Nanofiber–nanorod composites exhibiting light-induced reversible lower critical solution temperature transitions

Stimuli-responsive materials are promising as smart materials for a range of applications. In this work, a photo-crosslinkable, thermoresponsive macromer was electrospun into fibrous scaffolds containing gold nanorods (AuNRs). The resulting fibrous nanocomposites composed of poly(N-isopropylacrylamide-co-polyethylene glycol acrylate) (PNPA) and PEGylated AuNRs were crosslinked and swollen in water. AuNRs strongly absorb in the near-infrared (NIR) region to generate heat, which triggered the fiber thermal transition upon NIR light exposure. During the thermal transition, scaffolds collapsed both macroscopically and microscopically, with individual fibers deswelling and pulling together. Exposure to a 1.1 W NIR laser decreased the diameter of swollen fibers by 34.7% from 1332 ± 193.3 to 868.9 ± 168.3 nm, and increased fiber density 116% from 209.5 ± 26.34 to 451.9 ± 23.68 fibers mm−1. This transition was dependent on the incorporation of the AuNRs, and was utilized to trigger the release of encapsulated proteins from the nanocomposite fiber mats. The expulsion of water from fibers upon NIR exposure caused the release rate of incorporated protein to increase greater than tenfold, from 0.038 ± 0.052 without external stimulus to 0.462 ± 0.227 µg protein/mg polymer/min with NIR exposure. These results suggest that light-responsive fibrous nanocomposites can be utilized in applications such as drug delivery.