Kinetic models of swelling and thermal stability of silver/poly(vinyl alcohol)/chitosan/graphene hydrogels

Silver nanoparticles (AgNPs) were synthesized by in situ electrochemical reduction of Ag⁺ ions in poly(vinyl alcohol)/chitosan/graphene (PVA/CHI/Gr) hydrogel matrices with different concentrations of chitosan. The physicochemical properties of nanocomposite hydrogels were investigated by UV–vis spectroscopy (UV–vis), dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM) and Fourier-transform infrared spectroscopy (FT-IR), thermal characteristics were determined by differential scanning calorimetry (DSC) and mechanical properties were measured by tensile test. The swelling studies were carried out in phosphate buffer to simulate natural physiological environment and data were fitted by several kinetic models to determine the diffusion mechanism and diffusion coefficients of the swelling medium through the hydrogel matrices. It was shown that the presence of silver nanoparticles increased the uptake capability and equilibrium swelling degree of the composite hydrogels. The antibacterial activity was confirmed against Escherichia coli and Staphylococcus aureus, while the hydrogels without AgNPs exhibited antibacterial properties due to the presence of chitosan. With the addition of AgNPs, the samples showed stronger activity and fast reduction in the number of colonies, confirming the synergistic effect of chitosan and AgNPs on the antibacterial activity.