Fabrication of antiseptic, conductive and robust polyvinyl alcohol/chitosan composite hydrogels

Fabricating robust and multi-functional hydrogels is of great importance and challenge. In this work, chitosan (CS) and polyvinyl alcohol (PVA) were used to design antiseptic, conductive and robust hydrogels by a two-step method. Chemical structures of gels, the degree of crystallinity, the state of water in hydrogels, as well as their microstructures were characterized via a combination of FT-IR, XRD, DSC and SEM. Segment lengths of cross-linking points were calculated from elastic rubber theory. Their mechanical properties were evaluated on the electronic testing machine. It was shown that the tensile strength and elongation at break of single PVA hydrogel were only 200 kPa and 135%, respectively, due to the heterogenous structure with pore sizes between 1.5 ~ 8.2 μm. By introducing CS into PVA matrix followed with soaking in a saturated NaCl solution, the network became homogeneous with a pore size of 0.5 ~ 1.1 μm. Moreover, free water changed to bond water, and frictions between polymer chains increased because of hydrophobic associations and entanglements of CS segments. As a result, the tensile stress and strain increased to 3800 kPa and 270%, respectively. The gel also exhibited antiseptic property, electrical conductivity and swelling-resistant properties. The strength after reaching swell equilibrium was 3400 kPa, much higher than most gels at swollen states. This gel might find applications in bionic cartilage, sensors, food preservation and wearable devices.