Improvement of microstructural and physical properties of porous xydroxyapatite by adding silica and glass for use as a bone replacement material

Abstract

The aim of this study was to improve strength of porous hydroxyapatite (HA) for use as a bone replacement material. Microstructural and physical properties were also studied and evaluated. Methods of processing the HA ceramic to high density yet retaining the large open pores required for biocompatibility were investigated. Uniaxial pressing, to fabricate standard pellets and the polymer foam technique, were employed to produce the desired structures. Fabrication of porous HA with and without additives using these methods was also undertaken for comparison. Silica (SiO2) and commercially available glass frit were used as additives. The silica powder and glass frit were added to the HA powder in the range of 0.5 to 20 wt% to fabricate the final ceramic structures. Sintering was done at 1150oC and 1300oC for 4 h. XRD and SEM analysis were used to characterize the sintered HA samples. FT-IR analysis was used for chemical functional analysis. Compressive strength and hardness measured the mechanical properties. The sintered HA samples were immersed in simulated body fluid (SBF) for various periods of time to determine bioactivity. For uniaxially pressed HA, the transformation of HA to TCP occurred at the higher sintering temperature and the amount of additive was related to mechanical strength and bioactivity. For HA doped with the silica or glass frit, < 5.0wt%, faster precipitation of new layers of Ca-P was noted. HA fabricated from the polymeric foam method, after sintering at 1300oC, had a pore size in the range 100-420 m with interconnected pores suitable for bone ingrowth. HA with glass from 0.5 to 20.0wt% had a slightly decreased porosity from 85 to 78%, and the compressive strength varied between 0.67 to 11 MPa. This study indicates that porous HA with glass additive can be used as a bone replacement material in medical applications due to its combination of attractive properties.