  Incomplete release profiles of protein delivery systems can be caused by
unfolding and denaturation of proteins due to protein-biomaterial interactions.
This paper investigates the mechanisms causing incomplete release of the wound
healing protein, Keratinocyte Growth Factor (KGF), from a
hydroxyethyl(methacrylate) (HEMA) hydrogel by FTIR-ATR spectroscopy and 2D
correlation spectroscopy. This work characterizes KGF secondary structure
reflected in the amide I region of the FTIR-ATR spectrum, and differences
between active and heat denatured KGF. These results have been used to
investigate the sequence of time-dependent changes in KGF at the surface of the
HEMA hydrogel during uptake and release by 2D correlation spectroscopy. KGF
stays active throughout the uptake process, and the KGF loop structures
interact with HEMA moieties, potentially mimicking receptor-ligand
interactions. KGF denatures during release via changes in the loops and
unfolding of the extended strands. Our results suggest that a high affinity
interaction between the HEMA hydrogel and KGF is beneficial for efficient
loading of KGF into the hydrogel, but is too strong and prevents complete KGF
release due to unfolding and denaturation of KGF. This work informs future
material design that will target different secondary structural elements of KGF
in order to preserve its native conformation and allow for complete release.
