Differential orientation and conformation of surface-bound keratinocyte growth factor on (hydroxyethyl)methacrylate, (hydroxyethyl)methacrylate/methyl methacrylate, and (hydroxyethyl)methacrylate/methacrylic acid hydrogel copolymers.

The development of hydrogels for protein delivery requires protein-hydrogel interactions that cause minimal disruption of the protein's biological activity. Biological activity can be influenced by factors such as orientational accessibility for receptor binding and conformational changes, and these factors can be influenced by the hydrogel surface chemistry. (Hydroxyethyl)methacrylate (HEMA) hydrogels are of interest as drug delivery vehicles for keratinocyte growth factor (KGF) which is known to promote re-epithelialization in wound healing. The authors report here the surface characterization of three different HEMA hydrogel copolymers and their effects on the orientation and conformation of surface-bound KGF. In this work, they characterize two copolymers in addition to HEMA alone and report how protein orientation and conformation is affected. The first copolymer incorporates methyl methacrylate (MMA), which is known to promote the adsorption of protein to its surface due to its hydrophobicity. The second copolymer incorporates methacrylic acid (MAA), which is known to promote the diffusion of protein into its surface due to its hydrophilicity. They find that KGF at the surface of the HEMA/MMA copolymer appears to be more orientationally accessible and conformationally active than KGF at the surface of the HEMA/MAA copolymer. They also report that KGF at the surface of the HEMA/MAA copolymer becomes conformationally unfolded, likely due to hydrogen bonding. KGF at the surface of these copolymers can be differentiated by Fourier-transform infrared-attenuated total reflectance spectroscopy and time-of-flight secondary ion mass spectrometry in conjunction with principal component analysis. The differences in KGF orientation and conformation between these copolymers may result in different biological responses in future cell-based experiments.