(353e) Steric Stabilization and Bio-Functionalization of Thermally-Responsive Colloidal Hydrogels
Aqueous colloidal suspensions of crosslinked poly(N-isopropyl acrylamide) (PNIPAM) display significant changes in particle size with temperature. Near room temperature, the hydrogel particles are swollen by water and in an expanded state. The particle size decreases with increasing temperature as polar interactions and hydrogen bonding with water is disrupted. Depending on the crosslink density, particles at physiological temperature of 37 Celsius can have a diameter of 1/3 or 1/4 that at room temperature. Colloidal PNIPAM particles are typically synthesized by aqueous dispersion polymerization using ionic surfactants. At room temperature, the particles are stabilized by a combination of electrostatic stabilization from the surfactant and steric stabilization from dangling PNIPAM chain extending from the particle surface. In the collapsed state at physiological temperature, the particles are stabilized solely by electrostatic repulsion. As a result, typical PNIPAM particles aggregate at physiological conditions when dispersed in solutions of moderate ionic strength due to shielding of electrostatic repulsion.
Our group has developed techniques to graft steric stabilizers (poly(vinyl alcohol), poly(N-vinyl pyrrolidone), or poly(ethylene glycol)) to the surface of PNIPAM to produce particles that are stable under high ionic strength conditions at physiological temperature. In addition, we have functionalized the particle surface to facilitate bioconjugation. Particles have been synthesized with surface functional groups that specifically interact with histidine-tagged peptides and proteins. We demonstrate that the novel PNIPAM particles coated with peptides and proteins exhibit temperature-adjustable size, and the peptides or proteins can be released from the particle surface upon the addition of imidazole. A discussion will be provided on how these size-tunable carriers of proteins and peptides can be used to aid in micropatterning devices used in detecting pathogens.