Water-Immersed Polymer Interfaces and the Role of their Interfacial Properties on Bio-Interfacial Forces

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(CBET- 0651983 / Notre Dame U. / Zhu, Y.)Responsive Polymeric Biointerfaces with Tunable Interfacial ForcesThis nano-bio-related project addresses the science and engineering challenge of understanding the role of interfacial properties of biological fluid-immersed polymeric thin films on biolubrication. While this project focuses on fundamentals, the PI has in mind biomedical engineering applications related to polymer interfacial interactions that underlie friction reduction and wear prevention in biological systems such as moving cartilage joints and the development of biocompatible and non-biofouling coatings. Specifically, this proposal aims to understand the superlubricity mechanism in biological soft tissues, and to go beyond this to manipulate the ultra-low friction responses of synthetic polymeric biointerfaces on demand by judicious choice of surface chemistry and viscoelasticity, as well as imposed external stimuli. The immediate objectives of this research are: 1) to characterize interfacial properties of polymer thin films immersed in biological fluids and to probe the coupling ofnormal and frictional forces at deformable polymeric biointerfaces that possibly induce lift to reduce wear; 2) to elucidate how the biolubrication behavior differs at contrasting hard interfaces; and 3) to address the roles of temperature, surface end-functionality and adsorbed protein on interfacial forces at polymer interfaces in aqueous media. The proposed research will focus on aqueous solutions including simulated body fluids, lubricin and synovial fluids at interfaces of: 1) a low-elastic polymer brush-like coating, poly (N-isopropylacrylamide) whose phase and viscoelastic behaviors are thermally and chemically tunable, and 2) self-assembled monolayers (SAM) where surface hydrophobicity and thus protein affinity are systematically varied to control the friction.Intellectual Merit. Understanding how molecular structure endows specific interfacial forces and dynamic properties of biomimetic interfaces would enhance our knowledge of synovial joint lubrication, arthritis or chronic joint symptoms, as well as the engineering of intelligent polymeric thin film with optimal interfacial properties. It will be the first time that the structure-rheological relationship of interfacial biofilms can be deciphered with concurrent microscopic and interfacial force measurements by a novel experimental setup in the PI's lab. The unique correlated facilityintegrates an interfacial force apparatus with a confocal microscope to simultaneously measure interfacial forces and visualize 3-dimensional transient microstructure dynamics of the underlying polymer films due to external stimuli. It offers a new molecular approach to examine biolubrication mechanisms at soft biomacromolecular interfaces. The technical significance also includes thedevelopment of new molecular design paradigm for intelligent biological thin films with optimized interfacial properties. The study of the interplay between interfacial forces and microstructure on soft interfaces with a confine fluid thin film is scientifically important, not only in basic tribology science, but in a number of areas including microfluidics, drug delivery and biomedical devices.Broader Impact. A broad-based education/outreach program is integrated with thisinterdisciplinary research program. Already active in the local chapter of the Society of Women in Engineering (SWE), the PI is committed to the recruitment and retention of female students who continue to be under-represented in many engineering disciplines. The PI also actively participates in a co-exchange program with the neighboring St. Mary's College, a leading private woman's Catholic University in educating woman students. Central to this proposal is curriculum development and research mentoring to strengthen the biomolecular engineering program at Notre Dame. Finally, this project seeks to establish a strong coalition with the lubricant and automotive industries such as Ford Motor and ExxonMobil, and Indiana's active orthopedic industry to help students, scientists and engineers communicate and interact on molecular design of interfacial lubricants.