Improving the cytocompatibility and infection, wear and corrosion resistances of commercially pure titanium by laser micropatterning and ceramic conversion treatment

Commercially pure titanium (cp-Ti) is a popular material choice for biomedical implants due to its good cytocompatibility, high corrosion resistance and mechanical properties. Nevertheless, titanium surfaces are susceptible to infection and wear which has led to implant failure and removal. Ceramic conversion treatment (CCT) has displayed improved wear resistances and surface hardness’s of titanium whereas, laser induced periodic surface structures (LIPSS) have displayed good antibacterial capabilities. Nonetheless, LIPSS have poor durability. There is limited research in combining these surface engineering techniques to create a duplex treated surface on titanium. It is hoped that by combining LIPSS with CCT, the durability of the LIPSS will improve whilst also maintaining the antibacterial, cytocompatible and wear resistances. Hence, the aim of this study was to investigate the antibacterial efficacy, cytocompatibility, wear resistance and corrosion resistance of a duplex surface treatment that involved CCT and LIPSS undertaken on commercially pure titanium (grade II). In this study femtosecond pulsed laser micro-patterning was applied to polished cp-Ti and CCT treated cp-Ti to form LIPSS with a depth of about 1 μm and a spacing of approximately 300 nm. CCT was undertaken at 600˚C for 85 hours to produce an approximately 2 μm thick rutile-based TiO\(_2\) layer that had good bonding to the substrate and was supported by the formation of oxygen diffusion zones. The LIPSS and CCT were tested for their antibacterial efficacy against S. aureus and E. coli and also, the cytocompatibility of these surface treatments was measured using osteoblast like SaOS-2 cells. The wear resistance was also assessed in dry (air) and lubricated (Ringer’s solution) conditions. Using Ringer’s solution, the corrosion resistance was measured of the surface treatments. The LIPSS had the greatest effect on the antibacterial resistance due to the small size and the limited contact area for the bacteria to attach to. The highest percentage reduction for both bacteria was seen for the duplex treated sample (oxide first then pattern) which indicated that when combining the two surface treatments, the antibacterial properties are the most optimum. The TiO\(_2\) led to high SaOS-2 cell viabilities whereas LIPSS reduced the SaOS-2 cell number. However, when LIPSS was combined with CCT the SaOS-2 cell numbers increased which suggested when the surface treatments are combined they are cytocompatible, non-toxic and also antibacterial. Untreated cp-Ti underwent severe adhesive and abrasive wear in both air and Ringer’s solution. The wear resistance of untreated and laser micro-patterned cp-Ti was improved by CCT however, LIPSS treated cp-Ti revealed very poor wear resistances causing the LIPSS to be fully destroyed. This demonstrates that the durability of the LIPSS formed on cp-Ti is very low. The durability of LIPSS on cp-Ti was however, effectively improved by the novel duplex treatment combining LIPSS with pre-CCT under both dry and lubricated conditions. Nearly all of the surface treated samples had lower corrosion rates and higher corrosion potentials when compared with untreated cp-Ti. The novel duplex surface system developed from the research by combining CCT treatment with laser micro-patterning provided the best antibacterial results, good cytocompatibility, high corrosion and wear resistances and thus, long durability. This study has demonstrated that when combined, CCT and LIPSS have the potential to be applied in medical implants in order to improve the infection and wear resistance whilst also maintaining the good corrosion resistance of cp-Ti and causing no toxicity issues