Doctoral Dissertation Defense – Jeongmin Hwang

BME PhD Candidate Jeongmin Hwang will be defending her dissertation:


Extracellular Matrix (ECM)-Based Biomaterial Strategies to Control Delivery of Gene and Small Molecule Therapies in Wound Repair



Despite the great potential of topically administered therapeutics in wound repair, due to the harsh wound environment, topically administered therapeutics are cleared from the wound quickly, resulting in reduced local concentration and limiting their effectiveness as therapeutics. To overcome this limitation, the overall goal of my dissertation work is to improve the efficacy of topically administered therapeutics through the control over the therapeutic delivery kinetics, using interactions between therapeutic carriers and matrices. I specifically leverage the hybridization of collagen mimetic/like peptides (CMP or CLP) with a native collagen through a strand invasion process to tether CMP/CLP modified nanostructure carriers onto collagen-containing matrices. I hypothesize that CMP/CLP modified carrier and collagen tether approach should result in the extended duration of therapeutic effects and control over the delivery of the cargo in response to cell-mediated collagen degradation.

The first/second objectives of this thesis were to control growth factor gene transfer kinetics while regulating cell behaviors via manipulating both the number of CMP-collagen tethers and the ECM composition for improved wound repair. Disruption in vascularization during wound healing can severely impair healing. Pro-angiogenic growth factor therapies have shown great healing potential; however, controlling growth factor activity and cellular behavior over desired healing time scales remains a critical challenge. I developed gene-activating hyaluronic acid-collagen matrix (GAHCM) comprising DNA/polyethylenimine (PEI) polyplexes retained on hyaluronic acid (HA)-collagen (HCM) hydrogels using CMPs. First, I observed that polyplexes with 50% CMP-modified PEI (50 CP) showed enhanced retention of polyplexes in HCM hydrogels by 2.7-fold as compared to non-CMP modified polyplexes. Moreover, the enhanced retention of polyplex through CMP modification, as well as through HA-CD44 interaction via the incorporation of HA in the collagen hydrogel, increased gene transfection efficiency to fibroblasts. Furthermore, when fibroblasts were exposed to pro-angiogenic and pro-healing vascular endothelial growth factor-A (VEGF-A)-GAHCM, the 50 CP matrix facilitated sustained VEGF-A production for up to 7 days, with maximal expression at day 5. This sustained VEGF-A production using VEGF-GAHCM with 50 CP stimulated prolonged pro-healing responses, including TGF-β1-induced myofibroblast transformation. In addition, application of fibroblasts containing VEGF-GAHCM with 50 CP stimulated the increased growth and persistent migration of endothelial cells (ECs) for at least 7 days, as compared to non-CMP modified GAHCM. Moreover, this resulted in elevated CD31 expression on ECs and formation of an interconnected EC network with a significantly higher network volume and a larger diameter network structure. Lastly, application of VEGF-GAHCM with 50 CP in murine splinted excisional wounds facilitated prolonged pro-healing and pro-angiogenic responses resulting in the overall enhanced wound closure via increased myofibroblast differentiation and blood vessel formation, improved granulation tissue formation, and faster re-epithelialization. Overall, these findings demonstrate the use of ECM-based materials to stimulate efficient gene transfer and regulate cellular phenotype, resulting in improved control of growth factor activity for wound repair.

The third objective of this thesis was to design new antibiotic delivery systems that maximize pharmacological effects and minimize side effects. Despite the great promise for antibiotic therapy in wound infections, antibiotic resistance stemming from frequent dosing diminishes drug efficacy and contributes to recurrent infection. To overcome the limitations of current antibiotic therapies, I developed elastin-like peptide and collagen-like peptide (ELP-CLP) nanovesicles tethered to collagen-containing matrices to control vancomycin delivery and provide extended antibacterial effects against methicillin-resistant Staphylococcus aureus (MRSA). I observed that as compared to liposome formulations, ELP-CLP nanovesicles showed enhanced entrapment efficacy of vancomycin by 3-fold and enabled the controlled release of vancomycin at a constant rate with zero-order kinetics. Moreover, ELP-CLP nanovesicles could be retained on both collagen-fibrin (co-gel) matrices and collagen-only matrices, with differential retention and release on/from the two biomaterials resulting in different release profiles of vancomycin. Overall, the biphasic release profiles of vancomycin from ELP-CLP tethered collagen/co-gel more effectively inhibited and delayed the growth of MRSA even after repeated bacterial inoculation as compared to matrices containing free vancomycin. Thus, this newly developed antibiotic delivery system exhibited distinct advantages for controlled vancomycin delivery and prolonged antibacterial activity relevant to the treatment of wound infections.

In summary, this dissertation describes that CMP modification of nanocarriers enables not only the extended delivery of therapeutics from collagen-containing matrices through CMP and collagen tethers, but also through improvements in therapeutic effects in vitro. Thus, this work suggest that CMP-collagen tether approach has significant potential to overcome key challenges in the topical administration of therapeutics for wound healing and regenerative medicine.