Mechanically interlocked 3D multi-material micromachines

Magnetic Microrobot Swarms with Polymeric Hands Catching Bacteria and Microplastics in Water

The forefront of micro- and nanorobot research involves the development of smart swimming micromachines emulating the complexity of natural systems, such as the swarming and collective behaviors typically observed in animals and microorganisms, for efficient task execution. This study introduces magnetically controlled microrobots that possess polymeric sequestrant "hands" decorating a magnetic core. Under the influence of external magnetic fields, the functionalized magnetic beads dynamically self-assemble from individual microparticles into well-defined rotating planes of diverse dimensions, allowing modulation of their propulsion speed, and exhibiting a collective motion. These mobile microrobotic swarms can actively capture free-swimming bacteria and dispersed microplastics "on-the-fly", thereby cleaning aquatic environments. Unlike conventional methods, these microrobots can be collected from the complex media and can release the captured contaminants in a second vessel in a controllable manner, that is, using ultrasound, offering a sustainable solution for repeated use in decontamination processes. Additionally, the residual water is subjected to UV irradiation to eliminate any remaining bacteria, providing a comprehensive cleaning solution. In summary, this study shows a swarming microrobot design for water decontamination processes.

On-Command Disassembly of Microrobotic Superstructures for Transport and Delivery of Magnetic Micromachines

Magnetic microrobots have been developed for navigating microscale environments by means of remote magnetic fields. However, limited propulsion speeds at small scales remain an issue in the maneuverability of these devices as magnetic force and torque are proportional to their magnetic volume. Here, a microrobotic superstructure is proposed, which, as analogous to a supramolecular system, consists of two or more microrobotic units that are interconnected and organized through a physical (transient) component (a polymeric frame or a thread). The superstructures consist of microfabricated magnetic helical micromachines interlocked by a magnetic gelatin nanocomposite containing iron oxide nanoparticles (IONPs). While the microhelices enable the motion of the superstructure, the IONPs serve as heating transducers for dissolving the gelatin chassis via magnetic hyperthermia. In a practical demonstration, the superstructure's motion with a gradient magnetic field in a large channel, the disassembly of the superstructure and release of the helical micromachines by a high-frequency alternating magnetic field, and the corkscrew locomotion of the released helices through a small channel via a rotating magnetic field, is showcased. This adaptable microrobotic superstructure reacts to different magnetic inputs, which can be used to perform complex delivery procedures within intricate regions of the human body.

Electrochemically Responsive 3D Nanoarchitectures

Responsive nanomaterials are being developed to create new unique functionalities such as switchable colors and adhesive properties or other programmable features in response to external stimuli. While many existing examples rely on changes in temperature, humidity, or pH, this study aims to explore an alternative approach relying on simple electric input signals. More specifically, 3D electrochromic architected microstructures are developed using carbon nanotube-Tin (Sn) composites that can be reconfigured by lithiating Sn with low power electric input (≈50 nanowatts). These microstructures have a continuous, regulated, and non-volatile actuation determined by the extent of the electrochemical lithiation process. In addition, this proposed fabrication process relies only on batch lithographic techniques, enabling the parallel production of thousands of 3D microstructures. Structures with a 30-97% change in open-end area upon actuation are demonstrated and the importance of geometric factors in the response and structural integrity of 3D architected microstructures during electrochemical actuation is highlighted.

Delivering drugs with microrobots

Biomedical microrobots could overcome current challenges in targeted therapies.

Microrobots for Biomedicine: Unsolved Challenges and Opportunities for Translation

Microrobots are being explored for biomedical applications, such as drug delivery, biological cargo transport, and minimally invasive surgery. However, current efforts largely focus on proof-of-concept studies with nontranslatable materials through a "design-and-apply" approach, limiting the potential for clinical adaptation. While these proof-of-concept studies have been key to advancing microrobot technologies, we believe that the distinguishing capabilities of microrobots will be most readily brought to patient bedsides through a "design-by-problem" approach, which involves focusing on unsolved problems to inform the design of microrobots with practical capabilities. As outlined below, we propose that the clinical translation of microrobots will be accelerated by a judicious choice of target applications, improved delivery considerations, and the rational selection of translation-ready biomaterials, ultimately reducing patient burden and enhancing the efficacy of therapeutic drugs for difficult-to-treat diseases.

