Altering the surface morphology and wettability of chitosan/graphene coatings by femtosecond and nanosecond laser processing

A major drawback of the currently used orthopedic implants is the formation of a bacterial biofilm on their surface after implantation. A potential strategy for overcoming this problem is developing micro- and nano-structured motifs on the implant's surface to prevent bacterial attachment. Additionally, the use of materials with inherent antimicrobial properties could further stall the aggregation of bacteria. This paper demonstrates an approach to obtaining a modified surface topography on chitosan-graphene 2D films via femtosecond and nanosecond laser treatment. Atomic force microscopy (AFM) revealed that laser irradiation leads to a strong surface roughness increase due to formation of non-ordered topography features with peak-to-valley distance ranging between 200 nm and 1 μm. Interestingly, sharp single protrusions (â1/4200 nm) were observed on the untreated samples. Transmission electron microscopy analysis confirmed the presence of graphene monolayers within the composite films. Wettability tests showed that nanosecond laser ablation of the samples resulted in super hydrophilic surface properties, which repel bacteria per se. Based on our findings, we hypothesized that the topography motifs of both laser treated and untreated samples could potentially impede bacterial attachment via different mechanisms - reduction of contact points for adhesion or restriction of motility.