Effects of multiscale porosity and pore interconnectivity on in vitro and in vivo degradation and biocompatibility of Fe-Mn-Cu scaffold

Iron (Fe) based scaffolds are promising candidates as degradable metallic scaffolds. High strength and ability to control the degradation with tailormade composition and porosity are specific advantages of these scaffolds. In this research work, iron-manganese-copper (Fe-Mn-Cu) based scaffolds, with multiscale porosity, are developed through powder metallurgy route using naphthalene as spacer material. Porosity in the scaffolds ranged from 42-76%, where majority of the macro-pores (≥20µm) form interconnected channel network. XRD analysis confirms the presence of MRI compatible and antiferromagnetic austenite as major phase in all the scaffolds. Developed scaffolds in this study have minimum ultimate compressive strength of 7.21 MPa (for 30 Naph), which lies within the range of human cancellous bone UCS (2–12 MPa). Degradation rates of the scaffolds are determined from static immersion test, where scaffold with highest porosity (76%) shows highest degradation rate of 2.71 mmpy when immersed in Hank’s balanced salt solution (HBSS) at 37°C for 30 days. Increased degradation rate of the scaffolds has no cytotoxic effects on MG63 cells as studied by alamar blue assay and live/dead imaging. When implanted in rabbit femur, scaffold with higher porosity showed enhanced osteogenesis, as evident through micro-CT and histological analysis. It is hypothesized that presence of multiscale porosity with high degree of interconnectivity facilitated the better bone regeneration within and around the Fe-Mn-Cu scaffolds.