Biocompatible dually reinforced gellan gum hydrogels with selective antibacterial activity

The poor mechanics and functionality of natural-polymer hydrogels from gellan gum (GG) prohibit their practical application, despite the intrinsic thermo-reversible gelation nature, structural and quality consistency, biocompatibility, biodegradability and sustainability of microbial fermentation-produced GG. Herein, a dual-reinforcing strategy, i.e., ionic-crosslinking along with rigid nano-particulate reinforcing, was realized to modify pristine GG hydrogels for the first time during the in-situ formation of zeolitic imidazolate framework-8 (ZIF-8). Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, rheology and X-ray diffraction confirm the synchronous formation of ZIF-8 and ionic bonds between Zn²⁺ and -COO^- of GG molecules. The mechanics of the final hydrogels are far superior to GG hydrogel, with the maximum compressive and tensile strength attaining 1.17 MPa and 592.2 kPa, ~4 times and ~ 66 times respectively of the corresponding GG hydrogel. Especially, the obtained hydrogels display selective antibacterial activity against Staphylococcus aureus as a modeling Gram positive strain. Whereas, the hydrogels retain good biocompatibility despite the introduction of ZIF-8 and Zn²⁺ crosslinks, with the cell viability (NIH3T3 cells as the model) >79 % after 48 h' cultivation in either the hydrogels or gel extracts. The excellent properties suggest them tremendous application prospects as biomedical materials, instrumental in averting drug-resistant problems.