GB2513599A - Bone Growth Scaffold - Google Patents

Abstract

A composite comprises an inorganic filler such as calcium metaphosphate, a polymer formed from a hydrogel monomer and a multifunctional comonomer. Preferably, 2-hydroxyethyl methacrylate and pyromellitic glycerol dimethacrylate are utilised as the hydrogel monomer and a multifunctional comonomer respectively. In another aspect, a composite comprises a metastable inorganic filler and a polymer formed from a hydrogel monomer. A composition for preparing the composite, a method of forming the composite, a synthetic bone graft comprising the composite and the composite for use in surgery, therapy or diagnosis are all claimed. The composites can be produced with a controllably variable mineral content either prefabricated or by in vivo assembly upon delivery of an injectable slurry. Other claimed aspects include the use of a metastable inorganic filler as an inorganic filler in synthetic bone substitute materials and the use of a multifunctional comonomer in polymeric synthetic bone substitute materials.

Description

Bone Growth Scaffold

FIELD OF THE INVENTION

This invention is concerned generally to the field of synthetic bone substitutes, scaffolds for bone tissue engineering and grafts. More particularly, the invention relates to a composition and method for providing bone substitutes, bone grafts and enhancing bonc growth.

BACKGROUND OF THE INVENTION

Musculoskeletal related medical conditions are a major cause of ill health across a large age span, especially within the ageing population. Bone regeneration in clinical cases associated with impaired bone healing, bone loss or bone voids is challenging. Surgical treatment for age, trauma or cancer induced critical size bone loss is a particular challenge.

Bone is the second most transplanted tissue after blood and the transplantation of bone and bone reconstructions presents a diverse spectrum of clinical challenges often dependent on the anatomic site concerned.

Current grafting material options include autogenic bone grafts (autografts, allogenic bone grafts allografts), and synthetic bone substitutes.

Autografts utilize bone sourced from the patient on whom the graft is being performed. It is currently the gold standard method in bone grafting and benefits from several advantages, namely it can provide a scaffold for bone growth, typically contains viable bone cells and bone growth factors and should typically not elicit an immune response. However, it typically does not necessarily provide the temporary load support that may be desirable, may risk complications arising from possible donor-site morbidity and is characterised by a limited quantity of grafting material. In addition, the autograft option is limited within the aging population as the elderly are less likely to be qualified for such a procedure due to higher incidences of osteoporosis and metabolic diseases.

Allografts utilize bone from a donor of the same species, typically from a cadaver source. They have the advantage of plentiful potential supply and also are capable of providing a scaffold for growth. They typically lack viable bone cells and do not provide particularly effective structural load support. The may also elicit an immune response from the patient. Xenografts offer similar performance. Demineralised bond matrix (DBM) such as the bovine-derived BioOss' is commonly used for allograft or xenograft procedures.

The above problems have led to increasing interest in synthetic bone It is believed that in excess of 2 million grafting procedures are performed worldwide each year. The global market for bone graft substitutes was believed to be in the region of $1.9 bfflion in 2010 and is forecast to reach up to $3.3 billion by 2017.

Aside from autogenic and allogenic bone graft materials discussed above, currently clinically used bone graft substitutes include calcium phosphates, brushite, bioactive glasses and hydroxyapatite among others. They are typically brittle ceramics with many exhibiting extremely slow resorption characteristics.

Synthetic calcium phosphate materials form a wide variety of bone substitutes either as ceramic blocks/granules or as self-setting cements. These materials exhibit excellent biocompatibility and bioactive glasses have the ability to bond to living bone. Hydroxyapatite, J3-triealcium phosphate and J3-triealeium pyrophosphate have been used to develop porous three-dimensional matrices for bone substitutes. These typically have a similar mineral content to human bone. In general, these ceramic bone substitutes are porous and brittle and exhibit osteoconductive properties.

Currently, the most common non-metallic material for treating bone defects are poly(methyl methacrylate) (PMMA) based materials such as PlexiglastmM. Whilst known for good tissue compatibility, these are brittle and prone to mechanical fatigue failures.

Most current synthetic bone scaffolds are only able to integrate with the edges of the wound bed with the core remaining isolated compounded with lack of vascularisation and replacement of the material with new bone caused by poor scaffold performance, very low resorption rate and low growth induction.

This results in graft failures, especially where larger sized defects are concerned.

Ideally, bone grafis and bone scaffolds should exhibit beneficial biological properties but also should present and optimal biomechanical strength, which ideally should be approaching or similar to the bone being replaced. For example, calcium sulphates provide minimal support and bioaetive glasses whilst possessing good comprcssive strength arc weak in tcnsion. Some calcium phosphate grafts possess compressive strengths similar to that of cancellous bone, but usually are in the form of sintered ceramic blocks and clinical placement and integration takes a long period of time. Accordingly, some current bone substitutes do present suitable mechanical properties for grafting cortical bone. In situ self-setting injectable bone substitutes have several benefits over pre-formed bone grafi as they can bc uscd in a varicty of clinical situations such as in treating osteoporotic fractures, maxillofacial defects, spinal defects and irregular bone defects. However, injectable substitutes typically display significantly poorer mechanical properties.

Recent efforts have been directed to produce improved synthetic Poly(2-hydroxyethyl methacrylate) or pHEMA and certain derivatives thereof are biocompatible hydrogels which have been used in medical applications, products and tissue engineering. Existing applications include its use as a material for contact lenses, cartilage replacement, spinal cord injury repair and fabrication of ceramic scaffolds.

WO-A-2006/091653 dcscribcs a synthctic bone substitutc composite formed by mixing an organic phase of a hydrogel monomer (especially 2-hydroxyethyl methacrylate), a cross linker (especially ethylene glycol dimethacrylate) and a radical initiator and an inorganic composition which is preferably hydroxyapatitc. According to WO-A-2006/09 1653, a high inorganic content product is achievable which produces a flexible load bearing three-dimensional composite suitable as a bone substitute, the properties (e.g. porosity, strength and flexibility) of which may be varied by varying the reintive proportions of the components. The bone substitute produced in a preferred embodiment described has hydroxyapatite as the inorganic filler. This is very stable and is slowly resorbed.

It is desirable to provide an improved synthetic bone substitute that overcomes the aforementioned shortcomings and in particular is capable of enhanced performance by way in one or more of the following properties: flexibility, high mineral content, sufficient porosity, good resorption rate, structural integrity, structural strength under load, load bearing, improved osteoconduction, improved osteoinduetion and optionally improved osteopromotion and preferably improved osteogenesis.

The present inventors have invented a novel composition and method for bone grafis that allows them to overcome or address the above problems.

PROBLEM TO BE SOLVED BY THE INVENTION

There remains a need for improvements in bone grafts and synthetic It is an object of this invention to provide a synthetic bone It is a fhrther object of the invention to provide a composition and method for improved bone graft performance.

