Tribological efficacy and stability of phospholipid-based membrane lubricants in varying pH chemical conditions

Abstract

In this study, the authors examine the influence of joint chemical environment by measuring changes in the tribological properties (friction coefficient and charge density) of contacting surfaces of normal and degenerated cartilage samples in bath solutions of varying pH (2.0-9.0). Bovine articular cartilage samples (n = 54) were subjected to several surface measurements, including interfacial energy, contact angle, and friction coefficient, at varying pH. The samples were delipidized and then subjected to the same measurement protocols. Our results reveal that the interfacial energy and charge density, which have been shown to be related to friction coefficient, decrease with pH in the acidic range and approach constant values at physiological (or synovial fluid) pH of 7.4 and beyond it, i.e., toward basic pH domain. The authors conclude that this rather complex response explains the long-term efficacy with respect to ageing and associated pH changes, of the phospholipid layers that facilitate the almost frictionless, hydration-lubrication involving contact in the mammalian musculoskeletal system.

Unravelling a Self-healing Thermo- and Hydrodynamic Mechanism of Transient Pore's Late-stage Closing in Vesicles, and Related Soft-matter Systems, in Terms of Liaison Between Surface-tension and Bending Effects

“…AC shows very low friction coefficient which can be µ ≈ 10 −3 ÷ 10 −2 , and a lubrication is to be considered of hydrodynamic nature [18]. There is a growing amount of recent papers [17,[22][23][24][25][26][27] that indicate the role of vesicles in biolubrication. They propose, at least at the laboratorial scale, that the mechanism of biolubrication can be explained in terms of vesicles' response to both: loading and (small) shearing force factors.…”

“…They propose, at least at the laboratorial scale, that the mechanism of biolubrication can be explained in terms of vesicles' response to both: loading and (small) shearing force factors. The basic notion staying behind this mechanism is proposed to be the hydration repulsion, possibly assisted by laminae shearing over one another [23,27]. The overall name coined for the mechanism is the hydration lubrication.…”

“…It implies that the (pores-affecting) self-healing mechanism does not apply, and the layers reform at suitable surfaces of articulating system. This, in turn, forces somehow the system to make use of the shear involving part of the hydration-lubrication event: the layers may slide then one over another [25,27]. The self-healing phenomenon does not preserve any longer until the curvilinearly shaped micelle-or vesicle-type soft object eventually rebuilds.…”

Toward a quantified, validated, and verifiable understanding of the Biointerface

“…2 which explored how bioactive molecule interacted with these systems while Pawlak et al 3 demonstrated how friction and lubrication could be moderated by varying these chemical conditions. These systems present interesting characterization challenges and Shrestha and Banquy 4 reviewed how force probe experiments give insight into hydration forces and the conformation of molecules within these biological structures.…”

Ions and solvation at biointerfaces

“…In this context, Pramanik et al describe the interactions of phospholipid based assemblies with bioactive molecules, 25 and Pawlak et al the moderation of dynamic processes such as friction and lubrication by the chemical conditions. 26 Kroning et al report on thin polyoxazoline brushes and their interaction with water as an interesting class of synthetic coatings with a broad range of future applications due to their biocompatibility. 27 Furthermore, undulations of bilayer surfaces are controlled by penetration and interaction of ions and water at hydrophilic surface regions of bilayers, and Shrestha and Banquy review how force probe experiments can help us to understand hydration forces and interactions at soft and hard hydrophilic structures, including, in particular, the dominant role of the lipid head group conformation.…”