of Bioglass in the polymer reaches a significant amount.
The stiffness of the polymer changes dramatically when different amounts of Bioglass is added to the polymer matrix. The stiffness of the polymer increases with increasing presence of Bioglass, until around 10 weight percent is added.
After this point, the stiffness begins to reduce again, as can be seen by the decline in stiffness from 10 to 15 weight percentage. Typically, when a ceramic is added to the polymer matrix, the overall stiffness, max strain and stress required to cause fracture do not all increase simultaneously. This surprising property of the composites of the present invention mean that the properties of the composite may be tailored to a particular application.
Example 7: PGS- hydroxyapatite (HA) composite A series of PGS-hydroxyapatite composites were prepared by mixing hydroxyapatite (HA) powder into the PGS prepolymer solution prepared in Example 1 to produce 1, 5, 10 and 15 wt % percentage PGS-BG composite. As a reference, a PGS
polymer was prepared which contained 0% wt% HA. The slurries were then vigorously stirred for at least 1 hour and the resulting solution cast onto glass slides to produce sheet materials. The cast slurry was then dried at ambient condition for 24 hours and under vacuum in oven for another 24 hours. Finally, the materials were then treated at 120-130 C for 2-5 days to crosslink the PGS. After soaking in deionizer water for 5 hours, the sheets could be easily peeled off.
Example 8: Mechanical Properties of PGS-HA composites Mechanical properties for each of the PGS-HA composites were determined including ultimate tensile strength (UTS), Young's modulus and strain at rupture, as shown in Figures 10 to 12. The UTS and young's modulus increased with the percentage of added HA. The strain at break/rupture decreased first at 5 wt%
HA then increased significantly in PGS -10 wt% HA, changing from less than 150% in pure PGS in this system to larger than 200% in PGS -10 wt% HA. The qualitative strength is potentially sintered The above unusual increment in strain at rupture by second fillers has been reported in elastomers filled with nano-particles, but not with micro particles. The particles size of the present bioceramics is 1-5 microns.
Example 9: Synthesis of poly(xylitol sebacate) (PXS) prepolymer PXS prepolymer was synthesized by polycondensation of xylitol and sebacic acid at 120-130 C under argon for 12-24 hr. The prepolymer was then dissolved in tetrahydrofuran (THF) to produce a 50 wt/v % solution.

HO OH + O O
HO OH ~ OR
OH $ OR OR 8 Scheme 2: Reaction of xylitol and sebacic acid to form poly(xylitol sebacate).

Example 10: PXS- Bioglass (BG) composite A series of PXS-bioceramic composites were prepared by mixing BG powder into the PXS prepolymer solution prepared in Example 9 to produce 2, 5, 10 and 15 wt % percentage PGS-BG composites. As a reference, a PXS polymer was prepared 5 which contained 0% wt% BG. The slurries were then vigorously stirred for at least 1 hour and the resulting solution cast onto glass slides to produce sheet materials. The cast slurry was then dried at ambient condition for 24 hours and under vacuum in oven for another 24 hours. Finally, the materials were then treated at 120-130 C
for 2-5 days to crosslink the PXS. After soaking in deionizer water for 5 hours, the sheets could be 10 easily peeled off.
Example 11: pH testing of PXS- BG composites Acidity testing was carried out as described above on small pieces of the polymer samples, weighing approximately 0.4 g. These miniature pieces were sterilized in a 70% alcohol/deionised water solution. After allowing the samples to dry 15 for 2 hours, each sample was then soaked in 4 mL of Dulbecco's Modified Eagle's Medium (DMEM) tissue culture medium and placed in a sterilised 15 mL
centrifuge tubes. These tubes were then placed in an incubator at 37 C under 5% CO2 atmosphere in order to simulate similar conditions that you would find in the human body.
The acidity measurements were carried out by using a pH meter while the samples were still inside the incubator at the prescribed environmental conditions. On day 0, the first acidity measurement was made after incubation of the samples had preceded for hours when the conditions in the incubator matched 37 C and 5% CO2 atmosphere.
These measurements were repeated 24 and 48 hours later on day 1 and day 2 respectively to determine the pH levels over the testing period.
Figure 13 illustrates the pH values of culture medium when incubated with PXS-BG composite samples. It was revealed that the pH value of the culture microenvironment could be maintained at the normal (nearly neutral) level of the body with 2, 5 and 10 wt% PXS-BG composites, and shows an improvement in pH
stability compared to even for the PXS blank where there was a drop in the pH of almost 1 pH
unit in series 5 after a period of time.
Example 12: Mechanical Properties of PXS-BG composites Mechanical properties for each of the PXS-BG composites were determined including elongation at rupture (Figure 14), ultimate tensile strength (UTS, MPa) (Figure 15) and Young's modulus (Figure 16). The UTS and young's modulus increased with the percentage of added BG to the PXS polymer system reaching a maximum at 5% before decreasing again at 10%. The strain at rupture decreased first with the increasing of BG concentration.
Example 13: Fabrication of poly(polyol) crosslinked polymer networks Other poly(polyol) polymer networks may be prepared by reaction of a polyol and other carboxylic acids, for example, citric acid, which contains three carboxylic acid groups as shown in Scheme 3.

