Organic electrochemical transistors printed from degradable materials as disposable biochemical sensors

Transient electronics hold promise in reducing electronic waste, especially in applications that require only a limited lifetime. While various degradable electronic and physical sensing devices have been proposed, there is growing interest in the development of degradable biochemical sensors. In this work, we present the development of an organic electrochemical transistor (OECT) with degradable electrodes, printed on an eco- and bioresorbable substrate. The influence of the design and materials for the contacts, channel and gate of the transducer, namely poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) and carbon, is systematically evaluated for the development of OECT-based transient biosensors. The sensing capabilities of the electrochemical transistors are demonstrated with ionic solutions as well as for the enzyme-based detection of glucose. The disposable OECTs show comparable performance to their non-degradable counterparts. Their integration with highly conductive degradable and printable zinc tracks is studied for the realization of interconnects. These eco-friendly OECTs may find applications as disposable and sustainable biochemical sensors, and constitute a step towards bioresorbable biosensors.

MXene/graphene oxide nanocomposites for friction and wear reduction of rough steel surfaces

Development of solid lubricant materials that render reliable performance in ambient conditions, are amenable to industrial size and design complexities, and work on engineered surfaces is reported. These coatings are composed of Ti3C2Tx-Graphene Oxide blends, spray-coated onto bearing steel surfaces. The tribological assessment was carried out in ambient environmental conditions and high contact pressures in a ball-on-disc experimental set-up. The evaluation yielded that the use of Ti3C2Tx-Graphene-Oxide coatings led to substantial reduction in friction down to 0.065 (at 1 GPa contact pressure and 100 mm/s) in comparison to the uncoated of single-component-coated surfaces, surpassing the state-of-the-art. The coatings also provided excellent protection against wear loss of the substrate and counter-face. The results were explained based on the observations from Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and nanoindentation measurements. In operando formation of a dense, hard and stiff, dangling-bond-saturated tribolayer was observed to be the reason for the sustained lubricity even at high test loads and sliding speeds. This report presents the holistic exploration and correlation of structure-property-processing pertaining to the advancement of solid lubrication science.

Pure edge-contact devices on single-layer-CVD-graphene integrated into a single chip

We present a simple and cost-effective fabrication technique for on-chip integration of pure edge contact two-terminal (2T) and Graphene field effect transistor (GFET) devices with low contact resistance and nonlinear characteristics based on single-layer chemical-vapor-deposited (CVD) graphene. We use a smart print-based mask projection technique with a 10X magnification objective lens for maskless lithography followed by thermal evaporation of the contact material Cr-Pd-Au through three different angles (90° and ± 45°) using a customized inclined-angle sample-holder to control the angle during normal incidence evaporation for edge-contact to graphene. Our fabrication technique, graphene quality, and contact geometry enable pure metal contact to 2D single-layer graphene allowing electron transport through the 1D atomic edge of graphene. Our devices show some signatures of edge contact to graphene in terms of very low contact resistance of 23.5 Ω, the sheet resistance of 11.5 Ω, and sharp nonlinear voltage-current characteristics (VCC) which are highly sensitive to the bias voltage. This study may find application in future graphene-integrated chip-scale passive or active low-power electronic devices.

Deposition of ultra-thin coatings by a nature-inspired Spray-on-Screen technology

Nanometre-thick, ultrathin coatings applied over a large area are of paramount importance for various application fields such as biomedicine, space and automotive, organic electronics, memory devices, or energy storage devices. So far wet chemical deposition as a cost-effective, scalable, and versatile method can only be used for thicker deposits. Here the formation of uniform ultra-thin coatings with thicknesses below 15 nm using a nature-inspired, roll-to-roll compatible Spray-on-Screen (SoS) technology is reported. For this, the finite micro-droplet generation of Ultrasonic Spray Coating (USSC) is combined with the coating formation from a screen printing mesh. Hydrophobic micro-threads of the mesh, resembling the micro-hair on the legs of water striders, produce millidroplets from micro droplets, and when applying an external pressure to the mesh, dynamic wetting is enforced. The proposed technology is applicable for a wide variety of substrates and applications. It is shown by theory and experiment that ultra-thin coatings below 5 nm homogeneous over a large area can be deposited without the use of extended ink formulation or high substrate temperatures during or after deposition. This simple yet effective technique enables the deposition of ultra-thin films on any substrates, and is very promising to fabricate the organic, inorganic electronics devices and batteries cost effectively.

