Three-dimensional control of engineered motile cellular microrobots

Abstract

Abstract-We demonstrate three-dimensional control with the eukaryotic cell Tetrahymena pyriformis (T. pyriformis) using two sets of Helmholtz coils for xy-plane motion and a single electromagnet for vertical motion. T. pyriformis is modified to have artificial magnetotaxis with internalized magnetite. Since the magnetic fields exerted by electromagnets are relatively uniform in the working space, the magnetite exerts only torque, without translational force, which enabled us to guide the cell's swimming direction while the swimming force is exerted only by the cell's motile organelles. A stronger magnetic force was necessary to steer cells to the z-axis, and, as a result, a single electromagnet placed just below our sample area is utilized for vertical motion. To track the cell's positions in the z-axis, intensity profiles of non-motile cells at varying distances from the focal plane are used. During vertical motion along the zaxis, the intensity difference from the background decreases while the cell size increases. Since the cell is pear-shaped, the eccentricity is high during planar motion, but lowers during vertical motion due to the change in orientation. The threedimensional control of the live organism T. pyriformis as a cellular robot shows great potential to be utilized for practical applications in microscale tasks, such as target transport and cell therapy.

Biomedical Applications of Untethered Mobile Milli/Microrobots

“…(c) Milli/microrobots pulled in 3D using magnetic field gradients include the nickel microrobot capable of five-degrees-of-freedom (DOF) motion in 3D using the OctoMag system [40] and the MRI-powered and imaged magnetic bead [71]. (d) Cell-actuated biohybrid approaches include the artificially-magnetotactic bacteria [72], the cardiomyocyte driven microswimmers [73], the chemotactic steering of bacteria-propelled microbeads [74], sperm-driven and magnetically steered microrobots [41], and the magnetotactic bacteria swarm manipulating microscale bricks [44]. …”

Optimization of the size of a magnetic microrobot for high throughput handling of micro-objects

“…An ambient environment would present a smaller viscosity but the adhesion force between the robot and the substrate would be high, leading to a poor reproducibility of the control. In addition most of the current systems are in liquid environments since it enables biomedical applications [8], [7], [10]. The workspace is located in the center of the magnetic actuation device.…”

Closed-Loop Control of a Magnetic Particle at the Air–Liquid Interface

“…A wide range of microrobots are controlled using several coils or electromagnets [18], [19], [20], [21], [22], [23]. To give only a few examples, helical microrobots are moved using a rotating magnetic field [24], [25]; some bacteria such as Tetrahymena pyriformis are actuated by magnetic field and used as microrobots [26], [27], [28]. This success can be attributed to the ability of magnetic actuation to produce fast displacements.…”