SUM MARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided a composite comprising an inorganic filler and a polymer formed from a hydrogel monomer and a multiflinctional eomonomer.

In a second aspect of the invention, there is provided a composition for preparing a composite of the first aspect, the composition comprising an inorganic filler, a hydrogel monomer, a multifunctional comonomer, a polymerization initiator and optionally a s&vent.

In a third aspect of the invention, there is provided a composite comprising a metastable inorganic filler and a polymer formed from a hydrogel monomer.

In a fourth aspect of the invention, there is provided a composition for preparing a composite of the third aspect, the composition comprising a metastable inorganic filler, a hydrogel monomer, a polymerization initiator and optionally a solvent.

In a fifth aspect of the invention, there is provided a composite comprising a metastable inorganic filler and a polymer formed from a hydrogel monomer and a multiflinctional comonomer.

In a sixth aspect of the invention, there is provided a composition for preparing a composite of the fifth aspect, the composition comprising a metastable inorganic filler, a hydrogel monomer, a multifunctional comonomer, a polymerization initiator and optionally a solvent.

In a seventh aspect of the invention, there is provided a method of forming a three dimensional composite matrix for use as a prefabricated bone growth scaffold, the method comprising providing a mould for the bone growth scaffold, disposing therein a quantity of the composition as defined above, causing a polymerization step of the composition to produce a three dimensional composite matrix within the mould and releasing the resulting composite matrix from the mould.

In an eighth aspect of the invention, there is provided a method of forming in vivo a three dimensional composite matrix for use as a bone growth scaffold, the method comprising preparing an in vivo site associated with fracture, bone loss or excavation, injecting into the site a slurry of a composition as defined above, and causing a polymerization step of the composition to produce a three dimensional composite matrix within the site.

In a ninth aspect of the invention, there is provided a synthetic bone graft comprising a compositc as dcfmcd above.

In a tenth aspect of the invention, there is provided the use of a metastable inorganic filler as an inorganic filler in synthetic bone substitute materials.

In an eleventh aspect of the invention, there is provided the use of a multifunctional comonomer in polymeric synthetic bone substitute materials.

In a twelfth aspect of the invention, there is provided an injectable sluny for bone growth matrix assembly in situ by polymerization, the sluny comprising an inorganic filler, a hydrogel monomer, a multiThnctional comonomer, an aqueous solvent-compatible polymerization initiator and an aqueous solvent, characterised in that the polymerization reaction has an exotherm of 40°C or less.

In a thirteenth aspect of the invention, there is provided a calcium phosphate particulate material obtainable by milling a sintered porous calcium phosphate block.

In a fourteenth aspect of the invention, there is provided a composite comprising a polymer formed from a hydrogel monomer and an inorganic filler obtainable by milling an sintered porous block of an inorganic filler.

In a fifteenth aspect of the invention, there is provided a composition for preparing a composite of the fourteenth aspect, the composition comprising a particulate inorganic filler obtainable by milling an sintered porous block of an inorganic filler, a hydrogel monomer, a polymerization initintor and optionally a solvent.

ADVANTAGES OF THE INVENTION

The compositions and composites of the present invention can be produced with controllably variable mineral content and mechanical properties as prefabricated composites or injectable slurries for in vivo assembly. By enabling a high mineral content composite as a synthetic bone graft with adequate porosity and flexibility and unusually high resilience to compression and fracture, the compositions and composites of the present invention can produce a bone graft that mimics the mechanical performance of natural load bearing bone whilst enabling bone growth and vascularisation through the composite scaffold as the mineral content is resorbed. Use of a metastable inorganic filler according to a preferred aspect improves osteogenic properties of the material. Enhanced tissue adhesion may be achieved in a preferred aspect utilizing a multiflinctional comonomer. Thus an improved synthetic bone substitute and bone growth scaffold is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a microscope image (lOX) showing live fluorescent staining of fibroblasts on tissue culture plastic (control) at 7 days having been seeded at 1x105 atthe core; Figure 2 is a microscope image (40X) showing live fluorescent staining of fibroblasts on the scaffold (60% CMP) of the invention at 7 days having been seeded at lxlO at the core; Figure 3 is a microscope image (lOX) showing live fluorescent staining of fibroblasts on the scaffold (60% CMP) of the invention at 7 days having been seeded at lxlO at the core; Figure 4 is a microscope image (lOX) showing live fluorescent staining of mcsenchymal stem cells on the scaffold (60% CMP) of the invention at 7 days having been seeded at lxlO at the core; Figure 5 is a 2 photon imaging (MSC cells) stained to view MSCs interaction at 21 days with the composite (cytoskeletal protein staining). Vimentin is one of the 5 major intermediate filaments and is stained green (FITC). Nuclear stain (DALI) highlights nuclei which are stained blue.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides composites and compositions for improved synthetic bone substitutes and improved bone growth scaffolds capable of being pre-fabricated or used as an injectable slurry for in vivo formation.

The compositions and composites of the invention provide the particular benefit of being capable of incorporating a high mineral content whilst maintaining its mechanical properties of strength, compressive resilience and flexibility. Yet, it is sufficiently porous, providing ideally an osteoconductive scaffold. This makes it highly tunable for a range of applications and particularly suited for use as a synthetic bone substitute and bone growth scaffold and more particularly as a load bearing synthetic bone substitute.

The composite of the first aspect of the invention may be defined as comprising an inorganic filler and a polymer formed from a hydrogel monomer and a multifanctional comonomcr. A composition for preparing the compositc may comprise an inorganic filler, a hydrogel monomer, a multiftrnctional comonomer, a polymerization initiator and optionally a solvent.

The inorganic filler is preferably a calcium phosphate. The inorganic filler is preferably a metastable inorganic particulate. The inorganic filler is preferably a metastable calcium phosphate.

By the use of the multifunctional comonomer in the copolymer of the composite with a hydrogcl monomer, such as 2-hydroxyctheyl methacrylate (HEMA), a less dense and more porous polymer scaffold is produced whilst compressive resilience and mechanical strength are enhanced by crosslinking and/or adhesive binding by the multifunctional comonomer. An adhesive multifunctional comonomer provides a further advantage, especially when utilizing a high mineral content, of good binding to mineralized and soft tissue, such as bone, dcntine and enamel. This is particularly useful at the bone-graft interface and reduces the risk of graft failure.

The composite of a second aspect of the invention maybe defined as comprising a metastable inorganic filler and a polymer formed from a hydrogel monomer. A composition for preparing the composite may comprise a metastable inorganic filler, a hydrogel monomer, a polymerization initiator and optionally a solvent.

Preferably, the metastable inorganic filler is a metastable calcium salt, preferably calcium metaphosphate.

By usc of a mctastablc inorganic filler, such as calcium metaphosphate in a composite comprising a hydrogel polymer such as a po1yHEMA or copolymer of poIyHEMA, desirably enhanced resorption properties are achieved. Thus, resorption may occur at a rate that allows high initial mineral content, whilst encouraging uptake and growth of bone into the scaffold.

