Enzymatic- and light-degradable hybrid nanogels: Crosslinking of polyacrylamide with acrylate-functionalized Dextrans containing photocleavable linkers

Enzymatically cleavable and light-degradable hybrid nanogels were prepared by free radical inverse miniemulsion copolymerization of acrylamide (AAm) with a newly synthesized functional dextran crosslinker containing acrylate moieties attached to the backbone via a photolabile linker, that is, dextran-photolabile linker-acrylate (Dex-PL-A). The Dex-PL-A/AAm feed ratio was systematically varied to investigate the influence of the particle composition on the gel properties. The resulting hydrogel nanoparticles were examined with regard to their degradation behavior upon the appliance of the two orthogonal stimuli by turbidity measurements in combination with dynamic light scattering. Although continuous photolytic cleavage of the photolabile linkers between polyacrylamide chains and dextran molecules was found to proceed fast and quantitatively yielding completely disintegrated networks, stepwise irradiation resulted in partial degradation of crosslinking points. Thus, nanogels of a desired specific degree of swelling (DGS) can be obtained by adjusting the irradiation time accordingly. Partial enzymatic cleavage of the dextran backbones of the Dex-PL-A crosslinking molecules resulted in an increase in the DGS of the nanogels up to a constant value. Subsequent irradiation of those swollen hydrogel particles was used to fully degrade the network structure in a second step. Hence, a two-step degradation profile was realized by the combination of the two orthogonal stimuli. (c) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012