WO2012117218A1

WO2012117218A1 - Biomaterial

Info

Publication number: WO2012117218A1
Application number: PCT/GB2012/000197
Authority: WO
Inventors: Benjamin Peter McCARTHY; Xiang Cheng Zhang; Anthony KINZELLA; Philip Robert Jackson
Original assignee: Ceram Research Limited
Priority date: 2011-03-02
Filing date: 2012-02-29
Publication date: 2012-09-07
Also published as: GB201103606D0

Abstract

A biomaterial comprising synthetic hydroxyapatite in which up to 10% by molar composition in total of substituent components for the phosphate are provided, with the phosphate substituent components comprising at least two of a sulphate, silicate or borate, with the total mean charge difference by virtue of the phosphate substituent components being less than 1.8 F.mol^-2.

Description

Biomaterial

This invention concerns a biomaterial, and particularly a biomaterial comprising synthetic hydroxyapatite into which one or more substituent components has been introduced.

Hydroxyapatite (HA) is used in a range of applications relating to bone replacement/interface. Typical uses include coatings on bio-inert metallic implants in order to improve biocompatibility (and so new bone in-growth) and to reduce the risk of rejection. In another use porous HA granulates may be employed to encourage fresh bone growth in voids arising from disease or trauma.

Previous attempts have been made to increase or tailor the biocompatibility and/or bioactivity of hydroxyapatite through substitution of different materials into the calcium phosphate crystal lattice. A number of difficulties have been encountered in providing substituted materials with a required proportion of a substituent material, whilst attaining required physical chemical characteristics. The calcium (Ca) to phosphorous (P) ratio in HA is 1.667. In order for any substitution to be incorporated into the lattice it is important to keep the cation:anion ratio of the starting reagents substantially to the same value (1.667).

According to the present invention there is provided a biomaterial comprising synthetic hydroxyapatite in which up to 10% by molar composition in total of substituent components for the phosphate are provided, with the phosphate substituent components comprising at least two of a sulphate, silicate or borate, with the total mean charge difference by virtue of the phosphate substituent components being less than 1.8 F.mol^'2.

The total mean charge difference by virtue of the phosphate substituent components may be less than 0.9 F.mol^'2 and may be less than 0.432 F.mol^'2. The substituent components for the phosphate may be derived from an element, or a compound of an element and oxygen. The substituent components for the phosphate may be anions. The substituent component for the phosphate may therefore also include aluminate or titanate.

A substituent component may also be provided for the calcium. The substituent component for the calcium may be an element. The substituent component for the calcium may be a cation. The substituent component for the calcium may be any of magnesium, silver, barium, strontium, zinc, sodium, potassium, aluminium, titanium, yttrium, lanthanum, Iron, a lanthanide, an actinide, a transition metal, or copper

A substituent component may also be provided for the hydroxyl. The substituent component for the hydroxyl may be an anion. The substituent component for the hydroxyl may be any of fluorine, chlorine, bromine, iodine or carbonate.

The synthetic hydroxyapatite may comprise up to 10% by molar composition in total of substituent components for the calcium.

The synthetic hydroxyapatite may comprise up to 10% by molar composition in total of a substituent components for the hydroxyl. The synthetic hydroxyapatite may comprise up to 10% by molar composition in total of substituent components for phosphate, calcium and hydroxyl.

The substituent components may comprise a combination of silicate, sulphate and strontium. The substituent components may comprise a combination of silicate and sulphate.

The substituent components may comprise a combination of silicate, borate and strontium.

The substituent components may comprise a combination of sulphate, borate and strontium. The substituent components may comprise a combination of silicate, borate and Magnesium.

The substituent components may comprise a combination of sulphate, borate and magnesium

The substituent components may comprise a combination of silicate, sulphate and Magnesium

The substituent components may comprise a combination of sulphate, silicate and borate.

The substituent components may comprise a combination of sulphate, silicate, borate and sodium. The substituent components may comprise a combination of sulphate, borate and sodium.

The substituent components may comprise a combination of silicate, borate, sodium and yttrium.

The substituent components may comprise a combination of sulphate, borate and chlorine. The biomaterial may be made by a precipitation method, and may be made so as to produce crystallites of less than 250 nanometres. Following precipitation the material may be filtered, dried and sintered.