A preferred aspect of the invention combines the above mentioned aspects and provides a composite comprising a metastable inorganic filler and a polymer formed from a hydrogel monomer and a multifunctional comonomer. A composition for preparing the composite may comprise a metastable inorganic filler, a hydrogel monomer, a multifunctional comonomer, a polymerization initiator and optionally a solvent.

Any proportion of inorganic filler may be utilized in the composites and compositions of the invention, for example in the range ito 99 % by weight of total dry composite weight and total combined weight of monomer and inorganic components of composition (% byweight/% bywt). Reference herein to the amount of a composite component should unless otherwise stated or is out of context be understood as the amount by dry weight of the composite. Preferably, the composite and composition comprises inorganic filler in an amount of at least 30% by wt and more preferably at least 40% by wt. Preferably, the composite and composition comprises inorganic filler in an amount up to 80% bywt and more preferably up to about 75% by weight such as up to 70% or up to 60%. Still more preferably, the composite and composition comprises inorganic filler in the range 40 to 60 % by weight, such as 40% by weight, 45%, 50%, 55% or 60% by wt.

By utilizing a higher inorganic filler amount (e.g. 50% by weight or more), the mineral content of the resulting composite may approximate to that of dehydrated bone matter and by providing inorganic filler in a manner that enables relatively rapid resorption, bone growth at an appropriate density and speed is encouraged.

Any reference to the amount in terms of the percent amount of a monomer should be understood as being the amount by weight of the monomer as a percentage of the total dry or undiluted monomer weight (and not the total dry weight of the composite or composition).

A reference herein to monomer components of the polymer, or to other polymer components, may also be understood as referring to a composition for making such a polymer unless such an understanding is inconsistent in the context used.

The composite polymer (and composition) preferably comprises a hydrogel monomer component and a multifunctional comonomer component. The hydrogel monomer component is preferably a major component of the polymer so preferably comprises at least 50% by weight of total monomer, more preferably at least 75% by weight and still more preferably at least 85% by weight, optionally at least 90% or 95% by weight and up to, for example, about 98% or 99% by weight ofpolymer. For example, the hydrogel monomer component may be present in an amount of 85%, 88%, 90%, 93% or 95% by weight.

The polymer preferably comprises a multifunctional comonomer component in any required amount, and typically at least 1% by weight of polymer.

Preferably, a multiftmnctional comonomer component is present in an amount of at least 4%, more preferably 5% by weight ofpolymer. Preferably the multiflinctional comonomer component is present in an amount of no more than 50%, preferably up to about 40% by weight and more preferably in the range 5 to 20%, and more typically in the range 5 to 15% by weight of polymer, such as 5%, 7%, 10%, 12% or 15% by weight.

Preferably, the weight ratio of hydrogel monomer to multiThnctional comonomer is from about 98:2 to about 75:25, more preferably 95:5 to about 85:15 and most preferably about 90:10. Optionally, the molar ratio of hydrogel monomer to multifunetional comonomer is in the range of from about 30:1 to about 100:1 more preferablyabout 40:1 to about 60:1 and most preferablyabout 50:1, especially for the particularly preferred embodiment where the hydrogel monomer is 2-hydroxyethyl methacrylate and the multi±uinctional comonomer is pyromellitic glycerol dimethacrylate (PMGDM).

It is believed that by increasing the proportion of the multiftmnctional comonomer, the compressive strength and modulus of compression of the resulting polymer and composite in both dehydrated and hydrated state may be increased, whilst reducing the proportion of multifunctional comonomer will render a more flexible polymer and composite material. -10-

Preferably, a high mineral content composite (e.g. greater than 50% by weight) and a proportion of multifunctional comonomer of 5-15% by weight produce a load bearing composite that is of mineral content approximating dehydrated bone and having a compressive strength and Young's elasticity of compression approximating that of in situ bone whilst allowing effective binding to mineralized and soft tissue such as bone, dentine and enable, a low degree of swelling during formation and effective machinable properties for fixing and affixing to. The selection of a metastable inorganic filler, and especially a calcium metaphosphate filler, enables effective and timely resorption to encourage and support bone growth.

Without being bound by theory, it is believed that an adhesive nature of the multiffinctional comonomer enhances incorporation and homogeneity of distribution of inorganic filler in the composition and resulting composite, thereby enabling an aqueous composition to be used and allowing for an aqueous-compatible initiator system operable at low temperatures suitable for physiological use without tissue damage.

The composite andlor polymer preferably has an equilibrium water content of up to 50% by weight, preferably in the range 0.5% to 45% and more preferably in the range 1% to 30% by weight and still more preferably in the range 5% to 25%, e.g. from 7.5% to 20%. A relatively low equilibrium water content allows less swelling of the composite to occur, which is particular advantageous for in situ bone growth scaffold assembly.

Any suitable solvent can be used in the method, system and in the composition for preparing a composite of the present invention. A particular advantage of the system and composition of the present invention is that it enables the composite to be produced using an aqueous solvent and so an aqueous solvent is preferred. By aqueous solvent, it is meant that the solvent or carrier fluid comprises water in an amount of at least 50% by weight, preferably at least 75%, more preferably at least 90% and still more preferably at least 98%. Optional co-solvents for water in the aqueous solvent include, for example, alcohols such as methanol or ethanol or any water-miscible solvent. Preferably, however, the aqueous solvent is substantially and preferably entirely absent glycol co-solvents.

The composition preferably comprises a purely aqueous solvent which comprises a carrier fluid consisting essentially of water.

Optionally, the multifunctional comonomer, if liquid, may act as a co-solvent until it is consumed in the polymerisation reaction.

As mentioned above, the composite and composition of the first aspect comprises an inorganic filler. Any suitable inorganic filler may be used and is preferably effective in promoting bone growth. Such fillers preferably comprise calcium, phosphorus and oxygen and more preferably are calcium phosphates, examples of which include hydroxyapatite, dicalcium phosphate, tricalcium phosphate, octacalcium phosphate, dahalite, hydroxyfluoroapatite, bioactive glass, brushite and monetite. Optionally, a calcium phosphate maybe an orthophosphate, metaphosphate or pyrophosphate. Optionally, the inorganic ifiler materinl may flirther be hydroxylated, carbonated and/or contain other additives ofF, Cl and/or Br. Optionally, for example, the inorganic component ratio of Ca to P may be between 0.5 and 4, or between 1 and 2.

According to the second and third aspects and in any case according to a preferred embodiment, the inorganic filler is a metastable inorganic ifiler, which preferably comprises calcium metaphosphate. More preferably, the metastable inorganic filler is (or consists essentially of) calcium metaphosphate.

Preferably, the metastable inorganic filler may be obtained by any suitable literature method.

The inorganic filler is preferably in the form of a particulate. The particulate inorganic filler may be of any suitable particulate form, such as crystalline, nanocrystalline or amorphous.

