(4cv) Synthetic Extracellular Matrix (ECM) Hydrogels and Localized Gene Delivery for Stem Cells and Tissue Regeneration

My first project focused on developing synthetic ECM hydrogels for stem cell engineering. In the body, stem cells reside in dynamic and complex 3D niches with spatially and temporally well-regulated biochemical & biophysical cues that control cell maintenance, self-renew and differentiation. We are developing synthetic hydrogels to mimic these niches for 3D stem cell culture, delivery and tissue regeneration. Polyethylene glycol (PEG) and hyaluronic acid (HA) are cross-linked with protease degradable peptides in the presence of cells to form the hydrogels. Peptides derived from ECM proteins are introduced into the scaffold as the adhesion points for cells. Proteins factors can be incorporated into the hydrogel through physical or chemical immobilization to guide cell behavior and fates. PEG and HA scaffolds are ideal for tissue regeneration because they are safe and have low immunogenicity. In addition, they have a low biological background, thus allowing us to engineer the hydrogel bioactivity through introducing protein factors, DNAs or siRNAs. With these hydrogels, we built a 3D model for studying the calcification of vascular stem cells (VSCs), which may contribute to the calcific atherosclerosis in the body. Then we cultured mesenchymal stem cells (MSCs) in these gels and found the 3D environments including the mechanics, adhesion peptide identity, concentration and presentation significantly affected their proliferation, spreading and migration. Currently, we are using these hydrogels to culture and deliver neural progenitor stem cells (NPCs) to treat stroke with our collaborators, with the objective that these synthetic ECM can improve the cell survival rate and integration into the surrounding tissue.

My second project is to develop novel technologies that can deliver genes (encoding for growth, transcription factors) and siRNAs to the diseased sites locally in a method that is cell-controlled to promote wound healing, tissue regeneration and to reprogram cells. Our approach is through using hydrogels to carry and deliver DNAs, siRNAs. The challenge along with this approach is to incorporate non-viral gene delivery nanoparticles (polyplexes) into the hydrogels without losing their activity, which results from their aggregation or disintegration in the hydrogel precursor solution before and during the gelation. We successfully developed a universal process to load concentrated, un-aggregated and active polyplexes into various hydrogels (up to 5mg pDNA/mL hydrogel tested). Both in vitro and in vivo tests show the encapsulated polyplexes remain active. Currently, we are studying the kinetics of transgene expression after implanting these DNA loaded hydrogels in vivo with a mouse skin wound model and a mouse subcutaneous implantation model. Through this kinetics study, we hope to find out methods to control the gene transfer from hydrogels in vivo through tailoring the hydrogels properties. We are also investigating if hydrogels loaded with VEGF, PDGF genes can promote angiogenesis and wound healing in vivo.

My future research will focus on manipulating cell fates (stem cells to mature cells; mature cells to stem cells and mature cell type one to another cell type) in vivo through synthetic cell niche and gene delivery technology for regenerative medicine. The ultimate goal is to generate the degenerated cells in situ instead of delivering cells to the diseased sites.