Optimizing the antimicrobial performance of metallic glass composites through surface texturing

In the present work, we analyse the influence of laser texturing on the physicochemical and bactericidal properties of Cu55Zr40Al5 Bulk Metallic Glass Composite (BMGC) to develop novel antimicrobial touch surfaces. Laser ablation was employed to increase the average roughness of BMGC samples from 0.08 ± 0.02 μm to 3.07 ± 0.96 μm using a maximum laser fluence of 2.82 J/cm2. This treatment also influenced surface chemistry causing the formation of CuO, CuO2, ZrO2, more prominent as the laser fluence was increased. Alongside chemical and topographic changes, the initial contact angle of the as-cast sample was found to increase from 85.81° to angles between 105.72° and 126.17° after texturing. The influence of these modifications on the antimicrobial performance of all rapidly solidified alloys was studied with Escherichia coli K12 modified to drive lux expression. Luminescence measurements revealed a reduction in bacterial growth as the laser fluence applied was risen. This increase in bactericidal effect as laser fluence rose was corroborated with recovery tests, which showed an increase in log reduction of E. coli K12 from 1.10 (for as-cast sample) to 2.16 (textured at 2.82 J/cm2) after 4 h of contact. Variations in bacterial morphology were observed with SEM imaging, specifically, a length increase of E. coli cells from 2 μm up to 20 μm could be observed in cells deposited on the textured surfaces. Deposited bacteria on laser treated samples revealed loss of membrane integrity, which along the aforementioned morphological changes suggest both external and DNA damage in all ablated samples. These findings reveal the possibility of tailoring the antimicrobial behaviour of BMGCs through laser texturing, which could be used as novel touch surfaces to tackle nosocomial infections along antibiotic resistance.