Hydroxyapatite calcium phosphates, their method of preparation and their applications
The present invention is directed to calcium phosphates in granular form having an X-ray diffraction pattern characteristic of hydroxyapatite in which a portion of the anions of the crystal lattice are substituted with carbonate anions and which have good compressibility and flow properties in direct compression applications. The invention is also directed to the methods for preparing the calcium phosphate aforesaid granules characterized in that the methods include the processing of a brushite dicalcium phosphate solution having a specified particle size distribution using a solution of an alkaline earth carbonate for a sufficient period of time to allow the transformation of the brushite calcium phosphate into hydroxyapatite calcium phosphate.
1. A composition comprising calcium phosphate in granular form having an X-ray diffraction pattern characteristic of hydroxyapatite in which a portion but not more than 10% of the phosphate anions of the crystal lattice are substituted with carbonate anions, and wherein the size of the calcium phosphate granules expressed by the median diameter (d 50 ) is between 100 μm and 250 μm.
2. The composition of claim 1 , wherein the apparent non-compacted density of the granules is at least 0.6.
3. The composition of claim 1 , wherein the apparent non-compacted density of the granules is between about 0.68 and about 0.72.
4. The composition of claim 1 , wherein the apparent compacted density of the granules is at least 0.7.
5. The composition of claim 1 , wherein the apparent compacted density of the granules is between about 0.76 and about 0.82.
6. The composition of claim 1 , wherein the granules have an instantaneous flow index greater than about 7.
7. The composition of claim 1 , wherein the granules have the following compressibility profile:
from 15 to 40 KPa for compression of 30 KN,
from 7 to 25 KPa for compression of 20 KN,
from 3 to 10 KPa for compression of 10 KN.
8. The composition of claim 1 , wherein the granules have a disintegration speed in water of less than 60 seconds.
9. The composition of claim 1 , characterized in that it satisfies the following formula:
Ca 10 (PO 4 ) 6 (OH) 2-2x (CO 3 ) x
in which x is between 0 and 1.
10. The composition of claim 1 , characterized in that it satisfies the following formula:
Ca 6 M 4 (PO 4 ) 6 (OH) 2-2x (CO 3 ) x
in which M represents an alkaline earth cation other than calcium and x is between 0 and 1.
11. The composition of claim 10 , wherein M is magnesium.
12. The composition of claim 1 , wherein between about 3% and about 6% of the phosphate anions of the crystal lattice are substituted with carbonate anions.