Generation And Applications Of Polymeric Microparticles Based On Gas-liquid Shearing

Owing to its excellent biological features such as non-toxicity, biocompatibility, and biodegradation, chitosan is always considered for various biomedical and pharmaceutical applications. Microcapsules have been generated by different techniques, such as coacervation, emulsification solvent-evaporation and layer-by-layer assembly. The main disadvantage of the above methods is that the size and size distribution of the microcapsules are uncontrollable and non-uniform. Uniform-sized microcapsules can increase their bioavailability, reproducibility and repeatable release behavior. In order to obtain microcapsules with a controlled shape and uniform size, liquid-liquid microfluidic technique is employed to prepare chitosan microcapsules and nanoparticles. One of problem of this method is solvent-evaporation in the post-processing. Moreover, the wall of microcapsules prepared only by natural polymers always have low mechanical strength, which is a risk for drug delivery system since the pre-released chemicals possibly have bad effects for human body. In this work, we hope to develop a new method to prepare monodisperse microcapsules of chitosan and their derivatives. Moreover, it is possible to improve integrated properties through introducing inorganic microparticles or nano particles into the wall of microcapsules.Monodisperse chitosan microcapsules were prepared by using gas-liquid microfluidic technique. The effects of gas flow rate and liquid flow rate on the size and size distribution of the microcapsules were studied in detail. The optical microscope and SEM were used to characterize the size and morphology of microcapsules. The results showed that the prepared microcapsules were spherical and monodisperse. With the increase of gas flow rate, the size of microcapsules decreased. The liquid flow rate had a little influence on the size of the microcapsules. Gas-liquid microfluidic technique was also applied to embed the fluorescent substances or magnetic nanoparticles into the core of microcapsules, obtaining monodisperse microcapsules with characteristic fluorescence or magnetism.Chitosan/quaternized chitosan microcapsules with controlled dimension and narrow dimension distribution were obtained by gas-liquid microfluidic technique. The optimal condition was the gas rate at 0.5~0.8L/min, the concentration of SDS of 2wt% and a liquid phase(chitosan/quaternized chitosan acetic acid solution) rate at 3m L/hrs. The results of 3D video microscope test showed that the microcapsules had good p H stability and ionic stability. UV-VIS spectrum test proved that salicylic acid, sodium salicylate and 5-Fluorouracil could be loaded by the microcapsules. The drug release ratio was affected by the weight ratio of chitosan/quaternized chitosan and the release conditions.A quaternized chitosan/alginate/Ca CO3 composite microcapsule was prepared by the coacervation effect of quaternized chitosan and alginate, and in-situ precipitation of Ca CO3 particle. The composite microcapsules were formed in a microfluidic device based on gas-liquid shearing interaction. The effects of gas flow rate, liquid flow rate, the composition of liquid phase on the size and size distribution of the microcapsules were studied in detail. The morphology and average particle size were characterizated and analyzed by 3D video microscope and SEM. Swelling behavior of the composite microcapsules was studied in aqueous solutions with different p H values and ionic strength. The encapsulation and release of the microcapsules for model drug were evaluated by ultraviolet spectrophotometry. The microcapsules presented a more efficient drug release rate in alkaline solution and at 37 oC.Based on the electrostatic interaction between SDS and graphene modified by quaternized chitosan, a kind of chitosan/graphene microcapsule was fabricated by the gas-liquid microfluidic technique. Particle sizes and distribution of the microcapsules were related to gas rate, the concentration of chitosan and graphene dispersion. Uniform microcapsules were obtained when the gas rate was below 0.7 L/min. The introduction of graphene improved the mechanical strength of microcapsules. The release testing of model drug sodium salicylate revealed that the chitosan/graphene microcapsules had sustained release effects, compared with chitosan microcapsules.The gradient copolymers of styrene and fluorinated acrylate were synthesized by a emulsifier-free RAFT polymerization. Molecular weights and chemical structures were measured by GPC, 1H-NMR, FTIR and DSC. The gradient copolymer latex was used as an inner phase solution to build micro-particles, with the mixed soluiton of chitosan and Ca Cl2 as receiver. 3D microscopy is applied to study the effect of The latex viscosity, chitosan concentration and Ca Cl2 concentration on the formation of micro-particles. The results proved that the viscosity of the latex had an important effect on the morphology and size of micro-particles. The obtained micro-particles had good stability and could load fluorescent dyes.