Printable Smart Materials and Devices: Strategies and Applications

Fast and Sensitive Detection of Protein Markers Using an All-Printing Photonic Crystal Microarray via Fingertip Blood

With the demand for point-of-care testing (POCT) in cardiovascular diseases, the detection of biomarkers in trace blood samples is of great significance in emergency medicine settings. Here, we demonstrated an all-printed photonic crystal microarray for POCT of protein markers (named "P4 microarray"). The paired nanobodies were printed as probes to target the soluble suppression of tumorigenicity 2 (sST2) as a certified cardiovascular protein marker. Benefiting from photonic crystal-enhanced fluorescence and integrated microarrays, quantitative detection of sST2 is 2 orders of magnitude lower than that of a traditional fluorescent immunoassay. The limit of detection is down to 10 pg/mL with the coefficient of variation being less than 8%. Detection of sST2 via fingertip blood is achieved in 10 min. Moreover, the P4 microarray after 180 days of storage at room temperature showed excellent stability for detection. This P4 microarray, as a convenient and reliable immunoassay for rapid and quantitative detection of protein markers in trace blood samples, has high sensitivity and strong storage stability, which hold great potential to advance cardiovascular precision medicine.

Overflow Control for Sustainable Development by Superwetting Surface with Biomimetic Structure

Liquid flowing around a solid edge, i.e., overflow, is a commonly observed flow behavior. Recent research into surface wetting properties and microstructure-controlled overflow behavior has attracted much attention. Achieving controllable macroscale liquid dynamics by manipulating the micro-nanoscale liquid overflow has stimulated diverse scientific interest and fostered widespread use in practical applications. In this review, we outline the evolution of overflow and present a critical survey of the mechanism of surface wetting properties and microstructure-controlled liquid overflow in multilength scales ranging from centimeter to micro and even nanoscale. We summarize the latest progress in utilizing the mechanisms to manipulate liquid overflow and achieve macroscale liquid dynamics and in emerging applications to manipulate overflow for sustainable development in various fields, along with challenges and perspectives.

Intelligent Eucommia ulmoides Rubber/Ionomer Blends with Thermally Activated Shape Memory and Self-Healing Properties

Intelligent Eucommia ulmoides rubber (EUR) and ionomer Surlyn resin (SR) blends were prepared and studied in this manuscript. This is the first paper to combine EUR with SR to prepare blends with both the shape memory effect and self-healing capability. The mechanical, curing, thermal, shape memory and self-healing properties were studied by a universal testing machine, differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), respectively. Experimental results showed that the increase in ionomer content not only improved mechanical and shape memory properties but also endowed the compounds with excellent self-healing ability under the appropriate environmental conditions. Notably, the self-healing efficiency of the composites reached 87.41%, which is much higher than the efficiency of other covalent cross-linking composites. Therefore, these novel shape memory and self-healing blends can expand the use of natural Eucommia ulmoides rubber, such as in special medical devices, sensors and actuators.

Sophisticated yet Convenient Information Encryption/Decryption Based on Synergistically Time-/Temperature-Resolved Photonic Inks

Exploring high-safety but convenient encryption and decryption technologies to combat threats of information leakage is urgently needed but remains a great challenge. Here, a synergistically time- and temperature-resolved information coding/decoding solution based on functional photonic inks is demonstrated. Encrypted messages can be stored into multiple channels with dynamic-color patterns, and information decryption is only enabled at appointed temperature and time points. Notably, the ink can be easily processed into quick-response codes and multipixel plates. With high transparency and responsive color variations controlled by ink compositions and ambient temperatures, advanced 3D stacking multichannel coding and Morse coding techniques can be applied for multi-information storage, complex anticounterfeiting, and information interference. This study paves an avenue for the design and development of dynamic photonic inks and complex encryption technologies for high-end anticounterfeiting applications.

