(129d) Surface-Immobilized Fibronectin Conformation Drives Synovial Fluid Adsorption and Film Formation.

The interface between the articular cartilage extracellular matrix (AC-ECM) and synovial fluid (SF) plays a crucial role in dissipating mechanical energy and protecting the cartilage surface through the formation of a protein-based nanofilm. We hypothesize that fibronectin (FN), a glycoprotein present at the AC-ECM surface, contributes significantly to the formation and scaffolding of this protective layer, sometimes referred to as the lamina splendens. In this study, FN films were used as precursor layers on functionalized gold surfaces, as a simple model of the cartilage surface, to investigate FN’s ability to adsorb and retain synovial fluid. Conformational states of FN were modulated by deposition at pH 7 (extended conformation) or pH 4 (unfolded conformation) onto self-assembled monolayers on gold-coated quartz crystals, followed by the adsorption of diluted SF. FN films exhibited distinct pH-dependent properties, characterized through a combination of Atomic Force Microscopy (AFM), Quartz Crystal Microbalance with Dissipation (QCM-D) and Diffuse Reflectance Circular Dichroism (DRCD). FN films formed at pH 4 were thicker, more rigid, showed more homogeneous surface morphology, and had altered β-sheet content compared to films formed at pH 7. However, FN films deposited at pH 7 retained more synovial fluid than those at pH 4, highlighting the importance of FN conformation in facilitating the adsorption and retention of a thin, lubricating, and wear-protective synovial fluid layer. These findings enhance our understanding of the molecular mechanisms governing cartilage-SF interface homeostasis and joint health, revealing key interactions and synergies between the AC-ECM and SF that contribute to the complex nature of joint biotribology.