Plant-inspired TransfOrigami microfluidics

Controllable lubricant-infused wrinkled surface for light-manipulated droplet climbing/pinning on inclined surfaces

Stimuli-responsive droplet transport on solid surfaces holds significant importance in various engineering domains; however, achieving accurate and robust manipulation of droplets, particularly their climbing and pinning on inclined surfaces, remains an unresolved challenge. This study proposes a novel light-responsive surface that integrates wrinkle structure with a lubricant-infused photothermal film, enabling flexible light-controlled movement of droplets even on inclined surfaces. The key to constructing this surface lies in fine control of the lubricant infusion amount onto a wrinkled Fe3O4/polydimethylsiloxane (PDMS) composite film, where wrinkles were "half covered, half exposed". Thus, a droplet placed on this controllable lubricant-infused wrinkled surface (CLWS) comes into contact with both the lubricant and the raised parts of wrinkles. In the absence of light, the droplet pins onto the inclined surface, displaying a large sliding angle up to 50°. Upon exposure to external light, the droplet exhibits climbing ability on inclined surfaces with a tilt angle larger than 15°. This behavior is primarily attributed to the Marangoni effect generated by photothermal conversion, which not only provides the driving force for climbing but also alters the distribution of lubricant to mitigate the resistance. The proposed CLWS demonstrates its suitability for various droplets including water, glycol and glycerol, while enabling complex operations such as directional movement, Z-shape turning, and multi-droplet fusion on inclined or curved surfaces. We believe that our proposed CLWS, designed for light-induced droplet climbing/pinning on inclined surfaces, significantly augments the versatility and application potential in the realm of droplet manipulation techniques.

Mechanical and Light Activation of Materials for Chemical Production

Mechanical expansion and contraction of pores within photosynthetic organisms regulate a series of processes that are necessary to manage light absorption, control gas exchange, and regulate water loss. These pores, known as stoma, allow the plant to maximize photosynthetic output depending on environmental conditions such as light intensity, humidity, and temperature by actively changing the size of the stomal opening. Despite advances in artificial photosynthetic systems, little is known about the effect of such mechanical actuation in synthetic materials where chemical reactions occur. It is reported here on a hybrid hydrogel that combines light-activated supramolecular polymers for superoxide production with thermal mechanical actuation of a covalent polymer. Superoxide production is important in organic synthesis and environmental remediation, and is a potential precursor to hydrogen peroxide liquid fuel. It is shown that the closing of pores in the hybrid hydrogel results in a substantial decrease in photocatalysis, but cycles of swollen and contracted states enhance photocatalysis. The observations motivate the development of biomimetic photosynthetic materials that integrate large scale motion and chemical reactions.

Oligoadenine Strand Functionalized Polyacrylamide Hydrogel Film Exhibiting pH-Triggered High-Degree Inverse Shape Deformations

Smart shape-memory DNA hydrogels, which can respond to various types of external stimuli and undergo macroscopic shape deformations, have shown great potential in various applications. By constructing free-standing films, the deformation and response properties of these hydrogels can be further enhanced, and visualized deformation can be achieved. However, DNA hydrogels that can exhibit rapid and high-degree shape deformations, such as the inverse shape deformations, are still lacking. Herein, free-standing oligoadenine strand-functionalized polyacrylamide hydrogel films were developed that can exhibit reversible and high degree of inverse shape deformation upon cyclic pH changes. The oligoadenine strands exhibit a pH-stimulated reversible conformational transition between a flexible single-stranded state and parallel duplex A-motif structures, resulting in their role change in the film from negatively charged side chains to "head-to-head" crosslinking structures, driving a high degree of inverse shape deformation with a relative bending angle change of 223.7 % of the film, which is more than 5 times that of a film driven by pH-responsive i-motif structures, facilitating the development of bilayer hydrogel film actuators with potential in flexible sensors and robots.