Inkjet Printing of MnO2 Nanoflowers on Surface-Modified A4 Paper for Flexible All-Solid-State Microsupercapacitors

Printing technologies are gaining growing attention as a sustainable route for the fabrication of high-performance and flexible power sources such as microsupercapacitors (MSCs). Here, the inkjet printing method is utilized for the fabrication of manganese dioxide (MnO₂)-based, flexible all-solid-state MSCs on surface-modified A4 paper substrate. The appropriate rheology of the formulated ethanol-based ink (Fromm number <10) and the proper dimensions of MnO₂ nanoflowers (average size ∼600 nm) ensure a reliable inkjet printing process. Moreover, the underlying graphene/Ag nanowire pattern serves as a primer and highly conductive (R_s < 2 Ω sq^-1) layer on top of the paper to facilitate the anchoring of MnO₂ nanoflowers and rapid electron transportation. The resulting all-solid-state MSCs deliver a maximum areal capacitance of 0.68 mF cm^-2 at a current density of 25 μA cm^-2, reasonable durability (>80% of capacity remained after 3000 cycles), and remarkable foldability. Additionally, the inkjet-printed MSC devices deliver a superior areal energy density of 0.01 μWh cm^-2 and also a power density of 1.19 μW cm^-2. This study demonstrates the power of the inkjet printing method to produce MSCs on flexible substrates, which have great potential for flexible/wearable electronics.

A Ferroelectric Aminophosphonium Cyanoferrate with a Large Electrostrictive Coefficient as a Piezoelectric Nanogenerator

Hybrid materials possessing piezo- and ferroelectric properties emerge as excellent alternatives to conventional piezoceramics due to their merits of facile synthesis, lightweight nature, ease of fabrication and mechanical flexibility. Inspired by the structural stability of aminophosphonium compounds, here we report the first A₃ BX₆ type cyanometallate [Ph₂ (ⁱ PrNH)₂ P]₃ [Fe(CN)₆ ] (1), which shows a ferroelectric saturation polarization (P_s ) of 3.71 μC cm^-2 . Compound 1 exhibits a high electrostrictive coefficient (Q₃₃ ) of 0.73 m⁴  C^-2 , far exceeding those of piezoceramics (0.034-0.096 m⁴  C^-2 ). Piezoresponse force microscopy (PFM) analysis demonstrates the polarization switching and domain structure of 1 further confirming its ferroelectric nature. Furthermore, thermoplastic polyurethane (TPU) polymer composite films of 1 were prepared and employed as piezoelectric nanogenerators. Notably, the 15 wt % 1-TPU device gave a maximum output voltage of 13.57 V and a power density of 6.03 μW cm^-2 .

Recent Advances in Printable Flexible Optical Devices: From Printing Technology and Optimization Strategies to Perspectives

Recently, flexible optical devices have triggered booming developments in various research fields, including display equipment, sensors, energy conversion, and so on, due to their high compatibility, portability, and wearability. With the advantages of strong design ability, high precision, and high integration, printing technologies have been recognized as promising methods to realize flexible optical devices. In this Perspective, recent progress on printing strategies for fabricating flexible optical devices are introduced systematically. First, through adjusting the composition of inks, selecting flexible substrates, and controlling external stimulation, fabrication of flexible optical devices based on inkjet printing is illustrated. Then, flexible optical devices fabricated by template-induced printing, 3D printing, slot-die printing, and screen printing are summarized. Finally, prospects and future development directions based on printing technology for flexible optical devices are proposed.

Environmentally Stable, Stretchable, Adhesive, and Conductive Organohydrogels with Multiple Dynamic Interactions as High-Performance Strain and Temperature Sensors

