Kim:Research
Our research focuses on investigating how the engineered microenvironments direct cell function and tissue regeneration. In particular, we are exploring extracellular matrix (topology, rigidity, dimensionality, etc) regulation of cell fate and function in developmental, physiological and pathological process. Several specific thrusts of the current research program include: microengineered platforms for cell-matrix mechanobiology, mechanical regulation of cancer cell invasion and collective cell migration, microscale cardiovascular tissue engineering, and BioMEMS for stem/progenitor cell niche engineering. Here is a summary of our current research projects.
1. Biomimetic in vitro cell culture models
Our curent research focuses on engineering combinatorial cellular microenvironment through use of variable nano-patterns, and soluble and matrix-bound cell guidance cues in a single experiment, which better mimics the in vivo microenvironment under physiological conditions. For example, we are developing a microfluidics-based on chip assay integrated with complex nanoscale topographic features to enable the analysis of concerted cell responses to composite gradients of precisely generated and aligned surface-bound ECM molecules and diffusible guidance cues or topographic guidance cues. Using these tools, we can systematically expose live cells to wide spectra of dynamically changing combination of mechanical and chemical stimuli (e.g. ECM proteins, topographic, growth factors and signal transduction pathway inhibitors). The proposed measurements are highly resolved in time and space, using a variety of live cell probes and highly defined extracellular conditions. In collaboration with other nanofabrication groups, we are developing nanotopography-integrated cell culture systems and tissue scaffolds of biomaterials using UV-assisted capillary force lithography and/or nanoimprinting techniques. For high-throughput analysis, we are also working to combine nanopatterned substrates with traditional multi-well tissue culture plates. Ultimately, we will use these tools to gain new mechanistic insights into cell signaling and function, to design new therapies or diagnostic tests for cancer progression and cardiovascular diseases, and to establish organizing principles for development of precisely defined scaffolds for advanced tissue engineering applications.
2. Mechanics and signaling in cancer cell invasion and epithelial wound healing
Using a combination of various techniques, from molecular biology to nanotechnology with microrheological measurements, we have been accumulating interesting data suggesting that one of the most important factors distinguishing metastatic from non-metastatic cells could be their ability to physically interact with the surrounding ECM and re-organize it. We also found that inhibition of the PI3K interferes polarization and movement of metastatic melanoma (the most dangerous type of skin cancer) cells cultured on nanostructured substrata that mimic oriented matrix fibers in vivo. These results have important implications for our understanding of metastasis processes in melanoma and their control by ECM signals and topography. For additional evidence of cancer cell-matrix interactions, we also perform cancer cell migration experiments within 3D collagen gel culture construct, which would be more flexible and controllable than the in vivo experiments. In these experiments, we trace the movement of metastatic and/or non-metastatic cells integrated with collagen gel as well as the local re-organization of surrounding gel structure.
We also pursue to examine the biological mechanics and signaling in collective epithelial (and endothelial) cell migration in the context of wound healing driven by the hypothesis that the physical interaction of migrating cells with the surrounding ECM has a crucial role in the guidance of wound repair. To test this hypothesis, we recently developed a microfabricated epithelial wound model integrated with nanotopographic substrata as an experimental platform, allowing time-lapse high-resolution microscopy of fluorescently tagged cytoskeletal and signaling proteins. Using these tools, we explore the potential role of mechanical guidance in the regulation of collective cell migration under the presence/absence of growth factor-induced signals, and test their biomedical implication by screening cytoskeletal and signal transduction inhibitors, including Rho-associated kinase (ROCK) inhibitor (i.e. Y27632) and PI3K inhibitor (i.e. LY294002).
3. Nanostructure-cell interactions for stem cell and cardiovascular tissue engineering
With advances in nanofabrication and biomaterials, scaffolding materials can be designed to integrate biomimetic structural and mechanical cues present in the in vivo ECM environment. Based on ultrastructural analyses of the native heart tissue, we are developing a bio-inspired model cardiac tissue, to demonstrate that it is through the cardiac tissue engineering on the nano- rather than micro-scale that we can control the engineered cardiac tissue function most effectively and bio-mimetically (Kim et al., PNAS, 2010). We are also extending this work toward better understanding of cardiac tissue structure-function relationships, and seek applications in stem cell-based therapies for tissue repair and regeneration.
The ultimate goal of this project is to develop nanopatterned functional cardiac patches for heart tissue repair. The working hypothesis is that cultivation of cardiac cells and/or stem cells on novel biomaterials scaffolds integrated with nanotopographic cues promotes biomimetic anisotropic assembly of uniformly contractile engineered muscle, while simultaneously enabling control over local cell alignment. We further hypothesize that integrating the transplantable stem cells with the proposed nano-grafting techniques have therapeutic potential in repairing cardiac tissue damage and may prevent the onset of heart failure. In order to test these hypotheses, our research focuses on elucidating the relationships between scaffold-mediated nanostructural cues and tissue engineered cardiac graft contractility and function. In addition, the therapeutic potential of a nanopatterned cardiac stem cell graft will be studied in vitro and in vivo (implantation onto the left ventricle in an adult rat model of myocardial infarction). Tissue structure and function will be characterized at various hierarchical scales (molecular, structural, functional) and the obtained experimental data will be used to tailor the conditions and duration of cultivation, leading to engineering implantable grafts.
