Modification And Functionalization Of Hyaluronic Acid

Hyaluronic acid (HA), a biomacromolecule, now represents one of the most attractivesubjects for the design of advanced biological materials with functional application value dueto its excellent moisture retention, viscoelasticity, biological functions, environmentalfriendliness and renewability. The self-assembly of HA into biomacromolecular micelles hasnot only theoretical research value but also has application value. In this paper, amphiphilicHA was obtained by physical or chemical modification of HA. HA-based micelles wereprepared base on the technique of macromolecular self-assembly. At the same time, theself-assembled micelles were used as emulsifiers to prepare emulsions. The whole paperincludes three parts.1. Self-assembled HA/PDM particles and emulsification propertiesThe anionic biomacromolecule, hyaluronic acid, and cationic monomer,2-(dimethylamino)ethyl methacrylate (DM), were used to construct an opposing chargepolymer/monomer complex. Positively charged poly[2-(dimethylamino)ethyl methacrylate](PDM) was prepared when DM monomers polymerized in aqueous solution. Self-assemblybetween PDM and HA was driven by electrostatic interaction, and HA/PDM complex colloidparticles were formed in the aqueous medium. The HA/PDM complex structure wascharacterized by Fourier transform-infrared spectroscopy (FTIR). The self-assembly behaviorbetween HA and PDM, and the influence of polymerization time on HA/PDM complexcolloid particle size, were investigated by turbidity experiment and dynamic laser scattering(DLS). Zeta potential and morphologies of the colloid particles were characterized bytransmission electron microscopy (TEM). The influence of pH on the colloid particles properties was investigated, and the emulsification of the colloid particles was preliminarilyexplored. The results showed that no HA/DM complex aggregates were formed before thepolymerization of DM monomers. Spherical HA/PDM particles were spontaneously formedthrough electrostatic interaction between HA and PDM, coinciding with the gradualpolymerization of DM. Particle sizes gradually decreased and stabilized with increasingpolymerization time. The HA/PDM particles were pH sensitive and possessed improvedemulsification properties compared with uncomplexed HA and PDM.2. Preparation and self-assembly of dopamine-grafted hyaluronic acid derivativeDopamine-grafted hyaluronic acid derivative (HA-DOPA) was synthesized in aqueoussolution by the amidation reaction between HA and dopamine.The structure and degree ofsubstitution (DS) of HA-DOPA were characterized by UV-Vis spectrophotometer, FTIR and1H-NMR. The influence of initial reactant molar ratio and reaction temperature on DS wasinvestigated. The self-assembly behavior of HA-DOPA was characterized by fluorescenetechnique. The size, zeta potential and morphologies of HA-DOPA self-assembled micelleswere characterized by fluorescene technique, DLS/SLS, zeta potentiometer and TEM. Theinfluence of DS, molecular weight of HA and pH on the micellar properties was studied, too.The results showed that all the HA-DOPA with different DS could aggregate into negativelycharged and spherical micelles in aqueous solution. The critical aggregation concentration(CAC) of HA-DOPA was lower when the DS was higher, andt the micelles were more stable. The micelles were pH-responsive. Micelles were more stable and spherical at pH=3.5~4. Themolecular weight of HA have influence on the properties of micelles. The lower the molecularweight of HA, the smaller the size of the micelles.3. Emulsification of HA-DOPA self-assembled micellesHA-DOPA self-assembled micelles were used as biomacromolecule emulsifiers toprepare O/W emulsion. The effect of concentration, DS, pH, salt concentration, molecularweight of HA and oil typs on the emulsion was studied. The results showed that stableemulsions were prepared by HA derivative because of the introduction of DOPA whosesurface activity was high. The stability of emulsions increased with the increasing of micellesolution concentration. The stability of emulsions also increased with additionof salt whichincreased the shielding of carboxylic acid groups and made the hydrophilic segmentcollapse.The emulsification property of micelles with higher molecular weight was betterbecause of steric effect. The oil-in-water interfacial behavior of the micelles was affected bychanges of pH values.The emulsification of micelle solution under different pH was different.HA-DOPA micelle emulsifiers which could stabilize a broad range of oils in water wereimportant in potential applications.