In a preferred embodiment (and in alternative aspect of the invention), the inorganic filler is obtainable by milling a sintered porous block of an inorganic filler (e.g. selected from inorganic fillers mentioned above, but preferably calcium phosphate).

-12 -Optionally, the inorganic filler is at least partially amorphous (e.g. only at most partially crystalline) and more preferably amorphous calcium metaphosphate in order to enhance resorption characteristics of the filler.

The inorganic filler may be a particulate of any suitable shape, such as blocks, granules, rods, sheets, pellets.

Preferably, the inorganic filler is a calcium phosphate particulate obtainable by milling a porous block of sintered calcium phosphate. Preferably, the porous block of calcium phosphate is prepared by sintering calcium phosphate, preferably a calcium phosphate hydrate, in the presence of a pore-forming agent which is preferably an organic pore-forming agent such as a starch, wax, polyvinyl butyral and polyvinyl alcohol and is most preferably polyvinyl alcohol. More preferably, the sintered calcium phosphate porous block is prepared using (e.g. by sintering in a compressed mould) a calcium b/s-phosphate monohydrate [e.g.

available from FlukaTM under product code 20153] in the presence of a pore-forming agent, preferably polyvinyl alcohol by sintering. The porous block may, for example, be prepared by the method described in Ding et al, Ceramics International, 31, 2005, p 691-696 and references therein. Most preferably, the porous block of calcium phosphate is prepared by mixing a calcium his-phosphate monohydrate with polyvinyl alcohol (e.g. molecular weight 33,000) in a ratio of from 5:1 to 1:1, preferably 5:1 to 3:2 or 5:1 to 2:1, and optionally4:1 or 3:1 and most preferably 4:1 by weight. The mixture may then be placed in a mould and a compressive force applied to compact the mould and the block sintered (e.g. at 900 °C at 8 °C/min and maintained at 900 °C for 6 hours). The porous block is preferably ball milled to a desired particle size.

By producing inorganic particulate, especially calcium phosphate particles (e.g. metastable calcium phosphate) from a porous block of the calcium phosphate, an irregular-shaped particulate can be achieved, which is generally amorphous but with some crystallinity.

Optionally, the inorganic filler may comprisc ifirther materials, including but not limited to ceramics, including oxides and non-oxide ceramics (e.g. A1203, ZrO2, Si3N4, SiC, ferrites, piezoelectric ceramics such as barium -13 -titanate, bioceramics including hydroxyapatite, ceramic superconductors such as YBaCuO), metals and alloys (e.g. Mo, Cu, Ni, stainless steel, Ti6AI4V, Fe-Ni, Co-Cr), glasses including bioactive glasses (e.g. glasses in the Si-Na-Ca-P-O or Si-Na-K-Ca-Mg-P-O systems), and semiconductors including group HI, IV, V, VI and VII elements and compounds (e.g. CdS, GaAs, GaP).

Optionally, the inorganic filler used is a mixture of filler materials, such as a mixture of different forms of calcium phosphatc. For example, the inorganic filler may comprise a mixture of the metastable inorganic filler (such as calcium metaphosphate) and a second inorganic filler (e.g. hydroxyapatite) in any suitable ratio, such as a 50:50 weight ratio or from 1:99 to 99:1, or 10:90 to 90:10 or 20:80 to 80:20, and preferably in a ratio ofat least 80:20, e.g. at least 90:10 or at least 95:5 by weight. Preferably, however, the inorganic filler is majority metastable inorganic filler (such as calcium metaphosphate), more preferably at least 80% by weight metastable inorganic filler (such as calcium metaphosphate) and still more preferably consists essentially or entirely of metastable inorganic filler (such as calcium metaphosphate).

The inorganic particulate (and in particular, the porous block-derived inorganic particulate) can have any suitable particle size preferably has a particle size of form 0.1 to 500 tm, preferably from Ito 250 m, more preferably from 20 to 150 m, for example in the range 30-90 jim (e.g. in the range 30-50 jim, 40-70 am or 60-90 jim).

The composite and compositions of each aspect of the invention comprises at least one hydrogel monomer, which may be any suitable hydrogel monomer and preferably a physiologically compatible hydrogel monomer. The composite and compositions may comprise or lead to a polymer comprising at least one hydrogel monomer and optionally further hydrogel monomers and, optionally, ifirther non-hydrogel monomers.

By hydrogel monomer, it is intended to mean a monomer capable of polymerization into a hydrogel polymer.

Hydrogel monomers that may find particular utility in the working of the present invention include methaerylates, methlaerylamides, aerylates and -14 -acrylamides, and monomers comprising the structure R'-X-CO-CR2=CH2, wherein may be H or lower alkyl (e.g. methyl, ethyl, n-propyl, isopropyl), X may be 0, NH, S but preferably 0, and R1 may be H, optionally substituted alkyl or aralkyl, preferably optionally substitute lower allq'l and more preferably an hydroxyl alkyl such as hydroxyethyl. By lower alkyl, it is meant any saturated or unsaturated, branched, unbranehed, or cyclic hydrocarbon or combination thereoL typically I -carbon atoms preferably 1-10 and morc preferably 1-5 carbon atoms, and may include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, pentyl, cyclopentyl, neopentyl, hexyl, isohexyl, cyclohexyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, heptyl, octyl, nonyl and decyl. Preferably the lower alkyl is methyl, ethyl, n-propyl or isopropyl. Most preferably, R' is 2-hydroxyethyl.

In a preferred embodiment, the composite and composition of the invention includes as a hydrogel monomer, preferably as the hydrogel monomer, 2-hydroxethyl methacrylate (HEMA).

The polymer may be formed with a comonomer to the hydrogel monomer, which comonomer may be a further hydrogel monomer or a non-hydrogel monomer and which may be present in an amount of 0 to 99%, or 0 to 50% or Ito 25% or 2 to 20% of by weight of total monomer weight. This may be taken as the amount of eomonomer relative to HEMA as the preferred hydrogel monomer or as the amount of non-hydrogel eomonomer relative to total hydrogel monomer present.

Examples of optional hydrogel and non-hydrogel monomers or comonomers include ethylene glycol, lactic acid, hyaluronic acid, ethylene oxide, glycolic acid and dimethylacrylate Optionally, the composite and composition may comprise a erosslinker capable of crosslinking the hydrogel monomer or a comonomer included in the polymer. Any suitable erosslinker may be used which is preferably non-toxic and physiologically acceptable. Preferably a separate crosslinker is not provided but crosslinking effect is achieved by the inclusion in the composition of a multiftinctional eomonomer.

-15 -Preferably according to the second aspect of the invention, and in any case for the first and third aspects of the invention, the polymer or composition comprises a multffiinctional comonomer, present in the amounts defined above.

Preferably the multiflrnctional comonomer may be present instead of or absent any crosshnker, or optionally a reduced amount.