Nowadays, with the rapid development of artificial intelligence, conductive hydrogel-based sensors play an increasingly vital role in health monitoring and temperature sensing. However, the perfect integration of the environmental stability and applied performance of the hydrogel has always been a challenging and significant problem. Herein, we report an environmentally tolerant, stretchable, adhesive, self-healing conductive gel through multiple dynamic interactions in the water/glycerol/ionic liquids medium, which can be used as a high-performance strain and temperature sensor. The random copolymer poly(acrylic acid-co-acetoacetoxyethyl methacrylate) interacts with the branched poly(ethylene imine) (PEI) and Zr⁴⁺ ions via the dynamic covalent enamine bonds, coordinations, and electrostatic interactions to improve stretchable (1300%), compressible, fatigue-resistant (1000 cycles at 50% strain), and self-healing performance (95%, 24 h). The combination of water/glycerol/ionic liquids imparts the resulting gel with excellent electrical conductivity, anti-drying, and anti-freezing performance. By means of the above excellent performance, the gel could be used as the flexible strain or pressure sensor with high sensitivity and stability for the detection of the movement, expression, handwriting, pronouncing, and electrocardiogram (ECG) signals in various models. Meanwhile, the resulting gel can be assembled as the temperature sensor to trace the change of temperature accurately and steadily, which has a wide operating window (0 to 100 °C), an ultralow detection limit (0.2 °C), and high sensitivity (2.1% °C^-1). It is believed that the strategy for the multifunction and high-performance gel will blaze a new trail for the smart device in health management, temperature detection, and information transmission under various environmental conditions.

Fascinating Electrical Transport Behavior of Topological Insulator Bi2 Te3 Nanorods: Toward Electrically Responsive Smart Materials

Electrical conductivity and dielectric parameters are general inherent features of materials. Controlling these characteristics through applied bias will add a new dimension to regulate the dynamic response of smart materials. Here, a fascinating electrical transport behavior is observed in topological insulator (TI) Bi₂ Te₃ nanorods, which will play a vital role in intelligent materials or devices as a unit for information reception, processing or feedback. The Bi₂ Te₃ nanorod aggregates exhibit a monotonic resistance response to voltage, with observed four-fold change of electrical conductivity in a small range electric field of 1 V mm^-1 . The dielectric constant and dielectric loss of Bi₂ Te₃ nanorod composites also show strong dependences on bias voltage due to the unique electrical transport characteristics. The unique voltage-controlled electrical responses are attributed to the change of Fermi levels within the band structure of disordered TI nanorods, which are non-parallel to the applied electric field. The excellent controllable inherent characteristics through electric field endows Bi₂ Te₃ nanomaterials bright prospects for applications in smart devices and resistive random access memories.

Copper inks for printed electronics: a review

Conductive inks have attracted tremendous attention owing to their adaptability and the convenient large-scale fabrication. As a new type of conductive ink, copper-based ink is considered to be one of the best candidate materials for the conductive layer in flexible printed electronics owing to its high conductivity and low price, and suitability for large-scale manufacturing processes. Recently, tremendous progress has been made in the preparation of cooper-based inks for electronic applications, but the antioxidation ability of copper-based nanomaterials within inks or films, that is, long-term reliability upon exposure to water and oxygen, still needs more exploration. In this review, we present a comprehensive overview of copper inks for printed electronics from ink preparation, printing methods and sintering, to antioxidation strategies and electronic applications. The review begins with an overview of the development of copper inks, followed by a demonstration of various preparation methods for copper inks. Then, the diverse printing techniques and post-annealing strategies used to fabricate conductive copper patterns are discussed. In addition, antioxidation strategies utilized to stabilize the mechanical and electrical properties of copper nanomaterials are summarized. Then the diverse applications of copper inks for electronic devices, such as transparent conductive electrodes, sensors, optoelectronic devices, and thin-film transistors, are discussed. Finally, the future development of copper-based inks and the challenges of their application in printed electronics are discussed.

Lateral Heterostructured Vis-NIR Photodetectors with Multimodal Detection for Rapid and Precise Classification of Glioma

Precise diagnosis of the boundary and grade of tumors is especially important for surgical dissection. Recently, visible and near-infrared (Vis-NIR) absorption differences of tumors are demonstrated for a precise tumor diagnosis. Here, a template-assisted sequential printing strategy is investigated to construct lateral heterostructured Vis-NIR photodetectors, relying on the up-conversion nanoparticles (UCNPs)/perovskite arrays. Under the sequential printing process, the synergistic effect and co-confinement are demonstrated to induce the UCNPs to cover both sides of the perovskite microwire. The side-wrapped lateral heterogeneous UCNPs/perovskite structure exhibits more satisfactory responsiveness to Vis-NIR light than the common fully wrapped structure, due to sufficient visible-light-harvesting ability. The Vis-NIR photodetectors with R reaching 150 mA W^-1 at 980 nm and 1084 A W^-1 at 450 nm are employed for the rapid classification of glioma. The detection accuracy rate of 99.3% is achieved through a multimodal analysis covering the Vis-NIR light, which provides a reliable basis for glioma grade diagnosis. This work provides a concrete example for the application of photodetectors in tumor detection and surgical diagnosis.

