New insights on the structure of hexagonally faceted platelets from hydrophobically modified chitosan and α-cyclodextrin.

A new class of non-spherical particles was recently designed in our research group by mixing a polysaccharide grafted with fatty acids and α-cyclodextrin in water. Because their flat surfaces, and according to their size, particles are called micro- or nano-platelets. Here, we varied the composition of fatty acids grafted on chitosan (oleic acid, palmitic acid or stearic acid) and characterized platelet morphology. Transmission electron microscopy (TEM), cryogenic TEM, scanning electron microscopy, atomic force microscopy (AFM) and confocal laser scanning microscopy experiments showed that the platelets have a preferentially hexagonal shape with sharp edges, independently on alkyl chain grafted on chitosan. Furthermore, AFM topographic analysis of platelet surface showed parallel thin terraces with 12-14-nm height, suggesting a multi-layered structure alternating chitosan and fatty-acid/α-cyclodextrin inclusion complexes. We also revealed for the first time that a simple magnetic mixing of fatty acids with α-cyclodextrin in water results from solid inclusion complexes with a crystalline structural organization characterized by powder X-ray diffraction. Our results demonstrate that fatty acid/α-cyclodextrin interaction is the driving force for platelet formation.