Fabrication Of Layer-by-layer Self-assembled Starch-based Colloidal Microcapsules And Their Conlon-targeting Controlled Release Properties

One of the key and basic issues to be solved in the field of health food area is to obtain oral colon-targeting controlled release colloidal microcapsules delivery system to enhance the bioavailability of the bioactive components. This study aims to the requirements of the targeted controlled release of the polypeptide and protein biological macromolecules, the starch-based assemble carriers were prepared through the modification of different charge and molecular size, and the bioactive component is assembled with these starch-based carrier materials by layer-by-layer self-assembly technique and the structural properties of colloidal microcapsules, the delivery and release properties in vitro and in vivo were investigated for providing the foundation of the fabrication of the oral colon-targeting controlled release colloidal microcapsules delivery system for the bioactive components.Carboxymethyl anionic starch(CMS) carrier materials and cationic starch carrier materials were synthesized by carboxymethyl etherification, cationic amination modification, and double bienzyme hydrolysis of corn starch. With the increase of DS and pH, negatively charges of CMS increased; with the increase of Mw, negatively charges of CMS slowly increased; all CMS showed a lot of negative charges in pH≥3.0 conditions. For cationic starch, positive charges were substantially increased with the increase of DS; with the increase of pH value, positive charges decreased after increasing; and all cationic starchs showed the maximum amount of positively charges at pH=3 PBS. Internal orderly aggregates of the starch-based materials showed the characteristic of mass fractal; With the increase of Mw, internal orderly aggregates of CMS was more compact; with the increase of pH value, the tightness of internal orderly aggregates of CMS declined, while the tightness of internal orderly aggregates of cationic sstarch increased.Using layer-by-layer self-assembly technique, insulin, as a functional factor, was embedded by the electrostatic and hydrogen bonding interactions between starch-based carrier materials, obtaining assembled colloidal microcapsules with different layers. The interaction strength between the carrier materials during assembling, the surface Zeta-potential, average particle size and change of internal orderly aggregates of colloidal microcapsules were investigated. After that, the changes of surface Zeta- potential, average particle size and internal orderly aggregates of colloidal microcapsules with one, three, five layers were also respectively studied at simulated digestive fluids pH value. Through the simulation method in vitro, the release rate of insulin was systematically investigated. The results showed that CMS presented the highest insulin encapsulation efficiency, reaching 62.05%; During the simulation of transport process in vitro, the mass fractal dimension(Dm) of starch based colloidal micro capsule reduced with the increase of pH in the digestive tract, indicating compactness of the internal orderly aggregates presented a downward trend, while the interaction between anionic CMS carrier material and cationic amino starch carrier material enhanced and then weakend, which contributed to colon-targeting delivery of insulin for starch based colloidal micro capsule. In vitro release result showed in upper gastrointestinal the release rate of insulin was 15.86% and in the colon the cumulative release rate was 92.09%, which achieved colon-targeting delivery of insulin. Furthermore, based on this oral colloidal micro capsule colon-specific delivery system, the animal experiment was carried on and the transport situation for the delivery system in the digestive tract of mice was analyzed by in vivo imaging techniques. The result indicated that the delivery system possessed better colon-targeted transfer effect in vivo.The research shows that the carrier material of layer by layer self-assembled technique can be obtained by modified starch with charges and regulation of the molecular weight. The influence of the surface Zeta- potential, internal orderly aggregates and intermolecular interactions of starch-based carrier materials on the structure and release properties of colloidal microcapsules in a simulated digestive tract environment and animal digestive tract has been revealed. The oral colon-targeting controlled release colloidal microcapsule delivery system was designed through layer-by-layer self-assembly method using the srarch-based assembled carriers. The results can provide a suitable carrier material for microencapsulation and controlled-release delivery of bioactive components and have important guiding significances for the fabrication of targeting controlled release colloidal microcapsule delivery systems for the bioactive components.