Effects of a supercritical CO process on the mechanical properties and microarchitecture of trabecular bone using compression testing and microcomputed tomography.

Surgeons frequently use allograft bone due to its osteoconductive, osteoinductive, and osteogenic properties. Preservation processes are employed to clean the allograft, improve its conservation, and ensure its sterilization. Many current processes use the properties of supercritical CO to remove bone marrow. This study aims to measure the effect of a supercritical CO process on the microarchitecture and the mechanical properties of trabecular bone. Eleven femoral heads were harvested from patients undergoing total hip arthroplasty. Sixty-seven cubic samples with 10 mm sides from these femoral heads were distributed in 3 groups: frozen at -20 °C, gamma irradiated and frozen at -20 °C, and treated with a supercritical CO process including gamma irradiation. All the samples were tested with a microcomputer tomography scanner and a compression testing machine. The supercritical CO process has no significant effect on the microarchitectural parameters (BV/TV, Tb.th, Tb.sp, Tb.N, DA, and Conn.D). It has also no significant effect on the elastic modulus, yield stress, and ultimate stress. However, it has a significant effect on the densification stress. An advanced study on the correlation between the microarchitecture and the mechanical properties shows that for a given volume fraction of 0.26 (the mean value for our study), the elastic modulus and ultimate stress of the bone treated with supercritical CO were lower than those from the frozen group by 19% and 24% respectively.