Preparation And Characteristics Evaluation Of Two Chitosan Sustained Release System

Chitosan (CS) has been extensively examined in the pharmaceutical industry for its potential in the development of controlled release of drug delivery due to its excellent biocompatibility, biodegradability, bioactivity and nontoxicity. New chitosan microspheres and thermosensitive hydrogel were prepared and the characteristics were evaluated.New microspheres containing hydrophilic core and hydrophobic coating as controlled release system with no toxic reagents is proposed. W/O/W emulsion and solvent evaporation methods are used to make chitosan/cellulose acetate microspheres (CCAM). The appearance of microspheres was spherical, free-flowing and non-aggregated. Chitosan concentration, chitosan molecular weight, cellulose acetate (CA) concentration and the ratio of CA/chitosan (CS) had influence on the CCAM size, appearance, ranitidine hydrochloride loading and releasing efficiency in vitro. The microsphere size became bigger and the appearance of microspheres became more compacted with the increasing of chitosan concentration and chitosan molecular weight. While the CA concentration was increased from 1% to 5%, the microsphere size became bigger and the appearance of microspheres became more corrugated and the structure became more compact. The optimal condition for preparation of the microspheres was the ratio of CA/CS at 3/1.The loading efficiency of ranitidine decreased with the increasing of chitosan concentration. The CCAM prepared with high molecular weight (1130KD) and lower molecular weight (47, 145KD) chitosan had relatively high loading efficiency, however the loading efficiency was relatively low at middle molecular weight(308,499KD). The loading efficiency increased with the increasing of cellulose acetate concentration and the ratio of CA/CS. The release efficiency of ranitidine from the CCAM wasn't affected by the pH values of release medium. The size of microspheres affected the release of ranitidine and the bigger microspheres released slower than that of the smaller parts. Molecular weight and concentration of chitosan affected the release in vitro. The release rate became slower with the increasing of chitosan concentration and molecular weight and the release from CCAM prepared with highest molecular weight chitosan (1130KD) was the slowest. The optimal condition for preparation of the microspheres was CA concentration at 2% and the ratio of CA/CS at 3/1 which had the slowest release rate in vitro.A thermosensitive hydrogel was prepared with chitosan (dissolving in the acetic acid/sodium acetate buffer solution) andαβ-mixtured-glycerophosphate (αβ-GP) which could be transformed into gel at 37℃. The thermosensitive characteristics, appearance and structure of hydrogel were affected by the pH values, ion intensity and ratio of CS/αβ-GP and concentration, molecular weight (MW) and DD of chitosan. The pH 4.6, ion intensity 0.15mol/L, ratio of CS/αβ-GP 8.8/1.2, chitosan solution of 2%, MW of 1360KD and DD of 75.4% were the optimal condition to prepare CS-αβ-GP thermosensitive hydrogel. The appearance of hydrogel incubated at 37℃became more corrugated and the granule was almost disappeared. The appearance and characteristics of hydrogel changed with the different solvent condition and different characteristics of chitosan. The CS-αβ-GP hydrogel system was an ideal sustained release system and the release rate could be adjusted by the change of preparation conditions. Model drugs released from CS-αβ-GP hydrogel prepared by methodⅠwas slower than that from hydrogel prepared by methodⅡ. The CS-αβ-GP hydrogel made from different pH values of buffer solution and different molecular weight of chitosan had different release efficiency of adriamycin (ADR) in vitro. The hydrophilic model drug (ADR) released 60% to 70% during 24 hours which was slower than that of hydrophobic drug (6-MP).CCAM loaded different model drugs were prepared by the method of W/O/W emulsion. The loading efficiency was affected by the characteristics of model drugs and it increased with the increasing of hydrophilicity of model drugs. The release of different model drugs wasn't affected by the pH values of medium, so it illustrated that the affection of medium on the release was depended on the materials of microspheres but not the model drugs. The CCAM system had good effect on the controlled release in vitro of all model drugs of different hydrophobicity. However, the release rate became slower with the increasing of the hydrophobicity of model drugs.CCAM had good mucoadhensiveness and could adhere to the gastric mucosa tightly. The delivery system of CCAM had good adhesive ability to small intestine but the remaining percent decreased with the time lasting. The adding of model drugs made little difference in mucoadhensiveness from the blank CCAM. The mucoadhesive tests in vivo showed that CCAM could retain in gastrointestinal tract for an extended period of time. The time that 50% of CCAM remained in stomach after administered was 2.63h and that of 50% of CCAM get to colon after administered was 3.93h. These results suggest that CCAM is a useful dosage form targeting the gastric mucosa or prolonging gastric residence time as a multiple-unit mucoadhesive system.The hemolysis of CCAM and chitosan hydrogel samples were tested by direct contact methods, according to ISO 10 993-4 (1992). Under the conditions of this study, blood in contact with tested samples would not be considered hemolytic, showing hemolysis value less than 5%.The cell compatibility of chitosan hydrogel was evaluated by measuring the relative growth rate of MEF cell. The RGR of MEF cell at different extract concentration and different extract time were all more than 80% and even to 100%. The results showed that the hydrogel had good cell compatibility and the compatibility isn't affectted by the extract concentration and time.CCAM were implanted into muscles of rats and chitosan hydrogel were injected at the back of rats which transited into gel in situ. After a definite time interval, the CCAM or gel implanted were observed to evaluate the biocompatibility. It was observed that the two sustained release systems had no toxic effects on surrounding tissue and was slowly degraded after implanted into rat back muscular porch. The present study suggests that the two systems have good biocompatibility and biodegradation. A number of blood biochemical parameters were all in the normal range and had no obvious difference with constant group which illustrated that the two chitosan systems had good blood compatibility.CCAM was degraded gradually with the time lasting in PBS solution. Blank CCAM and CCAM loaded different model drugs had the same degraded trend and degraded in a slow speed. Lysozyme degradation rates of all kinds of CCAM was fast in the first 10 days. The Lysozyme degradation rates became slower after 10 days and the CCAM loaded 6-MP was degraded slower than that of blank CCAM. Chitosan thermosensitive hydrogel degraded with the time lasting in PBS solution. It degraded quickly in the first 10d and the remaining weight reached 40%. The ion intensity affected the degradation a little. The concentration of hydrogel had obvious affection on the degradation rate which decreased with the increasing of hydrogel concentration. The Lysozyme degradation of hydrogel was fast in the first week and then degraded in a slower speed in the following. The lysozyme degradation rate became quick with the increasing of lysozyme concentration. In the mean time, the lysozyme degradation of hydrogel was affected by the hydrogel concentration. The degradation rate maintained the same at low concentration(0.5%-2.0%)and decreased with the increasing of hydrogel concentration when it was higher than 2.0%.CCAM and chitosan thermosensitive hydrogel had good sustained release and good biocompatibility which could be the ideal delivery systems of active biomaterials.