Abstract
Tuning metal–support interaction has been considered as an effective approach to modulate the electronic structure and catalytic activity of supported metal catalysts. At the atomic level, ...the understanding of the structure–activity relationship still remains obscure in heterogeneous catalysis, such as the conversion of water (alkaline) or hydronium ions (acid) to hydrogen (hydrogen evolution reaction, HER). Here, we reveal that the fine control over the oxidation states of single-atom Pt catalysts through electronic metal–support interaction significantly modulates the catalytic activities in either acidic or alkaline HER. Combined with detailed spectroscopic and electrochemical characterizations, the structure–activity relationship is established by correlating the acidic/alkaline HER activity with the average oxidation state of single-atom Pt and the Pt–H/Pt–OH interaction. This study sheds light on the atomic-level mechanistic understanding of acidic and alkaline HER, and further provides guidelines for the rational design of high-performance single-atom catalysts.
Oriented liquid crystal networks (LCNs) can undergo reversible shape change at the macroscopic scale upon an order–disorder phase transition of the mesogens. This property is explored for developing ...soft robots that can move under external stimuli, such as light in most studies. Herein, electrically driven soft robots capable of executing various types of biomimetic locomotion are reported. The soft robots are composed of a uniaxially oriented LCN strip, a laminated Kapton layer, and thin resistive wires embedded in between. Taking advantage of the combined attributes of the actuator, namely, easy processing, reprogrammability, and reversible shape shift between two 3D shapes at electric power on and off state, the concept of a “Janus” soft robot is demonstrated, which is built from a single piece of the material and has two parts undergoing opposite deformations simultaneously under a uniform stimulation. In addition to complex shape morphing such as the movement of oarfish and sophisticated devices like self‐locking grippers, electrically powered “Janus” soft robots can accomplish versatile locomotion modes, including crawling on flat surfaces through body arching up and straightening down, crawling inside tubes through body stretching and contraction, walking like four‐leg animals, and human‐like two‐leg walking while pushing a load forward.
Soft robots based on liquid crystal polymers are built to possess two parts capable of simultaneous and opposite deformations upon an order–disorder phase transition. This design enables various electrically powered locomotion modes, including moving on flat surface through body arching up–straightening down, crawling in a tunnel‐like tube through body stretching–contraction, four‐leg walking, and two‐leg walking while pushing a load.
The ability to optically reconfigure an existing actuator of a liquid crystal polymer network (LCN) so that it can display a new actuation behavior or function is highly desired in developing ...materials for soft robotics applications. Demonstrated here is a powerful approach relying on selective polymer chain decrosslinking in a LCN actuator with uniaxial LC alignment. Using an anthracene‐containing LCN, spatially controlled optical decrosslinking can be realized through photocleavage of anthracene dimers under 254 nm UV light, which alters the distribution of actuation (crosslinked) and non‐actuation (decrosslinked) domains and thus determines the actuation behavior upon order‐disorder phase transitions. Based on this mechanism, a single actuator having a flat shape can be reconfigured in an on‐demand manner to exhibit reversible shape transformation such as self‐folding into origami three‐dimensional structures. Moreover, using a dye‐doped LCN actuator, a light‐fueled microwalker can be optically reconfigured to adopt different locomotion behaviors, changing from moving in the laser scanning direction to moving in the opposite direction.
Walk along: Selective polymer chain decrosslinking in a liquid crystal polymer network (LCN) actuator is demonstrated. Spatially controlled optical decrosslinking alters the distribution of the actuation (crosslinked) and non‐actuation (decrosslinked) domains, and determines the actuation behavior upon the order–disorder phase transition. By using a dye‐doped LCN actuator, a light‐fueled microwalker can be optically reconfigured.
Novel main‐chain liquid crystalline Diels—Alder dynamic networks (LCDANs) were prepared that exhibit unprecedented ease for actuator programming and reprocessing compared to existing liquid ...crystalline network (LCN) systems. Following cooling from 125 °C, LCDANs are deformed with aligned mesogens self‐locked at room temperature by slowly formed Diels–Alder (DA) bonds, which allows for the formation of solid 3D actuators capable of reversible shape change, and strip walker and wheel‐capable light‐driven locomotion upon either thermally or optically induced order–disorder phase transition. Any actuator can readily be erased at 125 °C and reprogrammed into a new one under ambient conditions. Moreover, LCDANs can be processed directly from melt (for example, fiber drawing) and from solution (for example, casting tubular actuators), which cannot be achieved with LCNs using exchangeable covalent bonds. The combined attributes of LCDANs offer significant progress toward developing easily programmable/processable LCN actuators.
