In recent years, magnetism has gained an enormous amount of interest among researchers for actuating different sizes and types of bio/soft robots, which can be via an electromagnetic‐coil system, or a system of moving permanent magnets. Different actuation strategies are used in robots with magnetic actuation having a number of advantages in possible realization of microscale robots such as bioinspired microrobots, tetherless microrobots, cellular microrobots, or even normal size soft robots such as electromagnetic soft robots and medical robots. This review provides a summary of recent research in magnetically actuated bio/soft robots, discussing fabrication processes and actuation methods together with relevant applications in biomedical area and discusses future prospects of this way of actuation for possible improvements in performance of different types of bio/soft robots.

Cellular phenotype is the conglomerate of multiple cellular processes involving gene and protein expression that result in the elaboration of a cell's particular morphology and function. It has been thought that differentiated postmitotic cells have their genomes hard wired, with little ability for phenotypic plasticity. Here we show that transfer of the transcriptome from differentiated rat astrocytes into a nondividing differentiated rat neuron resulted in the conversion of the neuron into a functional astrocyte-like cell in a time-dependent manner. This single-cell study permits high resolution of molecular and functional components that underlie phenotype identity. The RNA population from astrocytes contains RNAs in the appropriate relative abundances that give rise to regulatory RNAs and translated proteins that enable astrocyte identity. When transferred into the postmitotic neuron, the astrocyte RNA population converts 44% of the neuronal host cells into the destination astrocyte-like phenotype. In support of this observation, quantitative measures of cellular morphology, single-cell PCR, single-cell microarray, and single-cell functional analyses have been performed. The host-cell phenotypic changes develop over many weeks and are persistent. We call this process of RNA-induced phenotype changes, transcriptome-induced phenotype remodeling.neuron ͉ transcriptome-induced phenotype remodeling ͉ single cell ͉ Waddington I n multicellular organisms, all cells contain nearly identical copies of the genome but exhibit drastically different phenotypes. Even a single neuron has a set of phenotypic characteristics that distinguish it from other neurons as well as other cell types, such as the nearby astrocytes. Indeed, as Waddington proposed in his classical epigenetic landscape model, genetically predetermined cells can follow any specific permitted trajectories that eventually lead to different cellular phenotypes (1). From this point of view, the genome serves as a repository of dynamic control information whose state can be reprogrammed to match the stable phenotypic states.Emerging evidence has demonstrated the reversibility and flexibility of the cellular phenotype. Gurdon et al. first showed that the ability to obtain fertile adult male and female frogs by injecting endoderm nuclei into enucleated eggs (2). This result not only forms the foundation of the field in nuclear transplantation but also provides evidence that the cytoplasmic components of a differentiated cell can support nuclear reprograming. Generation of induced pluripotent stem (iPS) cells by transfection of transcription factors into dividing fibroblasts (3), followed by cell selection, represents a new strategy to globally revert a mature cell into a different cell type (4-9). The need for redifferentiation of these embryonic stem cell-like-iPS cells into desired cell types adds a layer of complexity that is difficult to control (10, 11). Nevertheless, studies of nuclear reprogramming from genomic and epigenetic modification, as seen from so...