Printing nanoparticle-based isotropic/anisotropic networks for directional electrical circuits

With the demand for integrated nanodevices, anisotropic conductive films are one type of interconnection structure for electronic components, which have been widely used for improving the integration of the system in printed circuit boards. This work presents a template-assisted printing strategy for the fabrication of nanoparticle-based networks with multi electrical properties. By manipulating the microfluid behavior under the guidance of the grid-shaped template, the continuity of liquid bridges can be precisely controlled in two directions. The isotropous circuits with crossbar paths, discrete paths as well as unidirectional paths are obtained, which achieve the switching of on/off states in the circuits. This work demonstrates a new type of directional circuits by the template-assisted printing method, which provides an effective fabrication strategy for electrical components and integrated systems.

Emerging Electrochromic Materials and Devices for Future Displays

With the rapid development of optoelectronic fields, electrochromic (EC) materials and devices have received remarkable attention and have shown attractive potential for use in emerging wearable and portable electronics, electronic papers/billboards, see-through displays, and other new-generation displays, due to the advantages of low power consumption, easy viewing, flexibility, stretchability, etc. Despite continuous progress in related fields, determining how to make electrochromics truly meet the requirements of mature displays (e.g., ideal overall performance) has been a long-term problem. Therefore, the commercialization of relevant high-quality products is still in its infancy. In this review, we will focus on the progress in emerging EC materials and devices for potential displays, including two mainstream EC display prototypes (segmented displays and pixel displays) and their commercial applications. Among these topics, the related materials/devices, EC performance, construction approaches, and processing techniques are comprehensively disscussed and reviewed. We also outline the current barriers with possible solutions and discuss the future of this field.

All-printed point-of-care immunosensing biochip for one drop blood diagnostics

Designing and preparing a fast and easy-to-use immunosensing biochip are of great significance for clinical diagnosis and biomedical research. In particular, sensitive, specific, and early detection of biomarkers in trace samples promotes the application of point-of-care testing (POCT). Here, we demonstrate an all-printed immunosensing biochip with the characteristics of hydrodynamic enrichment and photonic crystal-enhanced fluorescence. Direct quantitative detection of cardiac biomarkers via one drop of blood is achieved in 10 min. After simulating the hydrodynamic behavior of one droplet serum on the printed assay, creatine kinase-MB (CK-MB) has been recognized and located on the photonic crystal arrays. Benefiting from the fluorescence enhancement effect, quantitative detection of CK-MB has been demonstrated from 0.01 ng ml^-1 to 100 ng ml^-1, which is superior to the conventional enzyme-linked immunosorbent assay (ELISA). This strategy provides a general and easy-to-use approach for fast quantitative detection of biomarkers, which would be improved further for portable clinical diagnostics and home medical monitoring.

Tunable Capacitive Behavior in Metallopolymer-based Electrochromic Thin Film Supercapacitors

Volumetric capacitance is a more critical performance parameter for rechargeable power supply in lightweight and microelectronic devices as compared to gravimetric capacitance in larger devices. To this end, we report three electrochromic metallopolymer-based electrode materials containing Fe²⁺ as the coordinating metal ion with high volumetric capacitance and energy densities in a symmetric two-electrode supercapacitor setup. These metallopolymers exhibited volumetric capacitance up to 866.2 F cm^-3 at a constant current density of 0.25 A g^-1. The volumetric capacitance (poly-Fe-L2: 544.6 F cm^-3 > poly-Fe-L1: 313.8 F cm^-3 > poly-Fe-L3: 230.8 F cm^-3 at 1 A g^-1) and energy densities (poly-Fe-L2: 75.5 mWh cm^-3 > poly-Fe-L1: 43.6 mWh cm^-3 > poly-Fe-L3: 31.2 mWh cm^-3) followed the order of the electrical conductivity of the metallopolymers and are among the best values reported for metal-organic systems. The variation in the ligand structure was key toward achieving different electrical conductivities in these metallopolymers with excellent operational stability under continuous cycling. High volumetric capacitances and energy densities combined with tunable electro-optical properties and electrochromic behavior of these metallopolymers are expected to contribute to high performance and compact microenergy storage systems. We envision that the integration of smart functionalities with thin film supercapacitors would warrant the surge of miniaturized on-chip microsupercapacitors integrated in-plane with other microelectronic devices for wearable applications.

