Synergistic Interactions Between Grafted Hyaluronic Acid and Lubricin Provide Enhanced Wear Protection and Lubrication

Normal and friction forces were measured between physically adsorbed and chemically grafted layers of hyaluronic acid (HA), an anionic polyelectrolyte in presence the of lubricin (Lub), a mucinous glycoprotein on mica surface using a Surface Forces Apparatus (SFA) with a surface radius R~2cm. This work demonstrates that high friction coefficients does not necessarily correlate to surface damage and that chemically grafted HA acts synergistically with Lub  to provide enhanced wear protection to the surface. Increasing the concentration of Lub enhances the threshold load that a chemically grafted HA surface can be subjected to before the onset of wear. However, Lub fails to provide wear protection if HA is physically bound (not chemically grafted) to the mica surface and damage occurs at loads less than 1 mN (Pressure, P< 10atm) regardless of the amount of Lub, indicating that the molecules in the bulk play little or no role in camouflaging the surface from damage. Lub penetrates into the chemically bound HA to form a visco-elastic gel that reduces the coefficient of friction as well as boosts up the strength of surface against abrasion (wear/ damage).