Extracellular matrix controlled nanomechanics of self assembled synovial fluid films

The extracellular matrix (ECM) is a complex macromolecular network that regulates the proper function of several biointerfaces, such as synovial joints. The composition and conformation of ECM components have an important influence in the supramolecular assembly sequence of high-affinity biomolecules that form load bearing, lubricating, and wear protecting nanofilms, mediating its nanomechanical performance. Important ECM components include fibronectin (FN), collagen type I (Col-I), and collagen type II (Col-II). Their roles in mediating biomolecule adsorption, particularly boundary lubricating and wear protecting glycoproteins and glycosaminoglycans from natural biolubricants, such as synovial fluid, is of interest for elucidating the fundamental biotribological mechanisms. This study presents a biosurface model to elucidate how ECM surface molecular composition mediates adsorption and supramolecular assembly of protecting synovial fluid nanofilms. First, Col-I, Col-II, or FN were deposited on self-assembled monolayers to model the ECM surface, controlling protein grafting density and conformation at physiological temperatures (37°C). Next, synovial fluid component amounts and nanomechanical properties adsorbed onto Col-I, Col-II, or FN were quantified and characterized using a quartz crystal microbalance with dissipation (QCM-D) and surface forces apparatus (SFA). Our findings indicate that more synovial fluid components bind to FN precursor films and that the viscoelasticity of nanofilms under confinement depends on the precursor protein film. In summary, our proposed ECM surface model allows for a quantitative comparison of how the major components of cartilage contribute to synovial fluid nanomechanics and are thus more prone to dysfunction in the altered synovial joint environment.