Poly(N-isopropylacrylamide) Cross-Linked Coatings with Phototunable Swelling

A series of terpolymers were synthesized comprising the following monomers: N-isopropylacrylamide (NIPAAm), a stimuli-responsive structural unit that swells and collapses in response to temperature; methacryloxybenzophenone (MaBP), a photo-cross-linking unit that is activated at a wavelength of 365 nm; and phenacyl methacrylate (PHEm), a photolabile protected carboxyl group that can be deprotected at a wavelength of 254 nm. It is shown that the terpolymers can be photo-cross-linked at long UV wavelength light (lambda = 365 nm) to establish surface-attached, cross-linked coatings and subsequently photochemically cleaved at short UV wavelength light (lambda = 254 nm), which is found to be consistent with first-order kinetics. The photocleavage reaction produces free carboxylic groups, which can be used to locally tune the swelling characteristics and transition temperature of the coating, which depends on both the irradiation exposure and the overall PHEm content. For instance, for a terpolymer with 7.1 mol % PHEm, the transition temperature between the swollen and collapsed states increased from 20 to 50 degrees C at a pH of 8.5 with an exposure dose of 0.52 J/cm(2) at 254 nm. Finally, photocleavage can be used to create chemically patterned regions to provide a basis by which to conjugate cationic markers, proteins, or nanoparticles to the terpolymer coating.