Laser Improved NiTi Surface for Biomedical Applications

Abstract

The surface structure of medical implants and their chemical state are extremely important for their lifetime and reliability. There are problems with the degradation of NiTi implants due to structural fatigue, localized tribo-corrosion, and inconsistent hemocompatibility. These issues potentially can be solved by surface texturing by controlled short laser pulse treatments with a multibeam approach explored in this study. One of the unique surface textures in nanoscale is represented by introducing laser induced periodic surface structures (LIPSS) into the implant surface. The LIPSS formation involves the excitation of surface plasmon polaritons and material surface reorganization. Ripples with periodicity less than 1 ?m along with the catalytic activity of oxide surface with "rutile nanohairs" can significantly reduce bacterial film adhesion while promoting surface endothelialization and hemocompatibility. The morphological texturing of the surface allows for tuning the wetting properties from extreme hydrophobicity to hydrophilicity. Reduction of friction and wear of material surfaces can be achieved by introducing textures that reduce the contact friction area. The geometry of the LIPSS and dimples maintains an adhesive film of liquid among moving parts. Short laser "beam-shaped" pulses were applied in this work to NiTi surfaces. The results indicate that LIPSS processing of NiTi surface with controlled height profiles and periodicity gives rise to chemisorbed hydrocarbon molecules on rutile oxide layer, which leads to super-hydrophobicity and a beneficial antibacterial effect. Ultrashort laser pulse micromachining does not affect the microstructure and martensitic phase transformation. The corrosion resistance of LIPSS textured NiTi surface is not degraded, and the process reduces friction area and maintains an adhesive film of liquid between the moving parts.