Novel design of a coral-like open-cell porous degradable magnesium implant for orthopaedic application

The aim of this study was to use degradation prediction and in-vivo evaluation to inspire a novel design of magnesium (Mg) implant having a coral-like open-cell porous interior and an outer solid casing. In this design, the porous interior acts as a bone-mimic channel for tissue infiltration and cell adhesion, while the solid casing enables better structural strength and integrity. Different porosities of porous interiors, combined with different wall thicknesses of outer casing, were designed. By implementing a continuum damage mechanics (CDM)-based biodegradation model into finite element simulations, the mechanical properties and degradation rates of the implant were predicted. The results showed that the implant with 70%–75% porosity and 0.5 mm wall thickness had the optimal structural strength and degradation rate. This implant structure was then fabricated. Compression tests and X-ray computed tomography (CT) scanning were carried out to investigate the material properties and the structural transformation of the implants respectively. Moreover, an in-vivo rabbit model was used to evaluate the degradation behaviours of the implant at different time points. The results showed that this novel Mg implant had a relatively sturdy material strength and the porous structure did benefit the ingrowth of bone tissue and expedite the healing process. Keywords: Open-cell porous Mg alloys, Continuum damage mechanics, Biodegradation model, Finite element simulation, X-ray computed tomography, In-vivo rabbit model