This paper presents an adaptive backstepping controller for the reference tracking of an alginate artificial cell. An adaptive controller was implemented to precisely manipulate a magnetic artificial cell actuated by rotating magnetic fields. The rolling motion of a small-scale robot in a fluidic environment is challenging, especially when the fluid imparts an unknown response at low Reynolds number. In order to compensate for this uncertainty, an unknown tuning parameter encapsulating these effects was added to the governing equations of motion. A controller with an update law was then designed to estimate the unknown parameter and force the artificial cell to produce the desired response. The stability of the proposed controller was established by a candidate Lyapunov function. Real-time experiments were conducted to demonstrate the effectiveness of the designed controller at guiding an artificial cell to an arbitrary target position. Alginate cells were guided through a maze using the controller and was later combined with wall constraints to allow multiple alginate cells to reach the same target location. This controller can be applied to both surface motion and swimming-based small-scale robots in future applications for micro-assembly and targeted drug delivery.

This paper presents scalable designs and fabrication, actuation, and manipulation techniques for soft millirobots under uniform magnetic field control. The millirobots were fabricated through an economic and robust moulding technique using polydimethylsiloxane (PDMS), acrylonitrile butadiene styrene (ABS) filaments, and 3D printed polylactic acid (PLA) rings. The soft millirobots were simple hollow rod-like structures with different configurations of embedded permanent magnets inside of their soft-body or at their ends. The soft-robots were actuated using six different motion modes including: pivot walking, rolling, tumbling, side-tapping, wiggling, and wavy-motion under an external uniform magnetic field control system. The velocities of the millirobots under different motion modes were analyzed under varying magnetic flux densities (B). Moreover, deformation of the soft-robotic body in response to the magnetic field strength was measured and a deflection curve showing bending angle (φ) was produced. Soft millirobots were navigated through a maze using a combination of the available motion modes. Different arrangements of the embedded permanent magnets enabled individual soft millirobots to respond heterogeneously under the same magnetic field inputs towards performing assembly and disassembly operation as modular subunits. Overall, this soft millirobot platform shows enormous potential for minimally invasive in vivo applications.

The modular assembly and actuation of 3D printed milliscale cuboid robots using a globally applied magnetic field is presented. Cuboids are composed of a rectangular resin shell embedded with two spherical permanent magnets that can independently align with any applied magnetic field. Placing cuboids within short distances of each other allows for modular assembly and disassembly by changing magnetic field direction. Assembled cuboids are demonstrated to stably self-propel under sequential field inputs allowing for both rolling and pivot walking motion modes. Swarms of cuboids could be actuated within the working space and exhibit near identical behavior. Specialized `trap robots' were developed to capture objects, transport them within the working space, and subsequently release the payload in a new location. Cuboids with male and female connectors were developed to exhibit the selective mating between cuboids. The results show that cuboids are a diverse and adaptable platform that has the potential to be scaled down to the sub-millimeter regime for use in medical or small-scale assembly applications.

This paper presents 2D feedback control and open loop 3D trajectories of heterogeneous chemically catalyzing Janus particles. Self-actuated particles have enormous implications for both in vivo and in vitro environments, which make them a diverse resource for a variety of medical and assembly applications. Janus particles, consisting of cobalt and platinum hemispheres, can self-propel in hydrogen peroxide solutions due to platinum's catalyzation properties. These particles are directionally controlled using static magnetic fields produced from a triaxial approximate Helmholtz coil system. Since the magnetization direction of Janus particles is often heterogeneous, and thereby not consistent with the propulsion direction, this creates a unique opportunity to explore the motion effects of these particles under 2D feedback control and open loop 3D control. Using a modified closed loop controller, Janus particles with magnetization both closely aligned and greatly misaligned to the propulsion vectors, were instructed to perform complex trajectories. These trajectories were then compared between trials to measure both consistency and accuracy. The effects of increasing offset between the magnetization and propulsion vectors were also analyzed. The effects this heterogeneity had on 3D motion is also briefly discussed. It is our hope going forward to develop a 3D closed loop control system that can retroactively account for variations in the magnetization vector.

This article discusses the design, modeling, and application of a powerful hexapole magnetic tweezer system for closed-loop 3D swarm control applications. The system consists of six sharp tapered magnetic poles that are integrated with six electromagnetic coils and mounted on two yokes composed of 3D printed magnetic material. Magnetic field gradients are generated at the sharp tips of the magnetic poles when current is applied through the attached electromagnetic coils. Different combinations of current input can interact with magnetized microparticles to create three-dimensional motion. A closed-loop control algorithm based on image processing and hardware integration through MATLAB was developed to automatically operate external power supplies connected to the magnetic tweezer system. Coordinate system transformation is utilized to transform the tilted actuation coordinates, by virtue of the system hardware configuration, to the measurement coordinates used during experiments and analysis. This magnetic tweezer system has the advantage of a larger working space and higher magnetic field strengths when compared to several other similar designs. The magnetic tweezer system allows for more diverse applications within the microscale, such as microparticle swarm control, cell penetration, and cell therapy. Experimental analysis performed in this article demonstrates the closed-loop navigation of a microparticle swarm moving freely in both 2D and 3D environments. Results show highly consistent trajectories within the swarm with only a few fluctuations due to microflows. This system will keep being updated and optimized to investigate the performance of microparticles in in vivo environments.

This paper presents the design, development and implementation of a novel, high power hexapole magnetic tweezer system for 3D micromanipulations. Six tapering-tipped magnetic poles are deployed in a tilted Cartesian coordinate system, with an electromagnetic coil on each for actuation, connected by two 3D printed magnetic yokes to form a double layer structure. The power source is integrated to the magnetic tweezer system through a control algorithm on the software level; image processing was used for experiment analysis. Because of the high magnetic field that the magnetic coils can generate, the working space in the system is relatively larger than other similar designs, which provides better performance on microscale robotic swimmer manipulations. Simulations and experiments performed in this paper demonstrate the agile and powerful manipulation of microswimmers with desired control input to follow complex trajectories, avoid obstacles and move against micro-flow in the samples. We prove that the developed hexapole magnetic tweezer has enough power and controllability to guide microswimmers in Newtonian and Non-Newtonian fluid environments. The system will be optimized continuously and implemented into cell penetration experiments. Finally, the application will be deployed into in vivo based environments.