Acoustojetting: fundamentals, nanolitre droplet dispensing and fertility diagnosis

Industries that develop automated laboratorial and clinical tools are in constant evolution towards more efficient and user-friendly platforms, aiming for alternatives that can be more economically competitive without compromising the excellence of the function performed. Envisioning to provide a new outlook into the long-established droplet dispensing technologies, in this study, we refashion a high frequency (MegaHertz scale) piezoelectric device into a finely controlled, surface acoustic wave (SAW)-driven microfluidic actuator with applications that range from droplet dispensing to extensional rheometry. We first adapt the SAW device into a nozzle-free platform for continuous dispensing of liquid droplets with diameter sizes varying from 60 to 500 µm, solely using pulse width duration to control the ejection rate of the droplets -from 1 to 25 droplets ejected per second- as well as their final sizes. When loaded with a solution containing HEK-293 cells, the platform was further proved to be biocompatible, not leading to significant loss to the cell's viability or proliferation ability, since the high frequency of the SAWs employed do not cause shear or cavitation damage on biomolecules. Later on, we propose a novel method of multidirectional droplet dispensing platform via capillary liquid bridge that can be used for serial dilutions and biochemical assays by tuning the volume of the dispensed droplet. The performance of the platform was compared to the one of conventional manual pipetting on a drug toxicity assay and returned overall smaller standard error (+/-12.4%) in contrast to that obtained via conventional manual pipetting (+/-18.5%). Finally, we configure the high frequency device as an acoustically driven microfluidic extensional rheometer (ADMiER) for rapid clinical assessment of male fertility by detecting changes in concentration of sperm cells ranging from 2.4 to 235.0 million cells/mL of solution. We also present the receiver operating characteristic (ROC)  curve for fertility analysis via ADMiER using the combination of five different analytical methods from OpenCASA and counting chamber measurements, providing averaged sensitivity, specificity and accuracy of, respectively, 91.5%, 98.8% and 94.3%. In summary, this thesis aims to establish acoustically-driven microfluidics as a promising field for the development of economically attractive technologies for laboratorial, pharmaceutical and medical applications.