Dynamics of a Lipid Vesicle across a Microfluidic Constriction: How does the Fluidity of the Encapsulation and its Micro-Environment Matter?

Abstract

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.