Inorganic Stimuli‐Responsive Nanomembranes for Small‐Scale Actuators and Robots

Abstract

The term small‐scale robotics describes a wide variety of miniature robotic systems, ranging from millimeter‐sized devices down to autonomous mobile systems with dimensions measured in nanometers. These systems can perform complex tasks that are impossible for humans to accomplish or at scales that humans cannot reach. In recent years, the rapid advancement of small‐scale robotics has benefited from the progress in synthesis and nanotechnology, providing access to nanomembranes with stimuli‐responsive materials, such as phase transition materials, shape memory alloys, and palladium. These materials are 2D sheets with a thickness ranging from 5 to 500 nm, and they have the ability to change their shape reversibly under extremal stimuli. Together with strain engineering for deterministic assembly, various stimuli‐responsive actuators and robots have been fabricated for medicine, manufacturing, and exploration by endowing them with the combined features of a continuously deformable structure, remote operation, and several degrees of freedom. Herein, the recent achievements in small‐scale actuators and robots based on inorganic stimuli‐responsive nanomembranes are reviewed and their advantages and properties highlighted.

Recent Advances on Nanocomposite Resists With Design Functionality for Lithographic Microfabrication

“…Finally, the use of microfluidics for maskless lithography is a research field of continuous interest. The reader is referred to the review by Tian et al (Tian et al, 2020) which discuss, in particular, the fabrication of complex 3D microparticles by microfluidic lithography. A combined system including a vertical step motor was recently explored by Yoon and coworkers.…”

“…The flow rate of the micropump was evaluated by particle tracking method showing a good performance. For a recent review covering several strategies regarding responsive membranes, the reader is referred to the work by Tian et al (Tian et al, 2020).…”

Fabrication and Functionality Integration Technologies for Small‐Scale Soft Robots

“…To further empower small-scale soft robots with rich function and ability, a plethora of integration techniques for functionalization have been developed during the past decades. [100,[289][290][291][292][293][294] These functionalized integration techniques enable extensive previously inaccessible behaviors, for example, somatosensitive/proprioceptive actuation and environment perception and response (Figure 4A), self-control locomotion (Figure 4B), remote communication (Figure 4C), energy harvest/storage/manage and power transferring (Figure 4D), tunable stiffness (Figure 4E), reconfigurable architectures (Figure 4F), self-healing (Figure 4G), and biodegradable body. [59,75,[295][296][297][298] Owing to the aforementioned properties and merits, functionalized small-scale robots also demonstrate various elegant applications.…”

Thin‐Film‐Shaped Flexible Actuators

“…The distinction between flexible and stiff is mainly determined by the magnitude of the flexural rigidity. [12][13][14] As such, an ultra-thin film made of stiff materials, such as shape memory alloys (SMAs), metals, piezoelectric materials (e.g., piezoelectric ceramics, PVDF) could also be "flexible". For example, Figure 1a (rightmost panel) shows an array of electrochemically actuated artificial cilia composed of a 7 nm thick platinum (Pt; %165 GPa) thin film and a passive layer of 3 nm thick titanium (Ti; %105 GPa), enabling control of flow patterns in liquids near a surface.…”