Tissue repair requires a carefully orchestrated series of events, which, when disrupted, can lead to impaired healing and loss of function. Sustained delivery of growth factors can stimulate endogenous repair mechanisms; however, typical biomaterial delivery vehicles lack the ability to spatially and temporally control in vivo protein presentation. In order to improve the clinical delivery of bone morphogenetic protein-2 (BMP-2) for bone regeneration, we developed heparin-based microparticles that harness the natural binding affinity between heparin and BMP-2. Heparin microparticles provide effective, local presentation of BMP-2 within femoral bone defects in rats, leading to robust healing and improved spatial localization of bone formation
While heparin-based biomaterials are promising for the delivery of heparin binding proteins, such as BMP-2, affinity-based biomaterials that rely on natural protein-matrix interactions provide limited tunability and cannot be applied widely to other potent proteins. In order to overcome these limitations to create a strategy for protein delivery to the brain, we engineered a fusion protein with a Src homology 3 (SH3) domain and controlled its release from a hydrogel using SH3 binding peptides. This strategy enabled the controlled delivery of the enzyme chondroitinase ABC (ChABC-SH3) to the stroke-injured brain, which degraded the proteoglycan component of the glial scar that forms after injury in the stroke lesion and inhibits tissue repair.
Designing effective biomaterials for protein delivery requires a thorough understanding of in vivo protein bio-transport, including diffusion through hydrogels and tissues and protein-material affinity interactions. We have developed in vitro assays to rapidly assess protein diffusion through hydrogels, as well as computational models to describe protein retention and release from biomaterial delivery vehicles implanted in vivo in large bone defects and subcutaneously.
Maintaining the long-term bioactivity of proteins delivered in vivo is an essential part of achieving sustained protein delivery. We have explored a variety of biochemical methods to stabilize the fragile enzyme chondroitinase ABC (ChABC), including chemical modification with poly(ethylene glycol) chains (i.e. PEGylation) and site-directed mutagenesis. Using computational modeling of protein structure, we have identified a number of stabilizing point mutations in the sequence of ChABC that enhance its stability at physiological temperatures and extend its bioactive half-life