Visible light laser direct-writing of high-resolution, biocompatible, super-multifunctional and tough hydrogels without photoinitiators in 30 s.

Currently, the lack of bioinks and long printing time limits the further development of biofabrication. Here we report a novel biocompatible, multi-functional and tough 3D printable hydrogel via visible light photocrosslinking of polyvinyl alcohol bearing styrylpyridinium group (PVA-SbQ). The high-resolution PVA-SbQ hydrogels with different designed shapes can be generated via laser direct-writing in 30 s without extra toxic crosslinkers or photoinitiators, and demonstrates excellent biocompatibility. The rapid laser direct-writing technology also results in a super-strong, tough hydrogel with excellent adhesive, swelling, self-healing, and photo-tunable properties due to the photodimerization of styrylpyridinium (SbQ) groups and the left-over massive amount of free hydroxyl groups in the hydrogel. For example, the maximum tensile strength, elongation, compressive strength adhesive strength of printed PVA-SbQ hydrogels can reach 1.0 MPa, 810 %, 33 MPa, 31 kPa, and 25,000 % respectively. And these properties can be adjusted by controlling the parameters for laser direct-writing. In addition, the introduced nitrogen cations by SbQ groups further endow hydrogels with the potential to develop novel functionality, which is demonstrated by integrating negatively charged nanocelluloses in the PVA-SbQ system to develop underwater adhesives, anti-freezing (-24.9 °C), and anti-bacterial hydrogels. This discovery opens multiple doors for developing PVA-SbQ based multi-functional hydrogel for various applications including biofabrication and tissue engineering.