Liquid crystalline dynamic networks can be shaped into 3D objects at room temperature while being stabilized by slowly formed Diels–Alder‐bonded (DA) cross‐links. The actuators demonstrate thermally or optically induced reversible shape change for the purpose of performing mechanical work or locomotion.
Liquid crystalline network (LCN) actuator normally deforms upon thermally or optically induced order-disorder phase transition, switching once between two shapes (shape 1 in LC phase and shape 2 in ...isotropic state) for each stimulation on/off cycle. Herein, we report an LCN actuator that deforms from shape 1 to shape 2 and then reverses the deformation direction to form shape 3 on heating or under light only, thus completing the shape switch twice for one stimulation on/off cycle. The deformation reversal capability is obtained with a monolithic LCN actuator whose two sides are made to start deforming at different temperatures and exerting different reversible strains, by means of asymmetrical crosslinking and/or asymmetrical stretching. This desynchronized actuation strategy offers possibilities in developing light-fueled LCN soft robots. In particular, the multi-stage bidirectional shape change enables multimodal, light-driven locomotion from the same LCN actuator by simply varying the light on/off times.
Soft actuators based on liquid crystal polymer networks (LCNs) have emerged as an exciting research topic due to many envisioned applications in areas such as soft robotics and self‐regulating ...devices. The infatuation stems from the amazing ability of LCNs to display reversible, large amplitude, and complex shape change as well as locomotion upon a stimuli‐triggered phase transition of mesogens between ordered liquid crystal and disordered isotropic state. Among the various stimuli, light arguably is the most attractive choice. Light can easily be adjusted for its wavelength, intensity, or polarization, structured by means of photomasks or interference patterns, and applied to a target remotely and with high spatiotemporal resolution. Indeed, much research effort is dedicated to LCN actuators that are designed to respond to light in many ways, with light being used not only as an external energy source to drive the shape changes or motion of LCN actuators, but also as a versatile tool in their fabrication and reconfiguration. In this Review, recent achievements are highlighted, a number of important issues are discussed, and critical analysis on the use of light in making, reconfiguring, and driving LCN actuators is provided.
Light plays a key role in the development of soft actuators based on liquid crystal polymer networks (LCNs). In this Review, the use of light for their fabrication, reconfiguration, and motion driving is highlighted and analyzed, a number of challenging issues are discussed, and an outlook on the future development is presented.
Few-layer black phosphorus (BP), as the most alluring graphene analogue owing to its similar structure as graphene and thickness dependent direct band-gap, has now triggered a new wave of research on ...two-dimensional (2D) materials based photonics and optoelectronics. However, a major obstacle of practical applications for few-layer BPs comes from their instabilities of laser-induced optical damage. Herein, we demonstrate that, few-layer BPs, which was fabricated through the liquid exfoliation approach, can be developed as a new and practical saturable absorber (SA) by depositing few-layer BPs with microfiber. The saturable absorption property of few-layer BPs had been verified through an open-aperture z-scan measurement at the telecommunication band. The microfiber-based BP device had been found to show a saturable average power of ~4.5 mW and a modulation depth of 10.9%, which is further confirmed through a balanced twin detection measurement. By integrating this optical SA device into an erbium-doped fiber laser, it was found that it can deliver the mode-locked pulse with duration down to 940 fs with central wavelength tunable from 1532 nm to 1570 nm. The prevention of BP from oxidation through the "lateral interaction scheme" owing to this microfiber-based few-layer BP SA device might partially mitigate the optical damage problem of BP. Our results not only demonstrate that black phosphorus might be another promising SA material for ultrafast photonics, but also provide a practical solution to solve the optical damage problem of black phosphorus by assembling with waveguide structures such as microfiber.
