Microvalve actuated by Vorticella: self-oscillating valve and improvement measures to calcium-responsive valve

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, t(MIN) = 2 s, and the valve efficiency, eta(max) = 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 degrees C for 30 min gave better valve efficiency than 0.15 wt.% saponin at RT for 10 min.