The Probable Explanation for the Low Friction of Natural Joints

Abstract

The surface of an articular cartilage, coated with phospholipid (PL) bilayers, plays an important role in its lubrication and movement. Intact (normal) and depleted surfaces of the joint were modelled and the pH influence on the surface interfacial energy, wettability and friction were investigated. In the experiments, the deterioration of the PL bilayer was controlled by its wettability and the applied friction. The surrounding fluid of an undamaged articular cartilage, the synovial fluid, has a pH value of approximately 7.4. Buffer solutions were formulated to represent the synovial fluid with various pH values. It was found that the surface interfacial energy was stabilised at its lowest values when the pH varied between 6.5 and 9.5. These results suggested that as the PL bilayers deteriorated, the hydration repulsion mechanism became less effective as friction increased. The decreased number of bilayers changed the wettability and lowered PL lubricant properties.

Understanding the Unique Role of Phospholipids in the Lubrication of Natural Joints: An Interfacial Tension Study

“…According to Pasquali-Ronchettiet et al [38], the facilitated lubrication in this regime is obtained using a brush-like lubrication mechanism by which the phospholipid heads attach to hyaluronic acid and form inverted cylindrical micelles. This mechanism of hydration repellency may also be involved in the ability to increase the absorption of the force field when the hydrophilic heads repeat over each other to form a cushioning effect, which is supported by a suitable electrostatic shielded condition [39], in addition to the reactive force of the diaphragm discussed earlier [40]. Consequently, the reverse micelles can reduce the friction coefficient by changing the mode of friction, i.e., the quasi-static friction effect may be replaced by its rolling equivalent [41].…”

A novel training-free method for real-time prediction of femoral strain

“…For each node in the patch, the SPM model was completed by the strain field calculated using a nominal force vector pointing to the hip joint centre. This condition represents a frictionless ball and socket joint consistent with a very low coefficient of friction characterising natural joints (Pawlak et al, 2015).…”

The Anomalies of Hyaluronan Structures in Presence of Surface Active Phospholipids—Molecular Mass Dependence

“…Surface active phospholipids play a vital role in biologic tissue systems, in large part due to an amphiphilic nature that allows for varied structural properties. In synovial joint organ systems, a surface active phospholipid layer (SAPL) covers normal articular surfaces in an oligolamellar structural formation [1,2,3,4,5]. The SAPL serves to integrate interfacial functions between juxtaposed surfaces and has been a subject of much inquiry due to its tribological features [6,7,8,9,10,11,12,13].…”