Current Projects
 | Mechanobiology of the Developing Left Atrioventricular Valve The development of atrioventricular(AV) valves occurs within a constantly changing mechanical environment, which plays an important role in the development process. Understanding the fundamental mechanobiology of the developing embryonic mesenchyme is thus important for devising tissue regeneration strategies, but quantative analysis of the development has been limited due to the small tissue size and rapid valvular development. To address this challenge, our lab has developed specialized microscale test platforms capable of evaluating 3D cell responses to defined mechanical loads in high throughput. We are currently investigating the role of fluid shear stress and matrix strain on the differentiation of these precursor cells into mature phenotypes in vivo, in vitro, and in silico. By perturbing the local microenvironment and quantifying biological responses, we aim to identify engineering paradigms that can be applied to direct the differentiation of stem and progenitor cells towards valvular phenotypes and the formation of mature valvular matrix. |
 | Mechanoregulation of Cardiac Differentiation and Morphogenesis The early heart forms from two bilaterally symmetric fields of mesoderm that migrate and fuse medially into a tubular structure that eventually begins rhythmic beating. The rapid assembly of 3D functional tissues from 2D cell sheets in vivo is a fascinating but relatively unknown process. While many studies have identified molecular players in this process, very little is known about how the local mechanical environment drives this process. We have developed specialized 4D time lapse imaging algorithms to monitor cell and matrix interactions during cardiogenesis in real time. We also monitor and perturb the local micro-mechanical environment to alter how the local cells differentiate and heart tube forms. Understanding these biophysical dynamics and how they control early cell fate will lead to new strategies to drive cardiac differentiation and de novo functional tissue assembly with pluripotent stem cell sources. |
 | 4D Imaging of Cardiovascular Morphogenesis and Function Via Micro-CT Visualizing and quantifying the complex changes that take place during embryonic development are crucial for understanding how congenital heart defects form and progress. Confocal microscopy and optical coherence tomography (OCT) are common techniques used to image early cardiac morphogenesis in animal models, but they lack the depth of field necessary to observe later-stage development. Magnetic resonance imaging (MRI) and ultrasound are used for studying later timepoints, but these strategies are often limited by low spatiotemporal resolution. In this project, we are aiming to address such limitations of noninvasively monitoring embryonic development using micro-computed tomography(Micro-CT). Through collaboration with GE Healthcare, we utilize the state-of-the-art Micro-CT imaging technology in combination with novel contrast agents we developed to generate and visualize embryonic heart development in 4D. We then implement custom-written algorithms to create finite element models and to quantify the mechanical and fluid dynamic environments in the functioning hearts. These unique datasets have led to better understanding of how the heart beats at different stages of development, which we believe will inform quantitative multiscale models that will help devise optimal treatment strategies for various congenital anomalies. |
 | Noninvasive Manipulation of Embryonic Development Through Focused Laser Microablation Congenital heart defects are common and serious disorder that often lead to birth-related deaths, yet only a small number of clinically observed cases (~10%) can be traced to a genetic deficiency. How cardiac morphogenesis is altered in these epigenetic cases is poorly understood, but the change is likely related to simultaneous misexpression of numerous genes that are coordinated in this complex process. The focus of this project thus is to create epigenetic models of congenital heart defects by mechanically perturbing embryonic development. To achieve this goal, we have been combining two different techniques. We first utilize microsurgery to band or ligate developing cardiac structures in order to shift hemodynamic patterns in the heart and to monitor downstream morphogenesis and cell fate. In collaboration with Professor Chris Schaffer (BME, Cornell), we then use two photon laser microscopy to noninvasively image and study deep into developing embryos. In addition to microsurgery ligation, we are also able to occlude and shunt localized regions of the developing hearts using focused ultrahigh frequency laser pulses. These noninvasive approaches enable unique ways of creating and studying consequences of clinically relevant congenital heart defects. |
