α-Ketoglutaric Acid as a Sustainable and Universal Photoinitiator for Hydrogels

Hydrogels have acquired numerous attentions in biomedicine and smart bioelectronics due to similar properties to our tissues. Initiators are crucial in vinyl polymerization for hydrogel preparation which can influence mechanical properties and physical/chemical structures. We report α-ketoglutaric acid (αKG), an intermediate in the citric acid cycle, as an ecofriendly photoinitiator for vinyl polymerization. We comprehensively investigated the mechanical properties of hydrogels initiated by comparing αKG with Irgacure 2959 (I-2959) and ammonium persulfate (APS). We found that αKG successfully initiated the polymerization in both synthetic and natural hydrogels (polyethylene glycol, polyacrylamide, gelatin, alginate, and chitosan). Meanwhile, the interactions between αKG and functional groups of macromolecules make αKG a potential additive in hydrogels, which could influence the hydrogel mechanics. In contrast to the potential toxicity of unreacted APS and the limited water solubility of I-2959, αKG proves to be a more versatile and sustainable option in gelation than the other two. This work throws new light on hydrogel fabrication with the initiator alteration for potential biomedical applications.