Rachith Kumar and coworkers report a bio-inspired coating technique able to deposit uniform films with thicknesses below 15 nm on various substrates. This method will not require the use of extended ink formulation or high substrate temperature as existing techniques do, potentially reducing the fabrication cost of future electronic devices and batteries.

A 3D printable alloy designed for extreme environments

Multiprincipal-element alloys are an enabling class of materials owing to their impressive mechanical and oxidation-resistant properties, especially in extreme environments1,2. Here we develop a new oxide-dispersion-strengthened NiCoCr-based alloy using a model-driven alloy design approach and laser-based additive manufacturing. This oxide-dispersion-strengthened alloy, called GRX-810, uses laser powder bed fusion to disperse nanoscale Y2O3 particles throughout the microstructure without the use of resource-intensive processing steps such as mechanical or in situ alloying3,4. We show the successful incorporation and dispersion of nanoscale oxides throughout the GRX-810 build volume via high-resolution characterization of its microstructure. The mechanical results of GRX-810 show a twofold improvement in strength, over 1,000-fold better creep performance and twofold improvement in oxidation resistance compared with the traditional polycrystalline wrought Ni-based alloys used extensively in additive manufacturing at 1,093 °C5,6. The success of this alloy highlights how model-driven alloy designs can provide superior compositions using far fewer resources compared with the 'trial-and-error' methods of the past. These results showcase how future alloy development that leverages dispersion strengthening combined with additive manufacturing processing can accelerate the discovery of revolutionary materials.

Twin-pulse seeding enables pump-probe capabilities in the EUV to soft X-ray spectrum at synchrotron light sources

Having previously reported that separating the two stages of echo-enabled harmonic generation (EEHG) with one or more bending magnet (BM) sections allows the BMs to serve as the desired source of momentum compaction, here we demonstrate that this arrangement can greatly reduce the total energy modulation required by any 4th generation synchrotron light source, leading to higher repetition rates as well as stronger coherent radiation output power, with significant benefits. Since the EEHG beamline performance is mainly determined by the momentum compaction, beam emittances and beta functions of a storage ring lattice, allowing for different separations between the two stages is a straightforward way to increase the momentum compaction of chicane 1. This also enables pump-probe capabilities in a novel context, where twin-pulse seeding on the same electron bunch would allow two distinct radiation pulses with an adjustable delay in the range of 0.1 to 10 ps. In the twin-pulse seeding scheme, the same electron bunch could undergo modulation from two distinct laser pulses. Later stages would produce independent harmonics in subsequent straight sections. There are two variations of this twin-pulse seeding scheme, supporting different scientific applications. With a common modulation in stage 1, the first option allows simultaneously two independent radiation sources, with a full coverage of the EUV (2.5 to 50 nm) to soft X-ray (1.25 to 2.5 nm) spectrum; for the second option, the same stage 2 undulator could generate two coherent pulses both fitting within the FEL bandwidth, or at distinct harmonics. We present particle tracking simulation studies based on the APS-U lattice, including quantum excitation and radiation damping. These simulations indicate that there is no degradation of the modulated longitudinal phase space even when the two stages are separated by as many as 10 BM sections.

AlphaFlow: autonomous discovery and optimization of multi-step chemistry using a self-driven fluidic lab guided by reinforcement learning

Closed-loop, autonomous experimentation enables accelerated and material-efficient exploration of large reaction spaces without the need for user intervention. However, autonomous exploration of advanced materials with complex, multi-step processes and data sparse environments remains a challenge. In this work, we present AlphaFlow, a self-driven fluidic lab capable of autonomous discovery of complex multi-step chemistries. AlphaFlow uses reinforcement learning integrated with a modular microdroplet reactor capable of performing reaction steps with variable sequence, phase separation, washing, and continuous in-situ spectral monitoring. To demonstrate the power of reinforcement learning toward high dimensionality multi-step chemistries, we use AlphaFlow to discover and optimize synthetic routes for shell-growth of core-shell semiconductor nanoparticles, inspired by colloidal atomic layer deposition (cALD). Without prior knowledge of conventional cALD parameters, AlphaFlow successfully identified and optimized a novel multi-step reaction route, with up to 40 parameters, that outperformed conventional sequences. Through this work, we demonstrate the capabilities of closed-loop, reinforcement learning-guided systems in exploring and solving challenges in multi-step nanoparticle syntheses, while relying solely on in-house generated data from a miniaturized microfluidic platform. Further application of AlphaFlow in multi-step chemistries beyond cALD can lead to accelerated fundamental knowledge generation as well as synthetic route discoveries and optimization.

