Modification And Assembly Of Biomacromolecules And Their Emulsion Performance

Macromolecular self-assembly as one of the hot topics in polymer science has attracted significant attentions in the last decade. The building blocks of self-assembly are gradually elaborated from the initial block copolymers to non-covalent copolymers, branched copolymers and random copolymers. The resultant assemblies are used extensively in sensor coatings, nano-reactors, drug release, biomimetic self-assembly and biomedicine. With the development of the research on macromolecular self-assembly, building blocks are getting more complex. The complex assembly of multicomponent and hierarchical assembly has been developed to fabricate functional aggregates. Recently, the majority of research reported that self-assembled nanoparticles could assemble at the oil-water interface and stabilized Pickering emulsion because of their controllable structures and surface activity.The hot topic of particulate emulsifiers focuses on inorganic nanoparticles, inorganic/organic hybrid nanoparticles, microgels, and some others. In 2005, Fujii first used self-assembled micelles based on amphiphilic triblock copolymers as particulate emulsifiers to assemble at the oil-water interface and stabilize Pickering emulsion. In our previous work, nanoparticles self-assembled from amphiphilic random copolymer were used to stabilize Pickering emulsion. The effect of polymer chain sequence, chemical modification, and environmental stimulation(such as ionic strength, pH, temperature, and UV irradiation) on the structure of nanoparticles and the properties of emulsions were investigated. The mechanism of emulsion stability based on self-assembled random copolymer nanoparticles was presented. However, most of the reported nanoparticles used to stabilize emulsions were prepared from synthetic copolymers with poor biocompatibility, which might limited their potential application in the food, cosmetic and pharmaceutical fields, it is essential to develop environmentally friendly and nontoxic natural materials-based particulate emulsifiers.Biomacromolecules originate from microbial sources and have been widely used in the fields of food, cosmetic and pharmaceutical due to their excellent biodegradability and biocompatibility. However, most of biomacromolecules are hydrophilic, which limited their application fields. Whether the biomacromolecules can be hydrophobically modify and endow them with amphiphilicity and assembly and then further to apply or not?The immobilization and active retention of enzyme is always the one of the hot topics in the field of biology. Most of enzymes are very sensitive to environment. The change of environment(such as pH, salt concentration, temperature) would lead to the change of the secondary structure or the tertiary structure, followed by a loss of enzyme activity. Studies showed that biocompatible molecules could be used to load enzyme, to sustain or improve enzyme activity. The amphiphilic biomacromolecules with excellent biocompatibility may be used as this kind of carrier for enzyme.In this work, the hydrophobic monomers were used to modify hydrophilic biomacromolecules. This work combined macromolecular composite assembly technology with hierarchical assembly technology. The amphiphilic biomacromolecules and the functional factor(enzyme) were used to prepare amphiphilic activity nanoparticles, which were further assembled at oil-water interface and prepared functional emulsion. The resultant Pickering emulsion system achieved functionalization of emulsions and expanded the application field of amphiphilic biomacromolecule composite nanoparticles. Firstly, the amphiphilic biomacromolecule was prepared through the hydrophobic modification of biomacromolecule, followed by the investigation of its self-assembly process. The composite nanoparticles were obtained from self-assembly of enzyme and the amphiphilic biomacromolecule via the interaction(such as hydrophobic, electrostatic interaction and hydrogen bonding) between them. The composite assembly process and influences factors were investigated. Subsequently, the resultant composite nanoparticles were assembled at oil-water interface and prepared Pickering emulsion. The effect of the structure of composite nanoparticles on the properties of emulsionsThe work in this dissertation includes the following parts:1. Modification and self-assembly of dextran and their emulsion propertiesCinnamic acid(CINN) was used to modify dextran(Dex) to prepare the amphiphilic biomacromolecule Dex-CINN. The modification degree of CINN, concentration of Dex-CINN and the rate of water addition in the morphology of self-assembly were investigated. In addition, the self-assembly aggregates were further assembled at sesame oil-water interface. The effects of the morphology of self-assembly aggregates on emulsion properties were investigated. The different types of small-molecule drugs were used to assemble with Dex-CINN to prepare stable surface-active composite nanoparticles. Under the drive of interface tension, the resultant composite nanoparticles were assembled at the sesame oil-water interface and stabilize Pickering emulsions. The properties and the biocompatibility of emulsion were further investigated. The results showed that the resultant Dex-CINN can self-assemble into bowl-shaped nanoparticles in selective solvent. The modification degree of CINN, concentration of Dex-CINN and the rate of