Biomedical engineering, cell biomechanics, vascular engineering

Sriram Neelamegham, Associate Professor

Application of Engineering in Medicine

Research in our laboratory lies in the field of Biomedical Engineering, with emphasis on vascular engineering and disease mechanics. The underlying theme is to apply novel bioengineering techniques and quantitative methodologies in combination with fundamental biological principles, to elucidate the parameters and mechanisms that regulate blood cell, protein and vascular endothelial cell function. Such studies are important since ailments of the blood account for a sizable fraction of inflammatory and cardiovascular disorders. Application of engineering in this research area can lead to new understanding that is not possible from typical biological or biochemical experimentation. Current projects in the laboratory can be broadly classified into three areas.

Leukocyte Adhesion Cascade: Inflammatory disease mechanics

Inflammation is a defense reaction caused by tissue damage or injury, characterized by reddening due to dilation of blood vessels, swelling due to the escape of blood proteins from the blood stream to surrounding tissue, and pain associated with various features including the release of toxic substrates by white blood cells (or leukocytes) that enter the inflamed tissue. While, inflammation is generally a beneficial process, inappropriate leukocyte deposition during vascular diseases like asthma, arthritis, reperfusion-injury etc. can lead to unwanted tissue damage and pain.

A cascade of events involving at least three families of adhesion molecules plays a role in leukocyte adhesion at sites of inflammation: these molecules are members of the selectin, integrin and Immunoglobulin gene superfamily (see Figure A). A better understanding of the physical and biological factors regulating leukocyte deposition in tissue can yield novel therapies to combat inflammatory diseases. With this in mind, we perform studies that contribute to a fundamental understanding of the roles of biomolecules, cell signaling processes and fluid forces in regulating the leukocyte adhesion cascade. Special emphasis is placed on understanding the features regulating the time- and stimulus- dependent transition of leukocytes from a quiescent state in the blood stream to an activated state at sites of inflammation. We are also involved in the development of new therapies/antagonist directed against some of these molecular interactions, especially those directed against the ligands of selectins.

Haemostasis and Coagulation: Fluid forces regulating cardiovascular diseases

Coagulation is a necessary process that prevents excessive bleeding following injury to the human body. When this process goes awry, unwanted aggregates and emboli can form, leading to cardiovascular ailments like heart attacks and stroke. These diseases represent leading causes of death in the modern world. Studies in our laboratory examine selected aspects of the processes regulating normal haemostasis and disease.

In one aspect, we are examining the biological and biophysical features regulating the size of a large polymeric blood protein called von Willebrand Factor (vWF) under both static and fluid flow conditions (Figure B). vWF plays a key role in regulating arterial thrombosis by aiding platelet deposition at sites of vascular injury. In these projects, we examine the features regulating the size and structure of the protein under static and hydrodynamic flow conditions. We are also interested in the mechanism by which fluid forces can cause vWF to bind to blood platelet receptor GpIb? and cause cellular activation and aggregation.

In another aspect, we are involved in determining the nature by which leukocytes can interact with platelets to enhance vascular emboli formation. These studies examine the dynamic nature by which an array of adhesion molecules selectively and sequentially participate in the formation of heterotypic cellular aggregates in both the venous and arterial circulation.

Bioengineering and Biophysical Model Development

The experimental work described above employ a range of methodologies including video microscopy and imaging, rheometry, molecular biology and recombinant DNA technology strategies, flow cytometry, cell culture, light scattering, small angle neutron and X-ray scattering and various types of chromatography. To complement these experiments, biophysical mathematical models are developed. The objective of model development is to acquire tools that may either: i) help us better interpret experimental data, or ii) that will allow us to design new experiments. Emphasis during mathematical modeling is placed on exploiting our strengths/knowledge in chemical reaction kinetics and transport phenomenon.

Examples of such modeling include: i) Examination of the role of secondary and non-linear flow in regulating cell adhesion rates; ii) Quantitation of molecular on-rates and adhesion efficiencies during cell adhesion studies carried out in flow chamber devices and viscometers; iii) Development of fundamental theories to quantify the nature and magnitude of hydrodynamic forces applied on intercellular bonds, soluble molecules, and cell-surface receptors; iv) Analysis of large biochemical networks in the area of bioinformatics to study cellular signal transduction and define rate controlling steps in the intracellular signaling cascade.