PEPI Lab: a flexible compact multi-modal setup for X-ray phase-contrast and spectral imaging

This paper presents a new flexible compact multi-modal imaging setup referred to as PEPI (Photon-counting Edge-illumination Phase-contrast imaging) Lab, which is based on the edge-illumination (EI) technique and a chromatic detector. The system enables both X-ray phase-contrast (XPCI) and spectral (XSI) imaging of samples on the centimeter scale. This work conceptually follows all the stages in its realization, from the design to the first imaging results. The setup can be operated in four different modes, i.e. photon-counting/conventional, spectral, double-mask EI, and single-mask EI, whereby the switch to any modality is fast, software controlled, and does not require any hardware modification or lengthy re-alignment procedures. The system specifications, ranging from the X-ray tube features to the mask material and aspect ratio, have been quantitatively studied and optimized through a dedicated Geant4 simulation platform, guiding the choice of the instrumentation. The realization of the imaging setup, both in terms of hardware and control software, is detailed and discussed with a focus on practical/experimental aspects. Flexibility and compactness (66 cm source-to-detector distance in EI) are ensured by dedicated motion stages, whereas spectral capabilities are enabled by the Pixirad-1/Pixie-III detector in combination with a tungsten anode X-ray source operating in the range 40-100 kVp. The stability of the system, when operated in EI, has been verified, and drifts leading to mask misalignment of less than 1 [Formula: see text]m have been measured over a period of 54 h. The first imaging results, one for each modality, demonstrate that the system fulfills its design requirements. Specifically, XSI tomographic images of an iodine-based phantom demonstrate the system's quantitativeness and sensibility to concentrations in the order of a few mg/ml. Planar XPCI images of a carpenter bee specimen, both in single and double-mask modes, demonstrate that refraction sensitivity (below 0.6 [Formula: see text]rad in double-mask mode) is comparable with other XPCI systems based on microfocus sources. Phase CT capabilities have also been tested on a dedicated plastic phantom, where the phase channel yielded a 15-fold higher signal-to-noise ratio with respect to attenuation.

Investigation of temperature variations on a Class-E inverter and proposing a compensation circuit to prevent harmful effects on biomedical implants

In this paper, a Class-E inverter and a thermal compensation circuit for wireless power transmission in biomedical implants are designed, simulated, and fabricated. In the analysis of the Class-E inverter, the voltage-dependent non-linearities of C_ds, C_gd, and R_ON as well as temperature-dependent non-linearity of R_ON of the transistor are considered simultaneously. Close agreement of theoretical, simulated and experimental results confirmed the validity of the proposed approach in taking into account these nonlinear effects. The paper investigated the effect of temperature variations on the characteristics of the inverter. Since both the output power and efficiency decrease with increasing temperature, a compensation circuit is proposed to keep them constant within a wide temperature range to enable its application as a reliable power source for medical implants in harsh environments. Simulations were performed and the results confirmed that the compensator enables significant improvements by maintaining the power and efficiency almost constant (8.46 ± 0.14 W and 90.4 ± 0.2%) within the temperature range of - 60 to 100 °C. Measurements performed at 25 °C and 80 °C with and without the compensation circuit were in good agreement with the theoretical and simulation results. The obtained measured output power and efficiency at 25 °C are equal to 7.42 W and 89.9%.

Robust flexural performance and fracture behavior of TiO2 decorated densified bamboo as sustainable structural materials

High-performance, fast-growing natural materials with sustainable and functional features currently arouse significant attention. Here, facile processing, involving delignification, in situ hydrothermal synthesis of TiO₂ and pressure densification, is employed to transform natural bamboo into a high-performance structural material. The resulting TiO₂-decorated densified bamboo exhibits high flexural strength and elastic stiffness, with both properties more than double that of natural bamboo. Real-time acoustic emission reveals the key role of the TiO₂ nanoparticles in enhancing the flexural properties. The introduction of nanoscale TiO₂ is found to markedly increase the degree of oxidation and the formation of hydrogen bonds in bamboo materials, leading to extensive interfacial failure between the microfibers, a micro-fibrillation process that results in substantial energy consumption and high fracture resistance. This work furthers the strategy of the synthetic reinforcement of fast-growing natural materials, which could lead to the expanded applications of sustainable materials for high-performance structural applications.