Embodiments of the present invention will now be described by way of example only, and with reference to the single figure of the accompanying drawings which is a block diagram of typical possible processing routes for materials according to the present invention.

Examples 1 and 2 show a wet chemical precipitation route used to prepare a synthetic hydroxyapatite biomaterial with sulphate and silicate substituent components. Example 1 :

Ca(OH)₂ (12.4g, 16.68 x 10^"2 mol) was dissolved in water (660 ml_). H₃P0₄ (0.6M, 153 mL, 9.180 x 10^"2 mol) H₂S0₄ (0.6M, 6.5 ml_, 0.39 x 10^'2 mol) and TEOS (0.85 mL, 0.39 x 10^~2 mol) were simultaneously added to the stirring mixture (NB. No titration). The mixture was left stirring at 40°C for 3 hours. After the reaction period, the mixture was vacuum filtered through a Whatman filter paper, number 44, and the powder dried at 60°C overnight. The cation to anion ratio is 1 .675, the total charge difference is 0 F.mor² and a total anion charge difference of 0 F.mol^'2.

Pre-calcination XRD showed a large amount of amorphous material (40-50%), with a HA phase evident. The powder was placed inside a ceramic crucible and calcined at 1100 °C for 3 hours. Ramp rate was controlled to 10 °C / hr. Following calcination XRD showed a significant decrease in the amount of amorphous, and a large increase in the crystallinity (shown by a sharpening of the HA peaks). The amorphous dropped to <5%, with the primary phase remaining being HA. Some CaO (aprx 1 %) was present as a result from the slightly high ratio.

Example 2:

Ca(OH)₂ (12.36g, 16.68 x 10^~2 mol) was dissolved in water (660 mL). H₃P0₄ (0.6 , 183.3 mL, 10.996 x 10^"2 mol) H₂S0₄ (0.6 , 7.5 mL, 0.45 x 10^'2 mol) and TEOS (0.998 mL, 0.45 x 10^"2 mol) were added at a total rate of 3.25 ml/min to the stirring mixture. The mixture had its pH controlled to pH 9 by way of automatic ammonia hydroxide addition. The mixture was left stirring at 45°C for 3 hours. After the reaction period, the mixture was vacuum filtered through a Whatman filter paper, number 44, and the powder dried at 60°C overnight. The cation to anion ratio is 1 .667, the total charge difference is 0 F.mol ² and a total anion charge difference of 0 F.mol^"2.

Example 3 shows a wet chemical precipitation route used to prepare a synthetic hydroxyapatite biomaterial with silicate, borate and strontium substituent components. Example 3:

Ca(OH)₂ (1 1.84 g, 16.01 x 10^'2 mol) and Sr(OH)₂ (1.77 g, 0.667 x 10^'2 mol) was dissolved in water (660 mL). Η₃Ρ0₄ (0.6 , 176.5 mL, 10.588 x 10^"2 mol), TEOS (0.554 mL, 0.25 x 10^'2 mol) and Η₃Β0₃ (0.6M, 5.0 mL, 0.300 x 10^' ² mol) were added at a total rate of 3.25 ml/min to the stirring mixture. The mixture had its pH controlled to pH 8.5 by way of automatic ammonia hydroxide addition. The mixture was left stirring at 45°C for 3 hours. After the reaction period, the mixture was vacuum filtered through a Whatman filter paper, number 44, and the powder dried at 60°C overnight. The cation to anion ratio is 1.667, the total charge difference is 0.6 F.mol^'2 and a total anion charge difference of 0.6 F.mol^'2. Examples 4 and 5 show a wet chemical precipitation route used to prepare a synthetic hydroxyapatite biomaterial with sulphate, borate and strontium substituent components.

