Surface modification of 316L stainless steel by laser-treated HA-PLA nanocomposite films toward enhanced biocompatibility and corrosion-resistance in vitro

Abstract

316L stainless steel substrate was coated by sol-gel derived nano-hydroxyapatite–polylactic acid (nHA-PLA) thin films. To improve the surface properties, nHA-PLA composite films were treated by continuous CO2 laser. The microstructure and microhardness of untreated and laser-treated thin films were studied by scanning electron microscopy (SEM), X-ray diffractometry (XRD), and surface hardness measurements. In vitro electrochemical and biological properties of the composite films were also investigated using potentiodynamic polarization test and MTT cytotoxicity assay. Cross-sectional SEM micrographs revealed a well-deposited, uniform thin film with good attachment to the substrate. The average surface hardness of the laser-treated composite films was found to be 159 HV compared to 102 HV recorded for the as-received stainless steel substrate. Electrochemical corrosion test in the simulated body fluid (SBF) showed the improved corrosion resistance of the nHA-PLA composite films, which was further improved upon laser treatment. This was attributed to the reduced transport of electrons and ions between the 316L substrate and SBF rovided by laser treated HA barrier coating, which caused the decrease of electrochemical reaction and subsequently corrosion rate. The cytotoxicity assay confirmed the normal growth and viability of human fibroblast cells (HFFF2) seeded on the surface-modified 316L substrates demonstrating their promising biotolerability for practical biomedical applications. Laser treatment found to positively affect the viability and adhesion of the cells through modification of the (i) surface roughness and (ii) crystallographic texture or grain orientation.