Microspheres of chitosan for controlled delivery of brassinosteroids with biological activity as agrochemicals

Chitosan microspheres (CS) were prepared by simple coacervation–cross-linking in the presence of sodium tripolyphosphate. Two synthetic analogues of brassinosteroids (BA) and diosgenin derivatives were dissolved in ethanol or methanol and encapsulated into CS microspheres. The extent of encapsulation was dependent on both the nature of the steroid and the solvent. For BA and derivatives encapsulation varied from 10% to 50%. Microspheres were characterized by FTIR spectroscopy. Particle sizes ranged from 790 to 1470 μm. Differential scanning calorimetry revealed the effect of the BA encapsulated on the thermal behaviour of the CS. In vitro release studies performed in ethanol and water at pH 7 indicated drug release dependence on the extent of encapsulation and the nature of the BA. Almost constant release rate was observed in all cases during the first 10 h. Release was always greater in ethanol than in water.