Lubrication and Adhesion by Charged Biopolymers for Biomedical Applications

Although thick polymer brush layers are currently thought to be the best biomimetic lubricants, we have found that subnanometer-thick monolayers of of an algae polysaccharide can exhibit stable low friction and good wear protection, up to 11MPa and over a 1000-fold range of sliding velocities. Such remarkable tribological behavior is attributed to the ability of the polysaccharide to adhere weakly to the surfaces (ensuring that the lubricant is not easily squeezed out of the shearing junction) and to be flexible and mobile enough to be shear-aligned and transferred into new unsheared areas. However, despite the superior lubrication demonstrated by the algae polysaccharide compared to HA, lubricin, and chitosan, we conclude that none of the systems investigated so far possesses the ideal combination of friction and adhesion properties when subjected to cyclic loading, high pressures, high impact, and large sliding distances, as found in natural tribological systems such as in the hip or knee joint. Indeed even the algae polysaccharide monolayer breaks down when sheared (at high pressures) over distances larger than twice the diameter of contact between surfaces. Hence, the best candidate for use in water-based lubricant fluids and/or as potential additives to synovial fluid in joints and other biolubricating fluids still needs to be identified. By further investigating this class of polysaccharides but also other natural polysaccharides and synthetic peptides, we expect to be able to identify the crucial chemical groups and/or sequences that determine their different functionalities, with obvious potential for biomedical (medical synthesis) and/or simply biomimetic applications.