Mechanical metamaterials made of freestanding quasi-BCC nanolattices of gold and copper with ultra-high energy absorption capacity

Nanolattices exhibit attractive mechanical properties such as high strength, high specific strength, and high energy absorption. However, at present, such materials cannot achieve effective fusion of the above properties and scalable production, which hinders their applications in energy conversion and other fields. Herein, we report gold and copper quasi-body centered cubic (quasi-BCC) nanolattices with the diameter of the nanobeams as small as 34 nm. We show that the compressive yield strengths of quasi-BCC nanolattices even exceed those of their bulk counterparts, despite their relative densities below 0.5. Simultaneously, these quasi-BCC nanolattices exhibit ultrahigh energy absorption capacities, i.e., 100 ± 6 MJ m^-3 for gold quasi-BCC nanolattice and 110 ± 10 MJ m^-3 for copper quasi-BCC nanolattice. Finite element simulations and theoretical calculations reveal that the deformation of quasi-BCC nanolattice is dominated by nanobeam bending. And the anomalous energy absorption capacities substantially stem from the synergy of the naturally high mechanical strength and plasticity of metals, the size reduction-induced mechanical enhancement, and the quasi-BCC nanolattice architecture. Since the sample size can be scaled up to macroscale at high efficiency and affordable cost, the quasi-BCC nanolattices with ultrahigh energy absorption capacity reported in this work may find great potentials in heat transfer, electric conduction, catalysis applications.

A facile novel synthesis of AgCuO2 delafossite nanoparticles and evaluation of their antimicrobial activity

Bi-functional nano-oxides are of growing interest to address environmental issues. In the present study, the structural and magnetic data are presented together with the antimicrobial activities (AMA). For the first time, silver delafossite oxide (AgCuO₂) is successfully fabricated using a simple, low-cost technique to target antibiotic photodegradation and inactivation of model waterborne pathogens. It is prepared with an equimolar initial Ag⁺:Cu⁺ concentration ratio. The structure, morphology, and magnetic properties are studied by different characterization techniques. The size and shape of AgCuO₂ NPs, in addition to their structural polytypes of 2H (hexagonal) or 3R (rhombohedral), are dependent on the preparation conditions. The existence of Cu, Ag, and O in the synthesized delafossite AgCuO₂ NPs with no evidence of any impurity is ratified by the XPS spectrum. AFM measurements are taken to characterize the surface morphologies of AgCuO₂. The distributed spiks are evaluated by roughness kurtosis (Rku). The roughness kurtosis has a value of 2.65 (< 3), indicating that the prepared sample is classified as bumpy. The prepared sample has 13.0, 10.0, 14.0, and 14.0 mm Inhibition Zone Diameter (IZD) antimicrobial activity against gram-positive Bacillus subtilis (B. subtilis), Bacillus cereus (B. cereus), Enterococcus faecalis (E. faecalis), and Staphylococcus aureus (S. aureus), respectively. The IZD for gram-negative Escherichia coli (E. coli), Neisseria Gonorrhoeae (N. Gonorrhoeae), Pseudomonas aeruginosa (P. aeruginosa), and Salmonella typhimrium (S. typhimrium) were found to be 12.0, 13.0, 14.0, and 13.0 mm, respectively. Therefore, the AgCuO₂ NPs reveal excellent antimicrobial efficiency, and they can be effortlessly separated using a tiny magnet or a simple magnetic separator. The adequate cytotoxicity and magnetic characteristics of the antimicrobial sample suggest a promising future for it in biomedical applications.

Mechanochemical effects underlying the mechanically activated catalytic hydrogenation of carbon monoxide

In this work, we highlight and measure the intensity of mechanochemical effects at work in the hydrogenation of carbon monoxide by comparing the activity of a supported Co-Fe catalyst subjected, respectively, to ball milling and simple powder agitation. Paying due regard to the discontinuous nature of ball milling, we show that mechanochemical hydrogenation proceeds at significantly higher rate and disclose its connection with individual impacts. Experimental evidence suggests that the enhanced catalytic activity we observe can be ascribed to local processes affecting the amount of powder that gets involved in individual impacts.

