Michael D. Weir, Joseph M. Antonucci and Francis W. Wang
Polymers Division, National Institute of Standards and Technology,
Gaithersburg, MD 20899-8545
A rapid screening method was developed to examine the effect of a wide array of potentially biodegradable crosslinking monomers on the lower critical solution temperature (LCST) of N-isopropylacrylamide (NIPAAm) hydrogels. Both the type of crosslinker and the concentration of crosslinker were systematically altered across a 96-well glass microplate. UV transmission was measured at 490 nm using a multilabel counter and the LCST was defined as the temperature at which the transmission at 490 nm is equal to 0.5. For all crosslinkers studied, the LCST was found to be between 28 oC and 31 oC, with little difference in temperature when altering crosslinker structure and/or concentration. Additionally, there appears to be significant effect of crosslinker hydrophilicity on the time required for gel collapse and subsequent release of water. Even at low crosslinker concentrations, the gels created from the more hydrophilic crosslinkers appear to have a decreased water release rate, while the gels with more hydrophobic crosslinkers exhibit a relative increase in water release rate.