Mechanical Characterization of Micrometric Chitosan-Coated Vesicle by Atomic Force Microscopy

The effect of chitosan/TiO2/hyaluronic acid subphase on the behaviour of 1,2-dioleoyl-sn-glycero-3-phosphocholine membrane

The main aim of the study was to determine the effect of two polysaccharides: chitosan (Ch) and hyaluronic acid (HA), and/or titanium dioxide (TiO₂) on the structure and behaviour of the 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membrane. To achieve this goal the surface pressure as a function of the area per molecule (π-A) isotherm for the phospholipid monolayer was recorded. The shape of the π-A isotherms and compression-decompression cycles, as well as the compression modulus values, were analysed in terms of biocompatibility. Besides, morphology and thickness of the phospholipid layers obtained by means of Brewster angle microscope at different π, were determined. The obtained results show that both polysaccharides Ch, HA, as well inorganic TiO₂ affect slightly the structure of the DOPC monolayer but do not disrupt it. Their presence brings no typical arrangements of both the polar heads and tails of DOPC molecules at the interface.

Ultrasonically synthesized organic liquid-filled chitosan microcapsules: part 2: characterization using AFM (atomic force microscopy) and combined AFM-confocal laser scanning fluorescence microscopy

Atomic Force Microscopy (AFM) is used to measure the stiffness and Young's modulus of individual microcapsules that have a chitosan cross-linked shell encapsulating tetradecane. The oil filled microcapsules were prepared using a one pot synthesis via ultrasonic emulsification of tetradecane and crosslinking of the chitosan shell in aqueous solutions of acetic acid. The concentration of acetic acid in aqueous solutions of chitosan was varied from 0.2% to 25% v/v. The effect of acetic acid concentration and size of the individual microcapsules on the strength was probed. The deformations and forces required to rupture the microcapsules were also measured. Three dimensional deformations of microcapsules under large applied loads were obtained by the combination of Laser Scanning Confocal Microscopy (LSCM) with Atomic Force Microscopy (AFM). The stiffness, and hence the modulus, of the microcapsules was found to decrease with an increase in size with the average stiffness ranging from 82 to 111 mN m-1 and average Young's modulus ranging from 0.4 to 6.5 MPa. The forces required to rupture the microcapsules varied from 150 to 250 nN with deformations of the microcapsules up to 62 to 110% relative to their radius, respectively. Three dimensional images obtained using laser scanning confocal microscopy showed that the microcapsules retained their structure and shape after being subjected to large deformations and subsequent removal of the loads. Based on the above observations, the oil filled chitosan crosslinked microcapsules are an ideal choice for use in the food and pharmaceutical industries as they would be able to withstand the process conditions encountered.