Effect of the Electrostatic Interactions on Lubrication in Biological and Polymeric Systems

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TECHNICAL SUMMARYThis award supports theoretical and computational research and education in biomaterials and their role in mammalian joint lubrication. Friction and lubrication play an important role in everyday experience. Many biological surfaces such as such as cartilage, airway surface layers in the lungs, mucin layers in the eyes, are covered with a brush-like polyelectrolyte layer consisting of glycoproteins. These brush layers have remarkably low friction coefficient in the range 0.001-0.03 and can withstand pressures of the order of ten atmospheres.The PI will use a combination of the molecular dynamics simulations, self-consistent field calculations, and scaling analysis to develop a model of lubrication of glycoprotein layers. This approach is based on a coarse-grained model of glycoprotein in which it is represented as a strongly charged molecular bottlebrush consisting of side chains grafted to the main chain backbone. The research will focus on the interaction between two bottlebrush layers. Theory and simulation will be used to calculate the brush layer thickness, the layer compressibility, and the chain relaxation dynamics as a function of salt concentration, solution pH, fraction of charged groups, the molecular architecture, and the sliding velocity. Molecular dynamics simulations will be performed with explicit solvent to elucidate the effect of the hydrodynamic coupling on the energy dissipation in sliding polyelectrolyte layers. The developed model will be applied to describe lubrication in multilayered polyelectrolyte coatings. The simulation and theoretical results will be compared with experimental data for friction coefficient between synthetic bottlebrush layers and between two multilayer coatings. This study may help to discover new routes for developing polymeric coatings with excellent lubricating properties for biomedical applications. This research project will train graduate students in modern analytical and computational techniques. High school students will also be exposed to the research through the UConn Mentor Connection Program. This will broaden students intellectually and provide each with a unique insight into the problems and technology of the future. Mentoring of students is integrated into every aspect of the proposed research. Graduate students will work with undergraduate physics, chemistry or chemical engineering students and with talented high school students. This experience will prepare them for future academic careers. Underrepresented groups in education and scientific research will be involved through the Honors Program and existing infrastructure of the REU sites.The results of the proposed research will be incorporated into the course sequences on "Polymer Physics", and "Polymer Physical Chemistry" as well as into a new special topics course "Ion-containing polymers".NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education in biomaterials and their role in lubrication in biological systems. Friction and lubrication are a part of our everyday experience ranging from machinery to biological organisms. Many connective tissues, such as cartilage, demonstrate excellent lubrication and wear characteristics. Cartilage in the joints of mammals can withstand pressures ten times atmospheric pressure and move with remarkably little friction. The surface of the cartilage is covered with a brush-like layer of large chain-like molecules that have electrical charges. This brush layer, which faces a similar layer on the opposing cartilage, is sheared as two surfaces slide passing each other during joint motion. The PI will use computer simulations and theoretical methods to understand the complex interaction between brush layers and how it leads to the lubricating properties of biological and chain-like molecular systems. This knowledge will enable the explanation of the low friction between sliding surfaces of the cartilage. This research will help advance understanding of lubrication properties of other biological surfaces, such as airways surface layer in lungs and the mucin layer in gastrointestinal tract, where brush-like molecules form protective interfacial layers.This research project will train graduate students in modern analytical and computational techniques. High school students will also be exposed to the research through the UConn Mentor Connection Program. This will broaden students intellectually and provide each with a unique insight into the problems and technology of the future. Mentoring of students is integrated into every aspect of the proposed research. Graduate students will work with undergraduate physics, chemistry or chemical engineering students and with talented high school students. This experience will prepare them for future academic careers. Underrepresented groups in education and scientific research will be involved through the Honors Program and existing infrastructure of the REU sites.The results of the proposed research will be incorporated into the course sequences on ?Polymer Physics?, and ?Polymer Physical Chemistry? as well as into a new special topics course ?Ion-containing polymers?.