  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 orientation
and conformation. Hydrogels must promote the adsorption of biomolecules onto
the surface and the diffusion of biomolecules into the porous network at the
surface, while maintaining native protein conformation, keeping the protein in
an accessible orientation for receptor binding, and maximizing protein release.
We report here the evaluation of (hydroxyethyl)methacrylate (HEMA)-based
hydrogel systems for the delivery of keratinocyte growth factor (KGF) to
promote re-epithelialization in wound healing. In this work, we characterize
two hydrogel blends in addition to HEMA alone, and report how protein
orientation, conformation, and protein release is affected. The first blend
incorporates methyl methacrylate (MMA), which is known to promote adsorption of
protein to its surface due to its hydrophobicity. The second blend incorporates
methacrylic acid (MAA), which is known to promote the diffusion of protein into
its surface due to its hydrophilicity. We find that KGF at the surface of the
HEMA/MMA blend appears to be more orientationally accessible and
conformationally active than KGF at the surface of the HEMA/MAA blend. We also
report that KGF at the surface of the HEMA/MAA blend becomes conformationally
denatured, likely due to hydrogen bonding. While KGF at the surface of these
blends can be differentiated by FTIR-ATR spectroscopy and ToF-SIMS in
conjunction with PCA, KGF swelling, uptake, and release profiles are
indistinguishable. The differences in KGF orientation and conformation between
these blends may result in different biological responses in future cell-based
experiments.