By multiflinctional comonomer it is meant a polymerisable monomer having at least 2 polymerisable moieties (being polymerisable under conditions suitable for polymerization of the hydrogel monomer and being polymerisable with the hydrogel monomer) and preferably at least one other functional group (preferably being a non-polymerisable functional group).

Preferably, the multifunctional comonomer comprises at least 3 polymerisable moieties and still more preferably 4 or more polymerisable moieties. By polymerisablc moicty, it is meant a moicty capable of participating in a polymerization chain reaction to contribute to a resultant polymer backbone.

Preferably, the muhifunctional comonomer comprises at least one other functional group (typically non-polymerisable moieties, in the sense mentioned above), more preferably two other functional groups, still more preferably three other functional groups and optionally four (or more) other functional groups.

Preferably, the at least one other functional group is selected (independently) from groups that have properties beneficial for bone graft substitutes and formation thereof, which are selected, for example, from one or more of tissue-adhesion properties, reactive cross-linking properties, hydrogen-bonding capability, structural rigidity, steric hinderance, etc. Optionally, the at least one other functional group may comprise a group including one or more of an allyne, phenyl, benzyl, heterocycle, each optionally substituted; a haloalkyl, an alcohol, a ketone, an aldehyde, an aeyl halide, a carbonate, a carboxylic acid or derivative, an ester, an acetal or hemiacetal, an amide, amine, imine, imide, cyanate, nitrile, thiol, thiocyanate, phophonic acid, phosphate or phosphodiester, more preferably the at least one other functional group comprises a hydroxyl, carboxyl, amide, ether, ester or lactam group for -16- improved tissue adhesion properties and optionally comprises an imido ester, p-nitrophenyl carbonate, NHS ester, epoxide, isocyanate, maleimide, aldehyde or iodoacctamide.

The at least one other functional group may comprise at least one polar and/or bronsted acid (preferably an organic bronsted acid) and/or crosslinicable functionality which is preferably a non-polymerisable moiety.

Preferably, a polar group is provided that wifi improve adhesion with mineral and ceramic surfaces. Preferably the at least one polar and/or bronsted acid and/or erosslinkable functionality is carboxylate and more preferably at least two, and preferably two, such moieties are provided. The multiftmnctional comonomer should preferably have the capacity to copolymerize with the hydrogel monomer to produce a eopolymer, typically a random eopolymer and preferably in two or more positions. Optionally, the multiftunctional monomer may have a structural core that confers a degree of rigidity onto the molecule, e.g. a cyclic structure or the core comprises one or more aromatic ring structures, such as a phenyl group. By use of the muhifunctional polymer a less flexible and more constrained polymer material may result which is not prone to significant swelling thus being particularly suited to in s/tie formation.

Preferably, the multifunctional comonomer has a molecular weight of 2-lOx the molecular weight of the hydrogel monomer (or when more than one hydrogel monomer is used, the average molecular weight or more preferably the molecular weight of the most prominent hydrogel monomer in molar terms), preferably 4-6x the molecular weight of the hydrogel monomer. By providing a multifunctional comonomer that is substantially larger than the hydrogel monomer, a more constrained but potentially less dense polymer material is produced, having good porosity but limited potential for swelling during formation.

Preferably the multifunetional eomonomer is capable of imparting an adhesive nature to the composite and, in particular improved adhesion to calcium phosphate material and ceramic materials whereby improved adhesion to bone may be achieved thereby reducing the risk of failure as between a composite -17-scaffold and adjacent bone and also improving the incorporation, amount and distribution of inorganic filler through the composite material.

Optionally, the multifunctional comonomer is derivable from the reaction between any dianhydride and a glycerol carrying at least two polymerisable moieties, such as glycerol dimethacrylate. Preferably, the dianhydride is a dianhydride of pyro mellitic acid (benzene tetracarboxylic acid) and the multiffinctional comonomer is preferably pyromellitic dianhydride glycerol dimethacrylate (PMGDM) [bis(glycerol dimethacrylate) pyromellitate]. The preferred multifunctional comonomer is illustrated as I below. 0 CH li I

a -00C arc_c_at j [ S 0 HG I H I II ft cC-c-o-cs 0 0

I

It is envisaged that an aromatic ring structure (e.g. a phenyl group) in the multiflinetional eomonomer imparts improved rigidity to the resulting composite and so preferably the multifunctional commoner comprises at least one aromatic ring structure, preferably from which functional moieties branch.

It is envisaged that the at least one polar andlor bronsted acid and/or erosslinkable functionality and/or aromatic moieties in the multifhnctional comonomer may enhance the adhesive capability of the composite.

The multiflinctional comonomer thus typically improves the composite's osteoconductive properties and preferably enhances its capability of supporting osteogenesis.

The composite may be formed from the composition according to aspects of the present invention either in situ or outside the body, for example in a mould. Formation is triggered by polymerization of initiation for which there is provided in the compositions a polymerization initiator. Any suitable -18-polymerization initiator system may be utilized. The polymerization may be UV, thermal or redox initiated, preferably thermal or redox initiated. Polymerisation may be carried out by photo-initiated hydrogen abstraction in which case the polymerization initiator may be, for example, benzophenoene, 2,2-demethoxy-2-phenylacetophenone (DMPAP), demthoxyacetophenone (DMAP), xanthone and/or thioxanthone and wherein the initiation step may be triggered by UV irradiation of the composition comprising the initiator. Polymcrisation may be carried out by thermal initiation and any suitable thermal initiation system may be used, e.g. where the thermal polymerization initiator is a peroxide, a hydroperoxide, preoxo or an azocompound, such as ammonium persulfate and sodium metasulfate, benzoylperoxide, potassium peroxide, ammonium peroxodisfulate, t-butyl hydroperoxide, 2,2'-azobisisobutyronitrile (AIBN) or azobisisocyanobutyric acid, wherein the initiation step may be triggered by heating of thc composition of thc invention comprising the initiator to, for example, in the range 50°C to 100°C.

Such higher temperatures, however, may not be compatible with a component of the composition to be included in the composite (e.g. a growth factor, viable cell or drug molecule) or maybe incompatible with tissue if polymerization is carried out in vito. Preferably, initiation is by a rcdox pair initiation system. Any suitable redox pair system may be utilized but is preferably characterised by having an initiation temperature of 50°C or less more preferably 40°C or less. Preferably, the polymerization initiator comprises ammonium persulphate and ascorbic acid. The ammonium persulphate, which is preferably provided in a 0. 1M solution, may be provided in an amount of from 5 to 15% by weight (preferably 10%) of total monomer weight and in a weight for weight ratio with ascorbic acid (also preferablyinao.IM solution)intherange from 1:5 to 5:1 preferablyo.5:1 to 1:2.

Preferably ascorbic acid may be provided in the range of is provided in an amount of about 5 to 15%, preferably 10% w/w of monomers (and typically also in a 0.IM solution) and the ammonium persulphate at 0. 1M is provided in a 1:1 ratio with the ascorbic acid.