 | Shared Inflammatory Signaling Pathways in Valvular Development and Disease Inflammatory activation of endothelial cells is a principal initiator of atherosclerotic degeneration in blood vessels and heart valves. Recent studies suggest that adult valvular endothelium can transform into mesenchyme in a manner similar to embryonic valve development, but how inflammation controls this process is yet unknown. We have identified common inflammatory inducers of endothelial-to-mesenchymal transition(EMT) events in adult and early embryonic valve endothelial cells, and we are currently exploring how mechanical signaling potentiates these responses. Developing embryonic and diseased adult valvular endothelial cells appear to have similar cell phenotypes, and recapitulation of embryonic phenotypes in valvular endothelial cells thus may be an important mechanism of disease progression. Studying both embryonic and adult valve environments in parallel is a powerful paradigm for identifying these unique disease mechanisms and testing the efficacy of novel therapeutic strategies. |
 | Role of Hemodynamics in the Progression of Aortic Valve Disease Vavlular disease progression is a complex process, and our limited understanding of the progression often impedes our ability to rescue the valve before it becomes irreparably damaged. Our goal of this project thus is to utilize ultrasound and molecular/cellular techniques to understand and predict valve deterioration. Through our surgical collaborators, we have been building a human patient database through which we have identified key groups that appear to tolerate valve disease differently. Within these database, we developed automated quantitative analysis tools to parse ultrasound data to identify new mechanical correlates that can predict valve deterioration. In addition to ultrasound analysis, we also isolate and culture human valve cells and study their responses to mechanical forces using custom built high throughput mechanical bioreactor systems. We also study genetic mutant models of heart valve disease, as well as surgical approaches to induce and control valve disease in animals. Our major focus is studying how mechanical forces potentiate valvular endothelial-interstitial cell interactions in healthy and diseased conditions. Uncovering the molecular and cellular mechanisms that drive valve disease will provide new therapeutic targets and strategies to treat patients with early stage disease before they progress to necessitate valve replacement. |
 | Biomechanical regulation of growth and matrix maturation in the embryonic heart Replicating valve tissue growth and adaptation is a key requirement of tissue engineered heart valves especially for pediatric applications, yet we do not sufficiently understand these development processes in vivo. Very rapid growth and structural remodeling occurs during embryonic development, which is concomitant with an increasingly demanding hemodynamic environment. We approach to better understand embryonic valve development using various techniques including in situ hybridization, histology staining, continuum mechanics theory, and computational simulations. In our growth model, we postulated that local stress states diverging from a homeostatic stress induce growth or atrophy. As a result, we have developed a stress based growth law which determines basic heart morphology as well as the evolution of the structural constituent volume fractions. The hemodynamic loading conditions of the tissue have been inferred from computational fluid dynamics simulations and validated with ventricular pressure measurements. This work promises important implications for tissue engineering, as specific loading regimes may enhance growth of replacement tissue. |
 | Development of Spatially Heterogeneous and Anatomically Accurate Living Heart Valves Using Cell-seeded Hydrogels The aortic valve is a complex heterogeneous structure designed to ensure unidirectional blood flow and to provide blood to the heart through the coronary ostia. Ongoing extracellular matrix (ECM) remodeling and valve repair are mediated by dynamic populations of aortic valvular interstitial cells (VICs) in leaflets and smooth muscle cells in the root. Heterogeneous cell and ECM distribution in the valve are thus important for appropriate mechanical function of the relatively stiff root and flexible leaflets. Current tissue engineering strategies, however, do not adequately replicate internal tissue heterogeneities, where the challenge in controlling tissue geometry still remains to be addressed. For this study, we are developing an approach that combines MicroCT image processing, custom algorithms, and solid freeform fabrication (3D printing) to generate cell-seeded valve constructs incorporating anatomic heterogeneities and complex geometry. To achieve this goal, we are collaborating with other groups, most notably with Dr. Hod Lipson’s group (developer of the 3D printing platform “Fabber”) and with Dr. C.C Chu’s group (developer of various novel biodegradable polymers). By testing specific micro-environments with defined geometries and mechanical properties, we can learn to control cell behaviors and differentiation characteristics needed for rational engineering of living tissues. |