Ultrasonic synthesis of stable oil filled microcapsules using thiolated chitosan and their characterization by AFM and numerical simulations

Abstract

An experimental protocol has been developed for synthesizing stable core-shell microcapsules using a biopolymer, chitosan, lacking cross-linkable thiol functional groups. In the first step, thiol moieties were introduced into the backbone of chitosan using dl-N-acetylhomocysteine thiolactone (AHT). In the second step, AHT-modified chitosan shelled microcapsules, encapsulating an oil core, were successfully prepared using high intensity 20 kHz ultrasound. The size of chitosan and AHT modified chitosan microcapsules was found to be in the range of 1-15 μm. The thickness of the microcapsule shell increased with an increase in thiol content. The mechanical properties of microcapsules were evaluated by subjecting the microcapsules to compressive forces by colloidal probe AFM. The stiffness and the Young's modulus of the shell of microcapsules were determined by analyzing the force versus indentation data using Reissner's theory for indentation of thin elastic shells. The stiffness of AHT modified chitosan microcapsules was found to be higher than unmodified chitosan microcapsules. The viability of microcapsules to be embedded into processed food, pharmaceutical and cosmetic products was tested via numerical simulations. The confined capsule in the micro-channel was subjected to linear shear and uniform flows. We used finite element numerical simulations to determine the deformation of microcapsules in flow as a function of shear rate and thickness of the shell. The deformation of capsule was found to be linear with an increase in the shear rate. The deformation decreased with an increase in the thickness of the shell. Based on the simulations, we predict that the microcapsules would survive processing conditions and shear rates used in industrial applications.

Thiolated Chitosans: A Multi-talented Class of Polymers for Various Applications

“…For the analysis of the amount of immobilized −SH groups of these thiolated chitosans, Ellman’s reagent optionally with previous reduction of disulfide bonds with borohydride or iodometric titration can be used . Phadungcharoen et al, for instance, have conducted the Ellman’s assay via smartphone, providing an easy, fast, and reliable analysis of thiolated polymers without access to sophisticated equipment. …”

Precise measurements of capsule mechanical properties using indentation

“…In capsule or particle compression studies where relative trends in stiffness or modulus have been measured 25 , the implications of the outcomes of this study are unlikely to affect the qualitative trends for similarly sized capsules or particles with similar shell thickness. However, studies where comparisons are made with disparate capsule or particle size or shell thickness 26 , or in comparison between a modulus obtained using AFM to a modu-lus measured via different techniques, the analysis presented here is expected to be critical. In the Supporting Information we provide tables and a simple MATLAB calculator giving the necessary parameters for the accurate calculation of Young's modulus for a given experimental setup.…”

Ultrasound-assisted encapsulation of Pandan (Pandanus amaryllifolius) extract

“…Typically, lysozyme microspheres are linked by stronger intermolecular crosslinked shell, whereby chitosan microsphere with a relatively weaker covalent crosslinked shell. The chitosan microspheres without additional crosslinker was found to be thinner than the one with external crosslinker [38] . Therefore, the loosely crosslinked system may cause the final microspheres to become more susceptible towards the changing parameter.…”