Bioinspired Liquid Pockets with Externally Induced Internal Microscale Flow

The gastric mucosal barrier, through its gastric pits, serves as a pathway for secretions, ensuring that mucus produced by the gastric glands is transferred to the gastric lumen, providing stable protection. Here a bioinspired liquid pockets material is shown, composed of a thermo-driven hydrogel that acts as an external activation unit to release interflowing liquid responsively, and porous matrices that serve as interconnected pockets to transfer it, enabling controlled internal flow and adaptive barrier functionality. Experiments and theoretical analysis demonstrate the stability and regulatory mechanisms of these liquid pockets, based on the interconnected pockets between the external activation unit and internal fluid flow. It exhibits a new pathway for regulating microscale flow at responsive material interfaces, enabling applications from sequential drug release, self-cleaning, and antifouling to anti-swelling. These unique capabilities address long-standing challenges in microscale flow control, with potential impacts in diverse fields including microfluidics, drug delivery, medical devices, 3D printing, and beyond.

Biomimetic Origami: A Biological Influence in Design

Origami, the art of paper folding, has long fascinated researchers and designers in its potential to replicate and tap the complexity of nature. In this paper, we pursue the crossing of origami engineering structures and biology, the realm of biologically-inspired origami structures categorized by the two biggest taxonomy kingdoms and DNA origami. Given the diversity of life forms that Earth comprises, we pursue an analysis of biomimetic designs that resemble intricate patterns and functionalities occurring in nature. Our research begins by setting out a taxonomic framework for the classification of origami structures based on biologically important kingdoms. From each of these, we explore the engineering structures inspired by morphological features, behaviors, and ecological adaptations of organisms. We also discuss implications in realms such as sustainability, biomaterials development, and bioinspired robotics. Thus, by parlaying the principles found in nature's design playbook through the art of folding, biologically inspired origami becomes fertile ground for interdisciplinary collaboration and creativity. Through this approach, we aim to inspire readers, researchers, and designers to embark on a journey of discovery in which the boundaries between art, science, and nature are blurred, providing a foundation for innovation to thrive.

Design and batch fabrication of anisotropic microparticles toward small-scale robots using microfluidics: recent advances

Small-scale robots with shape anisotropy have garnered significant scientific interest due to their enhanced mobility and precise control in recent years. Traditionally, these miniature robots are manufactured using established techniques such as molding, 3D printing, and microfabrication. However, the advent of microfluidics in recent years has emerged as a promising manufacturing technology, capitalizing on the precise and dynamic manipulation of fluids at the microscale to fabricate various complex-shaped anisotropic particles. This offers a versatile and controlled platform, enabling the efficient fabrication of small-scale robots with tailored morphologies and advanced functionalities from the microfluidic-derived anisotropic microparticles at high throughput. This review highlights the recent advances in the microfluidic fabrication of anisotropic microparticles and their potential applications in small-scale robots. In this review, the term 'small-scale robots' broadly encompasses micromotors endowed with capabilities for locomotion and manipulation. Firstly, the fundamental strategies for liquid template formation and the methodologies for generating anisotropic microparticles within the microfluidic system are briefly introduced. Subsequently, the functionality of shape-anisotropic particles in forming components for small-scale robots and actuation mechanisms are emphasized. Attention is then directed towards the diverse applications of these microparticle-derived microrobots in a variety of fields, including pollution remediation, cell microcarriers, drug delivery, and biofilm eradication. Finally, we discuss future directions for the fabrication and development of miniature robots from microfluidics, shedding light on the evolving landscape of this field.

Responsive-Hydrogel Aquabots

It remains a challenge to produce soft robots that can mimic the responsive adaptability of living organisms. Rather than fabricating soft robots from bulk hydrogels,hydrogels are integrated into the interfacial assembly of aqueous two-phase systems to generate ultra-soft and elastic all-aqueous aquabots that exhibit responsive adaptability, that can shrink on demand and have electrically conductive functions. The adaptive functions of the aquabots provide a new platform to develop minimally invasive surgical devices, targeted drug delivery systems, and flexible electronic sensors and actuators.