The rate ofpolymerization may be controlled by varying the respective quantities of initiation components and/or by further additives. -19-

The composition and!or polymerization initiator system enables composite formation to take place with a relatively low exotherm, typically no greater than 40 °C, thus enhancing its suitablility for in vivo assembly as well as providing a suitable carrier composition for seeded cells to promote vascularisation.

For some embodiments, further components may optionally be included in the composition for incorporation into the composite material, either to add or change a property of the composite, to provide a function to the composite or by way of being delivered to the patient (e.g. whereby the composite is a delivery means). By embodying an additional component in the composite comprising a polymer which degrades at a controlled rate in the body, such components maybe delivered in a controlled release andlor delayed release manner at a pre-dctermined desirable rate. Examples of optional additive components include stabilizers, growth factors, cytokines and drugs (e.g. antibiotics).

Furthermore, cells may be seeded in a composite of the invention to provide new growth from within the composite.

Optional additional components, for example bioaetive agents that favour the bone regeneration process, include for example growth factors, hormones, polysaccharides, cells, proteins, peptides, anti-infectives, analgesics, anti-inflammatory agents, antibiotics, antigens, MMP inhibitors or any combination thereof Incorporation of such components can be carried out on the composite by means of adsorption or immersion in solutions containing the component.

Preferably, however, the component maybe incorporated in the composition for forming the composite and thereby incorporated during the formation of the composite. Growth factors may include, for example, platelet derived growth factor (PDGF), vascular endotheial growth factor (VEGF), bone morphogenic proteins (BMP), transforming growth factor-beta-I (TGF-[beta]-[Iota]), growth hormone (GH), insulin like growth factor-1 (IGF1), insulin like growth factor-2 (IGF2), fibroblast growth factor (FGF) or any combination thereof Proteins, for example, may include collagen, fibronectin, albumin or any of their combinations -20 -thereof Furthermore undefined media may also be incorporated to promote bone regeneration, such as blood, serum or plasma.

Optional stabilizing agents may include, for example, trehalose, sucrose, raffinose, manitol, albumin or collagen.

Optionally, strontium or any of its salts may be incorporated into the composite (e.g. by incorporation into a composition for forming the composite) and preferably in concentrations up to 10% by total dry weight of the composite.

In a preferred embodiment of the invention, the composite is a composite ofpoly(HEMA-co-PMGDM) and calcium metaphosphate and the composition comprises HEMA, PMGDM, calcium metaphosphate, a low temperature polymerization initiator, such as a redox initiator and preferably ammonium persulphate-ascorbic acid, and optionally aqueous solvent. Preferably, thc prcferrcd relative proportions of componcnts as defined abovc arc used.

The composite and composition of the present invention provide a highly tunable system whereby properties of high mineral content, flexibility, good compressive strength, low swellability, adequate porosity, adequate resorption rate and polymer degradation rate maybe achieved in concert to produce a system suitable for a range of applications and having particular applicability to load bearing, high mineral content bone growth scaffolds which have good osteoinduetivity.

The composite can be made injectable and porous and the filler can resorb at a desired rate without requiring interference.

The composite according to the invention may be tuned according to preferred embodiments to produce a bone growth scaffold or synthetic bone substitute that has suitable compressive and tensile strength at physiological conditions so that it can be used as a load bearing bone growth scaffold or synthetic bone substitute. Preferably, therefore, a composite according to the preferred embodiment of the invention may have a compressive strength in the range 10 MPa to 50 MPa, e.g. 30 MPa to 40 MPa.

The composite according to the invention may also in preferred embodiments be readily machinable enabling fixing with conventional fixing systems, cutting and shaping, provided with pre-drill channels etc. The composite according to the invention may aLso in preferred embodiments demonstrate advantageous viscoelastic properties having suitable energy damping and elastic properties to allow the composite or scaffold formed therefrom to absorb cncrgy rather than suffer brittle fractures that are commonplace with ceramic bone substitutes. Further, the composite's material properties are such that even on fracture, it can maintain its integrity.

The composite may, for example, be formed by conducting the polymerization step in a mould, as an injectable slurry for in situ fabrication or by 3D printing.

Thcrc is thus, as a fiarthcr aspcct of the invention a method of forming a three dimensional composite matrix for use as a prefabricated bone growth scaffold, the method comprising providing a mould for the bone growth scaffold, disposing therein a quantity of the composition as defined above, causing a polymerization step of the composition to produce a three dimensional composite matrix within thc mould and rclcasing thc resulting composite matrix from thc mould.

A further aspect is thus a method of forming in vivo a three dimensional composite matrix for use as a bone growth scaffold, the method comprising preparing an in vivo site associated with fracture, bone loss or excavation, injecting into the site a slurry of a composition as defined above, and causing a polymerization stcp of thc composition to producc a three dimensional composite matrix within the site.

A synthetic bone graft according to a further aspect of the invention comprises a composite as defined above and obtainable by any of the above mcthods. Optionally, the synthetic bone graft is in a load bearing bone, for

example a mandible.

As discussed above, the invention preferably comprises the use of a metastable inorganic filler as an inorganic filler in synthetic bone substitute materials. The metastable inorganic filler may be any suitable material as discussed above, but is preferably a calcium metaphosphate.

The use of a metastable inorganic filler in accordance with the present invention it is believed enables resorption of bone-forming or osteoinductive mineral at a rate that is compatible with the bone healing procedure in vivo. Existing prior art mineral resorption rates arc typically too fast or too slow.

The use of a multituinctional comonomer in polymeric synthetic bone substitute materials, in accordance with the present invention, it is believed enables the formation of lower density, lower water-content polymers which are thereby not in need of cross linkers, and are more compatible with in situ fabrication by way of an injectable slurry. Furthermore, the preferred multifunctional comonomer has a further adhesive quality that cnhanccs adhesion to mineral and thus supports higher mineral content in the composite and provides improved adhesion and reduce risk of failure or fracture at the juncture with natural bone in vivo.

There is further provided a kit for forming a bone growth scaffold or synthetic bone substitute composite, the kit comprising a hydrogel comonomer along with a multiThnctional comonomer and/or an inorganic filler, preferably a metast able inorganic filler. Typically, the kit further comprises a polymerization initiator or initiator system which is preferably a redox pair initiator system, and more preferably an ammonium persulphate solution (e.g. at 0. 1M) and ascorbic acid, in separate containment. Optionally the kit comprises a solvent, preferably an aqueous solvent and preferably water. The components of the kit may preferably provided in pre-filled ampoules, or other sealed packaging and may be provided in pre-determined amounts according to a particular purpose, or may be provided in unitary amounts with instructions as to how to formulate a composite for a particular purpose. Optionally, a kit may comprise a suitable injection means in hermetically sealed packaging whereby the composition according to a desired pre-determined and pre-packaged formulation for a particular purpose may be mixed (e.g. by breaking a series of frangible barriers separating the components in a -23 -mixing chamber), drawn up into an injection means, which may be removed from the packaging and injected into the treatment side for in situ fabrication. In an alternative embodiment, the kit comprises a mixing mcans comprising two barrcls of material to be mixed immediately prior to injection, the two barrels of material feeding into a mixing tip prior to injecting/delivering the mixed material into the targct site. According to this kit and mcthod, risk of crror in measurcmcnt and risk of infection during opcration may bc minimized.

