Creating an antibacterial surface on beta TNZT alloys for hip implant applications by laser nitriding

Abstract

The National Joint Registry reported that the main causes for hip implant revision surgery include aseptic loosening, infection and adverse soft tissue reaction to particulate debris. There is a great need to improve the implant properties which can be achieved through a combined solution of beta titanium alloy (TNZT) with low elastic modulus and laser surface nitriding to improve mechanical properties and biological response. While titanium nitride (TiN) possesses good biocompatibility and remarkable antibacterial properties; its effectiveness as a coating on Ti-35Nb-7Zr-6Ta has not been investigated in relation to stem cell response and antibacterial capability. TNZT surfaces were laser-nitrided in incremental power, specifically 35, 40 and 45 W. Investigation included surface roughness and topography in microscale (WLI and SEM), microstructure (XRD) and wettability (water contact angle).Biological studies of the laser-nitrided surfaces included in vitro culture for 24 hours using mesenchymal stem cell (MSC) fluorescence staining and Staphylococcus aureus (S. aureus) Live/Dead staining. Sample groups consisted of control base metal (BM), laser-nitrided at 35 W (LT35), 40 W (LT40) and 45 W (LT45). Results revealed that laser nitriding generates significantly rougher surfaces (Ra value of BM was 199 nm, LT35 was 723 nm, LT40 was 458 nm and LT45 was 1180 nm) with distinctive surface features (Rsk < 0 and Rku > 3). Surfaces after laser nitriding, regardless of laser power, can be tailored to become hydrophilic (27 -34°).Fibre laser nitriding can be used to create antibacterial surface patterns on TNZT in a high power regime. A laser power of 45 W proved to be the most effective in this study, creating an overlapping crescent shape which becomes more obvious with increasing power. To summarise, laser-nitrided surfaces led to a significant antibacterial effect but offered no particular advantage to MSC response.

Titanium for Orthopedic Applications: An Overview of Surface Modification to Improve Biocompatibility and Prevent Bacterial Biofilm Formation

“…Ti6Al4V and Ti6Al7Nb are regarded as two of the most commonly used titanium α-β alloys in practice ( Elias et al., 2008 ). It is therefore understandable as to why a great deal of attention has recently been focused into the investigation of metastable-β Ti alloys with the intention of discovering novel approaches to improve in vivo performance of titanium-based medical devices ( Chan et al., 2016 ; Donaghy et al., 2020 ; Kopova et al., 2016 ; Yamako et al., 2017 ).…”

“…Although this review addresses approaches for surface modification, we have not ignored the bulk structure of the biomaterial and the mechanical requirements that are needed to ensure implant success. Recent innovations intending to mimic the elastic modulus of cortical bone in an effort to prevent bone resorption via the addition of β-stabilizers to titanium have proven to be successful ( Chan et al., 2016 ; Donaghy et al., 2019 , 2020 ). Other research has focused on improving the porosity of the implant structure, again with the intention of mimicking the intrinsic porosity of bone and has shown to improve bone-implant attachment ( Pałka and Pokrowiecki, 2018 ).…”

β-Ti Alloys for Orthopedic and Dental Applications: A Review of Progress on Improvement of Properties through Surface Modification

“…The untreated sample had the highest biofilm coverage of 29.8%, and the total biofilm coverage was significantly decreased and reached 2.9% (DC60). A laser nitriding treatment was performed on the Ti-35Nb-7Zr-6Ta surface [104]. Biological studies of the laser-nitrided surfaces included in vitro culture for 24 h using mesenchymal stem cell (MSC) fluorescence staining and Staphylococcus aureus (S. aureus) live/dead staining.…”

A single parameter approach to enhance the microstructural and mechanical properties of beta Ti-Nb alloy via open-air fiber laser nitriding

“…The newly developed technique was successfully applied to different Ti-based materials, e.g. commercially pure (CP) Ti [13,14], Ti6Al4V [13,14] and Ti-Nb-Zr-Ta (TNZT) alloys [15]. However, these open-air laser nitriding processes were conducted in the continuous wave (CW) mode, and cracks can occasionally appear in the nitrided surfaces.…”