Tissue injury initiates a cascade of complex cellular and molecular events that coordinate the healing response. With disruption of vascular networks the supply of oxygen becomes limiting with a concomitant increased demand to support inflammatory processes and cell proliferation leading to a reduction in tissue oxygenation and hypoxia. Additionally, immediately post injury, a gradient of chemokine and growth factor signals emanate from the wound site to orchestrate the repair response. One role of these signals is to elicit the recruitment of cells from the local tissue microenvironment as well as those from the circulation. One of the most recently identified cell populations to participate in repair is a novel bone marrow-derived stem cell population that is mobilized through the peripheral circulation, homes to sites of tissue damage, and contributes to the wound repair process. Within the skin, these mesenchymal stem cells (MSCs) contribute to the healing wound as collagen expressing fibroblasts, a protein and cell type vital to the success of the repair process. However, those chemokines or combinations of chemokines and local oxygen concentrations that elicit MSC recruitment to sites of tissue damage and their subsequent proliferation and differentiation within the wound remain to be elucidated. Current approaches for examining cell migration generally involve exposure to a constant concentration of a single chemokine under controlled oxygen tension. These methods are therefore only capable of providing a very limited view of the milieu to which cells are exposed, for example during wound repair. This proposal seeks to develop a family of novel and innovative microfluidic devices to examine cellular behavior in complex chemokine gradients and oxygen tensions more reminiscent of the in vivo situation. BioMEMs technology will be employed to design, fabricate and optimize three device subclasses: 1) devices that will generate defined, single and combinatorial chemokine gradients, 2) devices that will produce sensitively monitored, time-stable oxygen gradients, and 3) devices that will combine chemokine and oxygen gradients. Each class of device will be validated with known cell populations, chemokines, and oxygen tensions (e.g. Fibroblasts, PDGF, and normoxia). Once standardized, these devices could be easily adapted for use in other ex vivo analyses and applications that seek to examine cellular migration and behavioral responses. To this end, we will use our devices as experimental tools to provide highly-controlled, in vitro micro-environments to identify those chemokines/growth factors and oxygen concentrations that facilitate migration, stimulate proliferation and induce differentiation of MSCs. It is our hope to exploit the data generated from the proposed studies to develop novel therapeutic modalities to augment the wound site to potentiate repair and enhance clinical outcomes.
Wounds that do not heal appreciably reduce patient quality of life, especially for those individuals who are of advanced age and/or suffer from diabetes. Effective wound care treatments are therefore of significant public health concern. This study will utilize bioengineering to generate novel devices to determine those molecules and conditions that enhance the recruitment, proliferation and differentiation of specific stem cell populations. It is anticipated that data obtained from the proposed experiments will be useful in designing therapeutic modalities to enhance wound repair, decrease scarring, and produce a better clinical outcome.