Recent Advances in 4D Printing of Advanced Materials and Structures for Functional Applications

Mechanical metamaterials (MMs) receive widespread attention due to their unprecedented mechanical properties. However, in the next‐generation MMs, the cognitive function of information processing can be realized while maintaining superior mechanical properties. Herein, a mechanical metamaterial‐based self‐powered electronic skin (e‐skin) with multimodal fusion perception capability and shape memory reconfigurability is proposed. Benefiting from an MM skeleton and its analytical model, e‐skin realizes biomimetic nonlinear mechanical behavior and mechanical reconfigurability to imitate target biotissues. Its integrated perovskite‐based elastic sensors enable high‐precision collection of physiological movements and auditory, tactile, and precontact distance signals. Further, by imitating the integration and interaction functions in biological multisensory neural networks, the system achieves advanced cognitive functions of acquiring, identifying, and integrating information across modalities. Applications of e‐skin are demonstrated in motion monitoring, speech recognition, and somatosensory game operation. These capabilities can be applied to cross‐modal perception robot systems based on multisensory neural networks.

Metamaterial‐Based Electronic Skin with Conformality and Multisensory Integration

Li,

Liu,

Liu

et al. 2024

Coaxial‐Spun Hollow Liquid Crystal Elastomer Fiber as a Versatile Platform for Functional Composites

Li,

Gholami,

Yue

et al. 2024

The design and engineering of liquid crystal elastomers (LCE) composites for enhanced multifunctionality and responsiveness is highly desired. Here, a hollow LCE (h‐LCE) fiber fabricated via coaxial spinning, enabling the straightforward yet effective creation of functional LCE composites, is reported. Inspired by the fiber‐tubule architecture in skeletal muscles, the hollow fiber features an LCE outer shell for programmable actuation and an inner channel allowing for the integration of a variety of functional media. Thus, the h‐LCE fiber can serve as a versatile platform for multifunctionalities in LCE composites. With this unique design strategy, h‐LCE fibers are fabricated with lengths exceeding 3 meters in the lab with outer and inner diameters as small as 250 mm and 120 µm, respectively. The versatility of these h‐LCE fibers across various applications are further demonstrated, from fast‐response stiffness‐tunable actuators by integrating water flow as triggering media and shape memory polymer (SMP) for enhanced mechanical properties, to electrically driven actuating systems through the incorporation of liquid metal, and actuating light‐guides by combining SMP and PDMS optical fiber. The conception of h‐LCE fiber not only advances the design of multifunctional LCE composites but also paves the way for their application in soft robotics, artificial muscles, and beyond.

4D Direct Laser Writing for Intelligent Micromachines

Wang,

Sai,

Tang

et al. 2024

Intelligent micromachines are devices with sizes ranging from submillimeters to nanometers, capable of performing complex tasks adaptively at small scales. Smart micromachines have recently been developed that exhibit shape‐morphing capability in response to various stimuli to adapt to their environment. However, for such micromachines to be effective in harsh environments, micromachines should be more than adaptive. Essentially, they must exhibit a high degree of intelligence, characterized by enhanced locomotion capability, self‐adaptability, programmability, reconfigurability, and multifunctionality. 4D direct laser writing has enabled the rapid prototyping of stimulus‐responsive adaptive micromechanisms and diverse functional microcomponents, including microscale sensors, actuators, data processors, memory structures, and power‐supply structures. This review provides a comprehensive overview of the current state of the art in 4D microprinting technology based on two‐photon polymerization for the intelligentization of micromachines. Further, it offers insights into the fabrication of intelligent micromachines via the integration of diverse functional components through the 4D direct laser writing technology.