Lubricants play an integral role in the operation of several technologies and in biology, ranging from moving parts in machinery to the biolubrication of articular joints. The main purposes of a lubricant are to reduce friction and surface wear. We propose a collaborative project involving 3 faculty members fromTulane University and a faculty member from the University of Maryland, each bearing unique expertise required for the success of the project. The PI (N. Pesika) is a junior faculty in his 2nd year and was a postdoctoral associate in the Interface laboratory at UCSB working under the guidance of Dr. Israelachvili. In recent years, N. Pesika has done theoretical and experimental work to understand the adhesion mechanism of the gecko and has become proficient in tribology and the characterization of lubricants. V. John is a senior faculty member with experience in the field of surface and colloidal science, specifically in the synthesis and modification of colloids. H. Ashbaugh's research focuses on the multiscale simulation and the theory of self-assembly processes of molecules including surfactants, polymer melts, and biopolymer gels. S. Raghavan heads the complex fluid and nanomaterials group at the University of Maryland, and is an authority on self assembling soft materials. We have found that an easily synthesized system of monodisperse hard carbon submicron spherical particles (HCS) has frictional coefficients that start approaching those of synovial fluids. When these observations are coupled with a novel discovery in S. Raghavan's laboratory that a modified biopolymer (chitosan) is able to gel vesicles, we are able to realize a unique gel system containing the carbon microspheres serving as nodes in a network of this biopolymer. This forms the basis of our proposed work to develop novel gel based lubricants containing monodisperse particles or cushioning vesicles. Our hypothesis is that these composite materials will be able to reduce friction and minimize surface wear synergistically through the boundary lubrication of biomolecules/biopolymers and the rolling mechanism (similar to ball bearings) employed by HCS particles. We therefore propose to develop biomimetic lubricants with ultralow coefficients of friction that are robust and easy to synthesize. Several formulations composed of phospholipid based liposomes, biopolymers and carbon microspheres will be systematically explored to optimize the lubrication properties, including a low coefficient of friction and minimal surface wear, through molecular and particulate design.
Broader Impacts of research: While several types of lubricants have been formulated water-based lubricants that mimic synovial fluid remain elusive. A biomimetic lubricant exhibiting ultralow coefficient of friction has several applications including potential substitutes for synovial fluid in diseased or damaged articular joints or in applications to microfluidics or microelectromechanical devices. The potential scientific impact is extremely broad, affecting all industries utilizing lubricants.
Broader Educational and Outreach efforts: N. Pesika and H. Ashbaugh are committed to improving local K-12 education and have established a service learning course at the New Orleans Charter Science and Mathematics (NOCSM) High School. The demography of the school closely parallels that of the community, with 85% being from households classified as economically disadvantaged, and 86% of the student population belonging to a minority (82% African American). The outreach program was designed to present every day uses of the scientific method through presentation made by Tulane students followed up with experiments to illuminate the nature of the demonstrated phenomenon, like the rheological properties of biopolymers and the operation of heat engines. V. John has been a consistent participant of the LAMP (Louisiana Alliance for Minority Participation in Research) program for the last 8 years supervising one or two students every summer while N. Pesika will begin participation in the LAMP program over the summer. These minority students are typically from the minority institutions in the state (Xavier, Southern, Grambling State) or from non-minority New Orleans institutions including Tulane. We plan to apply for REU supplements which will be leveraged through the LAMP program.
The focus of this project was on a class of materials formed by combining a biopolymer with nanoscale particles. We sought to create materials with a gel-like consistency, much like synovial fluid, which is the lubricant material found in knee joints. Synovial fluid has a very low coefficient of friction, which is why it is an excellent lubricant. Our project sought to develop gels that could mimic the properties of synovial fluid. The project involved a collaboration between three professors at Tulane University (who were experts at studying the frictional properties of materials) and Prof. Srinivasa R. Raghavan at the University of Maryland (UMD), whose expertise was in biopolymers and gels. The long-term impact of this research was that it could one day lead to the development of benign alternatives to synovial fluid ("injectable gels"), which would be a boon to patients who suffer from arthritis. Our hypothesis, based on preliminary work done in our UMD lab, was that gels could be created by combining nanoparticles with a special kind of biopolymer, viz. one that had "hydrophobic tails" attached to its backbone. As an analogy for this kind of biopolymer, imagine a strand of spaghetti with small "oily" hooks attached at different points along the strand. Further, imagine that these hooks, being oil-loving, can attach onto nanoscale particles that have oily surfaces. Under certain conditions, the same strand of spaghetti can "hook" on to more than one particle, leading to the particles effectively being connected together by the strands. If a large number of particles and spaghetti-like strands are present, such "hydrophobic hooking" can lead to all the particles being connected by strands, and if so, the result would be a macroscopic gel (3-D network of the particles). The consistency of the gel would be in-between that of ketchup and egg white, and this consistency would also ensure that the gel would hold its weight in an inverted tube. This implies that a gel would stay in one location rather than flow like water. During the course of this project, we discovered new ways to make the above gels. We found that gels could be created by combining our special biopolymer with either "hard" nanoparticles (made of carbon or silica) or "soft" nanoparticles (made of biological lipids). Nanoparticles made from lipids are called vesicles or liposomes and they are akin to primitive versions of biological cells. A gel formed by combining vesicles and biopolymers is particularly significant because all its components have a biological origin and thus the resulting gel could be biocompatible. We also found that such gels could be reversed (i.e., converted back from gel to liquid) by adding a special kind of barrel-shaped molecule made from sugars. The simplicity with which we can make and break these gels is an attractive aspect of our studies. The results of our studies are published in several peer-reviewed articles in the journals Soft Matter (administered by the Royal Society of Chemistry from the UK) and Langmuir (administered by the American Chemical Society). We believe our studies have attracted significant attention from the community of chemical engineers engaged in research on soft materials and gels.