Toward High Sensitivity: Perspective on Colorimetric Photonic Crystal Sensors

The sensitivity of colorimetric photonic crystal (PC) sensors have been significantly improved with the advancement of deformable structural color materials, structures design, sensing signal analysis methods, and fabrication strategies. In this perspective, the strategies toward high-sensitivity colorimetric PC sensors are discussed, from the perspectives of molecular design, single sensor construction, and multisensor assembly, which include incorporation of flexible polymer chains, construction of strong sensor-analyte interactions, incorporation of more soft materials, construction of stimuli-angle/orientation relationship, design of colorimetric sensors in series, and assembly of colorimetric PC sensors in parallel. Based on these strategies, progress of high-sensitivity colorimetric PC sensors in recent years is summarized, in terms of mechano-sensors and chemo-/biosensors. Specifically, PC based optical-electrical dual-signal sensing devices are included. Finally, the future development and challenges of high-sensitivity colorimetric PC sensors are presented, in regards to deformable properties, optical properties, analysis methods, and fabrication strategies.

Fully Inkjet-Printed Chemiresistive Sensor Array Based on Molecularly Imprinted Sol-Gel Active Materials

The fabrication of chemiresistive sensors by inkjet printing is recognized as a breakthrough in gas-sensing applications. One challenge of this technology, however, is how to enhance the cross-selectivity of the sensor array. Herein, we present a ketjen black (KB) ink and molecularly imprinted sol-gel (MISG) inks to support the fabrication of a fully inkjet-printed chemiresistive sensor array, enabling the highly accurate recognition of volatile organic acids (VOAs) on the molecular level. The MISG/KB sensor array was prepared on a glossy photographic paper with a three-layer structure: a circuit layer by a commercial silver ink, a conductive layer by a KB ink, and an active selective layer by MISG inks imprinted by different templates. Hexanoic acid (HA), heptanoic acid, and octanoic acid were used as templates to prepare the MISGs and as targets to evaluate the detection and discrimination performance of the sensor array. Three resultant MISG/KB sensors exhibited high sensitivity and selectivity to VOA vapors. The limit of detection and imprinting factor were 0.018 ppm and 7.82, respectively, for HA-MISG/KB sensors to the corresponding target. With linear discriminant analysis of the gas responses, the MISG/KB sensor array can realize high discrimination to VOAs in single and binary mixtures. Furthermore, the proposed sensor array showed strong sensor robustness with excellent consistency, durability, bending, and humidity resistance. This work developed a fully inkjet-printed chemiresistive sensor array, enabling the realization of high cross-selectivity detection, achieving low-cost, scalable, and highly reproducible sensor fabrication, moving it closer to reliable, commercial, and wearable multi-analyte human body odor analysis potential.

Polymer-Tethered Nanoparticles: From Surface Engineering to Directional Self-Assembly

