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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:
The Pivotal Role of the Endothelial
Glycocalyx 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.
Fluid Flow in Bone/Cartilage
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.
Bio-Mimicry
Soft/Super Lubrication:
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.
Skiing Mechanics
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.
Fluid Dynamics
Lift Generation in Highly Compressible
Porous Media
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.
Stagnation Point Flow in a Porous Media
Using Jet Impingement Technique
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.
Hydrodynamic Study for US Navy Unmanned
Surface Vehicle (USV) Control
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.
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