“Engineering Healing - From Scarring to Regeneration”
Ken Webb, Ph.D.
Associate Chair of Undergraduate Affairs
The central goal of the Microenvironmental Engineering Laboratory at Clemson University is to develop therapeutic strategies to improve the outcome of the wound healing response, including both inhibiting fibrotic scarring and inducing tissue regeneration. Excessive deposition of collagenous matrix is a key characteristic of fibrotic scarring, as well as a diverse range of fibroproliferative pathologies. We have recently looked to the mechanobiology of the human vocal folds as a novel source of anti-fibrotic therapies. The identification of macrophages and myofibroblasts in the superficial layer of the lamina propria (SLLP) within the vocal folds of healthy patients suggests that routine speech results in repetitive microtrauma, which is generally repaired without permanent alterations in matrix composition or vocal quality. Based on the role of mechanical stimulation in the regulation of connective tissue matrix metabolism, we hypothesized that high frequency vibration inhibits fibrotic scarring. Human dermal fibroblasts subjected to vibration (100 Hz, 1 mm amplitude, 6 hours) exhibited significant increases in expression levels of the fibrotic cytokines TGFβ2, CTGF, and endothelin-1 relative to static controls. However, vibration also significantly affected the TGFβ signaling pathway, with a net effect of antagonizing signal transduction through reduced expression of TGFβ receptors and SMAD 2, 3, and 4 signal transduction molecules and increased expression of the signaling inhibitors SMAD7, SKIL, and SIK1. Using in vitro models of fibrosis, vibration was found to inhibit the induction of fibroblast collagen synthesis and mechanical strengthening of 3D porous substrates by cyclic strain or exogenous TGF1. These results suggest that the vibratory microenvironment of SLLP provides not only the biomechanical basis for voice production, but also influences biochemical signaling to provide resistance to fibrotic scarring. Identifying the mechanotransduction pathways activated by vibration may offer opportunities for the development of anti-fibrotic therapies. In addition to preventing scarring, regenerative healing of large tissue defects, for example in orthopaedics, often requires cell transplantation. Intraoperative therapies in which stem cells are isolated, concentrated, and immediately transplanted back to the patient within the operating room offer lower regulatory barriers and greater potential for rapid clinical translation. This approach creates a critical need for scaffolds that can simultaneously deliver stem cells and bioactive stimuli to direct their differentiation in situ. We have recently prepared semi-IPN hydrogels composed of dexamethasone-conjugated hyaluronic acid (HA-DXM) and hydrolytically degradable, photocrosslinkable PEG-bis-(2-acryloyloxy propanoate) (PEG-bis-AP) for bone regeneration. Dexamethasone (DX) release from semi-IPNs was minimal in physiological buffer and significantly greater from semi-IPNs containing encapsulated human mesenchymal stem cells (hMSCs) than acellular controls, indicating release by cell-mediated enzymatic degradation. hMSCs encapsulated in PEG-bis-AP/HA-DXM semi-IPNs increased osteoblast-specific gene expression, alkaline phosphatase activity, and matrix mineralization, attaining levels that were not significantly different from positive controls consisting of hMSCs in PEG-bis-AP/native HA cultured with conventional DX supplementation. These studies demonstrate that PEG-bis-AP/HA-DXM semi-IPNs can provide cell-mediated release of bioactive DX that induces hMSC osteogenic differentiation and may offer a novel system for local delivery of osteogenic molecules empowering point of care transplantation.
Faculty host- Andrés García, Ph.D.
The Bioengineering Seminar Series is a joint seminar series between the Petit Institute and the Wallace H. Coulter Department of Biomedical Engineering.