Digital manufacturing of personalised footwear with embedded sensors

The strong clinical demand for more accurate and personalized health monitoring technologies has called for the development of additively manufactured wearable devices. While the materials palette for additive manufacturing continues to expand, the integration of materials, designs and digital fabrication methods in a unified workflow remains challenging. In this work, a 3D printing platform is proposed for the integrated fabrication of silicone-based soft wearables with embedded piezoresistive sensors. Silicone-based inks containing cellulose nanocrystals and/or carbon black fillers were thoroughly designed and used for the direct ink writing of a shoe insole demonstrator with encapsulated sensors capable of measuring both normal and shear forces. By fine-tuning the material properties to the expected plantar pressures, the patient-customized shoe insole was fully 3D printed at room temperature to measure in-situ gait forces during physical activity. Moreover, the digitized approach allows for rapid adaptation of the sensor layout to meet specific user needs and thereby fabricate improved insoles in multiple quick iterations. The developed materials and workflow enable a new generation of fully 3D printed soft electronic devices for health monitoring.

Piezo robotic hand for motion manipulation from micro to macro

Multiple degrees of freedom (DOFs) motion manipulation of various objects is a crucial skill for robotic systems, which relies on various robotic hands. However, traditional robotic hands suffer from problems of low manipulation accuracy, poor electromagnetic compatibility and complex system due to limitations in structures, principles and transmissions. Here we present a direct-drive rigid piezo robotic hand (PRH) constructed on functional piezoelectric ceramic. Our PRH holds four piezo fingers and twelve motion DOFs. It achieves high adaptability motion manipulation of ten objects employing pre-planned functionalized hand gestures, manipulating plates to achieve 2L (linear) and 1R (rotary) motions, cylindrical objects to generate 1L and 1R motions and spherical objects to produce 3R motions. It holds promising prospects in constructing multi-DOF ultra-precision manipulation devices, and an integrated system of our PRH is developed to implement several applications. This work provides a new direction to develop robotic hand for multi-DOF motion manipulation from micro scale to macro scale.

A new class of transformable kirigami metamaterials for reconfigurable electromagnetic systems

The rapid development of radio frequency (RF) components requires smart multifunctional materials that can adapt their physical shapes and properties according to the environment. While most current reconfigurable systems provide limited flexibility with high manufacturing cost, this research proposes to harness the transformable properties of kirigami-inspired multistable mechanical metasurfaces that can repeatedly deform and lock into different configurations to realize a novel class of low-cost reconfigurable electromagnetic structures with a broad design space. The metasurfaces are formed by designing kinematic-based unit cells with metallised coating that can provide adjustable resonant electromagnetic (EM) properties while rotating with respect to each other. Tailoring the cut length and geometry parameters of the patterns, we demonstrate programming of the topologies and shapes of different configurations. The influence of critical parameters on the structural multistability is illustrated by means of both a simplified energy model and finite element simulations. As examples of the reconfigurable electromagnetic devices that can be realized, we report the development of a tuneable half-wave dipole and two frequency selective surface (FSS) designs featuring isotropic and anisotropic responses. While the kirigami dipole can be tuned by mechanically stretching its arms, the FSSs exhibit distinct transmittance and reflectance spectra in each of the kirigami patterns stable states. The functionality of these kirigami devices is validated both by full-wave EM simulations and experiments. The proposed transformable structures can be mechanically actuated to tune the EM response in frequency or induce anisotropies for wave propagation.

2D Titanium carbide printed flexible ultrawideband monopole antenna for wireless communications

Flexible titanium carbide (Ti₃C₂) antenna offers a breakthrough in the penetration of information communications for the spread of Internet of Things (IoT) applications. Current configurations are constrained to multi-layer complicated designs due to the limited conformal integration of the dielectric substrate and additive-free Ti₃C₂ inks. Here, we report the flexible ultrawideband Ti₃C₂ monopole antenna by combining strategies of interfacial modification and advanced extrusion printing technology. The polydopamine, as molecular glue nano-binder, contributes the tight adhesion interactions between Ti₃C₂ film and commercial circuit boards for high spatial uniformity and mechanical flexibility. The bandwidth and center frequency of Ti₃C₂ antenna can be well maintained and the gain differences fluctuate within ±0.2 dBi at the low frequency range after the bent antenna returns to the flat state, which conquers the traditional inelastic Cu antenna. It also achieves the demo instance for the fluent and stable real-time wireless transmission in bending states.

