Poly(vinyl alcohol)-gelatin crosslinked by silane-functionalized guanidyl-hydroxyurethane oligomer as contact-killing non-leaching antibacterial wound dressings.

The present work aims to prepare efficient wound dressing with noncytotoxicity, proper mechanical strength, and the ability to preserve a hygienic environment over wounded skin tissue. To fulfill this goal, the synthesis of a novel silane crosslinking agent with antibacterial guanidinium chloride functional group is considered. The resulting reagent was applied to make a series of film-type stable crosslinked networks composed of poly(vinyl alcohol) and gelatin. The potential protection of wounds from external forces was confirmed, as these films had a very good tensile strength (16-31 MPa) and good elongation (54%-101%) under dry conditions. The good dimensional strength of dressings was preserved after hydration with simulated wound exudates. Based on the calculated fluid handling capacity of the prepared dressings (2.43-3.54 g 10-1cm-2d-1), they were suitable for treating wounds with 'light' to 'moderate' exudate volume. All the prepared dressings showed very good biocompatibility, as determined by the high viability of fibroblast cells directly contacted with dressing (over 80%) or leachates extracted from them (over 90%). In addition, dressings functionalized with guanidinium groups could effectively kill representative gram-positive and gram-negative bacterial strains.

pH-dependent swelling and antibiotic release from citric acid crosslinked poly(vinyl alcohol) (PVA)/nano silver hydrogels.

In this work, a pH-sensitive and antibacterial drug delivery system based on poly(vinyl alcohol) (PVA)/citric acid (CA)/Ag nanoparticles (NPs) was designed using a completely green, facile and one-step route. Interestingly, the crosslinking of PVA with CA, and in-situ formation of Ag NPs within the polymeric matrix were simultaneously and simply carried out using an annealing process without need for any toxic chemicals. The developed hydrogels were characterized by FTIR, UV-vis spectra, SEM and TEM techniques. It was found that CA not only acted as a crosslinker of PVA via esterification reaction, but also it endowed pH-responsiveness and antibacterial activity to the PVA matrix due to presence of free carboxylic acid groups on CA. Hydrogels demonstrated a pH-dependent swelling as well as drug release behavior, as the swelling ratio and the drug release at pH 7.4 were found higher than pH 1.2. Furthermore, the release of ciprofloxacin was more sustained when Ag NPs were incorporated into hydrogels. In addition, the incorporation of CA, Ag NPs and ciprofloxacin into the PVA matrix provided an effective antibacterial activity against E. coli and S. aureus microorganisms. The developed hydrogels can be considered as a promising material in the prolonged antibiotic therapy such as intestinal infection treatment.

Self-healing and tough hydrogels with physically cross-linked triple networks based on Agar/PVA/Graphene.

The aim of this work was to prepare polyvinyl alcohol (PVA)/Agar/Graphene nanocomposite hydrogels through a one-pot and green solution mixing method using water as solvent. Herein a novel strategy for designing stiff, tough and self-healing triple network (TN) hydrogels was proposed. The prepared TN hydrogels composed of strong Agar polysaccharide as the first network, tough PVA biopolymer gel as the second network, and graphene nanoplatelets as the third network. Interestingly, similar to natural biomaterials, all of the networks of the nanocomposite hydrogel were physically cross-linked via dynamic hydrogen bonding associations, i.e. Agar helix bundles, PVA crystallites and polymer chain physisorption on graphene. Therefore, the prepared hydrogels demonstrated simultaneous high strength, toughness, and autonomous self-healing within a short time of 10min, which is rare in the literature. The developed hydrogels can be a promising material in many biomedical applications, such as scaffolds, cartilages, tendons and muscles.

Thermally and Electrically Triggered Triple-Shape Memory Behavior of Poly(vinyl acetate)/Poly(lactic acid) Due to Graphene-Induced Phase Separation.

This work aimed to develop a facile and broadly applicable method for fabricating multistimuli responsive triple-shape memory polymers (SMPs). Hence, herein the SMPs were prepared through the simple physical blending of two commercially available biopolymers, poly(lactic acid) (PLA) and poly(vinyl acetate) (PVAc), in the presence of robust and conductive graphene nanoplatelets. Interestingly, atomic force microscopy observations and thermal analyses revealed that the presence of nanofillers led to phase separation and appearance of two well-separated transition temperatures in the blend of these two miscible polymers. Consequently, shape memory results showed that the unfilled blend of PLA/PVAc with a single thermal transition can only show moderate heat triggered dual-shape memory behavior. While, PLA/PVAc/graphene nanocomposite blends demonstrated excellent thermally and electrically actuated triple-shape memory effects besides their remarkable dual-shape memory behavior. In addition, electrical conductivity of the blend was enhanced by ∼14 orders of magnitude in the presence of graphene. More interestingly, electroactive shape recovery experiments exhibited that depending on the applied voltage, temporary shapes in each region of sample can be either individually or simultaneously recovered.

Bioinspired fully physically cross-linked double network hydrogels with a robust, tough and self-healing structure.

The conventional covalently cross-linked double network (DN) hydrogels with high stiffness often show low toughness and self-healing property due to the irreversible bond breakages in their networks. Therefore, scarcity of hydrogels that possess simultaneous features of stiffness, toughness, and autonomous self-healing properties at the same time remains a great challenge and seriously limits their biomedical applications. While, many natural materials acquire these features from their dynamic sacrificial bonds. Inspired by biomaterials, herein we propose a novel strategy to design stiff, tough and self-healing DN gels by substitution of both covalently cross-linked networks with strong, dynamic hydrogen bond cross-linked networks. The prepared fully physically cross-linked DN gels composed of strong agar biopolymer gel as the first network and tough polyvinyl alcohol (PVA) biopolymer gel as the second network. The DN gels demonstrated multiple-energy dissipating mechanisms with a high modulus up to 2200kPa, toughness up to 2111kJm-3, and ability to self-heal quickly and autonomously with regaining 67% of original strength only after 10min. The developed DN gels will open a new avenue to hydrogel research and holds high potential for diverse biomedical applications, such as scaffold, cartilage, tendon and muscle.