chitosan and plga microspheres as drug delivery ... - UniCA Eprints

2. Chitosan And PLGAloading. In first method, tetracycline was mixed with chitosan solution before thesimultaneous crosslinking and precipitation. In second method, the drug was incubated withpre-formed microspheres for 48 h. When the drug was added to the polymer solution beforecrosslinking and precipitation, only 8% (w/w) was optimally incorporated in the finalmicrosphere formulation. On the other hand, when the drug was incubated with the preformedmicrospheres, a maximum of 69% (w/w) could be loaded. This signifies that the drugcan be adsorbed on the chitosan microspheres to a greater extent using the latter method.Many parameters determine the drug release behavior from chitosan microspheres. Theseinclude concentration and molecular weight of the chitosan, the type and concentration ofcrosslinking agent, variables like stirring speed, type of oil, additives, crosslinking processused, drug-chitosan ratio, etc.Drug release studies from chitosan microspheres have generally shown that the release of thedrug decreases with an increase in molecular weight of chitosan. This may be attributed toswelling behavior of chitosan microspheres. An increase in molecular weight of chitosanleads to increase in viscosity of the gel layer, which influences the drug diffusion as well aserosion of the microspheres. Increasing the polymer concentration drug release decreases.A number of reports studying the effect of drug release have shown that the release of thedrug from the microspheres increases with increase in drug content in the microspheres.However, different results have also been reported. Cross-linking density has a remarkableeffect on the release of drugs from the microspheres. Jameela et al. (222) revealed that highlycrosslinked microspheres released only 35% of the progesterone in 40 days compared to 70%release from microspheres cross-linked lightly. Kumar et al. (223) encapsulated curcumin(upto an extent of 79.49 and 39.66%) in bovine serum albumin and chitosan to form a depotforming drug delivery system. Microspheres were prepared by emulsion–solvent evaporationmethod coupled with chemical crosslinking of the natural polymers. The concentration of thecrosslinking agent had remarkable influence on the drug release. In vitro release studiesindicated a biphasic drug release pattern, characterized by a typical burst-effect followed by aslow release which continued for several days. Dini et al. (224) studied the synthesis andcharacterization of GA crosslinked chitosan microspheres containing hydrophilic drug,hydroquinone. It was found that slow drug release rates were obtained from microspheresprepared by using a high initial concentration of chitosan, a high molecular weight of chitosanor/and a low drug concentration. It was established that the release rate of hydroquinone was39