Low biofouling chitosan-hyaluronic acid multilayers with ultra-low friction coefficients

Resistance to biofouling is an advantageous material property in a variety of biomedical and biofluid processing applications. Protein-resisting surface coatings must also be resistant to wear and degradation and in certain applications good aqueous lubricating properties are required. We show that cross-linked polyelectrolyte multilayers, consisting of chitosan and hyaluronan on polydimethylsiloxane (PDMS) surfaces, form a highly lubricating film that is resistant to wear and protein adsorption. The multilayer film shows much stronger resistance to protein adsorption from human whole saliva than both hydrophobic and hydrophilic PDMS surfaces; the latter two showed identical adsorbed salivary film thicknesses. The boundary friction coefficient under aqueous conditions was extremely low (mu approximately 0.01) between multilayer-coated PDMS substrates and the film is robust against dry rubbing and many hours of tribological experiments in a range of aqueous lubricants. The origins of the assembly's low friction coefficients and robustness are discussed. In addition, we found that the addition of negative phosphate ions to water lowers the boundary lubricating properties of negatively charged hydrophilic PDMS surfaces by 1 order of magnitude to mu approximately 0.01. We consider this to arise from the large hydration sheaths and resulting "ball-bearing" properties of the hydrated phosphate ions, which form a lubricating barrier against asperity contact. These findings offer new insights toward biolubrication processes and suggest that chitosan-hyaluronan polyelectrolyte multilayer films have the potential to be used in (bio-) applications requiring low friction as well as resistance to biofouling and wear.