Photothermally responsive double-network hydrogels with MoS₂ nanosheets: A high-toughness self-healing biomaterial

Smart hydrogels are good candidates for advanced technologies such as self-healing materials and tissue engineering due to their broad range of properties, including biocompatibility, although the lack of proper mechanical behavior is one of their main issues. To address this issue, we developed a double-network (DN) smart hydrogel composed of chitosan (CS) and polyvinyl alcohol (PVA), reinforced with MoS₂ nanosheets as a photothermally responsive nanofiller. Our results show that the tensile mechanical properties of this DN can be fine-tuned by changing: the freezing temperature for PVA crosslinking, the reaction time for CS crosslinking, and the order of the crosslinking, besides the use of a lyophilization step. Cell viability studies using umbilical cord-derived mesenchymal stem cells (UC-MSCs) revealed that our smart hydrogels allow the adhesion and growth of cells and that the presence of MoS₂ improves cell viability. Notably, the DN hydrogels could be 3D printed into scaffolds with enhanced mechanical stiffness (0.78 MPa), placing them within the mechanical range of soft tissues, and making them suitable for applications in soft tissue engineering. Thermal imaging confirmed that the incorporation of MoS₂ improved the photothermal response under infrared (IR) irradiation, with local temperature increases up to 40.3 °C. This triggered rapid and localized hydrogel contraction and bending, inducing photo-triggered deformation with response times 40 % faster than in non-reinforced samples. Our in vitro cell viability results support future exploration toward biomedical applications, for instance for soft tissue-related applications.