An acoustofluidic sputum liquefier

Abstract

We demonstrate the first microfluidic-based on-chip liquefaction device for human sputum samples. Our device is based on an acoustofluidic micromixer using oscillating sharp edges. This acoustofluidic sputum liquefier can effectively and uniformly liquefy sputum samples at a throughput of 30 μL min(-1). Cell viability and integrity are maintained during the sputum liquefaction process. Our acoustofluidic sputum liquefier can be conveniently integrated with other microfluidic units to enable automated on-chip sputum processing and analysis.

Fig. 1

(a) Schematic of the acoustofluidic sputum liquefier. Experimental images showing the mixing of fluorescein and DI water when (b) PZT was off: a laminar flow pattern was observed; (c) PZT was on: excellent mixing of two fluids was achieved. (d) Photograph of our acoustofluidic sputum liquefier. (e) Drawing showing the detailed design of our acoustofluidic sputum liquefier. Simulated results showing the Lagrangian mean flow velocity when the fluid is (f) water and (g) a high viscosity fluid (such as sputum) with a viscosity ten times that of the water. Circular streamlines are observed in both cases indicating excellent mixing in both cases.

Fig. 2

Photograph showing the visual comparison of human sputum samples: (R) an un-liquefied raw sputum sample; (V) a sputum sample liquefied using a vortex mixer; (A) a sputum sample liquefied using our acoustofluidic device.

Fig. 3

Cell viability of sputum samples liquefied using: (a)–(b) a standard sputum-liquefaction procedure; (c)–(d) our acoustofluidic sputum liquefier. (e) Statistical analysis showing the comparison of cell viability of two liquefaction procedures. Data represent an average of n = 3 to 4 independent experiments per group. In each independent experiment, over 500 cells were counted to assess cell viability. N.S. represents groups that are not statistically different (p > 0.05). Data are presented as group means ± standard deviation (SD). Scale bar: 200 μm.

Fig. 4

Representative of optical images (100x) showing modified Wright–Giemsa staining results of cell samples obtained from sputum samples liquefied using (a)–(c) a vortex mixer or (d)–(f) our acoustofluidic sputum liquefier. Inflammatory cells, such as eosinophils (yellow) and neutrophils (red), are indicated by colored arrows. Scale bar: 50 μm.

Fig. 5

Fluorescence (CD45) vs. fluorescence (CD15) plot of the cell samples obtained from the sputum samples liquefied by (a) a standard sputum-liquefaction procedure and by (b) our acoustofluidic sputum liquefier. The percentage of co-population of eosinophils and neutrophils are 20.4% and 24.9% for (a) and (b), respectively.