Nanosecond laser surface texturing of type 316L stainless steel for contact guidance of bone cells and superior corrosion resistance

Abstract

Osseointegration and corrosion resistance of artificial implants are two major factors that decide their acceptance or rejection by human bodies. This paper provides a robust method for improving the biological performance and corrosion resistance of type 316 L stainless steel (SS) through laser surface texturing (LST). Usage of the second harmonic of a nanosecond Nd:YAG laser, line focusing and optimized range of laser fluence enabled processing of a larger surface area making the method compatible for practical applications as artificial implants. Four different micro-groove patterns were generated on type 316 L SS sample at various laser powers such as 10 mW, 50 mW, 100 mW and 200 mW. Investigation pertaining to adhesion, orientation, and spreading of U2OS osteosarcoma bone cells on sample surface was carried out. Qualitative and quantitative analysis employing confocal and Field Emission-Scanning Electron Microscope imaging, revealed better alignment, larger density and contact guidance of the cells on LST samples. Corrosion studies were done by potentiodynamic polarization and electrochemical impedance spectroscopy coupled with Mott-Schottky (M-S) analysis in simulated body fluid at 37o C. Detailed electrochemical analysis showed significant improvement in corrosion resistance and reduced pitting corrosion for the sample laser treated at 200 mW. The superior anticorrosive behaviour of the sample was due to formation of a dense oxide layer of Fe, Cr and Ni with lower defect density on its surface. Present studies clearly indicated the advantages of nanosecond laser surface texturing to improve the biocompatibility of type 316 L SS in terms of contact guidance of cells with higher viability and superior corrosion resistance.