Ultrarapid molecular release from poly(N-isopropylacrylamide) hydrogels perforated using silica nanoparticle networks

Porous poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were successfully prepared in the presence of nanosized silica particles with network morphology and subsequent silica extraction by HF treatment. The nanosized pores induced very rapid deswelling of the hydrogels, accompanied by volume phase transitions from swelling to deswelling states at approximately 30 degrees C. Deswelling, which was analyzed by a quick change in temperature of the aqueous media from 20 to 40 degrees C, was facilitated by increased silica particle content. The deswelling rate constant of the hydrogel prepared using silica nanoparticles with a network morphology (NT gel) was about 1 900-fold greater than that of nonporous hydrogels and 13-fold larger than that of porous hydrogels perforated using spherical silica nanoparticles (SP gel). The releasing rate of the low-molecular weight chromophore from the NT gel was higher than that from the SP gel. In the chromophore-labeled macromolecules, the network morphology was effective for increasing the releasing rate based on the transfer inside the hydrogel, as well as for increasing the amount released based on the surface pore morphology.