Active Materials for Functional Origami

In recent decades, origami has been explored to aid in the design of engineering structures. These structures span multiple scales and have been demonstrated to be used toward various areas such as aerospace, metamaterial, biomedical, robotics, and architectural applications. Conventionally, origami or deployable structures have been actuated by hands, motors, or pneumatic actuators, which can result in heavy or bulky structures. On the other hand, active materials, which reconfigure in response to external stimulus, eliminate the need for external mechanical loads and bulky actuation systems. Thus, in recent years, active materials incorporated with deployable structures have shown promise for remote actuation of light weight, programmable origami. In this review, active materials such as shape memory polymers (SMPs) and alloys (SMAs), hydrogels, liquid crystal elastomers (LCEs), magnetic soft materials (MSMs), and covalent adaptable network (CAN) polymers, their actuation mechanisms, as well as how they have been utilized for active origami and where these structures are applicable is discussed. Additionally, the state-of-the-art fabrication methods to construct active origami are highlighted. The existing structural modeling strategies for origami, the constitutive models used to describe active materials, and the largest challenges and future directions for active origami research are summarized.

A Hyperspectral Camouflage Colorant Inspired by Natural Leaves

The unmet spectral mimicry of foliar green in camouflage materials is hampered by the lack of colorants with similar spectral properties to chlorophyll, resulting in substantial risks of exposure from hyperspectral target detection. By drawing inspiration from leaf chromogenesis, a microcapsule colorant with a chloroplast-like structure and chlorophyll-like absorption is developed, and a generic bilayer coating is designed to provide high spectral similarity to leaves with different growth stages, seasons, and species. Specifically, the microcapsule colorant preserves the monomeric absorption of the internal phthalocyanine and features the manufacturability of conventional pigments, such as amenability to painting and patterning, and compatibility to different substrates. The pigmented artificial leaves successfully deceive the hyperspectral classification algorithm in a foliar background, and outperforming the state-of-art spectral simulation materials. This coloration strategy expands the knowledge base of the spectral fine tuning of composite colorants, which are essential for their application in spectral-resolved optical materials.

Overcoming Water Diffusion Limitations in Hydrogels via Microtubular Graphene Networks for Soft Actuators

Hydrogel-based soft actuators can operate in sensitive environments, bridging the gap of rigid machines interacting with soft matter. However, while stimuli-responsive hydrogels can undergo extreme reversible volume changes of up to ≈90%, water transport in hydrogel actuators is in general limited by their poroelastic behavior. For poly(N-isopropylacrylamide) (PNIPAM) the actuation performance is even further compromised by the formation of a dense skin layer. Here it is shown, that incorporating a bioinspired microtube graphene network into a PNIPAM matrix with a total porosity of only 5.4% dramatically enhances actuation dynamics by up to ≈400% and actuation stress by ≈4000% without sacrificing the mechanical stability, overcoming the water transport limitations. The graphene network provides both untethered light-controlled and electrically powered actuation. It is anticipated that the concept provides a versatile platform for enhancing the functionality of soft matter by combining responsive and 2D materials, paving the way toward designing soft intelligent matter.

Phase-separation facilitated one-step fabrication of multiscale heterogeneous two-aqueous-phase gel

Engineering heterogeneous hydrogels with distinct phases at various lengths, which resemble biological tissues with high complexity, remains challenging by existing fabricating techniques that require complicated procedures and are often only applicable at bulk scales. Here, inspired by ubiquitous phase separation phenomena in biology, we present a one-step fabrication method based on aqueous phase separation to construct two-aqueous-phase gels that comprise multiple phases with distinct physicochemical properties. The gels fabricated by this approach exhibit enhanced interfacial mechanics compared with their counterparts obtained from conventional layer-by-layer methods. Moreover, two-aqueous-phase gels with programmable structures and tunable physicochemical properties can be conveniently constructed by adjusting the polymer constituents, gelation conditions, and combining different fabrication techniques, such as 3D-printing. The versatility of our approach is demonstrated by mimicking the key features of several biological architectures at different lengths: macroscale muscle-tendon connections; mesoscale cell patterning; microscale molecular compartmentalization. The present work advances the fabrication approach for designing heterogeneous multifunctional materials for various technological and biomedical applications.

