Traditional approaches for monitoring human gait have severe spatial and temporal restrictions with complex analysis methods and high cost, which are powerless to promote the development of intelligent life involving fitness, sport training, and healthcare. Herein, a portable smart insole system with high spatial resolution and simple manufacturing process to measure plantar pressure distribution anytime, anywhere for gait analysis is proposed. An insole-shaped array of 104 piezoresistive sensors with highly robust characteristics is assembled, exhibiting a good pressure-sensing uniformity. The smart insole not only detects the subtle displacement of the center of gravity of the body, but also exhibits a real-time, high-resolution thermodynamic diagram of the plantar pressure distribution during human activities. More importantly, the function of motion intelligence identification can be realized by regionalizing and digitizing the whole plantar pressure distribution, achieving an average recognition accuracy of 83.32% among six predefined motions. These results imply that the carbon fiber-based smart insole can provide an effective approach for convenient gait analysis and motion identification, which has a great potential in the application of future intelligent life.

Electrospinning is a powerful method to fabricate structures resembling the fibrous texture of the native extracellular matrix. However, the random fiber deposition of the process hinders a faithful reproduction of the fiber mesh morphology on multiple samples, which raises difficulties in experimental designs to systematically test and assess cell response in vitro. A multi-replication process to precisely reproduce the fiber morphology on different cell culture substrates is developed. The process involves a decoupling of the fiber structure, material, and porosity by combining the key advantages of electrospinning and imprinting. With this, fiber patterns having a diameter between 0.4 and 2.8 µm are replicated on polycarbonate, polystyrene, poly(methyl methacrylate), and cyclic olefin copolymer films. Identical fiber morphology is, then, obtained on porous films having a pore diameter between 2 and 12 µm. Having full control over these parameters allows the multireplication process to engineer well-characterized cell microenvironments, which can potentially be used to further investigate complex cell–material interactions.

This article reports a new approach toward fabrication and directed assembly of nanoparticulate reactive system (Nanofoils) on patterned substrates. Different from current state-of-the-art, gas phase electrodeposition uses nanoparticles instead of atoms to form densely packed multilayered thin films at room temperature-pressure. On ignition, the multilayer system undergoes an exothermic self-propagating reaction. The numerous contact points between two metallic nanoparticulate layers aid in high heat release. Sub-10-nm Platinum (Pt) and Aluminum (Al) particles are synthesized through cathode erosion of metal electrodes in a flow of pure nitrogen gas (spark ablation). Pt/Al bilayer stacks with total thickness of 3–8 µm undergo self-propagating reaction with a 10.3 mm s−1 wavefront velocity on local ignition. The reaction wavefront is captured using high speed videography. Calorimetry studies reveal two exothermic peaks suggesting Pt/Al alloy formation. The peak at 135 °C has a higher calorific value of 150 mW g−1 while the peak at 400 °C has a 12 mW g−1 exothermic peak. X-ray diffraction study shows reaction-products are cubic Al2Pt with small quantities of orthorhombic Al6Pt and orthorhombic AlPt2. Electron microscopy studies help draw a correlation between film morphology, bimetallic interface, nanoparticle oxidation, and self-propagating reaction kinetics that is significant in broadening our understanding towards nanoparticulate reactive systems.

Capacitive deionization (CDI) is proposed as a thermodynamically effective desalination method for treating non-potable water with a low-salt concentrator to address the growing need for clean drinking water. MXenes, 2D transition metal carbides derived from Mn+1AXn (n = 1, 2, 3, or 4) bulk phases, are an intriguing class of crystalline materials with unique physicochemical properties. However, a significant challenge for their practical use is the degradation and phase transition experienced by MXene flakes when exposed to aqueous conditions. Several strategies for improving MXene stability are proposed, including combining it with porous materials such as carbon and metal–organic frameworks (MOFs). In addition to ZIFs, antioxidants with amine functional groups are used to stabilize MXene. Additionally, amine-functionalized MXenes exhibit improved resistance to oxidation caused by water, enabling them to maintain their dispersity in aqueous solutions at room temperature. The produced A-ZIF@MXene electrode represents high desalination performance with the highest salt adsorption capacity up to 80.3 mg g−1 in 1000 mg L−1 The NaCl solution reserve more than 99% of its initial capacity in 50 cycles to the synergism of its surface amine groups, high hydrophilicity, and distinctive hierarchical porous structure.

