Temperature dependence of serum protein adsorption in PEGylated PNIPAm microgels

The effect of PEGylation on the thermal response and protein adsorption resistance of crosslinked PNIPAm microgels was investigated. It was found that the presence of PEG, its molecular weight (M(n) 300 and 1100 g/mol) and its concentration (10, 20, and 30 wt.%) each significantly influenced both the value and breadth of the volume phase transition temperature (VPTT) and the adsorption of bovine serum albumin (BSA) on the surface of the microgels. Specifically, as the degree of PEGylation increased, the value and breadth of the VPTT increased, and the adsorption of BSA decreased significantly. The critical concentration that minimizes protein adsorption on PNIPAm-co-PEGMa microgels was found to be 20 wt.% of PEGMa. This critical concentration was confirmed qualitatively using laser scanning confocal microscopy (LSCM). Evidence for the effect of the molecular weight of PEG on the structure of PNIPAm-co-PEGMa microgels was provided by thermal analysis using differential scanning calorimetry. The VPTT study revealed significant differences in the composition of the microgels when PEGMa samples with two different molecular weights were used as comonomers with PNIPAm. It was determined that the molecular weight and concentration of PEGMa controls the structure of the microgels, which in turn influences their temperature response and protein adsorption resistance properties of the microgels. Our work establishes specific design concepts for controlling the molecular architecture of the hydrogels in order to tune their temperature response and biocompatibility for use in a variety of biomedical applications such as, cell encapsulation, drug delivery and tissue engineering applications.