Mechanical properties of carbonated apatite bone mineral substitute: strength, fracture and fatigue behaviour.

The synthesis and properties of carbonated apatite materials have received considerable attention due to their importance for medical and dental applications. Such apatites closely resemble the mineral phase of bone, exhibiting superior osteoconductive and osteogenic properties. When formed at physiological temperature they present significant potential for bone repair and fracture fixation. The present study investigates the mechanical properties of a carbonated apatite cancellous bone cement. Flexural strength was measured in three and four point bending, and the fracture toughness and fatigue crack-growth behaviour was measured using chevron and disc-shaped compact tension specimens. The average flexural strength was found to be approximately 0.468 MPa, and the fracture toughness was approximately 0.14 MPa radical m. Fatigue crack-growth rates exhibited a power law dependence on the applied stress intensity range with a crack growth exponent m=17. The fatigue threshold value was found to be approximately 0.085 MPa radical m. The mechanical properties exhibited by the carbonated apatite were found to be similar to those of other brittle cellular foams. Toughness values and fatigue crack-growth thresholds were compared to other brittle foams, bone and ceramic materials. Implications for structural integrity and longer term reliability are discussed.