O OH
/~/~ O O
HO I OH + ~ Poly(polyol) crosslinked polymer network OH HO OH
OH
Scheme 3: Reaction of glycerol with citric acid to form a poly(glycerol citrate) PGC
crosslinked polymer network.
A polyol prepolymer may be synthesized by polycondensation of glycerol and citric acid at 110-150 C under argon for 12-48 hr to produce a poly(glycerol citric acid) polymer (PGC). The prepolymer was then dissolved in a suitable solvent to produce a 50 wt/v % solution.
A series of PGC-bioceramic composites may be prepared by mixing BG powder into the PGC prepolymer solution prepared to produce 2, 5, 10 and 15 wt %
percentage PGC-BG composites. As a reference, a PGC polymer may be prepared which contains 0% wt% BG. The slurries may then vigorously stirred for at least 1 hour and the resulting solution cast onto glass slides to produce sheet materials. The cast slurry may then be dried at ambient condition for 24 hours and under vacuum in oven for another 24 hours. Finally, the materials were then treated at 110-150 C for 2-5 days to crosslink the PGC. The mechanical and degradation properties of the PGC-BG
composite material can be manipulated by varying the degree of crosslinking (i.e.
curing temperature, length of cure, amount of citric acid, etc).
Example 14: Fabrication of ceramic scaffolds The techniques used for fabrication of bioactive glass foams are known, see for example, Chen QZ, Thompson ID, Boccaccini AR. 45S5 Bioglass (R)-derived glass-ceramic scaffolds for bone tissue engineering. Biomaterials. 2006 Apr;27(11):2414-25, the contents of which are incorporated by reference. In this example, the Bioglass-ceramic foams were sintered at 950 C for 1 hour in order to leave micro pores on the struts of foam. The micro pores allowed PGS infiltrate into the struts thoroughly such that the toughness of the scaffolds could significantly improved.
Example 15: PGS coating procedures PGS prepolymer was synthesized by condensation of one mole each of glycerol and sebasic acid at 120 C under nitrogen for 24 h. The prepolymer can be dissolved in tetrahydrofuran (THF). The coating solution was prepared as follows: the prepolymer of PGS was dissolved in THE at the ratio of 10 g PGS per 100 mL THE by magnetically stirring for 1 h. Bioglass -ceramic foams were soaked in the PGS-THF
solution for 5 min, during which the container was gently shaken so that the foams were coated homogeneously. After the coating procedure, the foams were dried in air at room temperature for at least 24 h. Finally, the PGS prepolymer coated scaffolds were treated at 120 C for 2 days for PGS to crosslink.
Example 16: Characterization using EM, XRD and FTIR
The microstructure of the foams was characterized in a JEOL 7001 filed emission gun scanning electron microscope (FEG SEM), before and after immersion in simulated body fluid (SBF). Samples were gold-coated and observed at an accelerating voltage of 15 W. Thin foils were prepared using the ultrathin sectioning technique, and examined by transmission electron microscope (TEM) JEOL 2011, at 200kV.
Foams were also characterized using x-ray diffraction (XRD) analysis with the aim to assess the crystallinity after sintering and possible formation of HA
crystals, after different times of immersion in a simulated body fluid (SBF). For XRD
analysis, the foams were first ground into a powder. Then 0.1 g of the powder was collected. A
Philips PW 1700 Series automated powder diffractometer was used, employing Cu Ka, radiation (at 40 kV and 25 mA) with a secondary crystal monochromator. Data were collected over the range 20 = 5-80 using a step size of 0.02 and a counting time of 10s per step. The measurement of Fourier transform infrared (FTIR) was performed on a Nicolet 6700 spectrometer. The spectrum was recorded with a resolution of 4 cm 1.
Mechanical testing The compression strength of foams was measured using an Instron Microtester 5848. The samples were rectangular in shape, with dimensions: 10mm in height and 5mmx5mm in cross-section. During compression testing, the load was applied until densification of the porous samples started to occur.
Assessment of bioactivity in simulated body fluid The bone bonding capability of a biomaterial to host bone is associated with the formation of a carbonated HA layer on the surface of the material when implanted or in contact with biological fluids. Hence, the ability to bond with bone can be assessed in vitro in simulated body fluid via monitoring the formation of HA on its surface, which was tested according to a method by Kokubo T, Hata K, Nakamura T, Yamamura T.
in the article entitled "Apatite formation on ceramics, metals, and polymers induced by a CaO-SiO2-Based glass in simulated body fluid". In: Bonfield W, Hastings GW, Tanner KE, editors. Bioceramics 4. London: Guildford, Butterworth-Heinemainn; 1991.
p.
113-20. The foams were immersed in 75 ml of acellular SBF in flasks. The flasks were placed inside an incubator at 37 C. The pH of the solution was maintained constant at 7.25. The size of all samples for these tests was 1 0mmx 10mmx 10mm. Two samples were extracted from the SBF solution after given times of 3, 7, 14, 30 and 60 days. The SBF was replaced twice a week because the cation concentration decreased during the course of the experiments, as a result of the changes in the chemistry of the samples.
Once removed from the incubation, the samples were rinsed gently, firstly in pure ethanol, then using deionised water, and finally left to dry at ambient temperature in a desiccator.
Biocompatibility evaluation: Elution test method Mouse fibroblasts, SNL (STO-Neo-LIF) (SNL), were used for the initial assessment because of their defined and reproducible proliferative activity.
Elution test method (ISO 10993) was adopted in the present work. In this method, extracts were obtained by placing the test (Bioglass -PGS composite) and control (PDLLA) materials in separate cell culture media under standard conditions (0.2 g/ml of culture medium for 24 h at 37 C). SNL cells were cultured in DMEM with 10% heat-inactivated foetal bovine serum, 0.1% penicillin/streptomycin at 37 C with 5%
CO2.
Cells were then plated on a 48-well tissue culture plate at a concentration of 2 x 104 cells/well. After 2-day culture, cell culture media was removed and replaced with the media containing the extractants. Cells were placed back in the incubator for a 24-h treatment. Cells are observed for visible signs of toxicity in response to the test and control materials.
