Reciprocation of micro-objects by contraction and extension of Vorticella convallaria using polylysine as adhesive material

Abstract

Integration of bioactuators in engineered microstructures is expected to be beneficial to further miniaturize and functionalize microelectromechanical systems. However, it is difficult to achieve reciprocation of micro-objects with common biological motors, although reciprocating movement is an important mechanism in constructing micromechanical systems. The ciliate protozoan Vorticella convallaria possesses a contractile filamentous stalk approximately 100 μm long, of which the contraction-extension cycle has the potential of being used as a linear reciprocating machine. In this study, we used polylysine (PLL) to attach micro-objects to Vorticella convallaria with the purpose of reciprocating the objects by contracting and extending the Vorticella cells. Two types of micro-objects, namely, polystyrene microspheres and glass grits, were coated with positively charged PLL and attached by electrostatic interaction to negatively charged V. convallaria. We characterized the adhesive performance and analyzed the movement of the objects by optical microscope observation. Microspheres of diameter 21 μm were moved back and forth by the contraction and extension of V. convallaria. Comparison of the adhesiveness of PLL-coated and COOH-terminated spheres confirmed the effectiveness of our attachment and actuation method. The grits were actuated in various ways depending on their size, the point of attachment to V. convallaria, and the number of cells. The typical motions were linear and rotational and were propelled by a few cells. V. convallaria cells displaced thin glass grits of thickness up to tens of micrometers. The adhesive force and the drag forces were estimated hydrodynamically. The implemented reciprocating motion can be applied to biohybrid microfluidic systems.