Interaction of Pluronic F-127 with serum proteins and its feasibility as a lubricant additive for CoCrMo/UHMWPE interface

In this study, we report the feasibility of Pluronic “F-127” as a lubricant for CoCrMo/ultrahigh molecular weight polyethylene (UHMWPE) interface in serum as a synovial fluid (SyF) model. While adsorption and lubrication properties of amphiphilic copolymers such as F-127 at a hydrophobic surface in aqueous media have been well established, its efficacy in serum can be more complicated due to potential interaction of F-127 with serum proteins or competitive adsorption onto UHMWPE surface. When an aliquot of F-127 solution (in concentration range of F-127 from 0.1% to 20% dissolved in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)) was added into serum where a CoCrMo pin is sliding against a UHMWPE disk, an immediate decrease in the coefficient of friction (COF) (ca. 20%) was observed. A spectroscopy study employing dynamic light scattering (DLS), circular dichroism (CD) spectroscopy, and ultraviolet (UV) absorbance spectroscopy has shown that serum associatively interacts with F-127 when the F-127 concentration is above critical micelle concentration (CMC), leading to an increase in hydrodynamic size and alteration of tertiary structure of proteins in serum. Mixing of F-127 with the solutions of selected single component biomolecules of serum showed that γ-globulin is the primary molecule that interacts with F-127 above CMC, followed by albumin. Meanwhile, no indication of interaction was observed when the F-127 concentration was below CMC. It is thus proposed that the observed lubricating effect of F-127 in serum is primarily due to the faster surface adsorption kinetics for its smaller molecular weight compared to serum proteins. Further, comparable % reduction in COF over a wide range of F-127 concentration indicates that unimeric F-127 molecules are dominant in contribution to friction-lowering effect even at above CMC at CoCrMo/UHMWPE interface in serum.