Thermosensitive Multilayer Hydrogels of Poly(N-vinylcaprolactam) as Nanothin Films and Shaped Capsules

We report on nanothin multilayer hydrogels of cross-linked poly(N-vinylcaprolactam) (PVCL) that exhibit distinctive and reversible thermoresponsive behavior. The single-component PVCL hydrogels were produced by selective cross-linking of PVCL in layer-by-layer films of PVCL-NH2 copolymers assembled with poly(methacrylic acid) (PMAA) via hydrogen bonding. The degree of the PVCL hydrogel film shrinkage, defined as the ratio of wet thicknesses at 25 to 50 degrees C, was demonstrated to be 1.9 +/- 0.1 and 1.3 +/- 0.1 for the films made from PVCL-NH2-7 and PVCL-NH2-14 copolymers, respectively. No temperature-responsive behavior was observed for noncross-linked two-component films because of the presence of PMAA. We also demonstrated that temperature-sensitive PVCL capsules of cubical and spherical shapes could be fabricated as hollow hydrogel replicas of inorganic templates. The cubical (PVCL)(7) capsules retained their cubical shape when temperature was elevated from 25 to 50 degrees C exhibiting 21 +/- 1% decrease in the capsule size. Spherical hydrogel capsules demonstrated similar shrinkage of 23 +/- 1%. The temperature-triggered capsule size changes were completely reversible. Our work opens new prospects for developing biocompatible and nanothin hydrogel-based coatings and containers for temperate-regulating drug delivery, cellular uptake, sensing, and transport behavior in microfluidic devices.