Single molecule force measurements of chitosan

Chitosan, a glucosamine polysaccharide derived form chitin, was studied by AFM-based single molecule force spectroscopy. The goal of this study was to investigate chitosan's adhesive properties to various surfaces ( i.e. mica, glass, quartz, polytetrafluoroethylene and self-assembled monolayers) as well as obtaining its mechanical constants. The results obtained were in the form of force-extension curves and mathematical fits. Well-defined features, characteristic of single molecule adhesion and stretching, such as constant force plateaus and peaks, were observed in the force curves. The lengths of the constant force plateaus obtained are consistent with the lengths of chitosan strands observed in high resolution AFM images. The energy of desorption of single glucosamine residues from various surfaces was calculated. The values obtained were: 1.8 x 10 -20 J/glucosamine residue on self-assembled monolayers of mercaptoundecanoic acid:dodecanethiol (1:1000), 2.0 x 10 -20 J/glucosamine residue on quartz, 3.5 x 10 -20 J/glucosamine residue on polytetrafluoroethylene and 3.9 x 10 -20 J/glucosamine residue on self-assembled monolayers of dithiobis(succinimidyl undecanoate). The Kuhn length of chitosan (DDA 92%) was calculated, using the freely jointed chain model, to be 2.1 ± 0.9 nm which corresponds to a stiffness of approximately 4 glucosamine residues. These single molecule level results could be applied towards the preparation of novel, chitosan-based biomaterials