Example 4:

Ca(OH)₂ (11.84 g, 16.01 x 10^"2 mol) and Sr(OH)₂ (1.77 g, 0.667 x 10^~2 mol) was dissolved in water (660 ml_). Η₃Ρ0₄ (0.6M, 176.5 ml_, 10.588 x 10^"2 mol), H₂S0₄ (0.6 , 4.17 ml_, 0.25 x 0^'2 mol) and Η₃Β0₃ (0.6M, 5.0 mL, 0.300 x 10^"2 mol) were added at a total rate of 3.25 ml/min to the stirring mixture. The mixture had no external pH control. The mixture was left stirring at 45°C for 3 hours. After the reaction period, the mixture was centrifuged, and the powder dried at 60°C overnight. The cation to anion ratio is 1.667, the total charge difference is -0.6 F.mol^"2 and a total anion charge difference of -0.6 F.mor².

Example 5: Ca(OH)₂ (1 1.74 g, 15.85 x 10^'2 mol) and Sr(OH)₂ (2.216 g, 0.834 x 10^"2 mol) was dissolved in water (660 mL). H₃P0₄ (0.6M, 173.72 mL, 10.423 x 10^"2 mol), H₂S0₄ (0.6M, 2.92 mL, 0.175 x 10^~2 mol) and H3BO3 (0.6M, 3.75 mL, 0.225 x 10^"2 mol) were added at a total rate of 1.2 ml/min to the stirring mixture. The mixture had no external pH control. The mixture was left stirring at 60°C for 3 hours. After the reaction period, the mixture was centrifuged, and the powder dried at 60°C overnight. The cation to anion ratio is 1.667, the total charge difference is -0.42 F.mol^'2 and a total anion charge difference of - 0.42 F.mol^"2. Example 6 shows a wet chemical precipitation route used to prepare a synthetic hydroxyapatite biomaterial with sulphate, borate and magnesium substituent components. Example 6:

Ca(OH)₂ (11.99 g, 16.18 x 10^"2 mol) and Mg(OH)₂ (0.292 g, 0.5 x 10^'2 mol) was dissolved in water (660 mL). Η₃Ρ0 (0.6 , 171 .92 mL, 10.316 x 10^'2 mol), H₂S0₄ (0.6M, 2.50 mL, 0.15 x 10^"2 mol) and H₃B0₃ (0.6M, 2.50 mL, 0.15 x 10^'2 mol) were added at a total rate of 1.2 ml/mtn to the stirring mixture. The mixture had no external pH control. The mixture was left stirring at 45°C for 3 hours. After the reaction period, the mixture was centrifuged, and the powder dried at 60°C overnight. The cation to anion ratio is .667, the total charge difference is -0.36 F.mol^"2 and a total anion charge difference of -0.36 F.mol^"2.

Example 7 shows a wet chemical precipitation route used to prepare a synthetic hydroxyapatite biomaterial with sulphate, silicate and borate substituent components.

Example 7:

Ca(OH)₂ ( 2.36 g, 16.68 x 10^"2 mol) was dissolved in water (330 mL). H3PO₄ (0.6M, 183.26 mL, 10.997 x 10^"2 mol), H₂S0₄ (0.6M, 5.00 mL, 0.300 x 10^"2 mol), TEOS (0.665 mL, 0.300 x 10^"2 mol) and H3BO3 (0.6M, 5.00 mL, 0.300 x 10^"2 mol) were added at a total rate of 10 ml/min to the stirring mixture. The mixture had no external pH control. The mixture was left stirring at 60°C for 3 hours. After the reaction period, the mixture was centrifuged, and the powder dried at 60°C overnight. The cation to anion ratio is 1.667, the total charge difference is 0 F.mol^'2 and a total anion charge difference of 0 F.mol^"2.

Example 8 shows a wet chemical precipitation route used to prepare a synthetic hydroxyapatite biomaterial with sulphate, silicate, borate and sodium substituent components.

Example 8: Ca(OH)₂ (12.11 g, 16.35 x 10^'2 mol) and NaOH (0.133 g, 0.334 x 10^"2 mol) was dissolved in water (660 ml_). Η₃Ρ0₄ (0.6M, 180.29 ml_, 10.817 x 10^"2 mol), H₂S0₄ (0.6M, 6.67 mL, 0.400 x 10^"2 mol), TEOS (0.554 ml_, 0.250 x 10^'2 mol) and Η₃Β0₃ (0.6M, 1.67 mL, 0.100 x 10^"2 mol) were added to the stirring mixture. The mixture had no external pH control. The mixture was left stirring at 45°C for 3 hours. After the reaction period, the mixture was centrifuged, and the powder dried at 60°C overnight. The cation to anion ratio is 1 .667, the total charge difference is -0.04 F.mol^'2, a total cation charge difference of 0.32 F.mol^"2 and a total anion charge difference of -0.36 F.mol^"2.