Optionally, in an aspect of the invention, there may be provided an injectable slurry or a kit for an injectable slurry, comprising a hydrogel comonomer along with a multiflinctional comonomer andlor an inorganic filler, preferably a metastable inorganic filler along with a polymerization initiator (preferably a redox pair initiator system, and more preferably an ammonium persulphate solution (e.g. at 0. 1M) and ascorbic acid) and an aqueous solvcnt. Thc slurry should bc of suitable rheology to enable injection into a site for bone growth in a patient.

The invention further comprises a composite as defined above for use in surgery, diagnosis or therapy. For example, the composite may generally be uscd in bonc rcgcneration and, for example, may be used in traumatology surgery, maxillofacial surgery, periodontal surgery, orthognathic surgery, oral surgery, neurosurgery, palatine fissure treatment, periodontaf treatment, treatment of dental conducts, treatment ofosteoporotic bone, and alveolar regeneration and horizontal alveolar regeneration, or bone regeneration. Generally, the composite may be used in bone regeneration in non-load bearing bones and/or in load bearing bones, but finds particular utility in the regeneration in load bearing bones (e.g. in supporting mandibular defects). The invention flirther provides a method of treatment comprising administering to a subject an effective amount of a mineral salt, preferably a metastable inorganic mineral salt and more preferably a calcium metaphosphate or product thereof Typically, the mineral salt may be administered by incorporating the mineral sah in a composite with a hydrogel polymer, preferably as defined above, which composite may be inserted or formed in situ in a treatment site being typically a bone cavity in which it is desired to promote bone -24 -regeneration. Thereby, the mineral salt may resorb at a desired rate in the formation of bone in the bone cavity.

The invention will now be described in more detail, without limitation, with reference to the following Examples.

EXAMPLES

Example 1

A composite having 50% by weight mineral content was prepared as follows. I g of monomers, comprising 0.9g 2-hydroxyethyl methacrylate (HEMA) and 0.1 g pyromellitic glycerol dimethacrylate (PMGDM), were placed in a vessel and mixed with magnetic stirrer for 10 minutes. 1 g of a 100% calcium metaphosphate (CMP) [see method of preparation below] and 0.lg distilled water (10% by w/w of monomers) was added and the components mixed. To initiate the reaction, an initiator system in an amount of 20% by weight of monomers, i.e. 0.2g, was added at room temperature and comprised of 0.lg of 0.IM ammonium persulphate and 0.lg of 0.1 M ascorbic acid. The resulting composition was mixed.

The resulting composite (sample 1) was a composite ofCMP in a poly[HEMA-eo-PMGDM].

The calcium metaphosphate was prepared by mixing for about 30 seconds in a porcelain mortar with pestle in a ratio of 4:1 by weight a calcium bis-phosphate monohydrate (Ca(H2P04)2H20) (MCP) (available from FlukaTM under product code 21053) and polyvinyl alcohol ([-CH2CHOH-]n) (PVA) of molecular weight: 33,000 (available from SIGMATM under product code P8136-250G) and then placing the mixture in moulds and applying a compressive force applied to compact it in the mould to form blocks. The blocks were then sintered at 900T at 8°C/mm and maintained at 900°C for 6h and then furnace-cooled to room temperature. The blocks were then ground in a pestle and mortar and then ball milled into particulate form. -25 -

Example 2

The method of Example I was repeated with the same proportion of distilled water to monomers (10% by weight) and of initiator system components, but with varying ratios of HEMA:PMGDM and various proportions of CMP as set out in Table 1 below. For comparison, Sample C was produced without any inorganic filler.

Table 1:

Sample HEMA:PMGDM ratio CMP content (wt % total dry weight of composite) C 90:10 0 1 90:10 40 2 90:10 50 3 90:10 60 4 85:15 60 80:20 60

Example 3

The Samples C and 1-5 were characterised according to various phyisco-chcmical characteristics. The characteristics examined include equilibrium water content (EWC), equilibrium water content at 100% humidity, pH of sample, degree of cure (according to FTIR -identif\jing relative proportion of residual monomer), glass transition temperature (by Differential Scanning Calorimetry, DSC), Commpressive Strength (Mpa) and elastic modulus (Mpa) in dry conditions, 100% humidity and maximum hydration (max EWC). The characteristics are summarised in the tables below. -26 -

Table 2: EWC

SAMPLE EWC % EWC AT 100%

HUMIDITY

C 26.5 - 1 21.0 15.0 2 17.8 11.1 3 15.1 9.0 The equilibrium water uptake of each of the composite compositions is shown in Table 2 above. EWC indicate the amount of water the hydrogel composite can take up when immersed in water at 37°C which is characteristic for each type of composition. Thus, it is shown that the EWC can be tailored by manipulating the components of the composition. Further, it is shown that the EWC can be varied by changing the relative proportions of polymer and mineral in the composite.

Tahle 3: pH SAMPLE pH C 5.5 1 4.4 2 4.2 3 4.0 Composite samples were prepared and the pH measured using a flat tip on the composite by placing distified water to measure the acidity/basicity on the sample. As Table 3 ifiustrates, the pH decreases with increasing CMP. -27 -

Table 4: FTIR Degree of cure SAMPLE % cure C 97.0 1 92.6 2 92.3 3 92.0 As can be seen from Table 4, even with 60% mineral content, greater than 90% cure is achieved (as determined by FTIR spectroscopy in which before and after polymerisation spectra were run and the extent of polymerisation determined by proportion of residual monomer present).

