Studies On Controlled Drug Delivery Systems Of Chitosan Oligosaccharide-fatty Acid Graft Copolymer

In recent years, polymeric micelles have emerged as a potential carrier in the various field of drug delivery, with the characters of solubilization, lowly toxicity, long-circulation and tumor localization. Polymeric micelles are self-assembled by amphiphatic block or grafted copolymers. Polymeric micelles are composed of hydrophobic segments as the internal core and hydrophilic segments as a surrounding corona in aqueous medium. In the article, chitosan oligosaccharide (CSO) is served as hydrophilic segments and fatty acid are served as hydrophobic segments.Chitosan oligosaccharide was obtained by enzymatic hydrolysis and ultrafiltration by various molecular weight cut off membranes. We get the weight average molecular (Mw, 18.4 Kda) by the determination of gel permeation chromatography. The CSO was easily dissolved in the distilled water at the pH below 7.4. The fatty acid was randomly grafted to a portion of the aminoes of CSO by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) mediated reaction. The fatty acid contained myristic acid (MA), palmitic acid (PA), stearic acid (SA) and behenic acid (BA). 1H-NMR spectrum was used to analyse synthesized copolymers. The substitute degree of amino group (SD) was determined by TNBS method. By afluorometry in the presence of pyrene as a fluorescent probe, the critical micelle concentration (CMC) was measured. The particle size and zeta potential of micelles were measured by dynamic light scattering using a Zetasizer. The SD of CSO-MA, CSO-PA, and CSO-BA were about 10%, of which the CMC was 0.019, 0.039. 0.041 mg/ml, respectively. At 1 mg/ml of copolymer concentration, the particle size of micelles was less than 100 nm of number average hydrodynamic diameter.A series of CSO-SA with different SD were obtained by controlling the amounts of SA and EDC. The SD of CSO-SA was 4.94%, 12.17%, 24.66%, and 41.82%, respectively. The CMC of CSO-SA with different SD was determined to be 0.064, 0.038, 0.021, 0.012 mg/ml, respectively. From the results, it could be found that the CMC value of the micelles decreased with the increase of SD. At 1 mg/ml of CSO-SA concentration, the particle size of micelles was less than 100 nm. The particle size increased and the zeta potential decreased as the concentration of CSO-SA decreased. On the other hand, for the CSO-SA micelles with different SD, the increase of SD caused the size of micelles to decrease. Low molecular heparin was used as model drug to prepare nanoparticles. CSO-SA grafted copolymer and CSO were used to modify the nanoparticles. Then the heparin nanoparticle, CSO-SA modified heparin nanoparticel, and CSO modified heparin nanoparticle were prepared, of which the size was 397.0, 487.0, 435.8 nm, respectively. Compared with the nanoparticle without copolymer, the drug entrapment efficiency (EE) increased and the drug release rate decreased.To increase the stability of the micelle in vivo and controll drug release, the shells of micelles were cross-linked by glutaraldehyde. By controlling the molar ratio of CSO-SA to glutaraldehyde, the nanoparticle with smaller size than that of its initial micelle was obtained. When glutaraldehyde concentration was higher (ncso-SA^ %u = 1:45), the cross-linking between micelles occurred and led to the increase of particlesize. When glutaraldehyde was added with appropriate ratio (1:20, 1:25, 1:30), the particle sizes decreased with reaction time. When glutaraldehyde concentration was lower (ncso-sA: ngiu = 1:10), there were no significantly changes for size and zeta potential due to the slightly cross-linking.The behavior of CSO-SA micelles as carriers of paclitaxel was investigated. The solubilization of paclitaxel in CSO-SA micellar solution of which the SD was 4.94%, 12.17% and 41.82% was 12.9, 29.6, 57.8 times, respectively. After the drug loaded, both of size and zeta potential of CSO-SA micelles were larger than that of drug free. The EE of paclitaxel in all micelles and nanoparticles were high, which were about 97%. The in vitro paclitaxel releases from CSO-SA micelles and cross-linked nanoparticles were investigated. The release rate of paclitaxel from micelles with low drug loading was faster than that with higher drug loading. But the release rates of the micelles with drug loading 3.8% and 5.5% were almost uniform. When the SD of CSO-SA micelles increased, the release rate decreased. When the drug-loaded micelles were cross-linked by glutaraldehyde, the release rate decreased. The lower drug release rate was observed with the increase of cross-linking degree of nanoparticles.