Investigation on the Effects of Diluted Synovial Fluid Adsorption to Model Surfaces

Abstract

Synovial fluid (SF) plays a crucial role in joint lubrication, responsible for the ultralow coefficient of friction and protection of cartilage. A healthy knee and other synovial joints contain several surface-active biomolecules, such as lubricin (concentration of 0.05-0.35 mg/mL), hyaluronic acid (concentration of 1-4 mg/mL), phospholipids (concentration of 0.1 mg/mL), among others. To our knowledge, there have been several studies investigating the adsorption of full SF or individual SF molecules to model joint surfaces. In this study, we are investigating the formation of SF films and its tribological behaviors by exposing model silica surfaces to different dilutions of SF. Using quartz crystal microbalance with dissipation (QCM-D), we quantified SF adsorption and film viscoelasticity. We characterized the tribological performance of the diluted SF films using a combination of Surface Forces Apparatus (nano-tribology) and micro-tribometer (micro-tribology). Initial data indicates that SF is highly saturated with surface active biomolecules, as 1:20 dilutions show very similar films on model silica surfaces as compared to non-diluted SF. These results suggest that our model oxide surfaces reach full SF saturation at the incredible low dilution of 1:20, based on Langmuir-isotherm models. These results can have important implications to further understand the role of SF interactions with oxide surfaces, as found in artificial hip or knee implants.