The demand in the biomedical field for fast and precise devices for in-vitro applications has increased in recent years. Mobile microrobots are significantly suitable for such applications and are developing rapidly. These microrobots offer untethered actuation towards a contamination-free environment while allowing for fast and precise handling of biological entities for applications such as positioning, sensing, delivery, and cell surgery that are highly effective for new drug discoveries and to improve our understanding of cells behavior on the single-cell level.Here, we present a review of the recent state-of-the-art in the actuation and implementation of mobile microrobots for in-vitro applications. We will first explore the widely used methods of wireless actuation. Next, we address the challenge of implementing an on-board interaction technique to handle the target biological entity without affecting the actuation of the microrobot. Finally, we will discuss the future directions that would draw the basic outline for the next generation of mobile microrobots for in-vitro applications.

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In this paper, we propose a laser actuated microgripper that can be activated remotely for micromanipulation applications. The gripper is based on an optothermally actuated polymeric chevron-shaped structure coated with optimized metallic layers to enhance its optical absorbance. Gold is used as a metallic layer due to its good absorption of visible light. The thermal deformation of the chevron-shaped actuator with metallic layers is first modeled to identify the parameters affecting its behavior. Then, an optimal thickness of the metallic layers that allows the largest possible deformation is obtained and compared with simulation results. Next, microgrippers are fabricated using conventional photolithography and metal deposition techniques for further characterization. The experiments show that the microgripper can realize an opening of 40 µm, a response time of 60 ms, and a generated force in the order of hundreds of µN. Finally, a pick-and-place experiment of 120 µm microbeads is conducted to confirm the performance of the microgripper. The remote actuation and the simple fabrication and actuation of the proposed microgripper makes it a highly promising candidate to be utilized as a mobile microrobot for lab-on-chip applications.

Researchers have developed a cell stretching device to mimic the in vivo mechanical environment in vitro in order to investigate cell mechanotransduction. Cyclic stretch is involved in lengthening and relaxation phases. Cells may respond to mechanical stimulation rapidly within a few seconds, and sudden disruption of cell cytoskeletons may also occur at any point in any phase of cyclic stretch. However, until now, no research has been done to establish a method of collecting cell images at the two phases of cyclic stretch. Because image processing is time-consuming, it is difficult to adjust focus and collect high-resolution images simultaneously at the two phases during the process. In this study, a three-motorized-stage system was developed to meet the requirements. The results demonstrated that linear compensation is effective for cell imaging, and it is applicable to have a feed-forward control method without image processing. A method was then developed to determine the maximum displacement of the target in the horizontal and vertical directions, and the linear compensation waveforms were designed using the C program automatically and immediately before stretching. Further, the cyclic stretch was applied to cells using the three motorized stages, and clear phase-contrast cell imaging (30 fps) were obtained almost at any point in time. Detailed cell changes such as sudden disruption of cell–cell junctions, not only long-term cell response, were observed. Therefore, our study established a methodology to greatly improve the time resolution of imaging of cyclic stretch for the research of detailed cellular mechanotransduction.

We propose a microrobotic platform for single motile microorganism observation and investigation. The platform utilizes a high-speed online vision sensor to realize real-time observation of a microorganism under a microscopic environment with a relatively high magnification ratio. A microfluidic chip was used to limit the vertical movement of the microorganism and reduce the tracking system complexity. We introduce a simple image processing method, which utilizes high-speed online vision characteristics and shows robustness against image noise to increase the overall tracking performance with low computational time consumption. The design also considers the future integration of a stimulation system using microtools. Successful long-time tracking of a freely swimming microorganism inside of a microfluidic chip for more than 30 min was achieved notwithstanding the presence of noises in the environment of the cell. The specific design of the platform, particularly the tracking system, is described, and the performance is evaluated and confirmed through basic experiments. The potential of the platform to apply mechanical stimulation to a freely swimming microorganism is demonstrated by using a 50-µm-thick microtool. The proposed platform can be used for long-term observation and to achieve different kinds of stimulations, which can induce new behavior of the cells and lead to unprecedented discoveries in biological fields.

In this paper, we propose a mobile microgripper actuated using laser optothermal and magnetic actuation in liquid environments. This hybrid actuation scheme allows the full decoupling between the in-plane positioning of the mobile microgripper and the actuation of its gripping mechanism, which reduces the control complexity of such microgrippers. The work is divided into three main parts: 1) The design and fabrication of an optothermally actuated microgripper using a spiral bimaterial microjoint. 2) The two dimensional positioning of the microgripper in the working area using magnetic fields generated by four electromagnets. 3) The two dimensional steering of the laser beam using a tip/tilt galvo mirror to optothermally actuate the gripping mechanism on demand. The developed mobile microgripper with the dimensions of 1500×700×250 µm can realize an open and close gripping motion of 35 µm, a magnetic positioning accuracy of 6 µm for translation over an area of 1×1 mm and 2°for rotation, and a laser steering accuracy of 25 µm. Finally, the mobile microgripper is used to control the position of a microbead inside a liquid environment. Our work provides a proof of concept of laser optothermalmagnetic hybrid actuation, which has the potential to enhance the deployment of microtools in biomedical applications including cell manipulation and lab-on-chip devices.

We propose a microrobotic platform that stimulates swimming microorganisms in a microfluidic chip with high speed and accuracy. The developed platform comprises (1) high-speed microrobots that can generate a millinewton-level driving force, micrometer-level positioning accuracy, and a millimeter per second level drive speed through the actuation of motorized stages with permanent magnets and (2) high-speed online vision sensor capable of capturing images on the order of 1000 frames per second. The specific design and architecture of the proposed platform are also presented. The proposed platform stimulates and observes swimming microorganisms in a microfluidic chip through a mechanical approach. This platform provides on-chip investigation with high functionality that has been difficult to achieve with previous approaches and contributes towards the discovery of previously unknown functions of swimming microorganisms in the bioscience fields.