Quantization of cell viability was achieved by measuring lactate dehydrogenase (LDH) release, using a commercial kit (Sigma-Aldrich Tox-7). Culture media (200 .tm per well) were collected after above SNL cells exposed to the media containing extracts. The number of dead cells during the treatment by extractants was determined from these samples. The number of live cells was measured using the total LDH
method of Tox-7, in which live cells were lysed and the media were collected.
The LDH levels were determined by measuring the absorbance (A490-A690), using the commercial kit Tox-7 and spectrophotometer. Our standard curve (appendix A) shows that there is a reasonably good linear relationship between the number of cells and LDH level in the range of 5x 103-5 x 104. Hence, the percentage of dead cells can be expressed by LDH of extractant medium (1) Total LDH
Statistics All experiments were run with five samples, and the data are represented as mean SE. Statistical difference was analysed using one-way analysis of variance (ANOVA) with Tukey's post-hoc test, and a p value of < 0.05 was considered significant.
Improved mechanical properties of as-fabricated scaffolds Figure 17 shows the porous network and microstructure of the foam struts before and after coating of PGS. The highly porous and connective network was maintained after the coating (Figure 17a-b), and microvoids on the foam struts (Figure 17c) were filled with PGS (Figure 17d). The cracks in the coating layer of PGS
in Figure 17d were induced by the electron radiation during examination.
Compressive mechanical strengths of PGS-coated scaffolds were significantly improved, compared with uncoated foams. Figure 18 shows the compressive mechanical strength values of the two groups of foams. The theoretical strength values (the solid line), which were calculated using Gibson and Ashby's theory, represent the upper bound of the strength of porous scaffolds. It can be seen from Figure 18 that the crosslinked PGS coating, which reduced the porosity about 0.05 on average, pushed the strength of the scaffolds toward the upper limit of the strength values of porous networks. Theoretically, no experimental strength value could go beyond the upper bound. Hence, the two points that are above the theoretical strength line in Figure 18 could be attributed to the experimental errors. One of error sources could be the size measurement of the highly porous foams.
Strengthening mechanism in as-fabricated scaffolds In the present work, the PGS coating, which infiltrated into the microstructure of the foam struts, was treated at 120 C for two days for crosslink. During the crosslink treatment, an acid-base reaction was expected to occur at the interface of the acidic PGS and alkaline Bioglass -ceramic due to partially dissolving of the particles. The expected chemical reaction was confirmed by the FTIR analysis, as shown in Figure 19. A new peak appears at the frequency of 1573 cm' in the spectrum of Bioglass -PGS. This peak is attributable to the metallic carboxylate groups, in particular -COONa. In 45S5 Bioglass (SiO2-Na2O-CaO-P2O5), sodium oxide is the most active component. Indeed, Na2O has been used in glass industry to reduce the melting point of silica-based glasses, whereas other components (e.g. CaO) are added to stabilize glass. It has previously been shown that the release of sodium ions from Bioglass -ceramic took place immediately after soaking in water. Hence, the carboxylic acid group -COOH could largely be carboxylated by Na+.
Without wishing to be bound by theory, it is thought that the strengthening is the result of bonding between the PGS and BG components of the composite. The 5 chemical reaction between Bioglass -ceramic and PGS was metallic carboxylation.
This chemical reaction formed a fusion, bonding layer around each Bioglass -ceramic particles. As a result of the strong chemical bonding between PGS and Bioglass -ceramic particles, the mechanical strength of the composite scaffolds was greatly improved towards the upper limit.
10 Stable mechanical performance during degradation in vitro It was found that the coating of PGS nether slow down the structural degradation of Bioglass -ceramic substance nor impair the bone-bonding ability of Bioglass -ceramic, as indicated in Figure 20. For both PGS-coated and uncoated scaffolds, the diffraction peaks of crystalline ceramic phase, Na2Ca2Si3O9, became 15 short with increasing of incubation time in SBF, eventually disappeared after incubation for 30 days, leaving a broad diffraction hill (indicting amorphous) overlapped with weak apatite peaks. The formation of apatite was confirmed by SEM
examination (Figure 21), where the fine fibres were apatite crystals.
However, it was surprisingly discovered that the mechanical strength values of 20 the Bioglass (ceramic)-PGS composite scaffolds remained at the same level up to 30 days (Figure 22) while the Bioglass-ceramic was degrading microscopically in SBF.
This unexpected mechanical performance is of great importance to achieve a mechanically steady state of bone implants at the initial period of post implantation.
The remodelling kinetics of bone is in S-shape, as illustrated in Figure 23.
After an initial lag period, the growth of new bone tissue enters a rapid, log phase, which is finally followed by a stationary state due to the limit of space. Ideally, the degradation kinetics of a structural implant should match the above growth kinetics of bone tissue, as indicated in Figure 23. Hence, a highly desirable scaffold is expected to be able to maintain mechanical strength during the initial lag growth period of host bone tissue post implantation, and only start to degrade when the growth of new bone tissue enters the log phase. In reality, however, this criterion seems difficult because all existing degradable implants would mechanically deteriorate immediately from the moment of implantation due to the structural breakdown of the degradable biomaterials, as demonstrated in Figure 23. This is compared to the results shown in Figure 22, from which the ideal degradation kinetics (inset in Figure 22) desired by bone tissue engineering may be achievable.

