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Cardiovascular Engineering is one of our major research focuses. Much of this research is motivated by the desire to understand the vital role of the endothelial glycocalyx layer (EGL) in the microcirculation. We are especially interested in the following two important problems in microcirculation:
Cardiovascular disease is the leading cause of death and illness in developed countries and imposes a huge economic burden on our society. The endothelium, a thin layer of cells that lines the internal surface of all blood vessels, is actively involved in a number of vascular functions, such as regulation of vascular tone, fluid and solute exchange, hemostasis and coagulations and inflammatory responses. The endothelial Glycocalyx layer (EGL) is a soft porous structure that covers the surface of the endothelium. In the past decade, there has been an explosion in research regarding the EGL. Data so far indicate that an intact EGL contributes to the protection of endothelial functions throughout the vasculature, and that many cardiovascular diseases are associated with the perturbations of the EGL. From the biophysical point of view, the structural integrity and the lift generation in this soft porous structure make it possible for the frictionless motion of the red blood cells. The questions that we are trying to are are (1) what are the physical mechanisms that determine the lift generation inside the EGL and its structural integrity; (2) what is the role of the EGL in sensing the mechanical signals outside the endothelium to help the protection of endothelial functions.
Osteoporosis and osteoarthritis are leading causes of disabilities that impact millions of patients. It is critical for the treatment of osteoporosis to understand the cellular and molecular mechanisms of how bone senses mechanical stimuli for new bone formation. The questions that we are trying to answer are (1) how to characterize the micro fluidics around bone cells; (2) what kind of signals the bone cells senses Much like the low frictional conditions a red blood cell experiences in microcirculation, cartilage lubricates joints using the hydrodynamic pressure of the interstitial synovial fluid. This question that we are working to address is: how the lubrication conditions affect the progression of osteoarthritis.
The exquisite structure and properties of the EGL have made it possible for the frictionless motion of the red cell squeezing through our blood vessels. This is a beautiful example of the design of nature which has significant potential for revolutionizing the design of lubricating bearings. In particular, it could lead to a new generation of soft bearings with far greater lift forces and much longer life. It inspires us to develop a very comprehensive bio-mimetic approach to implement the super lubrication concept, using both macro-scale synthetic fibers and functionalized nano porous media. This project, aiming to reduce friction which is the major component in the total energy required for operation, will have significant impact on the energy conservation and green house gas reduction.
The lessons learned from the frictionless motion of red cells over the EGL also inspired me to examine the lift mechanics of downhill skiing or snowboarding, because both of them follow the same physical idea, lift generation in soft porous media. The immediate objective of this research is to explain why a 70 kg human can glide over a soft snow layer without sinking to the base as would occur if the motion is arrested, while the ultimate objective is to provide theoretical guidelines for the optimization of skis/snowboards. More significantly, the skiing mechanics theory can be readily expanded to the soft/super lubrication applications.
Lift generation in highly compressible, soft porous media is a new concept in porous media flow. This concept is of extraordinary importance because of its superior potential applications in squeeze damping and soft lubrication. We aim to elucidate the dominant mechanisms that determine the lift generation process and have developed a very comprehensive, experimental and theoretical approach for this purpose.
In collaboration with Dr. Amy Fleisher, we are interested in (1) velocity and pressure distribution inside a porous foam as fluid is impinging on it. This application is of particular interest for such biological problems as mechanotransduction where flow is either impinging on cells or flowing past cells that are either imbedded in an interstitial matrix or whose surface is covered by a matrix-like layer at their apical surfaces. (2) enhanced heat transfer using porous foams as heat sinks.
This project has been funded by the Office of Naval Research since 2006, as one of the topics submitted through the Center for Nonlinear Dynamics and Control. A better understanding of the lift and drag forces acting on the USV in the presence of complex sea situations helps improve the boat's stability and control. Our research interest focuses on two aspects: (1) how to develop a theoretical approach to describe the interaction between a planning surface with either calm water or complex waves and thus provide critical inputs for the control systems of USV; (2) how to extend this theory to other applications, e.g. the active control of USV.