| The electrospray method has several unique advantages to fabricate polymeric par-ticles for drug delivery compared with other techniques. For example, it can achieve drug loaded particles by one step, and monodispersed particles can be produced using the cone-jet mode of the electrospray technique. In addition, either hydrophobic or water-soluble drugs can be facilely loaded into electrosprayed particles with high en-trapment efficiency. Despite the aforementioned advantages, the size of elec-trosprayed particles was always within micron to submicron range and the decrease of particle size by adjusting preparation parameters is limited.Compared with microparticles, nanoparticles show more excellent properties in flow property, targeting, circulation time, cellular uptake and so on. Therefore, a new strategy was proposed based on a coaxial tri-capillary electrospray-template removal process to control the size of electrosprayed particles. Briefly, microparticles with a core-shell-corona structure were first fabricated through coaxial tri-capillary elec-trospray. The corona layer was subsequently removed to decrease the particle size.To optimize the preparation parameters, the effects of solvent, fluid concentration, feed rate and voltage on morphologies and sizes of Poly(D, L-lactide-co-glycolide) (PLGA) particles fabricated by electrospray were studied. Poly(ethylene glycol) (PEG) with molecular weight of 20 kDa was chosen as template material. The concentration of PLGA fluid decreased to fabricate particles without fibers by coaxial electrospray when PLGA and PEG were used as core and shell materials.Spherical microparticles with average diameter of 1.8±0.8 μm were obtained us-ing a coaxial tri-capillary electrospray with bovine serum albumin (BSA), PLGA and PEG as core, shell and corona materials, respectively. LSCM images showed that the particles presented a distinct core-shell-corona structure. The particle size decreased to 94±8 nm after removing the PEG template by washing and SEM, TEM and AFM images showed that the nanoparticles kept spherical morphology and smooth surface.The nanoparticle size could be modulated by adjusting the feed rate of shell fluid, and the diameter of nanoparticles could be reduced to 68±8 nm when the shell fluid feed rate decreased to 0.5 ml/h. The drug loading content and entrapment efficiency of BSA were 3.7±1.2% and 78.3±5.3%, respectively, which were detected by Brad-ford. It found that BSA releasing lasted for 60 h. The second structure of BSA re-leased from particles was monitored with circular dichroism spectrum, and the results showed that the electrospray process did not affect the second structure of the protein.To promote the hydrophilicity of the particles, amphiphilic block copolymer Poly(lactide)-b-poly(ethylene glycol) (PLA-b-PEG) was used as shell material. It was found that this material showed good electrospray performance and surface hydro-philicity of PLA-b-PEG microparticles was better than PLGA microparticles detected by surface water contact angle. Nanoparticles with diameter about 100 nm were pro-duced by coaxial tri-capillary electrospray-template removal process when PEG, PLA-b-PEG and PEG were used as core, shell and corona materials, respectively. LSCM images showed that the thickness of corona layer in the microparticles in-creased as the increasing of corona fluid feed rate. Also, the diameters of microparti-cles and nanoparticles could be modulated by adjusting the feed rate of corona fluid. The nanoparticles displayed excellent dispersion stability in water and the diameter of the nanoparticles remained almost unchanged during 30 days. They also showed good dispersion stability in PBS and cell culture medium RPMI 1640. MTT results showed that PLA-b-PEG nanoparticles had good biocompatibility. The cellular uptake, mech-anism and exocytosis behavior of nanoparticles were studied by flow cytometry. It was found that nanoparticles could be uptaken by A549 cells with abundant quantity and the uptaken amount depended on nanoparticle concentration and incubation time. The endocytosis process was related to caveolate-mediated endocytosis, but had nothing to do with clathrin-mediated endocytosis. After 24 hours,45% nanoparticles were eliminated. The LSCM images showed that PLA-b-PEG nanoparticles enriched around the nucleus and some of them entered into lysosome eventually.Hydrophobic antitumor drug paclitaxel (PTX) was loaded into PLA-b-PEG nano- particles. The drug loading content, entrapment efficiency and drug release behavior was determined by HPLC. By increasing the drug fluid feed rate, the drug loading content could reach 50.7±1.5%, while entrapment efficiency exceed 70%. Sustained release of PTX achieved and drug release lasted for more than 40 days. The effects of drug loading content, drug location and release medium property on drug release were also studied. The results showed that all of increasing drug loading content, reducing pH value of release medium and adding proteinase could accelerate drug release, but there was no significant relationship between drug location and its release. The release mechanism was analyzed by Ritger-peppas equation. It was found that the release of PTX from PLA-b-PEG nanoparticles was controlled by both of diffusion and polymer degradation. When the pH value of release medium was 5.0 and proteinase was added simultaneously, the drug release was mainly controlled by the degradation of the polymers. In vitro antitumor activity of drug-loading nanoparticles was evaluated by MTT assay, and it found that the cytotoxicity of drug loaded nanoparticles increased with the extension of incubation time. |
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