Microfluidic Approaches for Microactuators: From Fabrication, Actuation, to Functionalization

Microactuators can autonomously convert external energy into specific mechanical motions. With the feature sizes varying from the micrometer to millimeter scale, microactuators offer many operation and control possibilities for miniaturized devices. In recent years, advanced microfluidic techniques have revolutionized the fabrication, actuation, and functionalization of microactuators. Microfluidics can not only facilitate fabrication with continuously changing materials but also deliver various signals to stimulate the microactuators as desired, and consequently improve microfluidic chips with multiple functions. Herein, this cross-field that systematically correlates microactuator properties and microfluidic functions is comprehensively reviewed. The fabrication strategies are classified into two types according to the flow state of the microfluids: stop-flow and continuous-flow prototyping. The working mechanism of microactuators in microfluidic chips is discussed in detail. Finally, the applications of microactuator-enriched functional chips, which include tunable imaging devices, micromanipulation tools, micromotors, and microsensors, are summarized. The existing challenges and future perspectives are also discussed. It is believed that with the rapid progress of this cutting-edge field, intelligent microsystems may realize high-throughput manipulation, characterization, and analysis of tiny objects and find broad applications in various fields, such as tissue engineering, micro/nanorobotics, and analytical devices.

Responsive Magnetic Nanocomposites for Intelligent Shape-Morphing Microrobots

With the development of advanced biomedical theragnosis and bioengineering tools, smart and soft responsive microstructures and nanostructures have emerged. These structures can transform their body shape on demand and convert external power into mechanical actions. Here, we survey the key advances in the design of responsive polymer-particle nanocomposites that led to the development of smart shape-morphing microscale robotic devices. We overview the technological roadmap of the field and highlight the emerging opportunities in programming magnetically responsive nanomaterials in polymeric matrixes, as magnetic materials offer a rich spectrum of properties that can be encoded with various magnetization information. The use of magnetic fields as a tether-free control can easily penetrate biological tissues. With the advances in nanotechnology and manufacturing techniques, microrobotic devices can be realized with the desired magnetic reconfigurability. We emphasize that future fabrication techniques will be the key to bridging the gaps between integrating sophisticated functionalities of nanoscale materials and reducing the complexity and footprints of microscale intelligent robots.

Self-folding soft-robotic chains with reconfigurable shapes and functionalities

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.

Rolling microswarms along acoustic virtual walls

Rolling is a ubiquitous transport mode utilized by living organisms and engineered systems. However, rolling at the microscale has been constrained by the requirement of a physical boundary to break the spatial homogeneity of surrounding mediums, which limits its prospects for navigation to locations with no boundaries. Here, in the absence of real boundaries, we show that microswarms can execute rolling along virtual walls in liquids, impelled by a combination of magnetic and acoustic fields. A rotational magnetic field causes individual particles to self-assemble and rotate, while the pressure nodes of an acoustic standing wave field serve as virtual walls. The acoustic radiation force pushes the microswarms towards a virtual wall and provides the reaction force needed to break their fore-aft motion symmetry and induce rolling along arbitrary trajectories. The concept of reconfigurable virtual walls overcomes the fundamental limitation of a physical boundary being required for universal rolling movements.

Reflow transfer for conformal three-dimensional microprinting

From microcircuits to metamaterials, the micropatterning of surfaces adds valuable functionality. For nonplanar surfaces, incompatibility with conventional microlithography requires the transfer of originally planar micropatterns onto those surfaces; however, existing approaches accommodate only limited curvatures. A microtransfer approach was developed using reflowable materials that transform between solid and liquid on demand, freely stretching to yield transfers that naturally conform down to nanoscale radii of curvature and arbitrarily complex topographies. Such reflow transfer helps generalize microprinting, extending the reach of precision planar microlithography to highly nonplanar substrates and microstructures. With gentle water-based processing, reflow transfer can be applied to a range of materials, with microprinting demonstrated onto metal, plastic, paper, glass, polystyrene, semiconductor, elastomer, hydrogel, and multiple biological surfaces.

