Hyaluronic acid hydrogel microspheres for delivery of protein therapeutics

The focus of this dissertation was in the development of an injectable depot for sustained, local delivery of angiogenic growth factors. The primary application of this work is in therapeutic angiogenesis, where clinical trials have demonstrated a need for sustained delivery to realize any therapeutic benefits of growth factor treatment. The ideal delivery system would be injectable through a small needle, have a high capacity for growth factor loading, protect the growth factor and retain high bioactivity, temporally control the release of growth factor over a long period of time, degrade away naturally once the growth factor dose had been delivered, and not induce a large foreign body response that could limit the transport of growth factors to the host. Hyaluronic acid (HA) was identified as a good candidate for the building block of our delivery system for numerous reasons. HA is a naturally-derived linear biopolymer that is non-immunogenic, non-adhesive, highly hygroscopic, enzymatically degradable, and possesses bioactivity in many cellular processes, including angiogenesis and regulation of inflammation. For these reasons and more, HA was used in this dissertation for the fabrication of hydrogel microspheres for the controlled release of basic fibroblast growth factor, a potent angiogenic factor. This dissertation describes a linear progression of work from the initial development of novel synthetic approaches to chemically modify HA for crosslinking, to injection of basic fibroblast growth factor- (bFGF-) loaded, HA hydrogel microsphere in vivo. Building on the chemistry that was originally developed, discs were first fabricated by UV photopolymerization and characterized to understand the effect of chemical modification on bulk hydrogel properties. Further building upon that body of knowledge, HA hydrogel microspheres were fabricated via a free-radical initiated inverse suspension polymerization and characterized. Finally, protein loading and release profiles were characterized in a variety of formulations before injecting the top formulation into a mouse model. This microsphere system, though developed for therapeutic angiogenesis applications, provides a universal platform for local delivery of a variety of cationic growth factors for a wide range of applications. We believe that these novel, crosslinked HA microspheres offer unique advantages over synthetic and protein-derived materials for applications requiring sustained, local delivery of protein therapeutics.