Chemokines play a key role in orchestrating the recruitment and positioning of myeloid cells within the tumor microenvironment. However, the tropism regulation and functions of these cells in ...hepatocellular carcinoma (HCC) are not completely understood. Herein, by scrutinizing the expression of all chemokines in HCC cell lines and tissues, we found that CCL15 was the most abundantly expressed chemokine in human HCC. Further analyses showed that CCL15 expression was regulated by genetic, epigenetic, and microenvironmental factors, and negatively correlated with patient clinical outcome. In addition to promoting tumor invasion in an autocrine manner, CCL15 specifically recruited CCR1+ cells toward HCC invasive margin, approximately 80% of which were CD14+ monocytes. Clinically, a high density of marginal CCR1+CD14+ monocytes positively correlated with CCL15 expression and was an independent index for dismal survival. Functionally, these tumor‐educated monocytes directly accelerated tumor invasion and metastasis through bursting various pro‐tumor factors and activating signal transducer and activator of transcription 1/3, extracellular signal‐regulated kinase 1/2, and v‐akt murine thymoma viral oncogene homolog signaling in HCC cells. Meanwhile, tumor‐derived CCR1+CD14+ monocytes expressed significantly higher levels of programmed cell death‐ligand 1, B7‐H3, and T‐cell immunoglobulin domain and mucin domain‐3 that may lead to immune suppression. Transcriptome sequencing confirmed that tumor‐infiltrating CCR1+CD14+ monocytes were reprogrammed to upregulate immune checkpoints, immune tolerogenic metabolic enzymes (indoleamine and arginase), inflammatory/pro‐angiogenic cytokines, matrix remodeling proteases, and inflammatory chemokines. Orthotopic animal models confirmed that CCL15‐CCR1 axis forested an inflammatory microenvironment enriched with CCR1+ monocytes and led to increased metastatic potential of HCC cells. Conclusion: A complex tumor‐promoting inflammatory microenvironment was shaped by CCL15‐CCR1 axis in human HCC. Blockade of CCL15‐CCR1 axis in HCC could be an effective anticancer therapy.
Background
The contribution of B‐cell subsets and T‐B cell interaction to the pathogenesis of allergic rhinitis (AR) and mechanisms of allergen immunotherapy (AIT) remain poorly understood. This ...study aimed to outline circulating B‐cell signature, the underlying mechanism, and its association with clinical response to AIT in patients with AR.
Methods
IgD/CD27 and CD24/CD38 core gating systems were used to determine frequencies and phenotypes of B cells. Correlations between B cells, T cells, antigen‐specific IgE, and disease severity in AR patients were investigated. Switched memory B cells were co‐cultured with type 2 follicular helper T (Tfh2) cells and follicular regulatory T (Tfr) cells. Associations between B‐cell subsets and clinical benefits of AIT were analyzed.
Results
Frequencies and absolute numbers of circulating memory B cells were increased in AR patients. CD23 expression on CD19+CD20+CD27+IgD− switched memory B cells was significantly enhanced and positively correlated with antigen‐specific IgE levels, symptom scores, and Tfh2/Tfr cell ratio in AR patients. Compared with those from healthy controls, Tfh2 cells from AR patients had a greater capacity to induce CD23 expression on switched memory B cells via IL‐4, which was unable to be sufficiently suppressed by AR‐associated Tfr cells with defective IL‐10 expression. CD23 expression on switched memory B cells was downregulated after 12‐month AIT, which positively associated with disease remission in AR patients.
Conclusion
T‐B cell interaction, bridged by CD23 expression particularly on switched memory B cells, may be involved in the disease pathogenesis and mechanism of AIT in patients with AR.
Circulating memory B cells are increased in AR patients. The enhanced expression of CD23 on switched memory B cells correlates with antigen‐specific IgE levels, symptom scores, and allergen immunotherapy efficacy in AR patients. Tfh2 cells from AR patients have a greater capacity to induce CD23 expression on switched memory B cells via IL‐4, which is unable to be sufficiently suppressed by AR‐associated Tfr cells with defective IL‐10 expression.
Abbreviations: AIT, allergen immunotherapy; AR, allergic rhinitis; HC, healthy controls; NSM, nonswitched memory; SM, switched memory; Tfh2, type 2 follicular helper T cells; Tfr, follicular regulatory T cell.
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