Structural color materials from existing natural organisms have been widely studied to enable artificial manufacture. Variable iridescence has attracted particular interest because of the displays of various brilliant examples. Existing synthetic, variable, structural color materials require external stimuli to provide changing displays, despite autonomous regulation being widespread among natural organisms, and therefore suffer from inherent limitations. Inspired by the structural color regulation mechanism of chameleons, we present a conceptually different structural color material that has autonomic regulation capability by assembling engineered cardiomyocyte tissues on synthetic inverse opal hydrogel films. The cell elongation and contraction in the beating processes of the cardiomyocytes caused the inverse opal structure of the substrate film to follow the same cycle of volume or morphology changes. This was observed as the synchronous shifting of its photonic band gap and structural colors. Such biohybrid structural color hydrogels can be used to construct a variety of living materials, such as two-dimensional selfregulating structural color patterns and three-dimensional dynamic Morpho butterflies. These examples indicated that the stratagem could provide an intrinsic color-sensing feedback to modify the system behavior/action for future biohybrid robots. In addition, by integrating the biohybrid structural color hydrogels into microfluidics, we developed a "heart-on-a-chip" platform featuring microphysiological visuality for biological research and drug screening. This biohybrid, living, structural color hydrogel may be widely used in the design of a variety of intelligent actuators and soft robotic devices.

"Organ-on-a-chip" systems integrate microengineering, microfluidic technologies, and biomimetic principles to create key aspects of living organs faithfully, including critical microarchitecture, spatiotemporal cell-cell interactions, and extracellular microenvironments. This creative platform and its multiorgan integration recapitulating organ-level structures and functions can bring unprecedented benefits to a diversity of applications, such as developing human in vitro models for healthy or diseased organs, enabling the investigation of fundamental mechanisms in disease etiology and organogenesis, benefiting drug development in toxicity screening and target discovery, and potentially serving as replacements for animal testing. Recent advances in novel designs and examples for developing organ-on-a-chip platforms are reviewed. The potential for using this emerging technology in understanding human physiology including mechanical, chemical, and electrical signals with precise spatiotemporal controls are discussed. The current challenges and future directions that need to be pursued for these proof-of-concept studies are also be highlighted.

2D materials are of particular interest in light‐to‐heat conversion, yet challenges remain in developing a facile method to suppress their light reflection. Herein, inspired by the black scales of Bitis rhinoceros, a generalized approach via sequential thermal actuations to construct biomimetic 2D‐material nanocoatings, including Ti3C2Tx MXene, reduced graphene oxide (rGO), and molybdenum disulfide (MoS2) is designed. The hierarchical MXene nanocoatings result in broadband light absorption (up to 93.2%), theoretically validated by optical modeling and simulations, and realize improved light‐to‐heat performance (equilibrium temperature of 65.4 °C under one‐sun illumination). With efficient light‐to‐heat conversion, the bioinspired MXene nanocoatings are next incorporated into solar steam‐generation devices and stretchable solar/electric dual‐heaters. The MXene steam‐generation devices require much lower solar‐thermal material loading (0.32 mg cm−2) and still guarantee high steam‐generation performance (1.33 kg m−2 h−1) compared with other state‐of‐the‐art devices. Additionally, the mechanically deformed MXene structures enable the fabrication of stretchable and wearable heaters dual‐powered by sunlight and electricity, which are reversibly stretched and heated above 100 °C. This simple fabrication process with effective utilization of active materials promises its practical application value for multiple solar–thermal technologies.

Helical objects are among the most important and landmark structures in nature, and represent an emerging group of materials with unique spiral geometry; because of their enriched physical and chemical properties, they can have multiple functionalities. However, the fabrication of such complex helical materials at the micro- or nanoscale level remains a challenge. Here, a coaxial capillary microfluidic system, with the functions of consecutive spinning and spiraling, is presented for scalable generation of helical microfibers. The generation processes can be precisely tuned by adjusting the flow rates, and thus the length, diameter, and pitch of the helical microfibers are highly controllable. Varying the injection capillary design of the microfluidics enables the generation of helical microfibers with structures such as the novel Janus, triplex, core-shell, and even double-helix structures. The potential use of these helical microfibers is also explored for magnetically and thermodynamically triggered microsprings, as well as for a force indicator for contraction of cardiomyocytes. These indicate that such helical microfibers are highly versatile for different applications.

Biologically inspired self-healing structural color hydrogels were developed by adding a glucose oxidase (GOX)- and catalase (CAT)-filled glutaraldehyde cross-linked BSA hydrogel into methacrylated gelatin (GelMA) inverse opal scaffolds. The composite hydrogel materials with the polymerized GelMA scaffold could maintain the stability of an inverse opal structure and its resultant structural colors, whereas the protein hydrogel filler could impart self-healing capability through the reversible covalent attachment of glutaraldehyde to lysine residues of BSA and enzyme additives. A series of unprecedented structural color materials could be created by assembling and healing the elements of the composite hydrogel. In addition, as both the GelMA and the protein hydrogels were derived from organisms, the composite materials presented high biocompatibility and plasticity. These features of self-healing structural color hydrogels make them excellent functional materials for different applications.