ConspectusCurrent interest in nanoparticle ensembles is motivated by their collective synergetic properties that are distinct from or better than those of individual nanoparticles and their bulk counterparts. These new advanced optical, electronic, magnetic, and catalytic properties can find applications in advanced nanomaterials and functional devices, if control is achieved over nanoparticle organization. Self-assembly offers a cost-efficient approach to produce ensembles of nanoparticles with well-defined and predictable structures. Nanoparticles functionalized with polymer molecules are promising building blocks for self-assembled nanostructures, due to the comparable dimensions of macromolecules and nanoparticles, the ability to synthesize polymers with various compositions, degrees of polymerization, and structures, and the ability of polymers to self-assemble in their own right. Moreover, polymer ligands can endow additional functionalities to nanoparticle assemblies, thus broadening the range of their applications.In this Account, we describe recent progress of our research groups in the development of new strategies for the self-assembly of nanoparticles tethered to macromolecules. At the beginning of our journey, we developed a new approach to patchy nanoparticles and their self-assembly. In a thermodynamically driven strategy, we used poor solvency conditions to induce homopolymer surface segregation in pinned micelles (patches). Patchy nanoparticles underwent self-assembly in a well-defined and controlled manner. Following this work, we overcame the limitation of low yield of the generation of patchy nanoparticles, by using block copolymer ligands. For block copolymer-capped nanoparticles, patch formation and self-assembly were "staged" by using distinct stimuli for each process. We expanded this work to the generation of patchy nanoparticles via dynamic exchange of block copolymer molecules between the nanoparticle surface and micelles in the solution. The scope of our work was further extended to a series of strategies that utilized the change in the configuration of block copolymer ligands during nanoparticle interactions. To this end, we explored the amphiphilicity of block copolymer-tethered nanoparticles and complementary interactions between reactive block copolymer ligands. Both approaches enabled exquisite control over directional and self-limiting self-assembly of complex hierarchical nanostructures. Next, we focused on the self-assembly of chiral nanostructures. To enable this goal, we attached chiral molecules to the surface of nanoparticles and organized these hybrid building blocks in ensembles with excellent chiroptical properties. In summary, our work enables surface engineering of polymer-capped nanoparticles and their controllable and predictable self-assembly. Future research in the field of nanoparticle self-assembly will include the development of effective characterization techniques, the synthesis of new functional polymers, and the development of environmentally responsive self-assembly of polymer-capped nanoparticles for the fabrication of nanomaterials with tailored functionalities.

Near-Infrared Responsive Droplet for Digital PCR

Digital PCR (dPCR) surpasses the performance of earlier PCR formats because of highly precise, absolute quantification and other unique merits. A simple thermocycling approach and durable microcarrier are of great value for dPCR advancement and application. Herein, a near-infrared (NIR) controlled thermocycling approach by embedding magnetic graphene oxide (GO) composite into the agarose microcarriers is developed. The core-shell composite is constructed by sequentially encapsulating GO and silica outside the magnetic nanocores. Benefiting from these additives, the resultant composite agarose gains appealing features as light-driven temperature changing, switchable gel-sol phase transforming, biocompatibility, and magnetic traction. By further emulsifying into droplets via the microfluidics method, the influence of typical parameters including material loading amount, laser intensity, and droplet diameter at various ranges is investigated for assembling microcarriers with different responsiveness. Then a paradigm of the NIR program can be easily tailored for PCR thermocycling. Finally, the feasibility of the approach is verified by detecting statistically diluted Klebsiella pneumoniae DNA samples, from 0.1 to 2 copies per drop. It is anticipated that this method has promising prospects for dPCR-based and other temperature-controlled applications.

Material Design for Enhancing Properties of 3D Printed Polymer Composites for Target Applications

Polymer composites are becoming an important class of materials for a diversified range of industrial applications due to their unique characteristics and natural and synthetic reinforcements. Traditional methods of polymer composite fabrication require machining, manual labor, and increased costs. Therefore, 3D printing technologies have come to the forefront of scientific, industrial, and public attention for customized manufacturing of composite parts having a high degree of control over design, processing parameters, and time. However, poor interfacial adhesion between 3D printed layers can lead to material failure, and therefore, researchers are trying to improve material functionality and extend material lifetime with the addition of reinforcements and self-healing capability. This review provides insights on different materials used for 3D printing of polymer composites to enhance mechanical properties and improve service life of polymer materials. Moreover, 3D printing of flexible energy-storage devices (FESD), including batteries, supercapacitors, and soft robotics using soft materials (polymers), is discussed as well as the application of 3D printing as a platform for bioengineering and earth science applications by using a variety of polymer materials, all of which have great potential for improving future conditions for humanity and planet Earth.