Study of thermal-sensitive alginate-Ca2+/poly(N-isopropylacrylamide) hydrogels supported by cotton fabric for wound dressing applications

In this study, direct deposition, 1,2,3,4-butanetetracarboxylic acid (BTCA) crosslinking, chelating and ultraviolet (UV) photo-grafting methods were employed to bond alginate-Ca2+/poly(N-isopropylacrylamide) (PNIPAAm) interpenetrating network hydrogel onto cotton fabric surface for wound dressing applications. Infrared spectroscopy confirmed the presence of alginate-Ca2+/PNIPAAm hydrogels on the cotton fabrics. Scanning electron microscopy was used to investigate surface and cross-section morphologies. Differential scanning calorimetry and three-dimensional video microscopy indicated that fabric-supported hydrogels maintained the thermal-sensitive property with a lower critical solution temperature (LCST) of around 34–35℃. The results of water vapor permeation revealed that the water vapor transmission rate at 37℃ was significantly higher than that at 25℃ for the shrink and collapse of the hydrogels above the LCST. Moreover, the breaking stress of the fabric-supported hydrogels was similar to that of the original cotton fabrics, but much larger than the hydrogels by themselves. The UV photo-grafting provided the strongest peel strength, followed by the BTCA crosslinking, the chelating and the direct deposition method. The cotton fabric-supported alginate-Ca2+/PNIPAAm hydrogels were stiffer than the original cotton fabric due to the high glass transition temperature of PNIPAAm (about 140℃). The in vitro drug release experiment confirmed that the cumulative release amount was much higher at around 37℃ (above the LCST) than at 25℃ (below the LCST). This showed that the fabric-supported thermal-sensitive hydrogels had functions of keeping the wound area breathable and comfortable, and provided controlled drug release with good mechanical properties, indicating a great potential and significance for wound dressing applications.