The aim of this study was to demonstrate the effect of different treatments on collagen self-assembly, the morphological and the qualitative analysis of collagen assembly were measured by atomic force microscopy. Collagen samples were treated with 0.02%, 0.04%, 0.10% and 0.20% glutaraldehyde individually at the first steps. Meanwhile, the other experimental groups were treated with 0.05%, 0.10%, 0.20% riboflavin, respectively, the structural change of the collagen network with 15, 30, 45, 60 min UV365 exposure and the fluorescent irradiation as the control group in turn was investigated by atomic force microscopy. The width and height of collagen assembly increased with the concentration of glutaraldehyde, which were changed from 36.45 ± 4.45nm to 64.35 ± 2.58nm and 2.26 ± 0.19nm to 4.93 ± 0.29 nm, respectively. The effect of different UV365 irradiation time on the height of collagen was greater than the effect on the width, the width and height of collagen were varied from 41.36 ± 4.30nm to 55.47 ± 4.53nm and 3.10 ± 0.39nm to 6.20 ± 0.85nm, which were changed 25.44% and 50.00%, respectively. The concentration of riboflavin was more efficiently than irradiation time, and the maximum width and height of collagen reached 106.98 ± 3.37nm and 11.17 ± 1.33 nm, respectively, the control group without a significant change at the fluorescent irradiation by the time. This optimized cross-linking method with riboflavin/UV365 would have great potential for tissue engineering in clinic and food packaging science.

The effect of different metal ions including K + , Na + , Mg 2+ , and Ca 2+ at different concentrations on the self-assembly of chitosan molecules deposited on the new cleaved mica sheet was investigated using atomic force microscopy imaging techniques and other affiliated offline analysis methods. Chitosan molecules self-assembled porous film first when combined with K + , Na + , or Mg 2+ ions, and then gradually fractured a granular structure with increasing concentration of metal ions. Chitosan molecules would be self-assembled to fibrous structure after adding calcium ions, and grew much thicker and more flat when the concentration increased. The investigations on the effects of metal ions on the self-assembly of chitosan molecules would be useful for food preservation, environmental protection, and pharmaceutical developments and industries.

The well-organized chitosan film on mica surface has drawn wide attention for its potential applications and studies on the process of self-assembly. In this article, atomic force microscopy was used to investigate the ultrastructure of the self-assembly of chitosan molecules with calcium ions in different concentrations. It was showed that calcium ions might affect the selfassembly of chitosan to a certain extent, and chitosan molecules gathered from fibrils to circular, and finally formed to film with the increasing concentration of calcium ions. Further, the formation mechanism of Ca(II)chitosan conjugates was adapted to explain the effects of calcium ions on the self-assembly of chitosan. These results and the related analysis would be valuable for guiding the pattern of chitosan self-assembly with a potential application in food packaging science and engineering. ARTICLE HISTORY