Biocompatibility of the composite scaffolds It was found that SNL cells proliferated equally well in the three culture media:
normal culture medium, medium with PDLLA or Bioglass (ceramic)-PGS extracts.
There were no significant differences in the percentage of dead cells (Figure 24).
Hence, the newly developed Bioglass (ceramic)-PGS composite is satisfactorily safe in terms of cytotoxicity, being comparable to the clinically applied polymer PDLLA.
Conclusions The Bioglass (ceramic)-PGS composite scaffold has unique mechanical properties that have not been reported with currently existing scaffolds.
First, it possesses a predictable mechanical strength that is close to theoretical strength value.
Second, it has a mechanical steady state over a period when immersed in a physiological environment while the two components of the composite are structurally biodegrading. Moreover, the composite system has a bone-bonding ability, as well as an excellent biocompatibility.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope of the invention as broadly described.
The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims (35)

1. A crosslinked polyol-bioceramic composite which comprises:
(A) a polymer matrix formed from the condensation reaction between (I) a polyol component containing at least three hydroxyl groups; (II) a polycarboxylic acid component containing at least two carboxylic groups; and (B) at least one bioceramic material phase substantially homogeneously distributed throughout the polymer matrix;
wherein the amount bioceramic material in the composite being at least about 0.5 % to about 20% by weight of the total weight of the composite.

