The supercritical CO2 process does not affect the mechanical properties and the microarchitecture of trabecular bone at the microscopic scale: A microindentation and microcomputed tomography study

Abstract

Bone allografts are frequently used in many surgical procedures because of their osteoconductive and osteoinductive properties. After being extracted from the donor, the graft is treated with a process that cleans and sterilizes it before being implanted in the patient. While they guarantee the safety of the patient receiving the graft, preservation processes often affect bone properties. This study aims to measure the effect of a supercritical CO₂ process on the microarchitecture and the mechanical properties of trabecular bone at a microscopic scale using microindentation. 7 femoral heads were harvested from patients who had undergone a total hip arthroplasty. 42 cubic samples of 10 mm side from these femoral heads were randomly distributed in 3 groups: frozen at -20 °C, gamma irradiated and frozen at -20 °C, and treated with a supercritical CO₂ process including gamma irradiation. All samples were imaged by microtomography and characterized by microindentation to correlate the bone microarchitecture with the mechanical properties at a microscopic scale. Our results show that the supercritical CO₂ process exerts no significant effect on the microarchitecture parameters, indentation elastic modulus, and indentation hardness. The correlations between the microarchitecture and the mechanical properties revealed that gamma irradiation appears to induce a slight alteration in mechanical properties. However, the process combining a supercritical CO₂ treatment and gamma irradiation does not induce any more alterations to the material than gamma irradiation itself. Thus, the supercritical CO₂ process has no more impact than gamma irradiation on the mechanical properties of trabecular bone at the microscopic scale.

Keywords: Bone allograft; Irradiation; Microarchitecture; Microindentation; Supercritical CO2; Trabecular bone.

Graphical abstract

Fig. 1

(a) Microindentation tester with a zoom on the sample holder. (b) Bone section taken with the microindentation tester, on which the indents are marked with diamonds. (c) Polished surface of trabecular bone taken with the microindentation tester. (d) Microindentation loading profile.

Fig. 2

Steps of analyzing the thickness of a bone trabecula.

Fig. 3

Bar graph of measured parameter averages by treatment.

Fig. 4

(A) Correlation curves between the indentation elastic modulus and the bone volume fraction. (B) Correlation curves between the microhardness and the bone volume fraction.

Fig. 5

Correlation curves between the indentation elastic modulus and the indentation hardness.

Fig. 6

Effect of trabecular thickness of the indented trabeculae on mechanical properties for rod-like and plate-like trabeculae by preservation process with linear regression.