Engineering tribological rehydration of cartilage interfaces: Assessment of potential polyelectrolyte mechanisms

Articular cartilage, primarily composed of water and collagen, is vital for synovial joint function. Traditional hard biomaterials like ceramic or cobalt-chrome used in hemiarthroplasty often result in abnormal contact pressures and premature implant failure. This study investigates the tribological properties of polyelectrolyte functionalised PEEK (SPMK-g-PEEK) in contact with cartilage, proposing a solution to these issues by utilising tribological rehydration and effective aqueous lubrication.

We demonstrate a new mode of polyelectrolyte enhanced tribological rehydration where SPMK-g-PEEK achieves low friction and promotes interstitial fluid recovery during sliding, independent of traditional hydrodynamic theories. This results in a rapid stabilisation of the coefficient of friction (CoF) to levels comparable to natural cartilage (CoF 0.01) and aids in approximately 8% cartilage strain recovery, indicating effective tribological rehydration even under cartilage degradation or altered osmotic conditions.

Furthermore, we find that lubrication and rehydration against an SPMK-g-PEEK interface depend minimally on biphasic lubrication but significantly on the hydrophilic sulfonic acid groups of SPMK, which act as a fluid reservoir. Our findings suggest SPMK-g-PEEK as a promising biomaterial for cartilage interfacing implants that offer low friction and modulate cartilage interstitial fluid pressure. This study enhances our understanding of biotribological interactions and contributes to the development of joint replacement materials that support the natural function of cartilage.