Cascaded microfluidic circuits for pulsatile filtration of extracellular vesicles from whole blood for early cancer diagnosis

Tumor-derived extracellular vesicles (EVs) hold the potential to substantially improve noninvasive early diagnosis of cancer. However, analysis of nanosized EVs in blood samples has been hampered by lack of effective, rapid, and standardized methods for isolating and detecting EVs. To address this difficulty, here we use the electric-hydraulic analogy to design cascaded microfluidic circuits for pulsatile filtration of EVs via integration of a cell-removal circuit and an EV-isolation circuit. The microfluidic device is solely driven by a pneumatic clock pulse generator, allowing for preprogrammed, clog-free, gentle, high-yield, and high-purity isolation of EVs directly from blood within 30 minutes. We demonstrate its clinical utility by detecting protein markers of isolated EVs from patient blood using a polyethylene glycol-enhanced thermophoretic aptasensor, with 91% accuracy for diagnosis of early-stage breast cancer. The cascaded microfluidic circuits can have broad applications in the field of EV research.

Pixelating Responsive Structural Color via a Bioinspired Morphable Concavity Array (MoCA) Composed of 2D Photonic Crystal Elastomer Actuators

Stimuli-responsive structural coloration allows the color change of soft substrates in response to environmental stimuli such as heat, humidity, and solvents. Such color-changing systems enable smart soft devices, such as the camouflageable skin of soft robots or chromatic sensors in wearable devices. However, individually and independently programmable stimuli-responsive color pixels remain significant challenges among the existing color-changing soft materials and devices, which are crucial for dynamic display. Inspired by the dual-color concavities on butterfly wings, a morphable concavity array to pixelate the structural color of two-dimensional photonic crystal elastomer and achieve individually and independently addressable stimuli-responsive color pixels is designed. The morphable concavity can convert its surface between concave and flat upon changes in the solvent and temperature, accompanied by angle-dependent color-shifting. Through multichannel microfluidics, the color of each concavity can be controllably switched. Based on the system, the dynamic display by forming reversibly editable letters and patterns for anti-counterfeiting and encryption are demonstrated. It is believed that the strategy of pixelating optical properties through locally altering surface topography can inspire the design of new transformable optical devices, such as artificial compound eyes or crystalline lenses for biomimetic and robotic applications.

Lithographic Microneedle-Motors from Multimodal Microfluidics for Cargo Delivery

Micromotors have led to an unprecedented revolution in the field of cargo delivery. Attempts in this area trend toward enriching their structures and improving their functions to promote their further applications. Herein, novel microneedle-motors (MNMs) for active drug delivery through a flexible multimodal microfluidic lithographic approach are presented. The multimodal microfluidics is composed of a co-flow geometry-derived droplet fluid and an active cargo mixed laminar flow in a triangular microchannel. The MNMs with sharp tips and spherical fuel-loading cavities are obtained continuously from microfluidics with the assistance of flow lithography. The structural parameters of the MNMs could be precisely tailored by simply choosing the flow speed or the shape of the photomask. As the actives are mixed into the phase solution during the generation, the resultant MNMs are loaded with cargoes for direct applications without any extra complex operation. Based on these features, it is demonstrated that with sharp tips and autonomous movement, the MNMs can efficiently penetrate the tissue-like substrates, indicating the potential in overcoming physiological barriers for cargo release. These results indicate that the proposed multimodal microfluidic lithographic MNMs are valuable for practical active cargo delivery in biomedical and other relative areas.

A perspective on plant robotics: from bioinspiration to hybrid systems

As miscellaneous as the Plant Kingdom is, correspondingly diverse are the opportunities for taking inspiration from plants for innovations in science and engineering. Especially in robotics, properties like growth, adaptation to environments, ingenious materials, sustainability, and energy-effectiveness of plants provide an extremely rich source of inspiration to develop new technologies-and many of them are still in the beginning of being discovered. In the last decade, researchers have begun to reproduce complex plant functions leading to functionality that goes far beyond conventional robotics and this includes sustainability, resource saving, and eco-friendliness. This perspective drawn by specialists in different related disciplines provides a snapshot from the last decade of research in the field and draws conclusions on the current challenges, unanswered questions on plant functions, plant-inspired robots, bioinspired materials, and plant-hybrid systems looking ahead to the future of these research fields.