Open-porous magnesium-based scaffolds withstand <i>in vitro</i> corrosion under cyclic loading: A mechanistic study.

Abstract

The successful application of magnesium (Mg) alloys as biodegradable bone substitutes for critical-sized defects may be comprised by their high degradation rate resulting in a loss of mechanical integrity. This study investigates the degradation pattern of an open-porous fluoride-coated Mg-based scaffold immersed in circulating Hanks' Balanced Salt Solution (HBSS) with and without <i>in situ</i> cyclic compression (30 N/1 Hz). The changes in morphological and mechanical properties have been studied by combining <i>in situ</i> high-resolution X-ray computed tomography mechanics and digital volume correlation. Although <i>in situ</i> cyclic compression induced acceleration of the corrosion rate, probably due to local disruption of the coating layer where fatigue microcracks were formed, no critical failures in the overall scaffold were observed, indicating that the mechanical integrity of the Mg scaffolds was preserved. Structural changes, due to the accumulation of corrosion debris between the scaffold fibres, resulted in a significant increase (p < 0.05) in the material volume fraction from 0.52 ± 0.07 to 0.47 ± 0.03 after 14 days of corrosion. However, despite an increase in fibre material loss, the accumulated corrosion products appear to have led to an increase in Young's modulus after 14 days as well as lower third principal strain (εp3) accumulation (-91000 ± 6361 με and -60093 ± 2414 με after 2 and 14 days, respectively). Therefore, this innovative Mg scaffold design and composition provide a bone replacement, capable of sustaining mechanical loads <i>in situ</i> during the postoperative phase allowing new bone formation to be initially supported as the scaffold resorbs.