In a composite material made of a thermo-responsive hydrogel and plasmonic nanoparticles, irradiation causes the nanoparticles to heat, which causes the hydrogel to collapse and release its content. For example, a gold nanoshell–hydrogel composite material made of gold-sulfide nanoshells (~ 40 nm diameter) imbedded in a thin film (~ 1.5 mm) of NIPAAm-co-AAm hydrogel was able to repeatedly release protein after irradiation with NIR light [46]. This strategy could be generalized to other therapeutics (small molecules, steroids, nucleic acids, etc.). Moreover, due to its high loading capacity, this drug delivery system could be used repeatedly, on demand.