Example 9 shows a wet chemical precipitation route used to prepare a synthetic hydroxyapatite biomaterial with sulphate, borate and sodium substituent components.

Example 9:

Ca(OH)₂ (12.11 g, 16.43 x 10² mol) and NaOH (0.100 g, 0.250 x 10^"2 mol) was dissolved in water (660 mL). Η₃Ρ0₄ (0.6M, 175.18 mL, 10.51 1 x 10^"2 mol), H₂S0₄ (0.6M, 4.00 mL, 0.240 x 10^"2 mol) and H₃B0₃ (0.6M, 4.00 mL, 0.240 x 10² mol) were added to the stirring mixture. The mixture had no external pH control. The mixture was left stirring at 45°C for 3 hours. After the reaction period, the mixture was centrifuged, and the powder dried at 60°C overnight. The cation to anion ratio is 1 .667, the total charge difference is - 0.336 F.mol^"2, a total cation charge difference of 0.24 F.mol^'2 and a total anion charge difference of -0.576 F.mol^'2.

Example 10 shows a wet chemical precipitation route used to prepare a synthetic hydroxyapatite biomaterial with silicate, borate, sodium and yttrium substituent components.

Example 10: Ca(OH)₂ (11 .94 g, 16.1 1 x 10^'2 mol), Y₂0₃ (0.320 g, 0.142 x 10^"2 mol) and NaOH (0.1 13 g, 0.284 x 10^'2 mol) was dissolved in water (660 ml_). H₃P0₄ (0.6M, 177.04 mL, 10.622 x 10^'2 mol), TEOS (0.621 ml_, 0.280 x ^,0"2 mol) and H3BO3 (0.6 , 5.00 mL, 0.300 x 10^"2 mol) were added to the stirring mixture. The mixture had no external pH control. The mixture was left stirring at 45°C for 3 hours. After the reaction period, the mixture was centrifuged, and the powder dried at 60°C overnight. The cation to anion ratio is 1 .667, the total charge difference is 0,672 F.mol^'2, a total cation charge difference of 0 F.mor² and a total anion charge difference of 0.672 F.mol^"2.

Example 11 shows a wet chemical precipitation route used to prepare a synthetic hydroxyapatite biomaterial with sulphate, borate, and chlorine substituent components.

Example 1 :

Ca(OH)₂ (1 1.94 g, 16.1 1 x 10^'2 mol) and CaCI₂ (0.185 g, 0.167 x 0^"2 mol) was dissolved in water (660 mL). H₃P0₄ (0.6M, 175.54 mL, 0.533 x 10^"2 mol), H2SO4 (0.6M, 3.34 mL, 0.200 x 10^"2 mol) and H3BO3 (0.6M, 5.00 mL, 0.300 x 10^"2 mol) were added to the stirring mixture. The mixture was controlled to pH 8 by the automatic titration of ammonium hydroxide. The mixture was left stirring at 55°C for 3 hours. After the reaction period, the mixture was centrifuged, and the powder dried at 60°C overnight. The cation to anion ratio is 1 .667, the total charge difference is -0.48 F.mol ² and a total anion charge difference of -0.48 F.mol^"2.

Table 1 provides an explanation of the terms used in table 2. Table 2 provides an overview of the mean charge difference calculated at the phosphate site (P), calcium site (Ca) and hydroxyl site (OH) for each of examples 1 to 1 1 above. Substituent

component Abbreviation Precursor

Silicate Si TEOS (Tetraethylorthosilicate)

Sulphate S H₂S0₄

Borate B H3BO3

Strontium Sr Sr(OH)₂

Magnesium Mq Mg(OH) ₂

Sodium Na NaOH

Yttrium Y Y2O3

Chlorine CI CaCfe

Table 1 - List of Potential Precursors

Faraday

Example mol (Electron)

