Effect of gelation temperature on PLA-PEO-PLA physical hydrogel morphology

Poly(lactic acid)-poly(ethylene oxide)-poly(lactic acid) (PLA-PEO-PLA) triblock copolymer hydrogels are a promising biomaterial, with applications to drug delivery and cell scaffolds for tissue engineering. Using L-lactic acid gives PLLA-PEO-PLLA, which has stereoregular end blocks. The resulting system forms lamellae with hydrophobic semi crystalline domains of PLLA with hydrophilic domains of PEO connecting them. Gelation is achieved by raising the temperature of the polymer/water mixture, and this study focuses on the effect on the nano- and microscale structures of the gel that the gelation temperature has. By confocal microscopy, we determine the average particle size on the microscale increases from 2.3 mum to 3 mum from an increase in gelation temperature of 40degC to 80degC. Meanwhile, small angle x-ray scattering indicates that the nanoscale structures, the lamellae, are unchanged over the same range. This implies that an annealing effect is occurring. The lamellae align to a greater degree with a higher temperature, increasing the size of the semi-crystalline domains.