Biomaterials, Testing and Structural Properties of

Abstract

AbstractPrevious studies have shown that the porous hydroxyapatite (HA) is bioactive and can be and used as a bone substitute in hard tissue prosthetics. However, the weak mechanical properties of HA are the primary obstacles to its applications. One approach to have a bone substitute with both required mechanical strength and bioactivity would be improve the bioactivity of some strong substrates. To this end, two major deposition methods, suspension method, and thermal deposition method, were employed in this work in which HA was uniformly coated onto the surfaces of highly porous and strong substrate of alumina. In suspension method, finely ground HA powders were mixed in an organic solvent and a binder to form suspension for coatings. In the thermal decomposition method, calcium 2‐ethyl hexanoate and bis(2‐ethyhexyl) phosphite were used as starting materials. Both techniques have proved to be effective in forming an adherent coating of HA onto a porous alumina substrate. The adherent strength of the HA coating is satisfactory for bone replacements. The thermal decomposition method, in comparison to the HA–glass suspension technique, eliminates all glasses (as sintering aids) that are not bioactive. Mechanical properties, interfacial adhesion behaviors, structural properties, and bioactive behaviors are studied using mechanical testing, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential thermal analysis (DTA). The coated HA layer bonds strongly to the substrate through interface diffusion, and the layer is microstructurally and chemically uniform on the surfaces of the interconnected pores in the matrix of the substrate. The mechanical property testing results demonstrate that porous substrates with HA coating are much stronger than porous substrate made of pure HA. The compressive strength of the HA composite reaches 10 MPa, a value 10 times higher than that of porous HA. Thein vitrobioactivity of HA coating on promoting the calcium phosphate deposition was affected by both structural crystallinity and specific surface area. High temperature sintering inevitably changes the crystallinity of the coated HA, and in turn affects its bioactivity. Well‐crystallized HA that is heat treated at high temperatures has resulted in a reduced bioactivity. The bio reaction rate was found to increase with the surface area of HA. The stability of the well crystallized HA is associated with the high driving force required for the formation of hydroxy‐carbonate apatite (HCA) phase. These results indicate a high potential for structural bone substitutes in the hard tissue prosthetics.