| A beating heart requires coordinated interactions among the contractile facility (cardiomyocytes), the vascular system (endothelial cells), and the connective tissue (fibroblasts) for its development and functionalization. The involved cell types undergoes differentiation and maturation during which both homotypic and heterotypic contacts form to mediate specialized interactions. Particularly, each individual cardiomyocyte (CM) interacts with its microenvironment composed of extracellular matrix (ECM), neighboring cells, and various diffusible molecules to complete its differentiation, sarcomerogenesis, electrical and mechanical couplings, and remolding. In this dissertation, I explore the use of cutting-edge microfabrication techniques to create in vivo-like microenvironment to study cardiomyocyte development, remodeling, and rescue. The first project is on the most inner layer of ECM, basement membrane (BM), enclosing each CM. Previous s has studies have revealed numerous important physiological functions of BMs: 1) as a mechanical support for contraction, 2) as a calcium buffering layer, and 3) as a growth- factor receptor based on the intense contact-mediated cell-ECM/cell-cell interactions. But how BM encloses each CM during development, its biological functions on the physiological behaviors of CMs, and how BM is involved in cardiac cell-cell interactions are still unclear. With establishment of an in vitro culture model with aligned collagen fibrils in vitro culture model, BM on each CM shows the morphological development from dot to line, then to fishnet network, and is intensively involved in the cardiac sarcomerogenesis via the mechanical transduction path of BM-integrin-Z-line. Further, BM deposition on the extracellular layer also influences the cardiac electrical properties through regulating calcium influx, and gap-junction formation through cell-cell interaction on gap junction formation over a short distance. Aside from the short distanced cell-cell interaction formed between cardiac cells, a long distance cell-cell interaction, tunneling- nanotube (TNT) formation, is newly discovered to be formed between a stem cell and a CMs. A The second project is on the development of a microfluidics- based biochip was microfabricated to unravel the structure and development of TNT formed between a mesenchymal stem cell and a neonatal CM (NCM)s. Moreover, the mitochondrial transfer via TNT was also studied, proving it showing its significance relevant to the stem cell therapy based cardiac rescue. Then, cardiac cell-microenvironment interaction with the respect to mechanical overload was investigated using a live-cell imaging technique and custom-designed static cell stretcher with a unique microstructure to study the mechanisms of sarcomeric remodeling during hypertrophies. The imaging results imply show two possible remodeling mechanisms of different corresponding to two types of hypertrophies: Sarcomeric addition on the ends in the longitudinal stretch (volume- overloaded hypertrophy); sarcomeric branching splitting in the lateral stretch (pressure overloaded hypertrophy).;Finally, limitations, possible improvements, and potential future directions are proposed discussed in the respect of cell-ECM, cell-cell, and cell-microenvironment interactions based on the current setups and device microfabrication designs. |
