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

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. Impact StatementThis study brings out a quantitative mechanistic insight into the dynamics of migrating lipid vesicles as they migrate through a constricted microfluidic passage. Having a direct similitude with the movement of red blood cells in human microvascular pathways, the resulting mapping between the initial shape and bending properties of the vesicle membrane with three distinct morphological transitions (stretching, rolling, and tumbling) provides cues for understanding the healthy and diseased states of the cells based on their morpho-dynamic features and establish exclusive connectivity of the same with the cell membrane as well as the cytoplasm properties, a paradigm that is currently non-existant. This, in turn, may lead to a novel mechanistic approach of label-free disease detection based on cellular imaging, for which the current understanding is mostly empirical rather than fundamental.