The research objective of this award is to examine biomimetic "smart" artificial lubricants and determine the role of interfacial interactions on the tribological properties of confined polymeric thin films at a microscopic level. The intelligent lubricious films will be constructed by molecular engineering of stimuli-responsive poly (N-isopropylacrylamide) (PNIPAM) hydrogel thin films added with hyaluronic acid (HA) to simulate the lubricin-HA complexes in natural synovial fluids. The interfacial materials properties of these colloidal lubricants can be actively tuned and optimized by external stimuli, such as temperature and biopolymer additives, to mimic the super-lubricity of synovial fluids. Concurrent single-particle imaging and interfacial force experiments will be conducted to examine how the polymeric microstructures and dynamics endow specific viscoelasticity of confined PNIPAM-HA thin films of varied film thickness.
If successful, the results of this research will elucidate the biolubrication mechanism and advance the understanding of arthritis and dry-eye symptoms as well as the engineering of intelligent thin films with optimal lubrication properties. The microstructure-viscoelasticity relationship of confined lubricious thin films, deciphered at a single-particle level, will give insight to the fundamentals in atomic and nano scale lubrication phenomena. The knowledge gained from this endeavor can be transformed to rationally design intelligent biomimetic polymeric assemblies or coatings relevant to artificial biolubricants and lubricious biomedical devices. Graduate and undergraduate student participants, as well as underrepresented minorities such as female students in engineering majors, will be trained with new and advanced materials characterization techniques through classroom instruction and laboratory research. This project also seeks to establish a strong coalition with lubrication and automotive industries as well as Indiana?s local orthopedic industry to help students, scientists, and engineers work well together.
Healthy synovial fluids (SFs) are complex fluids consisting of biopolymers, globule proteins, and lipids and regarded as super-lubricants to provide nearly life-long low friction and wear protection of synovial joints in mammals. In this project, the PI and her students have developed biocompatible artificial biolubricant based upon the aggregation of hyaluronic acid (HA) and hydrogel particles in aqueous suspensions to simulate the intricate structure and frictional characteristics of healty SFs. By optmizing the concentration ratio of HA to the synthetic polymer hydrogels, the bulk rheological properties of healthy synovial fluids are succesfully captured. It is also confirmed by direct microscopic observation that added hydrogel particles can enhance the HA network by hydrogel-mediated hydrogen bonding, leading to the fractal HA-hydrogel aggregating networks in aqueous suspensions. The potential application of HA-hydrogel particle aggregation as biomimetic superlubricants is supported by the comparable low friction at high load to that of healthy SFs. Results obtained from this research elucidate the biolubrication mechanism and advance the biomedical development to treat arthritis and dry-eye symptoms. Such biomimetic and bioinspired material design using synthetic polymer microgel assembly with biopolymers can be also used to engineer intelligentfunctional materials and thin films for broad materials applications from energy to drug delivery.
