Silicate-substituted hydroxyapatite
View Patent ↗An inorganic silicate-substituted calcium phosphate hydroxyapatite, useful as a biomaterial, has a Ca/P molar ratio in the range 2.05 to 2.55 and a Ca/(P+Si) molar ratio less than 1.66. The hydroxyapatite can be substantially free of carbonate ions. The material has relatively high solubility and is able to release silicon into solution.
1. A crystalline inorganic silicate-substituted calcium phosphate hydroxyapatite, having a Ca/P molar ratio in the range of 2.05 to 2.55 and a Ca/(P+Si) molar ratio in the range of 1.60 to 1.65.
2. A hydroxyapatite according to claim 1 , wherein the silicon atom content is in the range of 2.9 to 6 wt %.
3. A hydroxyapatite according to claim 1 , wherein the hydroxyapatite is free of impurity phases.
4. A hydroxyapatite according to claim 1 , wherein the Ca/P molar ratio is in the range of 2.3 to 2.5.
5. A hydroxyapatite according to claim 1 wherein the Ca/(P+Si) molar ratio is in the range of 1.60 to 1.64.
6. A hydroxyapatite according to claim 1 , wherein a maximum impurity level of carbonate ions is 0.1% as a molar ratio based on a total of silicate and phosphate ions.
7. A composition comprising a mixture of hydroxyapatite according to claim 1 and at least one other component.
8. A process for manufacturing an inorganic silicate-substituted calcium phosphate hydroxyapatite, comprising:
(a) precipitation of silicate-substituted apatite from reactants containing calcium, phosphorus and silicon at a pH of at least 9, wherein the molar ratio of Ca/P of the reactants is in the range of 2.05 to 2.55 and the molar ratio Ca/(P +Si) is in the range of 1.60 to 1.65, and
(b) calcining the precipitate at a temperature in the range of 400 to 1050° C.
9. A process according to claim 8 , wherein the silicon atom content of the reactants is in the range of 2.9 to 6 wt %.
10. A process according to claim 8 , comprising ageing the precipitate before calcining.
11. A process according to claim 8 , wherein the reactants include a calcium-containing reactant selected from the group consisting of: calcium hydroxide, calcium oxide, calcium carbonate, calcium chloride and calcium nitrate.
12. A process according to claim 8 , wherein the pH of the precipitation reaction is maintained in the range of 10 to 12.
13. A process according to claim 8 , wherein the calcining temperature is in the range of 700 to 1000° C.
14. A process according to claim 8 , wherein in step (b) the precipitate is calcined in an atmosphere containing water vapour.
15. A process according to claim 8 , wherein the silicon-containing reactant is added to the calcium-containing reactant, before addition of the phosphorus-containing reactant.
16. A process according to claim 8 , wherein the Ca/P molar ratio is in the range of 2.2 to 2.5.
17. A medical device containing a hydroxyapatite according to claim 1 .
18. A medical device according to claim 17 , which is selected from the group consisting of: a medical implant, a scaffold material, a bone replacement material, a bone implant, a dental implant, a bone substitute, a dental substitute, a soft tissue substitute, a drug delivery device, a cell delivery device, a cell growth substrate, a medicinal product, a component of an organic-inorganic composite implant, a component of an organic-inorganic composite scaffold, a component of an organic-inorganic composite bone substitute, a component of an organic-inorganic spinal cage implant, a component of an organic-inorganic composite fixation screw implant, a component of an organic-inorganic composite fixation plate implant, a component of an organic-inorganic composite fixation implant, a component of an organic-inorganic composite fixation device, a coating, a cement, a component of a cement, a filler or a filler supplement to another biomedical material.
19. A method for stimulating new bone formation, the method comprising implanting a medical implant material in a patient to release bone-stimulating ions to stimulate the formation of new bone, wherein the material is a crystalline inorganic silicate-substituted hydroxyapatite having a Ca/P molar ratio in the range of 2.05 to 2.55 and a Ca/(P+Si) molar ratio in the range of 1.60 to 1.65.
20. The method of claim 19 , wherein the silicon atom content is in the range of 2.9 to 6 wt %.
21. The method of claim 19 , wherein the hydroxyapatite is free of impurity phases.
22. The method of claim 19 , wherein the Ca/P molar ratio is in the range of 2.3 to 2.5.
23. The method of claim 19 , wherein the Ca/(P+Si) molar ratio is in the range of 1.60 to 1.64.
24. The method of claim 19 , wherein a maximum impurity level of carbonate ions is 0.1% as a molar ratio based on a total of silicate and phosphate ions.