water addition could affect the morphology of bowl-shaped NPs and further affect the properties of emulsion. The resultant composite nanoparticles based on the composite assembly of enzyme and Dex-CINN were easy to precipitate due to the rigid structure of CINN, indicating the rigid structure of Dex-CINN was unsuitable to assemble with enzyme. Stable spherical composite nanoparticles were obtained from self-assembly of the different types of small-molecule drugs and Dex-CINN. The influence of pH value and salt concentration on the structure of composite nanoparticles and properties of emulsion were carefully studied. Dex-CINN, composite nanoparticles and the emulsion stabilized by composite nanoparticles have good biocompatibility.2. Modification and self-assembly of hyaluronic acid and their emulsion propertiesIn the part, the L-phenylalanine ethyl ester(L-Phe) was used to modify hyaluronic acid(HA) to prepare the amphiphilic biomacromolecule HA-Phe with different modification degrees. The resultant HA-Phe can self-assemble into polymer vesicles in selective solution. The effects of modification degrees on the morphology of the vesicles were investigated. The polymer vesicles were further to assemble at white oil-water interface and the effect of the morphology of self-assembly aggregates on emulsion properties was investigated. Papain was then use to assemble with HA-Phe to fabricate stable composite nanoparticles. The resultant composite nanoparticles were to assemble at white oil-water interface and stabilize Pickering emulsions. The properties and the biocompatibility of emulsion were researched. The results showed that the modification degree of L-Phe could affect the sizes and wall thickness of polymer vesicles and further affect the properties of emulsion. The stable composite nanoparticles were obtained from self-assembly of Papain and HA-Phe via the interaction(such as hydrophobic, electrostatic interaction and hydrogen bonding) between them. Salt concentration and pH could affect the structure of composite nanoparticles and further affect the properties of emulsion. The emulsions stabilized by composite nanoparticles have good biocompatibility and retain the some activity of Papain.3. Hierarchical assembly and emulsion properties based on dopamine-modified γ-glutamic acidThe dopamine(DA) was used to modify γ-glutamic acid(γ-PGA) to prepare amphiphilic dopamine-modified γ-glutamic acid(PGA-DA). Negatively charged PGA-DA and positively charged Lys were used to composite assemble via electrostatic interaction. The composite assembly process and influence factors of PGA-DA and Lys in aqueous solutions were investigated. The resultant composite nanoparticles were further assembled at white oil-water interface and stabilized Pickering emulsions. The mechanism of emulsion stability and the biocompatibility of emulsion were investigated. The results showed that the composite nanoparticles were obtained from self-assembly of PGA-DA and Lys in aqueous solutions. The concentrations and weight ratios of PGA-DA and Lys could affect the structure and properties of composite nanoparticles. The composite nanoparticles were assembled at oil-water interface and obtained gel-like emulsions. The mechanism of emulsion stability with different pH value and salt concentration were carefully studied. The emulsions were stabilized by the synergistic effect of PGA-DA and Lys. Electrostatic repulsion and steric hindrance had a significant impact on the emulsion stability.4. Bioactivity of emulsionsBased on the third part, the bioactivities of emulsions(including the activity of Lys in emulsions, the antimicrobial activity of Lys in emulsions, the cell toxicity of emulsions) stabilized by Lys/PGA-DA complex nanoparticles were further investigated. The results showed that there were some changes in the conformation of Lys during the complex assembly with PGA-DA. Trp residues were gradually buried in a more hydrophobic environment, leading to the formation of ordered secondary structure in composite nanoparticles, following by the increase of the Lys activity. The influence of salt concentration and pH value on the conformation and the activity of Lys were studied. The emulsions stabilized by complex nanoparticles have the some antimicrobial activity and retain the excellent activity of Lys. The experimental results indicated that the amphiphilic macromolecule, composite nanoparticles and the emulsion stabilized by composite nanoparticles have excellent biocompatibility.In this thesis, three different types of biomacromolecule were hydrophobically modified to prepare different kinds of amphiphilic biomacromolecule. The obtained amphiphilic biomacromolecule and functional element were used as the building blocks of assembly to prepare the multi-component amphiphilic composite nanoparticles. The resultant composite nanoparticles were assembled at oil-water interface and prepared bioactive functional emulsions(Pickering emulsions). The structure of composite nanoparticles and the hierarchical assembly could be controlled by the structure of the building blocks and environments of self-assembly. The relationship of the building blocks, self-assembly environments and emulsion properties were systematically investigated. The stable functional emulsions were obtained via controlling the building blocks, self-assembly environments and the structures of composite nanoparticles, which established the basis for practical application.