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

1. General IntroductionThe jet nebulizer functions by the Bernoulli principle by which compressed gas (air oroxygen) passes through a narrow orifice creating an area of low pressure at the outlet of theadjacent liquid feed tube. This results in drug solution being drawn up from the fluid reservoirand shattered into droplets in the gas stream. Jet nebulizers produce smaller droplets than dopMDIs, and these smaller droplets penetrate more easily to the small airways (74).Figure 1.4: Jet-Nenulizer DeviceThe choice of a proper nebulizer system is very crucial for the efficient delivery ofaerosolized respiratory drugs (75). Jet nebulizers are widely used, because of their durability,ease of maintenance, and availability at low cost. In a jet nebulizer, compressed air is forcedthrough a narrow orifice, which leads to a decrease in lateral pressure, thereby drawing upliquid from the feed tube. The primary droplets are produced in the nozzle region and thenbroken down into smaller droplets. The non-respirable droplets are removed by baffles (76).The droplets may increase in diameter because of condensation of water vapor. Thiscondensation occurs because the droplets are at a low temperature (about 10°C) after beingreleased from the nebulizer, if the surrounding air stream was unsaturated (77).Fewer than 0.5% of the resultant droplets are small enough to leave the nebulizer; the largerdroplets drip back into the liquid to start the process again. Size distribution data for jetnebulizers come from a number of studies (78, 79, 80, 81, 82, 83). These kind of nebulizer areable to produce, from physiologically isotonic saline, initial droplets with aerodinamicdiameter from 1.6 to 4.9 µm.The size distribution of aerosol droplets from a jet nebulizer depends on the diameter of theliquid inlet orifice, the air velocity at the nozzle, and the ratio of the mass flow rate of air to19