Highly stretchable strain sensors with improved sensitivity enabled by a hybrid of carbon nanotube and graphene

The development of high-performance strain sensors has attracted significant attention in the field of smart wearable devices. However, stretchable strain sensors usually suffer from a trade-off between sensitivity and sensing range. In this study, we investigate a highly sensitive and stretchable piezoresistive strain sensor composed of a hybrid film of 1D multi-walled carbon nanotube (MWCNT) and 2D graphene that forms a percolation network on Ecoflex substrate by spray coating. The mass of spray-coated MWCNT and graphene and their mass ratio are modulated to overcome the trade-off between strain sensitivity and sensing range. We experimentally found that a stable percolation network is formed by 0.18 mg of MWCNTs (coating area of 200 mm2), with a maximum gauge factor (GF) of 1,935.6 and stretchability of 814.2%. By incorporating the 0.36 mg of graphene into the MWCNT film (i.e., a mass ratio of 1:2 between MWCNT and graphene), the GF is further improved to 12,144.7 in a strain range of 650–700%. This high GF is caused by the easy separation of the graphene network under the applied strain due to its two-dimensional (2D) shape. High stretchability originates from the high aspect ratio of MWCNTs that bridges the randomly distributed graphenes, maintaining a conductive network even under sizeable tensile strain. Furthermore, a small difference in work function between MWCNT and graphene and their stable percolation network enables sensitive UV light detection even under a significant strain of 300% that cannot be achieved by sensors composed of MWCNT- or graphene-only. The hybrids of MWCNT and graphene provide an opportunity to achieve high-performance stretchable devices.

Flow lithography for structured microparticles: fundamentals, methods and applications

Structured microparticles, with unique shapes, customizable sizes, multiple materials, and spatially-defined chemistries, are leading the way for emerging 'lab on a particle' technologies. These microparticles with engineered designs find applications in multiplexed diagnostics, drug delivery, single-cell secretion assays, single-molecule detection assays, high throughput cytometry, micro-robotics, self-assembly, and tissue engineering. In this article we review state-of-the-art particle manufacturing technologies based on flow-assisted photolithography performed inside microfluidic channels. Important physicochemical concepts are discussed to provide a basis for understanding the fabrication technologies. These photolithography technologies are compared based on the structural as well as compositional complexity of the fabricated particles. Particles are categorized, from 1D to 3D particles, based on the number of dimensions that can be independently controlled during the fabrication process. After discussing the advantages of the individual techniques, important applications of the fabricated particles are reviewed. Lastly, a future perspective is provided with potential directions to improve the throughput of particle fabrication, realize new particle shapes, measure particles in an automated manner, and adopt the 'lab on a particle' technologies to other areas of research.

Reduced rotational flows enable the translation of surface-rolling microrobots in confined spaces

Biological microorganisms overcome the Brownian motion at low Reynolds numbers by utilizing symmetry-breaking mechanisms. Inspired by them, various microrobot locomotion methods have been developed at the microscale by breaking the hydrodynamic symmetry. Although the boundary effects have been extensively studied for microswimmers and employed for surface-rolling microrobots, the behavior of microrobots in the proximity of multiple wall-based "confinement" is yet to be elucidated. Here, we study the confinement effect on the motion of surface-rolling microrobots. Our experiments demonstrate that the locomotion efficiency of spherical microrollers drastically decreases in confined spaces due to out-of-plane rotational flows generated during locomotion. Hence, a slender microroller design, generating smaller rotational flows, is shown to outperform spherical microrollers in confined spaces. Our results elucidate the underlying physics of surface rolling-based locomotion in confined spaces and present a design strategy with optimal flow generation for efficient propulsion in such areas, including blood vessels and microchannels.

Menezes L, Tittl A, Ren H, Maier SA. Optical Metasurfaces for Energy Conversion

Nanostructured surfaces with designed optical functionalities, such as metasurfaces, allow efficient harvesting of light at the nanoscale, enhancing light-matter interactions for a wide variety of material combinations. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale. In this review, we outline the impact, opportunities, applications, and challenges of optical metasurfaces in converting the energy of incoming photons into frequency-shifted photons, phonons, and energetic charge carriers. A myriad of opportunities await for the utilization of the converted energy. Here we cover the most pertinent aspects from a fundamental nanoscopic viewpoint all the way to applications.

