Maximizing the strength of calcium sulfate for structural bone grafts

Calcium sulfate (CS) combines remarkable properties of biodegradability, biocompatibility, and osteoconductivity but its low strength limits the range of its applications in orthopaedic surgery. In this study we have addressed this limitation by optimizing the fabrication process for pure CS, and by using mechanical testing procedures which are relevant for load carrying, or structural bone grafts (flexural tests in hydrated condition). By optimizing the processing parameters (pressure during setting, CS powder to water ratio, saturated solution) we produced CS samples with the highest flexural strength ever reported in hydrated conditions. Once these optimal conditions are used, the addition of "reinforcing" inclusions in the material decreased its strength because these inclusions actually act as defects instead of reinforcements. In addition, the CS can be formed in precise shapes while maintaining optimal processing conditions and provided a strength similar to that of bone with the same dimensions. Dense and porous materials can be combined to duplicate the trabecular and cortical architecture of long bones, with only a small loss of overall strength.