Existing proofs-of-concept have shown that microrobots can perform cell manipulation and enucleation, [4] selective gene transmission, [5] in vivo biopsy, [6] and cellular stimulation. [7] As the robots are too tiny to carry motors, control devices, and energy storages, they are commonly propelled using a magnetic gradient imparting a direct pull [8] or using a homogenous rotating field that in turn makes the microrobots rotate. [9] Developments in manufacturing technology made major contributions to the abovementioned achievements. Manufacturing processes can be categorized as top-down or bottom-up. The bottomup methods, such as precision additive manufacturing are widely applied. [10,11] Even, it tries to utilize smart material for developing 4D printing. [12] Two-photon lithography is a representative, additive microscale manufacturing process that uses laser scanning to polymerize photosensitive materials. Although this method can create a complete 3D structure, limitations exist on material selection, mostly polymers.On the other hand, top-down processes including focused ion beam (FIB) milling can be used to fabricate robots from a range of materials, including biocompatible or biodegradable materials. Furthermore, smart materials, such as shape memory alloys (SMAs), shape memory polymers (SMPs), and piezoelectric materials, can be used as actuators of the microrobot.The creation of movement in liquid is the first challenge when miniaturizing robots to microscales. As the size shrinks, the low Reynolds number due to more viscous effect and Brownian motion become major challenges. An efficient microscale robot thus requires a swimming strategy operative at low Reynolds numbers, and a navigation strategy that overcomes Brownian motion. As a traditional powering method to robot cannot be fitted at such small-scales, innovative design and actuation methods are required to satisfy the challenges of power and actuation. Various microrobots highlighting specific navigation principles have been developed over the past decade. [2] There are three categories of navigation strategies in microrobots: self-propulsion, external propulsion, and a hybrid strategy. [13] Self-propulsion is generated by result of local, smallscale chemical reactions on the robot surface; chemical energy is converted into kinetic energy. Generating local concentration Microrobotics has many potential applications, such as environmental remediation, in the biomedical arena. However, existing microrobots exhibit practical limitations including inadequate biocompatibility and imprecise control. Here, a microrobot made of shape memory alloy (SMA) actuator which can be driven by laser scanning to perform microscale motions is introduced. The 65 µm long microrobot having crawling-like motion can demonstrate the movement with 10.0 µm s −1 of the maximum speed. The microrobot is controlled by a laser affording wireless, spatiotemporally selective capabilities. During actuation, the robot exhibits crawling-like motions including trigger via the SMA as ...

Magnetic continuum soft robots can actively steer their tip under an external magnetic field, enabling them to effectively navigate in complex in vivo environments and perform minimally invasive interventions. However, the geometries and functionalities of these robotic tools are limited by the inner diameter of the supporting catheter as well as the natural orifices and access ports of the human body. Here, we present a class of magnetic soft-robotic chains (MaSoChains) that can self-fold into large assemblies with stable configurations using a combination of elastic and magnetic energies. By pushing and pulling the MaSoChain relative to its catheter sheath, repeated assembly and disassembly with programmable shapes and functions are achieved. MaSoChains are compatible with state-of-the-art magnetic navigation technologies and provide many desirable features and functions that are difficult to realize through existing surgical tools. This strategy can be further customized and implemented for a wide spectrum of tools for minimally invasive interventions.

The shape recovery ability of shape-memory alloys vanishes below a critical size (~50 nm), which prevents their practical applications at the nanoscale. In contrast, ferroic materials, even when scaled down to dimensions of a few nanometers, exhibit actuation strain through domain switching, though the generated strain is modest (~1%). Here, we develop freestanding twisted architectures of nanoscale ferroic oxides showing shape-memory effect with a giant recoverable strain (>8%). The twisted geometrical design amplifies the strain generated during ferroelectric domain switching, which cannot be achieved in bulk ceramics or substrate-bonded thin films. The twisted ferroic nanocomposites allow us to overcome the size limitations in traditional shape-memory alloys and open new avenues in engineering large-stroke shape-memory materials for small-scale actuating devices such as nanorobots and artificial muscle fibrils.

Light‐driven shape memory alloy (SMA)‐based microscale actuators show great promise for artificial muscle and biomedical applications, as they are actuated remotely and have a fast response speed. However, ultraviolet (UV) light is required for device actuation; thus, the operating environment has been limited. Here, an infrared (IR) light‐driven SMA actuator is proposed, in which the plasmonic effect is used to enhance IR light absorptance. A sub‐micrometer pattern is used to create an optical meta‐surface capable of tuning the light absorptance. Conical nanohole arrays are fabricated with a focused ion beam. The absorptance tuning effect is evaluated in terms of the optical characteristics and performance of the actuator. The nanopatterned surface increases the narrow‐band IR light absorption by up to 55%. Optics simulations are conducted to verify the experimental results. A pattern design method is proposed, based on the light wavelength of the stimulating source. Combining heterogeneous surfaces, both UV and IR light achieve decoupled microscale actuation. These actuators show a response similar to that of the iris muscle, which is responsible for the eye's pupillary reflex. It is expected that these actuators will broaden SMA applications in clinical devices and soft robotics.