This paper presents several variations of a microscale magnetic tumbling (μTUM) robot capable of traversing complex terrains in dry and wet environments. The robot is fabricated by photolithography techniques and consists of a polymeric body with two sections with embedded magnetic particles aligned at the ends and a middle nonmagnetic bridge section. The robot’s footprint dimensions are 400 μm × 800 μm. Different end geometries are used to test the optimal conditions for low adhesion and increased dynamic response to an actuating external rotating magnetic field. When subjected to a magnetic field as low as 7 mT in dry conditions, this magnetic microrobot is able to operate with a tumbling locomotion mode and translate with speeds of over 60 body lengths/s (48 mm/s) in dry environments and up to 17 body lengths/s (13.6 mm/s) in wet environments. Two different tumbling modes were observed and depend on the alignment of the magnetic particles. A technique was devised to measure the magnetic particle alignment angle relative to the robot’s geometry. Rotational frequency limits were observed experimentally, becoming more prohibitive as environment viscosity increases. The μTUM’s performance was studied when traversing inclined planes (up to 60°), showing promising climbing capabilities in both dry and wet conditions. Maximum open loop straight-line trajectory errors of less than 4% and 2% of the traversal distance in the vertical and horizontal directions, respectively, for the μTUM were observed. Full directional control of μTUM was demonstrated through the traversal of a P-shaped trajectory. Additionally, successful locomotion of the optimized μTUM design over complex terrains was also achieved. By implementing machine vision control and/or embedding of payloads in the middle section of the robot, it is possible in the future to upgrade the current design with computer-optimized mobility through multiple environments and the ability to perform drug delivery tasks for biomedical applications.

Robots the size of several microns have numerous application in medicine, biology, and manufacturing. However, simultaneous control of multiple robots at this scale is difficult since the robot itself is too small to carry power, sensors, communication, and control on-board. In this paper, we have summarized different approaches, ranging from specialized robot design and fabrication to specialized ways of actuating robots, with the aim of independent control of a team/swarm of microrobots. We have also discussed the challenges for each approach. In the light of the challenges, we have proposed some directions where the future researchers can focus in order to solve the problem of independent control of a team of microrobots.

In this paper, a novel approach to achieving the independent control of multiple magnetic microrobots is presented. The approach utilizes a specialized substrate consisting of a fine grid of planar, MEMS-fabricated micro coils of the same size as the microrobots (≤ 500 μm). The coils can be used to generate real magnetic potentials and, therefore, attractive and repulsive forces in the workspace to control the trajectories of the microrobots. Initial work on modelling the coil and microrobot behavior is reported along with simulation results for navigating one and two microrobots along independent desired trajectories. Qualitative results from a scaled-up printed circuit board version of the specialized substrate operating on permanent magnets are presented and offer proof-of-concept results for the approach. These tests also provide insights for practical implementations of such a system, which are similarly reported. The ultimate goal of this work is to use swarms of independently controlled microrobots in advanced, additive manufacturing applications.

Microscale machines are able to perform a number of tasks like micromanipulation, drug‐delivery, and noninvasive surgery. In particular, microscale polymer machines that can perform intelligent work for manipulation or transport, adaptive locomotion, or sensing are in‐demand. To achieve this goal, shape‐morphing smart polymers like hydrogels, liquid crystalline polymers, and other smart polymers are of great interest. Structures fabricated by these materials undergo mechanical motion under stimulation such as temperature, pH, light, and so on. The use of these materials renders microscale machines that undergo complex stimuli‐responsive transformation such as from planar to 3D by combining spatial design like introducing in‐plane or out‐plane differences. During the past decade, many techniques have been developed or adopted for fabricating structures with smart polymers including microfabrication methods and the well‐known milestone of 4D printing, starting in 2013. In this review, the existing or potential active smart polymers that could be used to fabricate active microscale machines to accomplish complex tasks are summarized.

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In this paper, we have developed an approach for independent autonomous navigation of multiple microrobots under the influence of magnetic fields and validated it experimentally. We first developed a heuristics based planning algorithm for generating collision-free trajectories for the microrobots that are suitable to be executed by an available magnetic field. Second, we have modeled the dynamics of the microrobots to develop a controller for determining the forces that need to be generated for the navigation of the robots along the trajectories at a suitable control frequency. Next, an optimization routine is developed to determine the input currents to the electromagnetic coils that can generate the required forces for the navigation of the robots at the controller frequency. We then validated our approach by simulating an electromagnetic system that contains an array of sixty-four magnetic microcoils designed for generating local magnetic fields suitable for simultaneous independent actuation of multiple microrobots. Finally, we prototyped an mm-scale version of the system and present experimental results showing the validity of our approach.