Interfacial Rheology of Biological Interfaces
Speaker: Dr. Gerald G. Fuller
Department of Chemical Engineering
Biological systems are normally high-interface systems and these surfaces are laden with biological molecules that render them rheologically complex. The resulting nonlinearities with response to surface stresses and strain are often essential to their proper function and these are explored using recently developed methods that reveal interfacial moduli and microstructure. Three applications are discussed.
1. The tear film of the eye is a composite structure of an aqueous solution of protein and biomacromolecules. This thin layer is further covered by a film comprised of meibomian lipids excreted during each blink. The purpose of the meibum has been largely unexplained although one prevailing suggestion is that it suppresses evaporation. Recent measurements in our laboratory demonstrate that this layer is strongly viscoelastic and this property has dramatic effects on the dynamics of the moving contact line and stability against dewetting.
2. Biofilms are protective layers produced by bacteria colonies that offer protection against desiccation and external agents that can attack the colonies. This layer, a result of amyloid fiber produced by the bacteria make it difficult to treat intestinal tract infections in our own bodies and methods to monitor the kinetics of biofilm development and the resulting response of the films to excipient materials that might upregulate or quench amyloid production are needed. Experiments are described where interfacial moduli are demonstrated to be very effective in sensing the presence of these films and provide a convenient format for the systematic introduction of external, chemical agents.
3. Vascular endothelial cells line the interior walls of our blood vessels and are sensitive to surface shear stresses. These stresses are known to affect the shape and orientation of endothelial cells. It is evident that the spatial homogeneity of flow can affect vascular health and it is well-documented that lesions form in regions of high curvature, bifurcations, and asperities in blood vessels. Experiments are described where stagnation point flows are used to create regions of well controlled flow stagnation and spatial variation of wall shear stresses. Live-cell imaging is used to monitor the fate of cells attached to surfaces experiencing flow impingement and it is revealed that endothelial cells migrate and oriented in such flows to create remarkable patterns of orientation and cell densification.
Dr. Gerald Fuller is the Fletcher Jones Professor of Chemical Engineering at Stanford University where he has carried out research and taught since graduating from Caltech in 1980. Professor Fuller's research has centered on three areas of rheology: optical rheometry, extensional rheology, and interfacial rheology. This experimental effort has been aimed at a wide range of soft materials that includes polymer solutions and melts, liquid crystals, suspensions, and surfactants. Recent applications are linked to biological materials. Professor Fuller received the Bingham Award fromThe Society of Rheology and is a member of the National Academy of Engineering.