Synthesis of Thermoresponsive Copolymers Composed of Poly(ethylene oxide) and Poly(N-isopropylacrylamide) for Cell Encapsulation

Thermoresponsive copolymers of poly(N- isopropyl acrylamide) (PNIPAm) and poly(acrylamide) microgels grafted with poly(ethylene glycol)(PEG) chains were synthesized by free-radical photopolymerization. Poly(ethylene glycol) methyl ether methacrylate (PEGMA) macromonomers with varying number-average molecular weights were used (Mn = 300 and 1,000 g/mol). A simple microarray technique coupled with a laser scanning confocal microscope (LSCM) was used to visualize the effect of temperature on the volume phase transition temperatures of the microgels. In general, increasing the concentration of PEGMA in the PNIPAm-co-Am-co-PEGMA copolymers resulted in a broader and higher lower critical solution temperature (LCST) compared to the PNIPAm microgels. We demonstrated that the PEGMA molecular weight and concentration influenced whether it was incorporated as a grafted copolymer or random copolymer in the PNIPAm microgel. The evidence for this is the shift in the LCST as determined by temperature and differential scanning calorimetry (DSC) measurements. This behavior suggests that incorporation of PEGMA in the copolymer depends on its hydrophilicity or water-solubility which in turn influenced the degree at which the copolymer chains collapsed from a coil-to-globule (volume phase transition) with increasing temperature.