Reinforcing of a Calcium Phosphate Cement with Hydroxyapatite Crystals of Various Morphologies

Abstract

A series of biocomposite materials was successfully prepared by reinforcing advanced calcium phosphate cement with hydroxyapatite fibrous and elongated plate-like particles. Powder X-ray diffraction showed that ball-milled biocomposite precursors (dicalcium and tetracalcium phosphates) entirely transform to a single phase hydroxyapatite end product within 7 h at 37 °C. Electron microscopy showed that the resultant biocomposites are constituted of nanoscaled cement particles intimately associated with the reinforcement crystals. The influence of shape, size, and concentration of the hydroxyapatite filler on the compression strength of reinforced cements is discussed. The best compression strength of 37 ± 3 MPa (enhancement of ∼50% compared to pure cement) was achieved using submicrometer-sized hydroxyapatite crystals with complementary shapes. Nanoindentation revealed that averaged elastic modulus and hardness values of the cements are consistent with those reported for trabecular and cortical human bones, indicating a good match of the micromechanical properties for their potential use for bone repair. The stiffness of the biocomposites was confirmed to gradate-compliant cement matrix, cement-filler interface, and stiff filler-as a result of the structuring at the nanometer-micrometer level. This architecture is critical in conditioning the final mechanical properties of the functional composite biomaterial. In vitro cell culture experiments showed that the developed biomaterial system is noncytotoxic.