Mechanical Engineering Journal (Nov 2021)
Microvalve actuated by Vorticella: self-oscillating valve and improvement measures to calcium-responsive valve
Abstract
Living machines have microactuators and are suitable for further miniaturization of microsystems, and their potential as autonomous microrobots has been investigated. The key motion of micromechanisms is self-oscillation, which has been achieved by the synchronized motion of cardiomyocytes. Pulsatile flows play an important role in a variety of microfluidic applications. The advantage of Vorticella is that a single cell generates several micrometers of displacement and can actuate a microsystem. Self-oscillation of Vorticella has yet to be used for a purpose other than actuating microstructure. This paper reports the extension of previous works to develop a self-oscillating microvalve and improvement of the sealing properties of a calcium-responsive valve actuated by Vorticella. V. convallaria was introduced into a microfluidic chamber and used to make a self-oscillating cellular microvalve. We demonstrated a self-oscillating cellular microvalve actuated by live Vorticella. While the extension of a stalk of live Vorticella sealed the opening of a channel and stopped a flow, the contraction moved the zooid and the flow resumed. The performance of a cellular valve was studied and we obtained the minimum transition time, tMIN = 2 s, and the valve efficiency, ηmax = 98.7%, by switching the fluid between the contraction and extension motions. The changes in Vorticella cell properties after the permeabilization treatment were studied to investigate improvement measures to a calcium-responsive valve. Fluid was also switched by manipulating the Ca2+ concentration using a stalk of membrane-treated Vorticella. The permeabilization conditions of 0.1 wt.% saponin solution at room temperature (RT) for 5 min and 0.01 vol% Triton X-100, 0°C for 30 min gave better valve efficiency than 0.15 wt.% saponin at RT for 10 min.
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