3 Subst Site % Difference (F.mol ²)

Anion

Si P 2.5 0.6 Balance 0.6

Cation

B P 3 0 Balance 0

Total

Sr Ca 4 0 Balance 0.6 Faraday

Example mol (Electron)

4 Subst Site % Difference (F.mor²)

Anion

S P 2.5 -0.6 Balance -0.6

Cation

B P 3 0 Balance 0

Total

Sr Ca 4 0 Balance -0.6

Faraday

Example mol (Electron)

7 Subst Site % Difference (F.mol ²)

Anion

S P 3 -0.72 Balance 0

Cation

B P 3 0 Balance 0

Total

Si P 3 0.72 Balance 0 Faraday

Example mol (Electron)

8 Subst Site % Difference (F.mol^'2)

Anion

S P 4 -0.96 Balance -0.36

Cation

B P 1 0 Balance 0.32

Total

Si P 2.5 0.6 Balance -0.04

Na Ca 2 0.32

Table 2 - Further Examples The drawing illustrates typical processing routes for such materials. Typically a granulate form of the raw powder material would be used. The subsequent processing in this case would involve creating a stable suspension of the HA powder, whether calcined or uncalcined, and then using one of various process routes (e.g.) foaming of a slurry and then curing, sintering and milling; freeze or spray dry granulation and sintering; direct coagulation casting with a sacrificial organic filler - that is removed during subsequent sintering - which is then milled. A typical sintering step following precipitation would be to sinter the material at 1200 °C for 3 hours, with a ramp up rate of 10 °C / hr. It is possible to sinter at higher or lower temperatures and the amount and form of the substitutions may affect the suitability of differing regimes.

The materia) prepared may be used as a biomaterial for use for instance as a raw powder material for bone void filler applications as a granulate. The material can also be used to prepare ceramic or composite shape bone implants using conventional shaping routes such as powder pressing, extrusion or novel routes such as Additive Layer Manufacturing (ALM). Furthermore such a material could be used as a coating for osteo- implants. Other potential uses include dentistry, arterial stents or slow release drug carriers.

The different substituents indicated have been picked for various reasons. For example, silicate has been extensively researched and its beneficial effect on healing bones is well documented. Borate is often medicated to people suffering from osteoporosis as it helps to activate osteoblasts, whereas strontium is beneficial in the opposite manner, by repressing osteoclasts. Silver and copper have been shown to be useful in making a surface toxic, and in low concentrations are anti-microbial, whilst not being cytotoxic. Sulphate is often used in bone repair in the form of CaSO₄.0.5H₂O as setting cement and shows a good healing response, but may be fully absorbed within a matter of weeks. The value for the total mean charge difference, F.mol^"2 (where F = Faraday and one Faraday = one mole of electrons), relates to the deviation from the lattice standard electron (e ) count where Ca²⁺ contributes a total cationic charge of 10⁺ and PCX,^3' contributes a total anionic charge of 9^' (the additional charge difference is accounted for by varying amounts of OH ). To work out the F.mol^"2 value, the molar percentage (M%) of a substitution (relative to the ion being replaced, not total substitution) is mult/plied by the (e^' ) count for the ion replaced, and finally multiplied by the (e ) count difference of the substituent. The anion and cation are worked out separately and summed at the end. This is demonstrated by method of example below:

7% of Ca²⁺ is replaced by Na⁺. This equates to 7% x 10 (total cation charge) x 1⁺ (electron difference of Ca²⁺ -> Na⁺) = 0.7 F.mol^"2.

A 7% substitution of Al³⁺ (which occupies the cationic site) would follow the same formula: 7% x 0 (total cation charge) x 1^" (electron difference of Ca²⁺ - Al³⁺) = -0.7 F.mol^'2. If the 10% total cation substitution was a mix of 5% Na⁺ and 5% Al³⁺, then the maths would be as follows: [5% x 10 (total cation charge) x (electron difference of Ca²⁺ Na⁺)] + [5% x 10 (total cation charge) x 1^" (electron difference of Ca²⁺ Al³⁺)] = 0 F.mol^'2. A 7.3% substitution of S0₄ ^2" (which occupies the anionic site) would have its F.mol^"2 worked out thus: 7.3% x 9 (total anion charge) x Γ (electron difference of P0₄ ^3" -> S0₄ ^2") = -0.657 F.mol^"2.

