A hydrogel system for stimulus-responsive, oxygen-sensitive in situ gelation

A hydrogel system that is designed to gel due to oxidation by molecular oxygen is described. This is achieved by the use of a branched poly(ethylene glycol) modified with thiol end groups. A stable precursor molecule, starPEG thioacetate, was synthesized by radical addition of thioacetic acid to an intermediate starPEG allyl ether. Rapid deprotection of the thiol can be achieved using a base, e.g. sodium hydroxide, quantitatively liberating a thiol group and a non-toxic acetate ion. This step can be carried out under anaerobic conditions, yielding a solution with known thiol content that can be stored. The reaction with oxygen is accelerated by the use of a catalyst based on Fenton chemistry, which makes the material useful for biomedical applications where in situ polymerization of an injectable material is beneficial. This gelation takes place under near physiological conditions without the need for a cross-linking agent.