Microfluidic on-demand engineering of longitudinal dynamic self-assembly of particles.

The lack of a simple operable method for on-demand engineering of longitudinal dynamic self-assembly of particles is one of the main problems in employing particle manipulation in biomedical research studies. Herein, a viscoelasticity-induced self-assembling microfluidic system is proposed to increase the maneuverability and orderliness of longitudinal dynamic self-assembly of particles, and achieve the on-demand control of interparticle spacings and frequencies of particles passing through an outlet. In our microfluidic system, two kinds of functional microstructures and a side-channel were designed to preprocess randomly distributed particles allowing them not to aggregate but rather to evenly distribute, and realize the on-demand control of the particle volume concentration. Randomly distributed particles could be focused into a line and become equally spaced on the center axis of a straight microchannel under transverse elastic force and longitudinal viscoelasticity-induced effective repulsive force. Besides, a finite element model was established to analyze the processes of particles flowing in each functional microstructure. Therefore, a step forward in the experimental method and realization of this microfluidic technology can provide opportunities for applications in biomedical engineering, materials science and beyond.