Single-Step-Lithography Micro-Stepper Based on Frictional Contact and Chiral Metamaterial

Stepper motors and actuators are among the main constituents of control motion devices. They are complex multibody systems with rather large overall volume due to their multifunctional parts and elaborate technological assembly processes. Miniaturization of individual parts is still posing assembly problems. In this paper, a single-step lithography process to fabricate a micro-stepper engine with an accurate micrometric rotation axis and an overall sub-millimeter size is demonstrated. The device is based on the frictional contacts and chiral metamaterials to get rid of the dependence on the accuracy of parts. The functional aspects of fabricated samples are discussed for many rotation cycles and for different frictional surfaces.

Swarming Magnetic Photoactive Microrobots for Dental Implant Biofilm Eradication

Titanium dental implants are a multibillion dollar market in the United States alone. The growth of a bacterial biofilm on a dental implant can cause gingivitis, implant loss, and expensive subsequent care. Herein, we demonstrate the efficient eradication of dental biofilm on titanium dental implants via swarming magnetic microrobots based on ferromagnetic (Fe₃O₄) and photoactive (BiVO₄) materials through polyethylenimine micelles. The ferromagnetic component serves as a propulsion force using a transversal rotating magnetic field while BiVO₄ is the photoactive generator of reactive oxygen species to eradicate the biofilm colonies. Such photoactive magnetically powered, precisely navigated microrobots are able to destroy biofilm colonies on titanium implants, demonstrating their use in precision medicine.

Creating three-dimensional magnetic functional microdevices via molding-integrated direct laser writing

Magnetically driven wireless miniature devices have become promising recently in healthcare, information technology, and many other fields. However, they lack advanced fabrication methods to go down to micrometer length scales with heterogeneous functional materials, complex three-dimensional (3D) geometries, and 3D programmable magnetization profiles. To fill this gap, we propose a molding-integrated direct laser writing-based microfabrication approach in this study and showcase its advanced enabling capabilities with various proof-of-concept functional microdevice prototypes. Unique motions and functionalities, such as metachronal coordinated motion, fluid mixing, function reprogramming, geometrical reconfiguring, multiple degrees-of-freedom rotation, and wireless stiffness tuning are exemplary demonstrations of the versatility of this fabrication method. Such facile fabrication strategy can be applied toward building next-generation smart microsystems in healthcare, robotics, metamaterials, microfluidics, and programmable matter.

An aquatic microrobot for microscale flow manipulation

Microrobots have been developed and extensively employed for performing the variety tasks with various applications. However, the intricate fabrication and actuation processes employed for microrobots further restrict their multitudinous applicability as well as the controllability in high accuracy. As an alternative, in this work an aquatic microrobot was developed using a distinctive concept of the building block technique where the microrobot was built based on the block to block design. An in-house electromagnetic system as well as the control algorithm were developed to achieve the precise real-time dynamics of the microrobot for extensive applications. In addition, pivotal control parameters of the microrobot including the actuating waveforms together with the operational parameters were verified and discussed in conjunction with the magnetic intensity simulation. A mixing task was performed with high efficiency based on the trajectory planning and rotation control of the microrobot to demonstrate its capability in flow manipulation which can be advantageous for microreactor applications down the load. Aside from it, a dissolution test was further conducted to provide an on-demand flow agitation function of the microrobot for the next level of lab chip applications. The presented work with detail dynamic analysis is envisaged to provide a new look of microrobot control and functions from the engineering perspective with profoundly potential applications.

Fundamentals of Curvilinear Ferromagnetism: Statics and Dynamics of Geometrically Curved Wires and Narrow Ribbons

Low-dimensional magnetic architectures including wires and thin films are key enablers of prospective ultrafast and energy efficient memory, logic, and sensor devices relying on spin-orbitronic and magnonic concepts. Curvilinear magnetism emerged as a novel approach in material science, which allows tailoring of the fundamental anisotropic and chiral responses relying on the geometrical curvature of magnetic architectures. Much attention is dedicated to magnetic wires of Möbius, helical, or DNA-like double helical shapes, which act as prototypical objects for the exploration of the fundamentals of curvilinear magnetism. Although there is a bulk number of original publications covering fabrication, characterization, and theory of magnetic wires, there is no comprehensive review of the theoretical framework of how to describe these architectures. Here, theoretical activities on the topic of curvilinear magnetic wires and narrow nanoribbons are summarized, providing a systematic review of the emergent interactions and novel physical effects caused by the curvature. Prospective research directions of curvilinear spintronics and spin-orbitronics are discussed, the fundamental framework for curvilinear magnonics are outlined, and mechanically flexible curvilinear architectures for soft robotics are introduced.