Volumetric additive manufacturing of pristine silk-based (bio)inks

Volumetric additive manufacturing (VAM) enables fast photopolymerization of three-dimensional constructs by illuminating dynamically evolving light patterns in the entire build volume. However, the lack of bioinks suitable for VAM is a critical limitation. This study reports rapid volumetric (bio)printing of pristine, unmodified silk-based (silk sericin (SS) and silk fibroin (SF)) (bio)inks to form sophisticated shapes and architectures. Of interest, combined with post-fabrication processing, the (bio)printed SS constructs reveal properties including reversible as well as repeated shrinkage and expansion, or shape-memory; whereas the (bio)printed SF constructs exhibit tunable mechanical performances ranging from a few hundred Pa to hundreds of MPa. Both types of silk-based (bio)inks are cytocompatible. This work supplies expanded bioink libraries for VAM and provides a path forward for rapid volumetric manufacturing of silk constructs, towards broadened biomedical applications.

3D printing of hollow geometries using blocking liquid substitution stereolithography

Micrometer scale arbitrary hollow geometries within a solid are needed for a variety of applications including microfluidics, thermal management and metamaterials. A major challenge to 3D printing hollow geometries using stereolithography is the ability to retain empty spaces in between the solidified regions. In order to prevent unwanted polymerization of the trapped resin in the hollow spaces-known as print-through-significant constraints are generally imposed on the primary process parameters such as resin formulation, exposure conditions and layer thickness. Here, we report on a stereolithography process which substitutes the trapped resin with a UV blocking liquid to mitigate print-through. We investigate the mechanism of the developed process and determine guidelines for the formulation of the blocking liquid. The reported method decouples the relationship between the primary process parameters and their effect on print-through. Without having to optimize the primary process parameters to reduce print-through, hollow heights that exceed the limits of conventional stereolithography can be realized. We demonstrate fabrication of a variety of complex hollow geometries with cross-sectional features ranging from tens of micrometer to hundreds of micrometers in size. With the framework presented, this method may be employed for 3D printing functional hollow geometries for a variety of applications, and with improved freedom over the printing process (e.g. material choices, speed and resulting properties of the printed parts).

A high-adaptability nozzle-array printing system based on a set covering printing planning model for printed display manufacturing

Inkjet printing technology is expected to enhance printed display mass production technology in the future. Nozzle-array printheads form the basis for printed display mass production applications. However, jet instability caused by air bubble entrapment and nozzle wettability changes during the printing process is a major challenge in the application of this technology. To adapt to possible nozzle abnormalities, a high-adaptability nozzle-array printing system based on a set covering printing planning (SCPP) model for printed display manufacturing is designed in this study. The study consists of two parts. First, a printing system based on multistep visual inspection and closed-loop feedback is proposed to accurately detect and screen abnormal nozzle positions. Notably, the inkjet printing system can identify nozzles with abnormal ejection characteristics and ensure that the remaining nozzles work accurately and stably. Then, an SCPP model is established for display pixel printing planning by using the remaining normal nozzles on the nozzle-array printhead. This model can output the most efficient printing path and nozzle printing action and can adapt to any pixel pattern, nozzle type, and abnormal nozzle distribution. The system and technology are highly adaptable and scalable for fabricating large-area printed display devices.

Centrifugal multimaterial 3D printing of multifunctional heterogeneous objects

There are growing demands for multimaterial three-dimensional (3D) printing to manufacture 3D object where voxels with different properties and functions are precisely arranged. Digital light processing (DLP) is a high-resolution fast-speed 3D printing technology suitable for various materials. However, multimaterial 3D printing is challenging for DLP as the current multimaterial switching methods require direct contact onto the printed part to remove residual resin. Here we report a DLP-based centrifugal multimaterial (CM) 3D printing method to generate large-volume heterogeneous 3D objects where composition, property and function are programmable at voxel scale. Centrifugal force enables non-contact, high-efficiency multimaterial switching, so that the CM 3D printer can print heterogenous 3D structures in large area (up to 180 mm × 130 mm) made of materials ranging from hydrogels to functional polymers, and even ceramics. Our CM 3D printing method exhibits excellent capability of fabricating digital materials, soft robots, and ceramic devices.