Table 5: DSC

SAMPLE DSC

C 117.0 1 124.0 2 127.0 3 130.0 The glass transition temperature (as determined by DSC) of the composite samples are shown in Table 5. As can be seen the high Tg is demonstrated in the composites of the invention having filler of 40-60% and thus will not undergo softening at body temperature, which is important. Further, there is not a great deal of difference between the Tg between the samples having from 40-60% filler, which, without being bound by theory, it is believed indicates that the ceramic may be interacting with the polar groups in the molecular structure (derived from the PMGDM). -28 -

Table 6: Compressive strength and elastic modulus under dry conditions SAMPLE Compressivc Strcngth (Mpa) Elastic Modulus (Mpa) Average Standard Dcv Average Standard Dcv 3 32.8 5.1 170 15.0 4 39.44 6.0 258 10.0 40.27 9.0 288 11.2 12 samples of each were tested Table 6: Compressive strength and elastic modulus at 100% humidity SAMPLE Compressive Strength (Mpa) Elastic Modulus (Mpa) Average Standard Dcv Average Standard Dcv 3 29.78 4.0 172.29 21.3 4 29.95 3.6 179.17 9.4 31.25 6.2 201.49 9.9 12 samples of each were tested Table 7: Compressive strength and elastic modulus at man EWC (completely hydrated) SAMPLE Compressive Strength (Mpa) Elastic Modulus (Mpa) Average Standard Dcv Average Standard Dcv 3 9.1 0.79 40.82 7.11 4 12.43 0.87 45.46 9.41 13.02 1.26 58.79 4.61 * 12 samples of each were tested The values illustrated in Table 6 show good compressive strength and elastic modulus for the composites of the invention (which are higher than other bone substitutes). Increasing PMGDM increases the compressive strength of the composite. -29 -

Example 4

Cytocompatibility of the composite of the invention was examined by the following process.

Cells were maintained in normal growth medium consisting of Dulbecco's Modified Eagle Medium (DMEM), penicillin (50 jig/ml), streptomycin (50 jig/mI), L-glutamine (2 mM) and 10% fetal bovine serum (FBS) (available from Sigma-Aldrich'TM) at 37°C in a humidified 5% C02: 90% air atmosphere.

Cells were seeded at a density of 1x106 cells/cm2 on disk shaped cements with dimension (d=8.4mni. h=4.2mm) and incubated for 4 days with media replenished every two days.

A Live/DeadTM viability staining system from InvitrogenTM was used (which comprises Calcein AM and ethidium homodimer-1) which stains green/red for livc/dcad.

Fibroblast cells were ceded at 0.5 x 105 onto the porous 3D hydrogel and composite scaffolds (10% PMGDM and 60% CMP made according to Sample 3 above). After 4 weeks in culture, the scaffolds were transferred to a fresh 24 well plate and media replaced with 1 OOjil of live/dead viability solution.

The livc/dcad solution was prcparcd by adding 2 jil of Calccin AM and Ethidium bromide to 2 ml of phosphate buffered saline. The plates were transferred to an incubator for lh and observed using a light microscope (Olympus IXSI) under fluorescence. The live (green) and dead (red) cells were viewed using 500 nm and 510 nm filters respectively. Photographic images of the cells were taken using a digital camera with CCD sensors.

This system was used to visualize cytocompatibility and sprcading.

Cells were seeded at 1x105 at the core to visualize spreading.

Figures 1 to 3 illustrate the findings.

Figure 1 is a control where fibroblasts are on tissue culture plastic.

As can be seen, the core is covered but the outer region becomes progressively more sparse. This is typical fibroblast morphology.

Figure 2 illustrates cells spreading (x40) in the composite of the invention. This shows typical fibroblast morphology and spreading occurs on the -30 -entire surface. Figure 3 (at X1O) shows complete surface coverage occurs within 7 days.

Figures 4 and 5 shows staining of Mesenchymal stem celLs afler 7 days and 21 days respectively using a composite of Sample 3 again. In Figure 4, it can be seen that there is complete surface coverage within 7 days. Figure 5 is a 2 photon image (of MSC cells) stained to view MSC's interaction at 21 days with the compositc using cytoskeletal protein staining. Vimentin is onc of the 5 major intermediate filaments and is stained green (FITC). The nuclear stain (DAPI) highlights nuclei in blue.

It is clear from the above that the scaffolds/composites of the invention are cytocompatible.

The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention.

Claims (23)

1. CLAIMS: I. A composite comprising an inorganic filler and a polymer formed from a hydro gel monomer and a multifiinctional comonomer.
2. 2. A composite as claimed in claim 1, wherein the inorganic filler is a metastablc inorganic filler.
3. 3. A composite as claimed in claim2, wherein the metastable inorganic filler is calcium metaphosphatc.
4. 4. A composite as claimed in anyone of the preceding claims, wherein the multifUnctional comonomer is pyrmcllitic glycerol dimethacrylate.
5. 5. A composite as claimed in anyone ofthe preceding claims wherein the hydro gel monomer is 2-hydroxyethyl methacrylate.
6. 6. A composite as claimed in any one of the preceding claims comprising an amount of inorganic fihlcr of at least 40% bywcight of thc composite.
7. 7. A composite as claimed in any one of the preceding claims comprising the multiflinctional comonomer in an amount of fix,m 5% to 20% by weight of total monomer.
8. 8. A composite comprising a mctastablc inorganic filler and a polymer formed from a hydrogel monomer.
9. 9. A composite as claimed in claims, whcrein the metastable inorganic filler is calcium metaphosphate.
10. 10. A composite as claimed in claimS or claim 9, wherein the hydrogel monomer is 2-hydroxyethyl methacrylate.
11. 11. A composition for preparing a composite of any one of claims Ito 7, the composition comprising an inorganic filler, a hydrogel monomer, a multifunctional comonomer, a polymerization initiator and optionally a solvent.
12. 12. A composition for preparing a composite of any one of claims 8 to 10, the composition comprising a metastable inorganic filler, a hydrogel monomer, a polymerization initiator and optionally a solvent.
13. 13. A composition as claimed in claim 11 or claim 12, wherein the polymerization initiator is redox pair initiator.
14. 14. A composition as claimed in claim 13, wherein the redox pair initiator comprises ammonium persulphate and ascorbic acid, preferably in an amount of from 15% to 25% by total weight of monomers.
15. 15. A composition as claimed in any one of claims 11 to 14, wherein the solvent is water.
16. 16. A method of forming a three dimensional composite matrix for use as a prefabricated bone growth scaffold, the method comprising providing a mould for the bone growth scaffold, disposing therein a quantity of the composition as defined in any one of claims 11 to 14, causing a polymerization step of the composition to produce a three dimensional composite matrix within the mould and releasing the resulting composite matrix from the mould.
17. 17. A method of forming in vim a three dimensional composite matrix for use as a bone growth scaffold, the method comprising preparing an in viva site associated with fracture, bone loss or excavation, injecting into the site a slurry of a -33 -composition as defined in any one of claims 11 to 14, and causing a polymerization step of the composition to produce a three dimensional composite matrix within the site.
18. 18. A synthetic bone graft comprising a composite as defined in any one of claims Ito 10.
19. 19. A synthetic bone graft as claimed in claim 18, which is for a load bearing bone.
20. 20. A composite or composition as defined in any one of claims ito 15 for use in surgery therapy or diagnosis.
21. 21. A composite or composition as claimed in claim 20, whKh is for use in 1 5 surgery or therapy, which further comprises a therapeutic drug for delayed and/or controlled and/or sustained release for eliciting a therapeutic effect on a patient.
22. 22. Use of a metastable inorganic filler as an inorganic filler in synthetic bone
23. 23. Use of a multifhnetional comonomer in polymeric synthetic bone substitute materials.-34 -