2. The composite of claim 1, wherein the amount of bioceramic material in the composite is at least about 5% to about 15% by weight of the total weight of the composite.

3. The composite of claim 1, wherein the amount of bioceramic material in the composite is at least about 10% by weight of the total weight of the composite.

4. The composite of any one of the preceding claims, wherein the polyol component is selected from the group comprising glycerol, erythritol, threitol, ribitol, arabinitol, xylitol, allitol, alritol, galactitol, sorbitol, mannitol, iditol and malitol.

5. The composite of claim 4, wherein the polyol component is selected from the group comprising glycerol, maltitol, sorbitol, xylitol and isomalt.

6. The composite of claim 5, wherein the polyol component is glycerol.

7. The composite of any one of the preceding claims wherein the polycarboxylic acid component is selected from the group comprising a metabolite, an aldaric acid, an alkanedioic acid, an alkenedioic acid, or an amino acid, or a derivative or salt thereof.

8. The composite according to claim 7, wherein the aldaric acid is selected from the group comprising 2-hydroxy- malonic acid, tartaric acid, ribaric acid, arabanaric acid, xylaric acid, allaric acid, altraric acid, galacteric acid, glucaric acid, or mannaric acid, or a derivative or salt thereof.

9. The composite of claim 7, wherein the metabolite is selected from the group comprising succinic acid, fumaric acid, .alpha.-ketoglutaric acid, oxaloacetic acid, malic acid, oxalosuccinic acid, isocitric acid, cis-aconitic acid, or citric acid, or a derivative or salt thereof.

10. The composite of claim 7, wherein the alkanedioic acid is selected from the group comprising dimercaptosuccinic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, or sebacic acid, or a derivative or salt thereof.

11. The composition of claim 10, wherein the alkanedioic acid is sebacic acid, or a derivative or salt thereof.

12. The composite according to claim 7, wherein the alkenedioic acid is selected from the group comprising fumaric acid, maleic acid, glutaconic acid, itaconic acid, mesaconic acid, or traumatic acid, or a derivative or salt thereof.

13. The composite according to claim 7, wherein the amino acid comprises aspartic acid or glutamic acid, or a derivative or salt thereof.

14. The composite according to any one of the preceding claims, wherein the at least one bioceramic is selected from the group comprising alumina, zirconia, apatites, calcium phosphates, silica based glasses, and bioactive glass ceramics and combinations and modified forms.

