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Abstract

Microspheres containing methylene blue and prednisolone acetate were prepared by one of three methods: freeze-drying, evaporation, and solvent-extraction-precipitation. An extremely porous structure was obtained by the freeze-dry and solvent-extraction-precipitation procedures. The specific surface area of 6.33-microns particles was 20.6 m2/g, or 35 times that of a particle devoid of pores, and the void space was 59-61%. The sphericity, size, and yields of the microspheres were influenced by the preparation procedure, surfactant type and concentration, temperature of the continuous phase, polymer concentration in the dispersed phase, and ratio of marker to polymer. The most suitable processing conditions were a polymer concentration of 5-10%, a marker loading of 10%, 0.1% sorbitan sesquioleate as the surfactant, and temperature adjustment of the continuous phase from 15 to 50 degrees C following the addition of the dispersed phase. Complete release of the highly water soluble methylene blue occurred within 72 hr, while the less soluble prednisolone acetate released much more slowly, i.e., 90% after 7 days. The microspheres remained relatively intact during the in vitro release of methylene blue, confirming that the incorporated agent was confined to the walls of the porous network. Collapse of the polymer structure was evident after 7 days. The release therefore was believed to be governed principally by the solubility of the drug and the porosity of the matrix.

Effect of Preparation Temperature in Solvent Evaporation Process on Eudragit RS Microsphere Properties

“…2,5) On the other hand, our previous study reports the insignificant influence of preparation temperature on microsphere properties. 3) We suppose that in that case the temperatures (40, 50, 60°C) were too high to produce any significant differences.…”

“…solvent evaporation rate, 1) temperature, [2][3][4][5] solubility of polymer, drug and excipients in both emulsion phases, 6,7) dispersion stirring rate, 7-9) viscosity, solubility, volume and volume ratio between the inner and outer phases, [10][11][12] the quantity of polymer and drug, 1,6) and the physico-chemical properties and concentration of the stabilizator.…”

“…11,13) Some authors have previously studied the effects of preparation temperature on microsphere formation and characteristics: mean microsphere diameter and size distribution width, 2,5) particles morphology, 2) porosity, 5) and drug loading. 5) One can find only one report on the effect of temperature on microspheres containing Eudragit.…”

“…2,5) Thus, the objective of this study was to investigate the effect of preparation temperature on Eudragit RS microsphere properties in a different temperature range. Lower temperatures were examined, where more pronounced influences were expected.…”

Drug Microencapsulation by PLA/PLGA Coacervation in the Light of Thermodynamics. 1. Overview and Theoretical Considerations

“…A few studies also compared the coacervation process with other microencapsulation methods such as solvent evaporation 48,63,64,[66][67][68] or extended the phase-separation process on other water-insoluble polymers such as poly- Table 1sReports a (glycolic acid), poly(hydroxybutyrate), 69 poly(1,4-butyleneco-succinate), 48 or poly( -caprolactone). 68 Although the obtained results may have favored one or the other technique, this is of course not generally valid, but only holds true for the particular drugs and process conditions used.…”