A Review of Single-Cell Microrobots: Classification, Driving Methods and Applications

Single-cell microrobots are new microartificial devices that use a combination of single cells and artificial devices, with the advantages of small size, easy degradation and ease of manufacture. With externally driven strategies such as light fields, sound fields and magnetic fields, microrobots are able to carry out precise micromanipulations and movements in complex microenvironments. Therefore, single-cell microrobots have received more and more attention and have been greatly developed in recent years. In this paper, we review the main classifications, control methods and recent advances in the field of single-cell microrobot applications. First, different types of robots, such as cell-based microrobots, bacteria-based microrobots, algae-based microrobots, etc., and their design strategies and fabrication processes are discussed separately. Next, three types of external field-driven technologies, optical, acoustic and magnetic, are presented and operations realized in vivo and in vitro by applying these three technologies are described. Subsequently, the results achieved by these robots in the fields of precise delivery, minimally invasive therapy are analyzed. Finally, a short summary is given and current challenges and future work on microbial-based robotics are discussed.

Diamagnetically levitated nanopositioners with large-range and multiple degrees of freedom

Precision positioning stages are often central to science and technology at the micrometer and nanometer length scales. Compact, multi-degree-of-freedom stages with large dynamic range are especially desirable, since they help to improve the throughput and versatility in manipulation without introducing spatial constraints. Here, we report compact diamagnetically levitated stages, which employ dual-sided actuation to achieve large-range, six degrees-of-freedom positioning. Dual-sided actuation is demonstrated to enable trapping a magnet array in 3D, with independent control of the trap stiffness about two axes, independent control of forces in 3D and torque about 2 axes. A simplified model is proposed to directly relate these physical quantities to the necessary actuation currents. Experimentally, we demonstrate six degrees-of-freedom positioning with low cross-axis motion, large range and nanometer-scale resolution. In particular, here we show linear motion range of 5 mm with positioning precision better than 1.88 nm, and angular motion range of 1.1 radian with a resolution of 50 micro-radian. With the volume of the stage being between 10-20 cm³, its utility as a compact nano-positioner is showcased by using it to automatically replace the tip of an atomic force microscope probe.

Precision positioning stages are often central to science and technology at the micrometer and nanometer length scales. Here, the authors report compact, diamagnetically levitated positioning stages that achieve large-range, six degrees-of-freedom positioning with nanometer-scale precision.

Accurate delivery of chemicals to a small target using a pressure-driven valved micropipette

We describe a new method for accurately and reproducibly delivering a minute amount of a chemical to a small target in an aqueous environment. Our method is based on a micropipette with a check valve at its tip that can be opened and closed on demand. We demonstrate that this device can produce a flux of 10^-12 l in a short pulse lasting less than 100 ms. The finite width of the pulse is due to molecular dispersion of the chemical, in this case, fluorescein. The chemical distribution near the micropipette tip is measured and compared with the results of a numerical integration assuming stokeslet flow. Our technique is of general utility and has applications in microbiology and neuroscience when a precise control of the spatiotemporal chemical distribution around a specimen is desired.