In this work, we present a means of controlling the cross-stream trajectory of a compound drop under the combined action of a transverse electric field and an oscillatory axial pressure gradient in a microfluidic channel. We bring out the decisive role of the flow pulsation in delaying the drop's attainment of a steady-state transverse position. With an enhancement in the frequency of oscillation, both the axial and transverse movement of the drop may be preferentially attenuated, with its dynamic traversal occurring in a locus offset to the central axis as precisely set in by the action of transverse electric forcing, to bring in exclusive controllability on the drop trajectory along with its eventual position of settlement. In addition, we observe that a leaky dielectric compound drop having the electrical permittivity ratio of the inner-to-outer droplet phase surpassing their respective electrical conductivity ratio is not only capable of selectively altering the direction of the resulting drop trajectory from towards the channel-centerline to away from the same, but at the same time facilitates a precise settling of the same at an intermediate transverse location by harnessing the interplay of electrical and hydrodynamic shear. We further identify the key dimensionless parameters along with their desirable ranges accountable for the directional switching of the drop trajectory with high specificity. These findings open up novel perspectives of controllable maneuvering of the double emulsion system in a confined microenvironment bearing decisive implications in engineering and biology.

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Constriction in the flow passage in the physiological circulatory system is central to the occurrence of several diseased conditions such as thrombosis and is also pivotal towards the understanding of several regulatory processes in the human microvasculature. It is, therefore, imperative to advance a mechanistic insight on the dynamics of the transiting cellular encapsulations in a physiologically-mimicking micro-confinement, with particular focus on deciphering the role of its mechano-physical properties. Here we bring out a quantitative depiction on the role of the membrane fluidity and the initial deflation (shape deviation from sphericity) of a lipid vesicle during its morphological transition from stretching to tumbling via rolling as it migrates across a microfluidic constriction. Based on our experimental observations as well as theoretical insights, we construct a regime map to elucidate the range of the key dimensionless parameters orchestrating the dynamic transition. Our results further bring out the role of the initial position of the lipid vesicle on its subsequent stretching dynamics, exhibiting characteristic nonlinearities and non-monotonic trends. In addition, our observations on the vesicles stretching dynamics emerge from mapping selectively with the viscosity contrast between the encapsulated and the suspending fluid medium, offering potential physiologically relevant cues on the impact of the aging of a cellular moiety on its deformability as it transits through a constricted path. Such mechanistic insights may potentially enable establishing quantitative correlations between the dynamical transition of a cellular encapsulation and its mechano-physical properties, which may in turn, have decisive implications in various states of health and disease while circulating across microvascular fluidic pathways.