Abstract
Observations and analyses of a microscopic object are essential processes in various fields such as chemical engineering and life science. Microfluidic techniques with various functions and extensions have often been used for such purposes to investigate the mechanical properties of microscopic objects such as biological cells. One of such extensions proposed in this context is a real-time visual feedback manipulation system, which is composed of a high-speed camera and a piezoelectric actuator with a single-line microfluidic channel. Although the on-chip manipulation system enables us to control the 1 degree-of-freedom position of a target object by the real-time pressure control, it has suffered from unintended changes in the object orientation, which is out of control in the previous system. In this study, we propose and demonstrate a novel shear-flow-based mechanism for the control of the orientation of a target object in addition to the position control in a microchannel to overcome the problem of the unintended rotation. We designed a tributary channel using a three-dimensional hydrodynamic simulation with boundary conditions appropriate for the particle manipulation to apply shear stress to the target particle placed at the junction and succeeded in rotating the particle at an angular velocity of 0.2 rad/s even under the position control in the experiment. The proposed mechanism would be applied to feedback controls of a target object in a microchannel to be in a desired orientation and at a desired position, which could be a universally useful function for various microfluidic platforms.
Highlights
Manipulation of a target object in a microscopic scale is an important technology to achieve object arrangements, incubation of cells and organs, and evaluation of three-dimensional structures and shapes at a single cell level in the fields of chemical engineering and life science
One of such extensions proposed in this context is a real-time visual feedback manipulation system, which is composed of a high-speed camera and a piezoelectric actuator with a single-line microfluidic channel
We focused on the working principle of the rotational manipulation in a microfluidic channel, and realtime control is not yet implemented
Summary
Manipulation of a target object in a microscopic scale is an important technology to achieve object arrangements, incubation of cells and organs, and evaluation of three-dimensional structures and shapes at a single cell level in the fields of chemical engineering and life science. With the aid of the combination of the position control and the orientation control, repetitive loadings from desired directions at a narrow constriction can be realized as an example of promising potential applications In addition to such uniaxially squeezed deformation, applying desired wall shear stress tangential to the object surface can be realized, enabling to measure the mechanical responses different from that to the squeezing stress normal to the object surface. The target cell is held at a desired position for a specified time, and its shape change is observed after specified-time deformation in a narrow constriction, which has revealed the cellular deformability depending on the deformation period or frequency.43–47 While this system enables the 1 DoF position control, the attitude of a target object is out of control, resulting in unintended rotation of the target object by fluctuation or wall shear stress. We report a novel 2 DoF manipulation mechanism that can control the orientation of a target object under the 1 DoF position control in a microchannel
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