| Colloidal PNIPAM hydrogel particles have found the potential applications in biomedical field because of their thermo-responsiveness. In the current work, two novel applications of PNIPAM microgels are demonstrated. PNIPAM microgels were engineered to serve as thermo-responsive protein transfer agents, which can be applied to modify the surface of 2-D photonic crystals to create ultrasensitive biosensors. The particles were functionalized with metal chelating groups to enable the reversible affinity binding of peptides or proteins, and also grafted with polymeric stabilizers to maintain the colloidal stability under physiological conditions. Two designs were demonstrated in the study. The first type of particle was synthesized by incorporating the stabilizers and the functional groups separately via a two-stage dispersion polymerization. Another type of particle was copolymerized with end-functionalized stabilizers that can be readily conjugated to the chelating groups. Both types of particles were thermo-sensitive, colloidally stable, and able to reversibly bind to the model peptides.;Nonionic block copolymers were used as surfactants for the dispersion polymerization of PNIPAM microgel particles to replace the less biocompatible ionic surfactants. The surfactants stabilized PNIPAM particles through physical adsorption but not chemical grafting. The effectiveness of the surfactants was evaluated by comparing the size of the resulting particles. Nonionic surfactants were also found to successfully enhance the colloidal stability at the post-polymerization stage. This allows one to use PNIPAM microgels in physiological environment in the form of particle dispersions without altering the particle composition and polymerization process.;PNIPAM microgels were also deposited in micropatterns on substrates for the cell sheet engineering application. A simple dip coating method was employed to micropattern flat substrates with PNIPAM particles in a template free manner. PNIPAM particles self-assembled into 2-D micropatterns, where stripe and spacing regions consisted of densely packed particles and sparsely distributed particles, respectively. With this versatile process the dimensions of the PNIPAM micropatterns can be controlled. Preferential adhesion of fibroblast cells was observed on the spacing regions initially, and the confluent cell sheet was obtained later on. The cell sheet successfully detached from the substrates upon cooling as the result of the thermo-responsiveness of PNIPAM. |
