Synergistic effect of deep ball burnishing and HA coating on surface integrity, corrosion and immune response of biodegradable AZ31B Mg alloys

The fast degradation and consequent loss of mechanical integrity is a major problem of biodegradable Mg alloy, which limits its clinical viability. This paper presents the influence of a synergistic approach combining deep ball burnishing and hydroxyapatite (HA) coating on biomechanical integrity, degradation and immune response of Mg alloy (AZ31B). The burnishing resulted in smooth surface topography, increased hardness from 0.87 to 1.45 GPa and induced microstructural disturbances with deformation twins/twin bands, which enabled formation of a dense and compact platelet-like crystals HA coating of 110 μm thickness. Compared to the untreated and burnished specimens, the burnished + HA coated surface provided remarkably higher corrosion resistance as indicated by lower corrosion current density and smaller mass loss. HA coating and surface integrity enhancement by burnishing were predominantly responsible for improved corrosion resistance. HA coating on the burnished surface exhibited hydrophilic properties and adequate bonding strength. While the modified surfaces promoted cell growth, the burnished + HA surface outperformed in exhibiting less pro-inflammatory and high anti-inflammatory cytokines, demonstrating that the treated surfaces were not posing any threat to immune cells. The findings indicate that the synergistic surface treatment can be a viable means to enhance corrosion resistance and immune response of Mg alloys implants.