Hydrogel Microparticles for MMP-Mediated Gene Delivery to Chronic Wounds

• Altaf Bacchus, Chemical Engineering, University of Delaware

• Millicent Sullivan, Chemical and Biomolecular Engineering, University of Delaware

Globally, millions of people are affected by chronic wounds and are further burdened by inefficient and expensive treatment methods. Growth factors are an important signaling molecule secreted during the normal wound healing process, but the timing and concentration of that signaling are disrupted in chronic wounds. One clinical treatment approach is growth factor replacement therapy. However, this approach is limited by the short half-life, finite supply, and off-target effect of exogenous proteins. This project aims to leverage the physical and chemical properties of hydrogel microparticles (microgels) to deliver therapeutic growth factor plasmid DNA to chronic wounds. Plasmid DNA, delivered in the form of polyplexes, allows cells to produce their own growth factors, bypassing the limitations of exogenous protein delivery. Polyplexes are nanostructures formed by electrostatic interactions between plasmid DNA and polyethyleneimine (PEI). Preparation of non-degradable microgels uses thiol-maleimide Michael addition to cross-link 4-armed polyethylene glycol (PEG) functionalized with thiol and maleimide. Using the copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction, we can crosslink polyplexes within the PEG network using MMP-degradable sequences, allowing for the controlled release of polyplexes facilitated by matrix metalloproteinases (MMPs), which are enzymes secreted into the ECM as a part of the inflammatory response. This Summer, we successfully encapsulated polyplexes into microgels and performed fundamental characterizations, including microscopy. Additionally, the peptide sequence for the MMP-degradable linker can be synthesized using solid-phase peptide synthesis and purified using high-performance liquid chromatography (HPLC). From this preliminary work, we can conclude that creating a polyplex crosslinked microgel is possible and from literature, it is a promising platform for the delivery of growth factors in chronic wounds. Future work includes studying the release profile of polyplexes from microgels in vivo and animal models, as well as tuning and optimizing the process.