Study of the Enhanced Antimicrobial Effect of Cu/Chitosan Composite Materials on Escherichia coli

Here, we report the development and comprehensive characterization of copper-chitosan (Cu/CS) antimicrobial films, investigated using a combination of spectroscopic techniques and atomic force microscopy (AFM), to elucidate their chemical composition, Cu²⁺ ionic release behavior, and physicochemical properties. Particular emphasis was placed on correlating the chemical and surface properties of the films with their antimicrobial performance, to relate the effects of Cu²⁺ release and physicochemical properties of the films to the antimicrobial action. AFM was employed to analyze the morphology, surface roughness, and integrity of Escherichia coli bacterial cells incubated on Cu/CS films for short (2 h) and prolonged (20 h) exposure times. Time-dependent morphological changes were observed in bacteria in contact with the Cu/CS surfaces, indicating pronounced cellular stress and progressive loss of viability over exposure time. These changes included a transition from the typical rod-like morphology of healthy E. coli to coccoid-shaped cells, the formation of membrane bleb-like protrusions, increased cell clustering, and severe membrane disruption ending in cell lysis. The observed variations in bacterial morphology and surface characteristics provided a direct proof of damage to the bacterial envelope and reduced cellular viability. These findings strongly suggest a combined antimicrobial effect arising from the simultaneous action of Cu²⁺ ion release (220 ppb in 24 h) and the intrinsic bioactivity of the CS matrix. The results highlight the potential of Cu/CS films as effective antimicrobial materials and support their further development for applications in antimicrobial coatings, packaging, and biomedical surfaces.