Mechanical properties of sintered hydroxyapatite and tricalcium phosphate ceramic

The ultimate values for compressive strength, Young's modulus, and toughnes s of cylindrical specimens of unitary aspect ratios and uniform grain-size distributions were extrapolated for hydroxyapatite (HAP) to 70 MPa, 9.2 GPa , and 0.36 J cm(-3), and for tricalcium phosphate (TCP), to 315 MPa, 21 GPa , and 2.34 J cm(-3). For total volume porosities of 50%, the corresponding values were determined: for HAP, 9.3 MPa, 1.2 GPa, 0.042 J cm(-3), for TCP, 13 MPa, 1.6 GP, 0.077 J cm(-3). Porosities of HAP specimens ranged from 3% -50%; TCP from 10%-70%. Two pore-size distributions were employed. Exponent ial dependencies of the mechanical properties were found upon porosity (p < 0.0001). No differences in measured mechanical properties, as determined i n compression, could be attributed to pore size. The superiority of TCP inc reases with density and suggests that a larger or more selective pore-size distribution could be effectively employed in TCP biological implants. This work also suggests the dominant role of secondary calcium phosphates in in creasing compressive strengths. (C) 1999 Kluwer Academic Publishers.