Effects of solid loadings and silica addition on microstructure and compressive strength of hydroxyapatite specimens fabricated by freeze casting technique

Attributed to its bioactivity, osteoconductivity, and chemical compositions similarly to those of human bones, hydroxyapatite (HAp, Ca-10(PO4)(6)(OH)(2)) is a well-known material suitable for bone graft applications. To achieve physical and mechanical properties desired for the practical applications, microstructure of the HAp specimen needs to be controlled. This study therefore aimed at fabricating freeze-cast hydroxyapatite specimens with the porosity, pore sizes and compressive strength with acceptable values for the applications. Effects of solids loadings and silica addition on compressive strength were also examined in this study. Experimental results indicated that enhanced strength could be obtained in the specimens prepared from slips with higher solids loadings. The results also revealed that the HAp specimens achieved average porosity, pore sizes, and compressive strength in the ranges of 43.3-72.8%, 94.2-128.4 gm, and 1.29-29.35 MPa, respectively. The highest compressive strength was evident in the specimens prepared from silica-added slip with 35 vol% solids loading. The pH value of simulated body fluid solution was relatively stable upon sample submersion. Slight increase of specimen weight and formation of apatite layer were observed. The findings suggested that the specimens could be potential candidates for biomedical applications.