If 10% of the cation was replaced with Na⁺, and 7.3% of the anion was replaced with S0₄ ^2', then the total charge difference can be worked out by: [Total cation difference] + [Total anion difference] = 1 + [-0.657] = 0.343 F.mol^"

2 There is thus described a biomaterial and a method of making a biomaterial which permits a wide range of substituent components to be incorporated into a hydroxyapatite lattice, by monitoring the mean charge differences caused by the substituent components. The substituent components may be incorporated in either of the positions occupied by calcium or phosphorous in pure hydroxyapatite.

It is to be realised that a wide range of variations may be made without departing from the scope of the invention. For instance different materials could be used than those indicated above. A different production method could be used than that described.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A biomaterial comprising synthetic hydroxyapatite in which up to 10% by molar composition in total of substituent components for the phosphate are provided, with the phosphate substituent components comprising at least two of a sulphate, silicate or borate, with the total mean charge difference by virtue of the phosphate substituent components being less than 1.8 F.mol^"2.

2. A biomaterial according to claim 1 , in which the total mean charge difference by virtue of the phosphate substituent components is less than 0.9 F.moP².

3. A biomaterial according to claims 1 or 2, in which the total mean charge difference by virtue of the phosphate substituent components is less than 0.432 F.mol^'2.

4. A biomaterial according to any of the preceding claims, in which the substituent components for the phosphate are derived from an element, or a compound of an element and oxygen.

5. A biomaterial according to any of the preceding claims, in which the substituent components for the phosphate are anions.

6. A biomaterial according to any of the preceding claims, in which the substituent components for the phosphate include aluminate or titanate.

7. A biomaterial according to any of the preceding claims, in which a substituent component is provided for the calcium.

8. A biomaterial according to claim 7, in which the substituent component for the calcium is an element.

9. A biomaterial according to claims 7 or 8, in which the substituent component for the calcium is a cation.

10. A biomaterial according to any of claims 7, to 9 in which the substituent component for the calcium is any of magnesium, silver, barium, strontium, zinc, sodium, potassium, aluminium, titanium, yttrium, lanthanum, Iron, a lanthanide, an actinide, a transition metal, or copper

11. A biomaterial according to any of the preceding claims, in which a substituent component is provided for the hydroxyl.

12. A biomaterial according to claim 1 , in which the substituent component for the hydroxyl is an anion.

13. A biomaterial according to claims 11 or 12, in which the substituent component for the hydroxyl is any of fluorine, chlorine, bromine, iodine or carbonate.

14. A biomaterial according to any of the preceding claims, in which the synthetic hydroxyapatite comprises up to 10% by molar composition in total of substituent components for the calcium.

15. A biomaterial according to any of the preceding claims, in which the synthetic hydroxyapatite comprises up to 10% by molar composition in total of substituent components for the hydroxyl.

16. A biomaterial according to any of the preceding claims, in which the synthetic hydroxyapatite comprises up to 10% by molar composition in total of substituent components for phosphate, calcium and hydroxyl.

17. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of silicate, sulphate and strontium.

18. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of silicate and sulphate.

19. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of silicate, borate and strontium.

20. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of sulphate, borate and strontium.

21. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of silicate, borate and Magnesium.

22. A biomaterial according to any of the preceding claims, in which the substituent components comprise a combination of sulphate, borate and magnesium

23. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of silicate, sulphate and

Magnesium

24. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of sulphate, silicate and borate.

25. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of sulphate, silicate, borate and sodium.

26. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of sulphate, borate and sodium.

27. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of silicate, borate, sodium and yttrium.

28. A biomaterial according to any of claims 1 to 16, in which the substituent components comprise a combination of sulphate, borate and chlorine.

29. A biomaterial according to any of the preceding claims, in which the biomaterial is made by a precipitation method.

30. A biomaterial according to claim 29, in which the biomaterial is made so as to produce crystallites of less than 250 nanometres.

31. A biomaterial according to claims 29 or 30, in which following precipitation the material is filtered, dried and sintered.

32. A biomaterial substantially as hereinbefore described.

33. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.