Powering and Fabrication of Small-Scale Robotics Systems

Purpose of Review

The increasing number of contributions in the field of small-scale robotics is significantly associated with the progress in material science and process engineering during the last half century. With the objective of integrating the most optimal materials for the propulsion of these motile micro- and nanosystems, several manufacturing strategies have been adopted or specifically developed. This brief review covers some recent advances in materials and fabrication of small-scale robots with a focus on the materials serving as components for their motion and actuation.

Recent Findings

Integration of a wealth of materials is now possible in several micro- and nanorobotic designs owing to the advances in micro- and nanofabrication and chemical synthesis. Regarding light-driven swimmers, novel photocatalytic materials and deformable liquid crystal elastomers have been recently reported. Acoustic swimmers are also gaining attention, with several prominent examples of acoustic bubble-based 3D swimmers being recently reported. Magnetic micro- and nanorobots are increasingly investigated for their prospective use in biomedical applications. The adoption of different materials and novel fabrication strategies based on 3D printing, template-assisted electrodeposition, or electrospinning is briefly discussed.

Summary

A brief review on fabrication and powering of small-scale robotics is presented. First, a concise introduction to the world of small-scale robotics and their propulsion by means of magnetic fields, ultrasound, and light is provided. Recent examples of materials and fabrication methodologies for the realization of these devices follow thereafter.

Biologically Safe, Degradable Self-Destruction System for On-Demand, Programmable Transient Electronics

The lifetime of transient electronic components can be programmed via the use of encapsulation/passivation layers or of on-demand, stimuli-responsive polymers (heat, light, or chemicals), but yet most research is limited to slow dissolution rate, hazardous constituents, or byproducts, or complicated synthesis of reactants. Here we present a physicochemical destruction system with dissolvable, nontoxic materials as an efficient, multipurpose platform, where chemically produced bubbles rapidly collapse device structures and acidic molecules accelerate dissolution of functional traces. Extensive studies of composites based on biodegradable polymers (gelatin and poly(lactic-co-glycolic acid)) and harmless blowing agents (organic acid and bicarbonate salt) validate the capability for the desired system. Integration with wearable/recyclable electronic components, fast-degradable device layouts, and wireless microfluidic devices highlights potential applicability toward versatile/multifunctional transient systems. In vivo toxicity tests demonstrate biological safety of the proposed system.

Ultrasound-activated ciliary bands for microrobotic systems inspired by starfish

Cilia are short, hair-like appendages ubiquitous in various biological systems, which have evolved to manipulate and gather food in liquids at regimes where viscosity dominates inertia. Inspired by these natural systems, synthetic cilia have been developed and utilized in microfluidics and microrobotics to achieve functionalities such as propulsion, liquid pumping and mixing, and particle manipulation. Here, we demonstrate ultrasound-activated synthetic ciliary bands that mimic the natural arrangements of ciliary bands on the surface of starfish larva. Our system leverages nonlinear acoustics at microscales to drive bulk fluid motion via acoustically actuated small-amplitude oscillations of synthetic cilia. By arranging the planar ciliary bands angled towards (+) or away (-) from each other, we achieve bulk fluid motion akin to a flow source or sink. We further combine these flow characteristics with a physical principle to circumvent the scallop theorem and realize acoustic-based propulsion at microscales. Finally, inspired by the feeding mechanism of a starfish larva, we demonstrate an analogous microparticle trap by arranging + and - ciliary bands adjacent to each other.

