Transparent thermo-responsive poly(N-isopropylacrylamide)-l-poly(ethylene glycol)acrylamide conetwork hydrogels with rapid deswelling response

Transparent thermo-responsive poly(N-isopropylacrylamide)-l-poly(ethylene glycol)acrylamide (PNIPAM-l-PEG) conetwork hydrogels with rapid deswelling response are prepared by using multi-arm star poly(ethylene glycol)acrylamide (multi-arm star PEGAAm) molecules as cross-linkers. The introduction of multi-arm star PEGAAm cross-linkers can restrain the formation of dense skin layers on the surface of PNIPAM-l-PEG hydrogels, and act like water channels to facilitate the release of water from the hydrogels, resulting in rapid deswelling response. Meanwhile, the internal conetwork structures of the PNIPAM-l-PEG hydrogels are much more homogeneous due to the regular chemical structures of the multi-arm star PEGAAm cross-linkers. The cross-linkers can directly cross-link PNIPAM chains and serve as the backbones of the conetworks. This reduces the strong aggregation of hydrophobic PNIPAM chains against the formation of heterogeneous microstructures within the hydrogels during the deswelling process, leading to the maintenance of their transparency even at a temperature higher than their gel collapse temperature (GCT). The transparent PNIPAM-l-PEG hydrogels with rapid deswelling response show great potential for engineering advanced sensors and devices for optical applications.