The electrospray and its application to targeted drug inhalation.
ABSTRACT This review explains the fundamentals of electrostatic spray (electrospray) atomization, with emphasis on operation in the so called cone-jet mode, which produces droplets with a very narrow size distribution. Since the control of droplet size is key to maximizing distal lung deposition, the electrospray should be well-suited to targeted drug inhalation. Electrospray droplets are a few micrometers in diameter, but they originate from a much larger nozzle, which allows nebulization of suspensions without clogging. Also discussed are: the physical principles of the break-up of the liquid ligament; droplet dispersion by Coulombic forces; and the most important scaling law linking the droplet size to liquid flow rate and liquid physical properties. The effects of the most critical of those properties may result in some restrictions on drug formulation. Droplets produced by electrospray are electrically charged, so to prevent electrostatic image forces from causing upper respiratory tract deposition. The charge is neutralized by generating a corona discharge of opposite polarity. Briefly discussed are the main differences between the laboratory systems (with which the electrospray has been quantitatively characterized during research in the past 10 years) and commercial electrospray inhalers under development at BattellePharma. Some remarkable miniaturization has incorporated liquid pump, power supply, breath activation, and dose counter into a palm-size portable device. The maximum flow rates dispersed from these devices are in the range of 8-16 microL/s, which makes them suitable for practical drug inhalation therapy. Fabrication is economically competitive with inexpensive nebulizers. Dramatic improvements in respirable dose efficiency (up to 78% by comparison with commercial metered-dose inhalers and dry powder inhalers) should ensure the commercialization of this promising technology for targeted drug inhalation.
Article: Reduction of droplet-size dispersion in parallel flow-focusing microdevices using a passive method[show abstract] [hide abstract]
ABSTRACT: Flow-focusing devices can be used to produce microparticles at low cost, with the added advantage of low dispersion in the size of the generated particles. However, when multiple parallel devices are used with common inputs to massively produce the microparticles, the overall production is polydisperse, usually due to differences in flow rates of the focused fluid through each single device. The solution to uniformize this flow rate can involve active, movable devices that would add complexity and cost to the system. A simpler solution is to add distribution and equalization channels that drive focused fluid to the inputs. Experimental results show that this method can reduce the total dispersion, and render the multiple device close to monodispersion.Journal of Micromechanics and Microengineering 03/2009; 19(4):045029. · 2.11 Impact Factor
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ABSTRACT: The effects of applying electrostatic charge to gasoline fuel sprays from a gasoline direct injection (GDI) injector have been investigated. The injector was modified by the addition of an electrically isolated electrode installed on its tip. The morphology of electrostatically charged and non-charged sprays was characterized using a Mie scattering visualization technique, Fraunhofer diffraction measurements of droplet size, and particle imaging velocimetry (PIV) measurements of the velocity field. The PIV measurements showed that the electrostatic charging of the sprays enhanced the vortical motion of the droplets and produced empty pockets within the spray. Furthermore, the charged sprays penetrated further and were wider than the non-charged sprays. The results of the PIV measurements were complemented by Fraunhofer diffraction (Malvern) measurements, which showed significantly increased consistency of droplet size for the electrostatically charged case. The extent of charging of the fuel sprays was determined with combined measurements of the mass and the charge carried by the sprays. In parallel, the electric field generated by the presence of the charged electrode was computed by numerically solving the Laplace equation at the vicinity of the injector tip. With this data, the relative magnitudes of the electrostatic and inertial forces were compared.Energy Conversion and Management.