Effects of molecular weight of grafted hyaluronic acid on wear initiation

Abstract

Hyaluronic acid (HA) of different molecular weights (M-w) was grafted onto mica surfaces to study the effects of M-w on the conformation and wear protection properties of a grafted HA (gHA) layer in lubricin (LUB) and bovine synovial fluid (BSF) using a surface forces apparatus. The M-w of gHA had significant effects on the wear pressure (P-w), at which point the wear initiates. Increasing the gHA M-w from 51 to 2590 kDa increased P-w from 4 to 8 MPa in LUB and from 15 to 31 MPa in BSF. The 2590 kDa gHA in BSF had the best wear protection (P-w similar to 31 MPa), even though it exhibited the highest friction coefficient (mu similar to 0.35), indicating that a low mu does not necessarily result in good wear protection, as is often assumed. The normal force profile indicated that BSF confines the gHA structure, making it polymer brush-like, commonly considered as an excellent structure for boundary lubrication.