ELECTROSTATIC SPRAYING AND ITS USE IN DRUG-DELIVERY - CHOLESTEROL MICROSPHERES

Electrostatic spraying can be achieved by applying a potential difference of a few thousand volts between two electrodes and the end of a capillary supplied with liquid or melts under atmospheric pressure or controlled temperature. The system involved in this investigation consisted of two electrodes positioned 0.2 cm apart, one of which being at the tip of the capillary. The system was used in the production of excipient-free microspheres of cholesterol. The thermal stability of cholesterol (m.p. 148.5 degrees C) allowed its electrostatic spraying at 170 degrees C. Cholesterol congealing on spraying afforded microsphere collection with no cooling of the system. Particle size was found to be dependent upon voltage, and positioning of the two electrodes. SEM analysis of the microspheres obtained at +3000 V d.c. voltage produced a mixture of spherical particles of 150-250 mu m and amorphous particles of 10-30 mu m size. Particle size distribution studies using a Coulter counter showed that 65% of particles produced are in the range of 13.5 +/- 3.76 mu m. Investigation of the dependence of electrostatic spraying behavior of solvent systems on their physico-chemical properties suggested an inverse relationship between electrostatic spraying flow rate and polarity, viscosity, and surface tension. Liquids with high dielectric constant required higher voltages to enter into electrospraying mode. Increase in molecular symmetry improves the electrostatic spraying properties of liquids and may be correlated to molecular packing in the liquid phase. The results of this study support electrostatic spraying as a promising technique for the production of excipient-free microspheres for the delivery of macromolecules as well as molecules of lower molecular weight.