Microorganisms move in challenging environments by periodic changes in body shape. By contrast, current artificial microrobots cannot actively deform, exhibiting at best passive bending under external fields. Here, by taking advantage of the wireless, scalable and spatiotemporally selective capabilities that light allows, we show that soft microrobots consisting of photoactive liquid-crystal elastomers can be driven by structured monochromatic light to perform sophisticated biomimetic motions. We realized continuum yet selectively addressable artificial microswimmers that generate travelling-wave motions to self-propel without external forces or torques, as well as microrobots capable of versatile locomotion behaviours on demand. Both theoretical predictions and experimental results confirm that multiple gaits, mimicking either symplectic or antiplectic metachrony of ciliate protozoa, can be achieved with single microrobots. The principle of using structured light can be extended to other applications that require microscale actuation with sophisticated spatiotemporal coordination for advanced microrobotic technologies. 3Mobile micro-scale robots are envisioned to navigate within the human body to perform minimally invasive diagnostic or therapeutic tasks 1,2 . Biological microorganisms represent the natural inspiration for this vision. For instance, microorganisms successfully swim and move through a variety of fluids and tissues.Locomotion in this regime, where viscous forces dominate over inertia (low Reynolds number), is only possible through non-reciprocal motions demanding spatiotemporal coordination of multiple actuators 3 . A variety of biological propulsion mechanisms at different scales, from the peristalsis of annelids (Fig. 1a) to the metachrony of ciliates (Fig. 1b), are based on the common principle of travelling waves (Fig. 1c). These emerge from the distributed and self-coordinated action of many independent molecular motors 4,5 .Implementing travelling wave propulsion in an artificial device would require many discrete actuators, each individually addressed and powered in a coordinated fashion (Fig. 1d). The integration of actuators into microrobots that are mobile poses additional hurdles, since power and control need to be distributed without affecting the microrobots' mobility. Existing microscale actuators generally rely on applying external magnetic 6-10 , electric 11 , or optical 12,13 fields globally over the entire workspace. However, these approaches do not permit the spatial selectivity required to independently address individual actuators within a micro-device. Nevertheless, complex non-reciprocal motion patterns have been achieved by carefully engineering the response of different regions in a device to a spatially uniform external field 13,14 .The drawback is that this complicates the fabrication process, inhibits down-scaling and constrains the device to a single predefined behaviour. These challenges mean that most artificial microrobots actually have no actuators. Rather...

The first microscopic artificial walker equipped with liquid‐crystalline elastomer muscle is reported. The walker is fabricated by direct laser writing, is smaller than any known living terrestrial creatures, and is capable of several autonomous locomotions on different surfaces.

The paper describes 3D structures made of liquid-crystalline elastomer (LCE) - rings, woodpiles, etc. - fabricated by two-photon absorption direct laser writing with sub-micrometer resolution while maintaining the desired molecular orientation. These results lay the foundations for creating 3D, micrometer-sized, light-controlled LCE structures.

Grabbing and holding objects at the microscale is a complex function, even for microscopic living animals. Inspired by the hominid-type hand, a microscopic equivalent able to catch microelements is engineered. This microhand is light sensitive and can be either remotely controlled by optical illumination or can act autonomously and grab small particles on the basis of their optical properties. Since the energy is delivered optically, without the need for wires or batteries, the artificial hand can be shrunk down to the micrometer scale. Soft material is used, in particular, a custom-made liquid-crystal network that is patterned by a photolithographic technique. The elastic reshaping properties of this material allow finger movement, using environmental light as the only energy source. The hand can be either controlled externally (via the light field), or else the conditions in which it autonomously grabs a particle in its vicinity can be created. This microrobot has the unique feature that it can distinguish between particles of different colors and gray levels. The realization of this autonomous hand constitutes a crucial element in the development of microscopic creatures that can perform tasks without human intervention and self-organized automation at the micrometer scale.

The miniaturization of robots and actuators down to the micrometer length scale constitutes a fascinating technological challenge. Their development faces fabrication issues due to the small dimensions and their design must take into account how physics laws behave on those length scales. Last but not least, a major issue is energy delivery and management. In this scenario, light emerges as a versatile tool for the fabrication and, even more importantly, as an energy source. Optically driven micromachines—in which optical stimuli can be efficiently converted into mechanical work—have been realized in various contexts. This Review collects recent advances in this field, focusing on optical micro robots realized in soft polymers. Starting from an overview of the photoresponsive materials that have been employed, the various designs and realizations of such devices are shown exhibiting tasks and capabilities like swimming, walking, and the manipulation of microscopic objects. In the last part, frontiers studies in the integration of polymeric structures with biological organisms are shown. In many of the reported studies, untethered operation is a key issue, seen as a fundamental requirement toward the development of smart robots that can autonomously perform tasks and respond to their environment.