| Magnetic polymer composite microparticle is a kind of microparticles with special structure and property, which is composed of polymer and inorganic magnetic materials. It not only has general properties of polymer microparticles, whose surfaces can be endowed with multiple function groups to meet various needs, but also can move to a specific site or be separated from surrounding medium quickly in exterior magnetic fields. These properties of composite microparticles show great prospects for potential applications in several fields, such as biomedicine, cytology, bioengineering, separating engineering, cosmetic, stealth technologies and so on.On the basis of summarizing the research fruits of magnetic polymer composite microparticles worldwide, this article selected N-isopropylacrylamide (NIPAM) with a special temperature-sensitive behavior as a basic monomer, hydrophilic methacrylate monomerα-MAA (containing -COOH) and super-paramagnetic Fe3O4 magnetic fluid prepared by co-precipitation method to copolymerize together in some appropriate conditions. A novel composite microparticle was successfully obtained with temperature, pH-sensitivity and magnetic responsiveness synchronously. Therefore, it was expected to be applied effectively in biology, pharmaceutical, engineering and other relevant fields, particularly in the areas of drug controlling and releasing.Important research results were summarized below, the best preparation condition of Fe3O4 by chemical co-precipitation method included that Fe2+/Fe3+=1/2 [n (Fe2+) beyond 20% of theory value], reaction environment pH=8, reaction temperature 60℃, reaction time 10min, maturation temperature 80℃, maturation time 0.5h and counteract environment pH=6. After these disposals, the obtained yield was well dispersive, anti-oxidative and had the greatest saturation magnetization.Formation of Fe3O4 magnetic nanoparticle experienced the process of forming core, growing up and reuniting. When the concentration of precipitation components solution (Ci) exceeded precipitation solubility (Cs) and achieved a forming core concentration (Cn), a large numbers of crystal cores appeared, this was a core stage. Going with the rapid decline of Ci, to maintain Ci slightly higher than Cs was very necessary in order to keep formed cores simultaneously growing up, this was a growth stage. The core grew up became a rigid aggregate because of a solvent action and there were also a dynamic balance between precipitates growing up and dissolved at the same time.Appropriately increasing reaction temperature and stirring rate could contribute to the diffuse of crystal core equally, accelerating to form a nuclear and finish the process of synchronous growth. In the condition of surfactant and controlling interface growth of Fe3O4 colloidal particles, maturation action could enhance integrity and compactness of Fe3O4 spinel crystal structure, also can significantly improve the magnetic property and anti-oxidation of Fe3O4 nanoparticles. Well dispersive yield prepared by PEG-4000 (volume fraction10%) as a surfactant showed apparent chemical stability if drying for 24h at 60℃.Fe3O4/P(NIPAM-MAA) composite microparticles presented a spherical and shell-core structure and showed a well swelling property in solution. Average diameters in swelling/shrinking state were 334.7nm/141.7nm respectively at 25℃and 45℃, and the swelling degree a was 13.2. These composite microparticles were all of temperature, pH-sensitivity and magnetic responsiveness synchronously. The volume phase transition behavior occurred at 30℃-36℃. When pH of the system gradually increased, volume phase transition temperature (VPTT) moved to the higher. The largest magnetization intensity of composite microparticle was up to 0.6306 emu/g, and both remanence (Mr) and coercivity (Hc) were very tiny showing a super-magnetic property.Fe3O4 nanoparticles modified by PEG-4000 adsorbed monomer and initiator in the solution to form a rich region around (trigger centre). After initiated polymerization, the monomer became to polymerize in the rich region and formed a mutual entanglement polymer chain in order to surround a magnetic nanoparticles, and generated oligomers (primary particles). Oligomers continued to gather, growth, depose and form a stable core-shell composite particles eventually.Monomer conversion rate enhanced as MAA dosage increased, but MAA dosage should not exceed 25% of monomer dosage, otherwise there was flocculation.0.35wt% magnetic fluid consumption should not exceed 40g in order to prevent a "phenomena of magnetic waste", which could affect polymerization reaction. As initiator APS dosage increased, monomer conversion rate and surface combined carboxyl amount increased. Average diameter of composite microparticle became larger and larger with crosslinker MBA dosage increasing gradually. Polymerizing for 30min at 70℃and then continuing to react for 5.5h at 60℃, as a result, a composite microparticle could appear with better performance and property.Critical flocculation concentrations of P(NIPAM-MAA), Fe3O4/P(NIPAM-MAA) were 1.2 mol/L,1.0mol/L respectively in NaCl solution at 25℃. The swelling/shrinking were reversible by ways of adjusting temperature, but the flocculation wasn’t reversible. With NaCl concentration increasing, both of volume phase transition temperature and critical flocculation temperature of Fe3O4/P(NIPAM-MAA) transferred to the lower. As the volume fraction of ethanol (VEtOH%) increased from 0-25%, volume phase transition behavior gradually weakened and even disappeared basically. However, when VEtOH% was up to 70%, composite microparticle began to appear weak contraction.Loading drug rate of Fe3O4/P(NIPAM-MAA) to salicylic acid was about 38.7%, with time goes by, releasing drug rate gradually slowed down. At a lower temperature (25℃),,there was a well releasing drug property, but at a higher temperature(45℃) the releasing rates became significantly slower than the former. For example, releasing drug rates were 55.6% and 39.8% respectively after 8h. In the beginning stage (0-2h), their releasing rates were similar basically. |
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