Conductive hydrogels are widely used in various applications such as artificial skin, flexible and implantable bioelectronics, and tissue engineering. However, it is still a challenge to formulate hydrogels with high electrical conductivity without compromising their physicochemical properties (e.g., toughness, stretchability, and biocompatibility). Additionally, incorporating other functions, such as self-healing, shape memory, and wet adhesion, into conductive hydrogels is critical to many practical applications of hydrogel bioelectronics. In this perspective, we highlight recent progress in the development of functional conductive hydrogels.We then discuss the potential applications and challenges faced by conductive hydrogels in the areas of wearable/implantable electronics and cell/tissue engineering. Conductive hydrogel can serve as an important building block for bioelectronic devices in personalized healthcare and other bioengineering areas.

Morpho butterflies are famous for their wings' brilliant structural colors arising from periodic nanostructures, which show great potential value for fundamental research and practical applications. Here, a novel cellular mechanical visualizable biosensor formed by assembling engineered cardiac tissues on the Morpho butterfly wings is presented. The assembled cardiomyocytes benefit from the periodic parallel nanoridges of the wings and can recover their autonomic beating ability with guided cellular orientation and good contraction performance. As the beating processes are accompanied by the cardiomyocytes' elongation and contraction, the elastic butterfly wing substrate undergoes the same cycle of deformations, which causes corresponding synchronous shifts in their structural colors and photonic bandgaps for self‐reporting of the cell mechanics. It is demonstrated that this self‐reporting performance can be further improved by adding oriented carbon nanotubes in the nanoridges of the wings for the culture. In addition, taking advantage of the similar size of the cardiomyocyte and a single Morpho wing scale, the investigation of single‐cell‐level mechanics can be realized by detecting the optical performance of a single scale. These remarkable properties make these butterfly wings ideal platforms for biomedical research.

In the emerging Internet of Things, stretchable antennas can facilitate wireless communication between wearable and mobile electronic devices around the body. The proliferation of wireless devices transmitting near the human body also raises interference and safety concerns that demand stretchable materials capable of shielding electromagnetic interference (EMI). Here, an ultrastretchable conductor is fabricated by depositing a crumple-textured coating composed of 2D Ti 3 C 2 T x nanosheets (MXene) and single-walled carbon nanotubes (SWNTs) onto latex, which can be fashioned into high-performance wearable antennas and EMI shields. The resulting MXene-SWNT (S-MXene)/latex devices are able to sustain up to an 800% areal strain and exhibit strain-insensitive resistance profiles during a 500-cycle fatigue test. A single layer of stretchable S-MXene conductors demonstrate a strain-invariant EMI shielding performance of ≈30 dB up to 800% areal strain, and the shielding performance is further improved to ≈47 and ≈52 dB by stacking 5 and 10 layers of S-MXene conductors, respectively. Additionally, a stretchable S-MXene dipole antenna is fabricated, which can be uniaxially stretched to 150% with unaffected reflected power <0.1%. By integrating S-MXene EMI shields with stretchable S-MXene antennas, a wearable wireless system is finally demonstrated that provides mechanically stable wireless transmission while attenuating EM absorption by the human body.existing mobile devices. [1] To enable highperformance wireless communication between wearable sensors, displays, and data processing devices around the body, new routes to fabricating for stretchable antennas that exhibit mechanically stable performance are needed. Furthermore, the proliferation of mobile and wearable devices based on various wireless technologies, including GPS, Bluetooth, Wi-Fi, and near-field communication, is increasing the frequency and duration of the human body exposed to electromagnetic (EM) fields, which raises interference and safety concerns that may require certain suitable materials for EM protection. [2] Therefore, in addition to the growing demand for stretchable antennas, electromagnetic interference (EMI) shielding materials that are stretchable, durable, and can be integrated closely with wearable wireless technologies are needed to reduce the exposure of the human body to EM fields. Integrating such stretchable antennas with on-site EMI shields not only provides protection against EM fields, but also prevents unauthorized wireless transmission between wearable electronics and mobile devices for enhanced wireless privacy.Both wearable antennas and stretchable EMI shields face similar technological challenges, where the key materials awaiting to be developed are the stretchable conductors with high strain tolerance and strain-invariant electrical conductivities.Metals (e.g., Cu and Al) are the conventionally used materials for EMI shields and antennas on many occasions. As the trend in today's electronic devices becomes faster, lighter, and...