Chitosan/PVA hydrogel films crosslinked by the freeze–thaw method and containing honey and allantoin were prepared for application as wound dressing materials. The effects of the freeze–thaw process and the addition of honey and allantoin on the swelling, the gel content and the mechanical properties of the samples were evaluated. The physicochemical properties of the samples, with and without the freeze–thaw process, were compared using FTIR, DSC and XRD. The results showed that the freeze–thaw process can increase the crystallinity and thermal stability of chitosan/PVA films. The freeze–thaw process increased the gel content but did not have a significant effect on the tensile strength. The presence of honey reduced the swelling and the tensile strength of the hydrogels due to hydrogen bonding interactions with PVA and chitosan chains. Long-term cell culture experiments using normal human dermal fibroblast (NHDF) cells showed that the hydrogels maintained their biocompatibility, and the cells showed extended morphology on the surface of the hydrogels for more than 30 days. The presence of honey significantly increased the biocompatibility of the hydrogels. The release of allantoin from the hydrogel was studied and, according to the Korsmeyer–Peppas and Weibull models, the mechanism was mainly diffusional. The results for the antimicrobial activity against E. coli and S. aureus bacteria showed that the allantoin-containing samples had a more remarkable antibacterial activity against S. aureus. According to the wound healing experiments, 98% of the wound area treated by the chitosan/PVA/honey hydrogel was closed, compared to 89% for the control. The results of this study suggest that the freeze–thaw process is a non-toxic crosslinking method for the preparation of chitosan/PVA hydrogels with long term biocompatibility that can be applied for wound healing and skin tissue engineering.

A green approach to the preparation of reduced graphene oxide (RGO) films has been developed using L-ascorbic acid/water vapor as the reducing agent. Except for the use of gaseous hydrazine hydrate or hydroiodic acid, this is the first reported use of an environmentally friendly gaseous phase for the reduction of graphene oxide (GO) films into RGO films. The as-prepared RGO films were flexible and showed a high electrical conductivity of up to 3500 S m⁻¹. The L-ascorbic acid/water vapor was able to penetrate into the GO films and reduce the Ag ions. The as-reduced RGO–Ag composite films could be used as effective surface-enhanced Raman scattering active substrates and the Raman signals could be adjusted by changing the amount of Ag ions. The RGO–Ag composites also showed antibacterial activity against Escherichia coli, Staphylococcus aureus and white rot fungi. This is a straightforward and green approach to fabricating RGO–Ag composites for use in biological applications and materials science.