Preparation And Evaluation Of Hydrogel Beads For Immobilizing Lipid-based Micro/Nano Delivery Systems

The efficacy of functional foods and personal care products is based on active ingredients,but the application of some active ingredients might be influenced seriously by their low solubility and stability.The use of appropriate micro/nano delivery systems could effectively improve the absorption of active ingredients,and lipid-based micro/nano delivery systems with the advantages of safety,universality,and easy production have been widely applied to deliver hydrophobic active ingredients and hydrophilic active ingredients.However,in practical application,lipid-based micro/nano delivery systems are still influenced by the poor stability and uncontrolled digestion,which should be resolved by secondary encapsulation.The secondary encapsulation using hydrogel beads could change the physical state of delivery systems and optimize the performance in practical application,resulting in a significant acceleration of industrial application.In this dissertation,hydrogel beads for immobilizing lipid-based micro/nano delivery systems were developed.Lipid nanoparticles for encapsulation of hydrophobic active ingredients and water-in-oil-in-water(W/O/W)double emulsions for encapsulation of hydrophilic active ingredients were immobilized in hydrogel beads,respectively.For food and skin applications,alginate and chitosan were respectively used as wall materials for the preparation of hydrogel beads,and the influence of the immobilization on digestion behavior and skin permeation was investigated.The main contents are as follows:(1)Firstly,for the application of lipid nanoparticles in functional foods,alginate hydrogel beads for immobilizing lipid nanoparticles were prepared.It appeared that the mean particle size of lipid nanoparticles recycled from the formed alginate hydrogel beads was 87.7 ± 2.1 nm,which had no significant difference from the mean particle size of original lipid nanoparticles(85.5 ± 1.4 nm),and the morphology of lipid nanoparticles was not changed significantly.The result of X-ray diffraction analysis indicated that the crystal structure of lipid matrix was not influenced significantly by the immobilization.The size distribution of lipid nanoparticles immobilized in hydrogel beads maintained a monomodal distribution over a period of 18 days at 40 ℃,indicating that the stability of lipid nanoparticles was improved by hydrogel beads.The dissolution study revealed that the dissolution of hydrophobic active ingredients from this system in simulated gastric fluid and simulated intestinal fluid was associated with Fickian diffusion and the swelling of hydrogel matrix,respectively.In vitro digestion study revealed that the lipolysis rate of lipid matrix and the bioaccessibility of hydrophobic active ingredients were decreased with the increase of alginate concentration,indicating that the release of hydrophobic active ingredients from lipid nanoparticles during digestion could be controlled by this system.(2)Secondly,chitosan hydrogel beads for immobilizing lipid nanoparticles were prepared for topical application.It appeared that lipid nanoparticles were confined in chitosan hydrogel beads through the electrostatic interaction.The relative change rate of particle size of original lipid nanoparticles was above 350% after 18 days of storage at 40 ℃,and the relative change rate of particle size of lipid nanoparticles immobilized in hydrogel beads was reduced to about110%.The permeation study revealed that,when the chitosan concentration was 2%,2.5%,and3%(w/v),the skin retention and the skin permeation of hydrophobic active ingredients loaded in lipid nanoparticles were significantly enhanced by hydrogel beads,indicating that this system could enhance the permeation.The routes for permeation of hydrophobic active ingredients loaded in lipid nanoparticles were not changed by the immobilization,which could still permeate into the skin through stratum corneum and hair follicles.(3)Thirdly,according to the destabilization mechanism of double emulsions,the feasibility of the immobilization of double emulsions reinforced by solid lipids in alginate hydrogel beads was discussed to further expand the scope of application of hydrogel beads.It appeared that,when the concentration of solid lipids in lipid phase was 10%(w/w),the size of double emulsions was relatively uniform,and the stability of double emulsions was significantly improved.There was no significant difference between the entrapment efficiency of sols and the yield efficiency of hydrogel beads under the same condition,indicating that the preparation process of hydrogel beads could not cause the extra leakage of inner aqueous phase.The result of microscopy observation showed that the morphology and the multiple structure of double emulsions were not changed by the immobilization,indicating that this method was suitable for the immobilization of double emulsions.The result of stability study revealed that double emulsions were effectively stabilized by the immobilization.In addition,the leakage of inner aqueous phase from immobilized double emulsions containing solid lipids after 24 weeks of storage was reduced by 30% compared with the group without solid lipids.(4)The digestion behavior of double emulsions immobilized in alginate hydrogel beads and relevant mechanisms were systematically investigated.Swelling study and fluorescence microscopy observation showed that compact beads gradually became swollen and heterogeneous during intestinal digestion.The microstructure of oil droplets in the digestive fluid was analyzed,and the result revealed that the microstructure transformation from(W/O/W)oil droplets to(O/W)oil droplets could occur within beads.The study of lipolysis and release during digestion revealed that the immobilization of double emulsions in alginate hydrogel beads could restrain the lipolysis of lipid phase without affecting the release of inner aqueous phase.When the alginate concentration was 1.5%(w/v),the lipolysis of lipid phase was associated with the swelling of hydrogel matrix,but the release of inner aqueous phase was mainly associated with Fickian diffusion mechanism.(5)Lastly,chitosan hydrogel beads for immobilizing double emulsions were prepared for topical application.The study of yield efficiency and microscopic observation showed that the inner aqueous phase was still encapsulated in double emulsions after the immobilization.The permeation study revealed that,when the chitosan concentration was 2.5% and 3%(w/v),the skin permeation of hydrophilic active ingredients loaded in double emulsions was significantly enhanced by hydrogel beads.The stratum corneum lipids were perturbed by this system,leading to the improvement of skin permeation.In addition,this immobilization could more effectively enhance the skin permeation of hydrophilic active ingredients contained in inner aqueous phase compared with the lipid phase of double emulsions.Through the above studies,the immobilization of lipid nanoparticles and double emulsions in hydrogel beads was implemented,and the influence of hydrogel beads on the stability of these two lipid-based micro/nano delivery systems was illuminated,which might provide a common strategy for improving the performance of lipid-based micro/nano delivery systems.Based on the destabilization mechanism of double emulsions,the effect of stabilizing double emulsions through hydrogel beads and solid lipids was investigated.The influence of the immobilization on digestion behavior and skin permeation was systematically elucidated,which would provide the theoretical base for the application of this system in functional foods and personal care products.