Molecularly Shielded, On-Demand, Ultrasound-Cured Polymer Networks

Networks formed from polymers can range from soft hydrogels to ultrahard protective coatings, making them useful for a wide range of applications from cell culture to highly bonded adhesives. Polymer networks are commonly crosslinked via heat or high energy light, and recently mechanical force has also been used to induce the formation of crosslinks in pre-existing networks. Here, we demonstrate a new strategy to use mechanical deformation and ultrasound to induce liquid-to-solid crosslinking. We synthesized graft copolymers with large poly(ethylene glycol) (PEG) side-chains acting as molecular shielding groups to protect otherwise highly reactive epoxide group. Solutions of highly shielded polymers could remain as a liquid solution when left undisturbed, and we could initiate gelation of these solutions with ultrasound in 20 seconds. These ultrasound-sensitive polymers are particularly useful in light and heat sensitive applications, and where precise control over the gelation time is required.