Friction Mediation via Synthetic Mucin Polymer Formation into Tribofilms

Student’s name: Margaret Lin Home Institution: Rutgers University NNCI Site: MANTH @ UPenn REU PI: Dr. Robert Carpick – Department of Mechanical Engineering and Applied Mechanics, UPenn REU Mentor: Dr. Brandon McClimon - Department of Mechanical Engineering and Applied Mechanics, UPenn Abstract: Mucus is a natural product of biological systems, playing many vital roles as an organ coating, germ barrier, lubricant, and even as an externally secreted adhesive. In particular, mucus consists of numerous proteins, cell debris, bacteria, as well as mucin polymers, which are thought to be primarily responsible for its physical properties. Investigating the mechanisms by which mucin polymers modulate frictional forces between surfaces may lead to a better understanding of diseases such as cystic fibrosis and irritable bowel syndrome, or advancements in medical implants, drug delivery, and joint and tissue adhesives. Synthetic mucin polymers offer many advantages over biological mucin, including homogeneity and monodispersity, allowing greater confidence in attributing the physical properties responsible for friction modulation. Using lateral force microscopy (LFM), the contact between a SiO2 colloidal probe and polydimethylsiloxane (PDMS) substrate can be approximated to a single asperity system with analytically tractable contact mechanics. As I will demonstrate, there are two primary interactions of mucin on these substrates – firstly, the adsorption as a thin layer over the surface of the probe, and secondly, the transformation of the adsorbed mucin under higher stresses into a tribofilm – both of which play a role in lubrication and adhesion. The growth of the tribofilm under applied loads can lead to dramatic decreases in friction under differing loads and speed. However, the degree of friction decrease relative to PDMS-SiO2 direct contact is observed to vary between nominally identical experiments. Context about what factors may control the formation, durability, and lubrication capacity of mucin tribofilms will be discussed.