Development of hydrogels with thermal-healing properties using a network of polyvinyl alcohol and boron nitride...

The biocompatibility, flexibility, and tissue-like mechanical properties of hydrogels suggest they are promising materials for wearable devices. However, the production of smart, self-healing hydrogels is limited by the unstable structure of load-bearing stressors and the need for long-term healing capacity. An important goal when developing such hydrogels is to improve their mechanical characteristics and rapid ability to self-repair in physiological environments. In this study, we aimed to create a thermo-responsive hydrogel that possessed thermal-healing and enhanced mechanical properties, without losing its self-healing capabilities, by employing two interpenetrating cross-linked networks of polyvinyl alcohol (PVA) and boron nitride nanosheets (BNNSs). We observed that addition of BNNSs significantly increased the glass transition temperature (T_g) and temperature-dependent swelling of PVA hydrogels, indicating a high compatibility between these two materials and a high thermal response to external stimuli. Our results suggest that PVA hydrogels combined with BNNSs outperform single-network PVA hydrogels in terms of thermal-healing capacity. As above T_g, the thermal energy gained during moisture loss leads to an increase in the thermal mobility of the polymer chains and in the free volume available for new hydrogen bonds at the fracture surface. This unique structure increases water content and confers better mechanical properties. Interestingly, this structure of the second network benefits the first PVA network during deformation by effectively dissipating energy and bearing force, and contrarily to single-network PVA hydrogels. Taken together, our results show that combining PVA and BNNSs to create a hybrid structure, exerts a synergistic effect and successfully improves the thermal-healing performance of wet hydrogels.