This paper reports the design and simulation of Si-based ultrasonic nozzles (or atomizers) that consist of multiple Fourier horns at ultrasonic frequency ranging from 0.57 to 2.75 MHz. Such high frequency ultrasonic nozzles should produce monodispersed droplets (or drops) 2 to 6 μm in diameter, which are ideal to efficiently target medications to different locations within the respiratory system depending on the site of disease. 3-D simulations on vibration mode shape and impedance of the nozzles using a commercial finite element method (FEM) program, ANSYS, yield resonant frequencies of pure longitudinal vibration in good agreement with the measured values. The mode shape simulation also shows that at the resonant frequency the longitudinal vibration amplitude gain at the nozzle tip for 3-horn nozzle is 8, four times that for a single-horn nozzle.
Monodisperse micron-sized aerosol is ideal for pulmonary drug delivery. This paper reports delivery of monodisperse aerosol of medicinal droplets generated by MHz ultrasonic nozzles using an anatomically realistic upper airway model. The MHz ultrasonic nozzle is fabricated using MEMS technology, and comprised of a piezoelectric drive section and a silicon resonator of multiple Fourier horns (see Fig. 1) [1]. The dissolved medication is pumped into a central channel (200×200 μm2) inside the nozzle and exits at the nozzle tip that vibrates longitudinally at the nozzle resonant frequency. The novel design of multiple horns facilitates generation of a column of monodisperse droplets at electric drive power as low as 15mW [1]. Monodisperse ethanol droplets 2.4 μm and water droplets 4.5 μm in diameter have been produced, respectively, using 1.5 MHz and 1.0 MHz nozzles. We used an aqueous solution of 25mg/ml (2.5wt%) β2-agonist (isoproterenol) for generation of monodisperse droplets using the 1.0 MHz ultrasonic nozzles. A yield of >54% (to the lower airways on total amount of inhaled isoproterenol basis), significantly higher than the reported highest lower airways deposition (32%) using metered-dose-inhalers (MDIs) [2], has been accomplished.
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