Synthesis and characterization of dual stimuli responsive macromers based on poly(N-isopropylacrylamide) and poly(vinylphosphonic acid).

Stimulus responsive materials hold great promise in biological applications as they can react to changes in physiological stimuli to produce a desired effect. Stimulus responsive macromers designed to respond to temperature changes at or around 37 degrees C and the presence of divalent cations were synthesized from N-isopropylacrylamide, pentaerythritol diacrylate monostearate, 2-hydroxyethyl acrylate, and vinylphosphonic acid by free radical polymerization. Monomers were incorporated into the macromers in ratios approximating the molar feed ratios, and macromers underwent thermogelation around normal body temperature (36.2-40.5 degrees C) as determined by rheology and differential scanning calorimetry. Macromers containing vinylphosphonic acid interacted with calcium ions in solution, displaying decreased sol-gel transition temperatures (27.6-34.4 degrees C in 100 mM CaCl(2)), with decreases of greater magnitude observed for macromers with higher relative vinylphosphonic acid content. Critical micellar concentrations also decreased in a dose-dependent manner with increased vinylphosphonic acid incorporation in solutions with CaCl(2) but not in solutions with NaCl. These dually responsive macromers allow examination of the effect of increasing vinylphosphonic acid content in a macromer, which holds promise in biological applications such as drug and cell delivery or tissue engineering due to the macromer responsiveness at physiological temperatures and concentrations of calcium.