Tribological Behavior of Medium Molecular Weight Chitosan in Acid Aqueous Solution

Natural biomacromolecules are widely used in biomimetic medicine engineering. Especially, polysaccharides have been extensively exploited in biomedical applications due to featuring desirable lower toxicity, biocompatibility, and degradability. Chitosan, as a typical natural polysaccharide, was widely utilized as a potential vector for gene/drug delivery according to its adhesion. However, it usually coexists with tribological behaviors in these application scenarios. Many studies have explored its adhesion properties, but the tribological behavior is not clear between the two chitosan-coated surfaces. Here, we investigated the tribological behavior of chitosan films by virtue of the surface forces apparatus (SFA) under shearing in 150 mM acetic acid. The thickness of chitosan films was observed, which would gradually increase and become stable once the two chitosan films under sliding, and the variation of the chitosan thickness is reversible. It could be attributed to the generation of a hemifusion layer at the bearingload area under the high load, and the new contact interfaces were generated when relative sliding occurred. Meanwhile, the configuration of chitosan films would be rearranged with elastic swelling deformation during a running-in stage. Interestingly, the kinetic friction exhibited a negative correlation with load, in which increasing the load would result in a decrease of friction force. Such phenomenon is primarily attributed to form a more compact configuration of the new contact interfaces with a higher charge density, which reduced the opportunities for the polymer interpenetration of entanglement of the chitosan chains and enhanced the electrostatic repulsion between the new contact interfaces, leading to smaller friction. Our findings provide useful information in understanding the tribology mechanism of soft materials, with implications onto designing chitosan-based lubricating materials for biomedical and bioengineering.