Subhas Nandy (IIT Madras)

Ultrasound-mediated manipulation of bioparticles in microfluidic shaped cavities

Ultrasonic wave propagation in microfluidic devices has emerged as a promising tool in microfluidics, with prospective applications pertaining to microscale manipulation relevant for fields in materials synthesis and biomedical research. Compared to manipulation using other active methodologies like electric, magnetic and optical field-assisted methods, ultrasonics offers unprecedented advantages of being contactless, non-invasive and biocompatible in nature while permitting extension of field gradients over larger spatial dimensions.

Recent advancements in the field of dynamic manipulation using acoustic waves have largely relied on usage of increasing number of piezoelectric sources; the superposition of waves generated from these sources eventually gives rise to complex field distributions. Programmed synchronization among actuation sources thus serves as a key factor in achieving dynamic acoustic field distributions within microfluidic devices. In this study, we will be focusing on the geometric aspects of microfluidic cavities that can give rise to varying acoustic field configurations using a single piezoelectric actuation source. In particular, external tuning of actuation frequency leads to a multitude of acoustic field configurations arising out of complex, spatially-varying wall vibration patterns. Numerical simulations employing full electromechanical coupling enables decoding the underlying vibrational patterns as well as acoustic field distributions. In addition, threshold diameter for microscale manipulation is established to be a strong function of frequency. We demonstrate the applicability of such a shaped microfluidic cavity through biological cell patterning, while establishing the retention of cellular viability post-ultrasonic treatment.

In the second part, we demonstrate how programmed variation of actuation frequency leads to continuous motion of a suspended microscale aggregate. We extend this capability of temporal modulation of actuation frequencies to expose biological cells in different microenvironments. Experimental observations reveal the bidirectional transport of reagents across the permeabilized cell membranes arising out of exposure to time-varying ultrasonic fields. Finally, we discuss the relevance of ultrasonic manipulation using shaped microcavities in areas pertaining to acoustic trapping, aggregation and enrichment in order to achieve high-throughput generation of microparticle clusters and cell spheroids for downstream analysis.