Enhancing silk fibroin structures and applications through angle-dependent Ar+ plasma treatment

This study tackles limitations of Silk Fibroin (SF), including availability of sites for modification. This is achieved by Direct Plasma Nanosynthesis (DPNS), an Ar+ bombardment method, to generate and modify nanostructures and nanoscale properties on the SF surface. SF samples were treated with DPNS at incidence angles of 45o and 60o, with specific ion dose and energy parameters (1 × 1018 ions/cm2 and 500 eV, respectively) maintained throughout the process. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) primarily underscored transformations in SF's nitrogenous components. Specifically, treatment produced a boost in C-NH2, particularly pronounced in the 45o-treated samples, suggesting changes were more superficial than alterations to the secondary structure. The DPNS treatment gave rise to periodic nanocone structures on the SF surface, with a scale increase correlated to a higher angle of incidence. This resulted in a decrease in surface stiffness and significant changes in the motility of J774 macrophages interacting with the transformed SF. Furthermore, the SF samples treated at a 60o incidence showcased a confinement effect, moderating the macrophages' motility, morphology, and inflammatory response. The DPNS-induced alterations not only mitigate SF's limitations but also affect cellular behavior, expanding potential for SF in biomaterials.