Bioinspired soft microrobots actuated by magnetic field

In contrast to traditional large-scale robots, which require complicated mechanical joints and material rigidity, microrobots made of soft materials have exhibited amazing features and great potential for extensive applications, such as minimally invasive surgery. However, microrobots are faced with energy supply and control issues due to the miniaturization. Magnetic field actuation emerges as an appropriate approach to tackle with these issues. This review summarizes the latest progress of biomimetic soft microrobots actuated by magnetic field. Starting with an overview of the soft material and magnetic material adopted in the magnetic field actuated soft microrobots, the various fabrication methods and design structures of soft microrobots are summarized. Subsequently, practical and potential applications, such as targeted therapy, surgical operation, and the transportation of microscopic objects, in the fields of biomedicine and environmental remediation are presented. In the end, some current challenges, and the future development trends of magnetic soft microrobots are briefly discussed. This review is expected to offer a helpful guidance for the new researchers of biomimetic soft microrobots actuated by magnetic field.

3D printed personalized magnetic micromachines from patient blood-derived biomaterials

While recent wireless micromachines have shown increasing potential for medical use, their potential safety risks concerning biocompatibility need to be mitigated. They are typically constructed from materials that are not intrinsically compatible with physiological environments. Here, we propose a personalized approach by using patient blood–derivable biomaterials as the main construction fabric of wireless medical micromachines to alleviate safety risks from biocompatibility. We demonstrate 3D printed multiresponsive microswimmers and microrollers made from magnetic nanocomposites of blood plasma, serum albumin protein, and platelet lysate. These micromachines respond to time-variant magnetic fields for torque-driven steerable motion and exhibit multiple cycles of pH-responsive two-way shape memory behavior for controlled cargo delivery and release applications. Their proteinaceous fabrics enable enzymatic degradability with proteinases, thereby lowering risks of long-term toxicity. The personalized micromachine fabrication strategy we conceptualize here can affect various future medical robots and devices made of autologous biomaterials to improve biocompatibility and smart functionality.

A Maze in Plastic Wastes: Autonomous Motile Photocatalytic Microrobots against Microplastics

An extremely high quantity of small pieces of synthetic polymers, namely, microplastics, has been recently identified in some of the most intact natural environments, e.g., on top of the Alps and Antarctic ice. This is a "scary wake-up call", considering the potential risks of microplastics for humans and marine systems. Sunlight-driven photocatalysis is the most energy-efficient currently known strategy for plastic degradation; however, attaining efficient photocatalyst-plastic interaction and thus an effective charge transfer in the micro/nanoscale is very difficult; that adds up to the common challenges of heterogeneous photocatalysis including low solubility, precipitation, and aggregation of the photocatalysts. Here, an active photocatalytic degradation procedure based on intelligent visible-light-driven microrobots with the capability of capturing and degrading microplastics "on-the-fly" in a complex multichannel maze is introduced. The robots with hybrid powers carry built-in photocatalytic (BiVO₄) and magnetic (Fe₃O₄) materials allowing a self-propelled motion under sunlight with the possibility of precise actuation under a magnetic field inside the macrochannels. The photocatalytic robots are able to efficiently degrade different synthetic microplastics, particularly polylactic acid, polycaprolactone, thanks to the generated local self-stirring effect in the nanoscale and enhanced interaction with microplastics without using any exterior mechanical stirrers, typically used in conventional systems. Overall, this proof-of-concept study using microrobots with hybrid wireless powers has shown for the first time the possibility of efficient degradation of ultrasmall plastic particles in confined complex spaces, which can impact research on microplastic treatments, with the final goal of diminishing microplastics as an emergent threat for humans and marine ecosystems.

Tethered and Untethered 3D Microactuators Fabricated by Two-Photon Polymerization: A Review

Microactuators, which can transform external stimuli into mechanical motion at microscale, have attracted extensive attention because they can be used to construct microelectromechanical systems (MEMS) and/or microrobots, resulting in extensive applications in a large number of fields such as noninvasive surgery, targeted delivery, and biomedical machines. In contrast to classical 2D MEMS devices, 3D microactuators provide a new platform for the research of stimuli-responsive functional devices. However, traditional planar processing techniques based on photolithography are inadequate in the construction of 3D microstructures. To solve this issue, researchers have proposed many strategies, among which 3D laser printing is becoming a prospective technique to create smart devices at the microscale because of its versatility, adjustability, and flexibility. Here, we review the recent progress in stimulus-responsive 3D microactuators fabricated with 3D laser printing depending on different stimuli. Then, an outlook of the design, fabrication, control, and applications of 3D laser-printed microactuators is propounded with the goal of providing a reference for related research.