15. The composite according to claim 14, wherein the at least one bioceramic is an apatite.

16. The composite according to claim 15, wherein the apatite is selected from the group comprising hydroxyapatite (Ca10(PO4)6(OH)2), floroapatite (Ca10(PO4)6F2), chlorapatite (Ca5C1(PO4)3), carbonate apatide (Ca10H2(PO4)6-5H2O)) and combinations and modified forms.

17. The composite according to claim 16, wherein the apatite is hydroxyapatite.

18. The composite according to claim 14, wherein the at least one bioceramic is a bioactive glass.

19. The composite according to claim 18, wherein the bioactive glass is selected from the group comprising 45S5, 58S, S53P4, S70C30 or combinations and modified forms thereof.

20. The composition of claim 19, wherein the bioactive glass is 45S5.

21. A method of preparing a crosslinked polyol-bioceramic composite, the method comprising the steps of:
(i) providing at least one polyol component containing at least three hydroxyl groups;
(ii) providing at least one polycarboxylic acid component containing at least two carboxylic acid;
(iii) partially reacting the polyol with the polycarboxylic acid to form a prepolymer solution;
(iv) substantially homogeneously distributing at least one bioceramic material throughout the prepolymer solution; and (v) subjecting the prepolymer solution of step (iv) to further reaction conditions to introduce further crosslinking to form the crosslinked polyol-bioceramic composite.

22. A method of treating a disease, condition, or disorder from which a subject is suffering, comprising administering to the subject a polyol-bioceramic composite according to any one of claims 1 to 20.

23. A crosslinked polyol-bioceramic composite according to any one of claims 1 to 20, wherein the polyol-bioceramic composite is adapted and constructed to have a shape selected from the group comprising particles, tube, sphere, strand, coilend strand, capillary network, film, fibre, mesh and sheet.

24. A method of using a crosslinked polyol-bioceramic composite according to any one of claims 1 to 20, wherein the polyol-bioceramic composite is used as a tissue engineering construct, as a nerve conduit, as a mesh to be used in surgical abdominal hernia repair, or in intervertebrate disc repair.

25 25. A crosslinked polyol-bioceramic scaffold composite comprising (A) a porous bioceramic foam formed from at least one bioceramic material;
and (B) a polyol polymer matrix wherein the polyol polymer matrix is formed in situ in the foam by the condensation reaction of (I) a polyol component containing at least three hydroxyl groups; (II) a polycarboxylic acid component containing at least two carboxylic groups;
wherein the amount bioceramic material in the polyol-bioceramic scaffold composite being at least about 50 % to about 70% by weight of the total weight of the polyol-bioceramic scaffold composite.

26. The polyol-bioceramic scaffold composite of claim 25, wherein the amount of bioceramic material is about 70% by weight of the total weight of the polyol-bioceramic scaffold composite.

27. The polyol-bioceramic scaffold composite of claim 25 or 26, wherein the bioceramic component used in the polyol-bioceramic scaffold composite is defined as in any one of claims 14 to 20.

28. The polyol-bioceramic scaffold composite of claim 25 or 26, wherein the pololy component used in the polyol-bioceramic scaffold composite is defined as in any one of claims 4 to 6.

29. The polyol-bioceramic scaffold composite of claim 25 or 26, wherein the polycarboxylic acid component used in the polyol-bioceramic scaffold composite is defined as in any one of claims 7 to 13.

30. Use of a polyol-bioceramic composite according to any one of claims 1 to 24, in a tissue engineering application.

31. A use of the crosslinked polyol-bioceramic scaffold composite of any one of claims 25 to 29 as a bone substitute.

32. A crosslinked polyol-bioceramic composite substantially as hereinbefore described with reference to the examples and excluding, if any, comparative examples.

33. A crosslinked polyol-bioceramic scaffold composite substantially as hereinbefore described with reference to the examples and excluding, if any, comparative examples.

34. A method of preparing a crosslinked polyol-bioceramic composite substantially as hereinbefore described with reference to the examples and excluding, if any, comparative examples.

35. A method of preparing a crosslinked polyol-bioceramic scaffold composite substantially as hereinbefore described with reference to the examples and excluding, if any, comparative examples.