LIQUID-PHASE SINTERING OF HYDROXYAPATITE BY PHOSPHATE AND SILICATE GLASS ADDITIONS - STRUCTURE AND PROPERTIES OF THE COMPOSITES

Phosphate- and silicate-based glasses were added to hydroxyapatite in order to improve its mechanical properties and to fabricate composites with different degrees of bioactivity. A strong chemical bonding was obtained between hydroxyapatite and the phosphate-based glasses leading to samples approaching theoretical density, according to density measurements and scanning electron microscopy. Bioglass(R) additions led to the formation of a complex calcium phosphate silicate which hampered the reinforcement process. The fracture toughness of the hydroxyapatite-glass composites was shown to be with in the 1.1-1.2 MPa mPam(1/2) range, which is double that determined for sintered hydroxyapatite. A 2 mu m thick apatite layer was observed on the surface of the hydroxyapatite-glass composites after 48 h immersion in a simulated human blood plasma, whereas only a few apatite crystals were detected on sintered hydroxyapatite after 7 days immersion. From the results obtained we anticipate that the composites might show a higher rate of bone bonding, leading to enhanced bioactivity.