Pulsed laser-assisted additive manufacturing of Ti-6Al-4V for in-situ grain refinement

Metal additive manufacturing (AM) enables rapid customization of complex parts. However, it leads to forming of columnar grain structures which give the AM parts anisotropic properties. In this study, we propose a pulsed laser-assisted AM (PLAAM) technique for in-situ grain refinement of Ti-6Al-4V parts. A nanosecond pulsed laser was focused onto a melt pool to generate a favorable environment for the promotion of fine equiaxed grains. The PLAAM technique provided an average prior-β grain size of 549.6 μm, compared to that of 1297 μm provided by the conventional AM technique. Moreover, the maximum value of multiples of uniform distribution of the β phase decreased from 16 to 7.7 when using the PLAAM technique, which indicates a weakened crystallographic texture. These changes confirm that the proposed PLAAM technique promotes finer and more equiaxed prior-β grains. Furthermore, because the proposed technique is a non-contact technique, it can be applied to existing processes without adjusting tool paths.

Enhanced electrical conductivity and stretchability of ionic-liquid PEDOT:PSS air-cathodes for aluminium-air batteries with long lifetime and high specific energy

A hydrogel film, poly-3,4-ethylenedioxythiophene (PEDOT):polystyrenesulfonate (PSS), containing an ionic liquid, is used as an air-cathode for a metal-air battery and its performance is investigated. This work presents the development of the air-cathode and the characterization of its physical, chemical and mechanical properties. Moreover, in view of wearable batteries, these air-cathodes are implemented within a flexible aluminium-air battery. It contains an aluminium anode, an electrolyte made of cellulose paper imbibed with an aqueous sodium chloride solution and the PEDOT:PSS air-cathode. Characterisation tests showed that the ionic liquid did not change the air-cathode chemically, while the electric conductivity increased considerably. The anode has an acceptable purity and was found to be resistant against self-corrosion. Discharge tests showed operating voltages up to 0.65 V, whereas two batteries in series could deliver up to 1.3 V at a current density of 0.9 mA cm^-2 for almost a day, sufficient for monitoring and medical devices. Several discharge tests with current densities from 0.25 up to 2.5 mA cm^-2 have presented operating lifetimes from 10 h up until over a day. At a current density of 2.8 mA cm^-2, the operating voltage and lifetime dropped considerably, explained by approaching the limiting current density of about 3 mA cm^-2, as evidenced by linear sweep voltammetry. The batteries showed high specific energies up to about 3140 Wh kg^-1. Mechanical tests revealed a sufficient stretchability of the air-cathode, even after battery discharge, implying an acceptable degree of wearability. Together with the reusability of the air-cathode, the battery is a promising route towards a low-cost viable way for wearable power supply for monitoring medical devices with long lifetimes and high specific energies. Optimization of the air-cathode could even lead to higher power applications.

Lithiated Prussian blue analogues as positive electrode active materials for stable non-aqueous lithium-ion batteries

Prussian blue analogues (PBAs) are appealing active materials for post-lithium electrochemical energy storage. However, PBAs are not generally suitable for non-aqueous Li-ion storage due to their instability upon prolonged cycling. Herein, we assess the feasibility of PBAs with various lithium content for non-aqueous Li-ion storage. We determine the crystal structure of the lithiated PBAs via neutron powder diffraction measurements and investigate the influence of water on structural stability and Li-ion migration through operando X-ray diffraction measurements and bond valence simulations. Furthermore, we demonstrate that a positive electrode containing Li_2-xFeFe(CN)₆⋅nH₂O (0 ≤ x ≤ 2) active material coupled with a Li metal electrode and a LiPF₆-containing organic-based electrolyte in coin cell configuration delivers an initial discharge capacity of 142 mAh g^-1 at 19 mA g^-1 and a discharge capacity retention of 80.7% after 1000 cycles at 1.9 A g^-1. By replacing the lithium metal with a graphite-based negative electrode, we also report a coin cell capable of cycling for more than 370 cycles at 190 mA g^-1 with a stable discharge capacity of about 105 mAh g^-1 and a discharge capacity retention of 98% at 25 °C.