Synthesis and thermally-induced gelation of interpenetrating nanogels.

Thermally-induced in-situ gelation of polymers and nanogels is of significant importance for injectable non-invasive tissue engineering and delivery systems of drug delivery system. In this study, we for the first time demonstrated that the interpenetrating (IPN) nanogel with two networks of poly (N-isopropylacrylamide) (PNIPAM) and poly (N-Acryloyl-l-phenylalanine) (PAphe) underwent a reversible temperature-triggered sol-gel transition and formed a structural color gel above the phase transition temperature (Tp). Dynamic light scattering (DLS) studies confirmed that the Tp of IPN nanogels are the same as that of PNIPAM, independent of Aphe content of the IPN nanogels at pH of 6.5 ∼ 7.4. The rheological and optical properties of IPN nanogels during sol-gel transition were studied by rheometer and optical fiber spectroscopy. The results showed that the gelation time of the hydrogel photonic crystals assembled by IPN nanogel was affected by temperature, PAphe composition, concentration, and sequence of interpenetration. As the temperature rose above the Tp, the Bragg reflection peak of IPN nanogels exhibited blue shift due to the shrinkage of IPN nanogels. In addition, these colored IPN nanogels demonstrated good injectability and had no obvious cytotoxicity. These IPN nanogels will open an avenue to the preparation and thermally-induced in-situ gelation of novel NIPAM-based nanogel system.