Lubrication by the red microalgae Porphyridium sp. polysaccharide

Using a surface forces apparatus (SFA) we have investigated the effects of normal load (compression) and shear on the tribological properties of mica surfaces bearing Porphyridium sp. (a common naturally-occurring polysaccharide of the red microalgae, which molecular weight has been estimated to be 2-7 x 10⁶ daltons) adsorbed from aqueous solution. The friction forces were monitored as a function of time, shearing distance and driving velocity, at different loads and for different polysaccharide concentrations. The friction results indicate a very low coefficient of friction (μ <0.01) at low compressions, increasing only to μ =0.015 at pressures of 10 MPa. Its low friction, its ability to resist to high pressure, as well as its weak (logarithmic) dependency of friction on sliding velocity make the Porphyridium sp. a good candidate for biolubrication (e.g. human joint lubrication). Atomic force microscopy measurements were also performed on each surface before and after a shearing experiment and showed ordering of the biopolymer chain molecules into layers over length-scales of several microns.