The effect of temperature on supported dipalmitoylphosphatidylcholine (DPPC) bilayers: Structure and lubrication performance

Abstract

Phospholipids fulfill an important role in joint lubrication. They, together with hyaluronan and glycoproteins, are the biolubricants that sustain low friction between cartilage surfaces bathed in synovial fluid. In this work we have investigated how the friction force and load bearing capacity of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers on silica surfaces are affected by temperature, covering the temperature range 25-52°C. Friction forces have been determined utilizing the AFM colloidal probe technique, which showed that DPPC bilayers are able to provide low friction forces over the whole temperature interval. However, the load bearing capacity is improved at higher temperatures. We interpret this finding as being a consequence of lower rigidity and higher self-healing capacity of the DPPC bilayer in the liquid disordered state compared to the gel state. The corresponding structure of solid supported DPPC bilayers at the silica-liquid interface has been followed using X-ray reflectivity measurements, which suggests that the DPPC bilayer is in the gel phase at 25°C and 39°C and in the liquid disordered state at 55°C. Well-defined bilayer structures were observed for both phases. The deposited DPPC bilayers were also imaged using AFM PeakForce Tapping mode, and these measurements indicated a less homogeneous layer at temperatures below 37°C.

Synergies in lubrication

“…Here the outer sheet of the lubricating phospholipid bilayer is eroded away at an applied load just below 20 nN, which corresponds to a pressure of about 42 MPa. 37 However, before erosion occurs the friction force may increase due to energy dissipation caused by load and shear induced lateral motion of adsorbed molecules along the surface. 38 This played a role in the work by Thormann et al, where the friction properties of hydrophobized surfaces coated with methylcellulose, MC, were explored.…”

“…Indeed, several reports have described very low friction forces between phospholipid bilayers up to high pressures. 11,37,49,50 Perhaps counterintuitively, it was found that DPPC bilayers in the fluid state have a higher load bearing capacity than such layers in the frozen state. 37 This is illustrated in Fig.…”

“…11,37,49,50 Perhaps counterintuitively, it was found that DPPC bilayers in the fluid state have a higher load bearing capacity than such layers in the frozen state. 37 This is illustrated in Fig. 5, which shows the fraction of experiments where the layer has been compromised at or below a load of 20 nN.…”

Influence of the Molecular Weight and the Presence of Calcium Ions on the Molecular Interaction of Hyaluronan and DPPC

“…For these reasons the interaction of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and HA has been the scope of different theoretical and experimental investigation to reveal the associate structures formed, their interactions and their behavior under load. Experimental investigations have reported on the accumulation of HA in-between dipalmitoylphosphaditcholin bilayers [ 23 ] and adsorption of HA to DPPC bilayers [ 17 , 24 , 25 , 26 , 27 ]. On the other hand, the study performed by Herzog et al using HA with a high molecular weight (MW) could not observe any adsorption of HA to DPPC [ 28 ].…”

Complex solutions under shear and pressure: a rheometer setup for X-ray scattering experiments

“…The components of the synovial fluid are likely to adapt to different loads and shear conditions by re-structuring and, thereby, provide extremely low friction coefficients under different pressures and shear rate conditions (Lee & Spencer, 2008). The self-assembly of the components promoting lubrication, as well as how this may lead to lubrication synergy, is not sufficiently understood, even though some progress has been made in recent years (Seror et al, 2012(Seror et al, , 2011Klein, 2006;Wang et al, 2015Wang et al, , 2013Wieland, Degen et al, 2016;Dė dinaitė, 2012). For example, investigations show that hyaluronic and albumin form complexes that can result in rheopexy behaviour of the mixed solutions under physiological conditions, which influences the mechanical properties of the synovial fluid (Oates et al, 2006;Lenormand et al, 2008).…”