Janus hydrogels: Pioneering dual-faced biomaterials for revolutionary tissue engineering

Janus hydrogels are novel biomaterials characterized by asymmetric structures and dual-faced functional designs, which exhibit substantial potential in tissue engineering. The nomenclature of these materials originates from the Roman two-faced deity Janus, reflecting the distinct physicochemical properties exhibited by opposing sides or heterogeneous regions of the material. The functionality of a Janus hydrogel is enabled by diverse structural designs, allowing for the accurate simulation of complex native tissue microenvironments and the intelligent responsiveness to external stimuli. With the rapid advancement in Janus hydrogel research, innovative synthesis techniques, functionalization strategies, and cross-disciplinary applications continue to emerge. This review systematically summarizes the recent progress in Janus hydrogel applications in tissue engineering and provides novel insights. Based on the unique structural attributes of Janus hydrogels, we highlight their superior performance in tissue regeneration, controlled drug delivery, antibacterial activity, and antiadhesive functionality. This review aims to provide researchers in related fields with new perspectives and promote advancements in regenerative medicine. Although Janus hydrogels have demonstrated excellent repair efficacy and intelligent responsiveness in tissue engineering applications for cardiac and skin regeneration, certain limitations require further investigation, including the high manufacturing costs of complex asymmetric structures and potential inflammatory responses triggered by degradation byproducts.