Differential in vitro degradation and protein adhesion behaviour of spark plasma sintering fabricated magnesium-based temporary orthopaedic implant in serum and simulated body fluid

The interaction of proteins with implantable metallic surfaces has a great influence on the bioactivity and biodegradation of orthopaedic implants. Initial osseointegration is known to be critical for the long term success of orthopaedic implants. The surface properties of the implant and electrochemical milieu of the surrounding solution such as electrostatic, hydrophobic, and hydrogen bonding interactions significantly modulate protein adsorption by implants. Magnesium (Mg) is considered to improve the adhesion of osteoblasts via ligand binding of the integrin receptors. Mg-based composites, reinforced with hydroxyapatite (HA), are potential candidates for temporary orthopaedic implants. However, their clinical translation requires enhanced degradation resistance in physiological environment so that it is in sync with the healing rate of the bone. The present study deals with the protein adsorption characteristics and degradation behaviour of Mg-HA-based biodegradable implants. Quantitative analysis of apatite inducing ability of composites was evaluated in terms of mass gain in simulated body fluid (SBF) as well as in foetal bovine serum (FBS), by an in vitro immersion study. Incorporation of 5 and 15 wt% HA to Mg-3Zn improved apatite formation up to 35% and 66%, respectively, after 14 days of immersion in SBF. Compared to FBS, SBF is found to be significantly more effective in precipitating apatite on a Mg-HA surface. However, FBS offered more corrosion resistance to Mg-HA than SBF did, as evident from the significant differences in the protein adhesion capabilities of the composite surface when incubated separately in these two mediums. The addition of 15 wt% HA enhanced the protein adsorption capability by ∼35%. These studies highlight the possibility of modulating the degradation and bioactivity of Mg-based composite by tailoring the composition of HA. These findings, in turn, warrant the suitability of Mg-HA composite in orthopaedic application.