Experimental research on surface acoustic wave microfluidic atomization for drug delivery

Abstract

This paper demonstrates that surface acoustic wave (SAW) atomization can produce suitable aerosol concentration and size distribution for efficient inhaled lung drug delivery and is a potential atomization device for asthma treatment. Using the SAW device, we present comprehensive experimental results exploring the complexity of the acoustic atomization process and the influence of input power, device frequency, and liquid flow rate on aerosol size distribution. It is hoped that these studies will explain the mechanism of SAW atomization aerosol generation and how they can be controlled. The insights from the high-speed flow visualization studies reveal that it is possible by setting the input power above 4.17 W, thus allowing atomization to occur from a relatively thin film, forming dense, monodisperse aerosols. Moreover, we found that the aerosol droplet size can be effectively changed by adjusting the input power and liquid flow rate to change the film conditions. In this work, we proposed a method to realize drug atomization by a microfluidic channel. A SU-8 flow channel was prepared on the surface of a piezoelectric substrate by photolithography technology. Combined with the silicon dioxide coating process and PDMS process closed microfluidic channel was prepared, and continuous drug atomization was provided to improve the deposition efficiency of drug atomization by microfluidic.

Figure 1

The top image shows a schematic diagram of atomization caused by SAW interacting with liquid. The bottom images show the piezoelectric substrate on which the SAW is generated (left) and portable battery-powered circuit used to generate the SAW (right). It uses three pieces of 3.7 V lithium batteries, and the maximum output of this driver circuit is about 110 Vp–p.

Figure 2

The device characterization (a) Image of the SAW substrate showing an enlargement of the IDTs for a 30 MHz SAW device. (b) Frequency response curves of SAW devices at different frequencies.

Figure 3

Schematic diagram of the glass twin-stage impinger lung model employed for the dose measurements. (a) schematic diagram of experimental device. (b) continuous atomization based on paper. (c) continuous atomization based on microchannel.

Figure 4

Schematic diagram of the fabrication scheme based on the SU-8 microchannel (a) SAW device. (b) Photolithography of SU-8 microchannels on the substrate surface. (c) Coating silicon dioxide film on the upper surface of the microchannel. (d) Bonding the PDMS layer with the microchannel to form a closed microchannel.

Figure 5

Continuous atomization process of liquid supplied by paper over time. The cross-hatched box indicates the position of the paper strip. (a) Atomization behavior with a SAW frequency of 30 MHz at a power of 4.17 W. (b) Atomization behavior with a SAW frequency of 30 MHz at a power of 6.62 W.

Figure 6

The aerosol size distribution of salbutamol solution atomized under different input powers.

Figure 7

Experimentally measured aerosol size distribution under different SAW powers for each of the two peaks.

Figure 8

Aerosol droplet size distribution of salbutamol solution atomized at 6.62 W and different frequencies, measured by laser diffractometry. Each frequency value was tested three times and then the results were averaged. Note that the mean diameters D_v50 for the three analysed frequencies were 10.66 μm, 5.13 μm, and 3.02 μm, respectively, and the the standard deviation were 1.298, 1.584, and 0.889, respectively.

Figure 9

Atomization process at different input power with working frequency of 60 MHz. (a) 2.09 W; (b) 6.62 W.

Figure 10

Aerosol droplet size distributions measured by laser diffractometry for different liquid flow rates with an SAW frequency of 30 MHz and input power of 6.62 W. Note that the Sauter mean diameter for the six analysed flow rates were 21.17 μm, 13.51 μm, 9.54 μm, 10.58 μm, 12.79 μm, and 32.51 μm, respectively.

Figure 11

Effect of flow rate and input power on aerosol droplet size: (a) aerosol droplet size changes versus input power and liquid flow rates. (b) three different atomization regimes were determined by the combination of input power and flow rates.

Figure 12

(a) UV absorption of salbutamol with different concentrations. (b) calibration curves based on the absorption peaks obtained in (a) used for the dose measurements from the different areas in the glass impinger.

Figure 13

Dose rate of salbutamol particles deposited in lung area at different flow rates.

Figure 14

High-speed camera captures images of SAW atomized salbutamol solution based on SU-8 microchannel fluid supply with an SAW frequency of 60 MHz and input power of 5.26 W.

Figure 15

The lung deposition rates obtained by atomizing salbutamol solution using a medical atomizer and a SAW atomizer. Note that the SAW atomized salbutamol solution based on SU-8 microchannel fluid supply with a flow rate of 90 μl/min and input power of 5.26 W.