The trend to integrate more electronic components in a limited space range motivates the development of advanced electronic packaging. Conventional electronic packaging is difficult to perform in stable interfacing interconnection pitch below 7 µm due to the possibility of short-circuit problems. Herein, a kind of anisotropic conductive film (μ-ACF) containing periodically arranged conductive microspheres for microscale pitch electrical interfacing interconnection is developed. The periodic arrangement can avert the contact of conductive microspheres, thus enabling stable interconnection with a pitch as small as 5 µm. By coating conductive microspheres with a layer of silicon insulation, the pitch can be further reduced to 3 µm, which can prevent the formation of conductive pathways between electrodes even if they come into contact with each other. Such high-quality arrangement is achieved by lithography and capillary self-assembly method, which is expected to be used in high-throughput production. Thanks to the delicate design, the μ-ACF can achieve a low contact resistance of 4.62 mΩ mm−2 and a spatial resolution of 3 µm without short-circuit failure. The spatial resolution can be further improved by adjusting the size of conductive microspheres, which is conducive to the development of highly integrated devices.

Powder-based additive manufacturing (AM) is an important technology in fabricating complex 3D products. In powder-based AM, a powder deposition system plays a key role in determining the resolution, density, and properties of printed parts. An acoustic-actuated particle deposition approach, which utilizes acoustic waves to actuate a glass nozzle, enables the deposition of particles in a cost-effective way. However, the capability to programmably deposit different particles using acoustic waves has yet to be fully demonstrated. Herein, a selective particle deposition approach via acoustic modulation for muti-material AM is demonstrated. Sequential and parallel depositions of two types of particles by modulating the signal inputs and resonant frequencies of piezo transducers are demonstrated. An AM process is demonstrated by integrating this acoustic-actuated particle deposition approach with a heat-curing mechanism. Several products from this system are produced as well. It is expected that this particle deposition approach can be used in a wide spectrum of applications, such as direct manufacturing of multi-functional materials/devices.

Ion-Selective Biosensors

The increasing use of wearable electronics calls for sustainable energy solutions. Biomechanical energy harvesting appears as an attractive solution to replace the use of batteries in wearables, as the body generates sufficient power to drive small electronics. In particular, triboelectric nanogenerators (TENGs) have emerged as a promising approach due to its lightweight and high power density. In this work, a TENG is hybridized with an electromagnetic generator (EMG) to harvest energy from the foot strike. An enclosed radial-flow turbine is optimized and used to convert the foot-strike low-frequency linear movement into a higher-frequency rotational motion (by a factor of ≈12). Besides increasing the motion frequency, the employed mechanism is physically robust and enables a continuous operation from irregular mechanical excitations. A single TENG unit operating in the freestanding mode generated an optimal power of 4.72 µW and transferred a short-circuit charge of 2.3 nC. The TENG+EMG hybridization allows to power a digital pedometer even after the mechanical input stopped. Finally, the energy harvester is incorporated into a commercial shoe to power the same pedometer from foot walking. The obtained results validate the developed prototype ability to serve as a portable power source that can drive sensors and wearable electronics.

Organic electrochemical transistors (OECTs) have drawn significant interest because of their low cost, biocompatibility, and ease of fabrication, allowing them to be utilized in various applications including flexible displays, electrochemical sensing, and biosensing. Key components of OECTs are the gate, source, and drain electrodes. Herein, OECTs with laser-induced graphene (LIG) electrodes are demonstrated. The electrode patterns for the source, drain, and gate are created by converting the polymer substrate polyimide (PI) into LIG using a scanned laser. The process is simple and inexpensive without complicated chemical synthesis routines or expensive materials such as gold. Patterns can be customized quickly and digitally. The low-cost and porous LIG electrodes with low contact resistance and good electrical stability play an essential role in device performance. The minimum sheet resistance achieved with this laser method for the square patterned electrodes is 7.86 Ω sq−1. The LIG-based OECTs demonstrate good electrical modulation with ON–OFF ratio of 72.80 and high ON current on the order of mA. The LIG-based OECTs exhibit comparable or better performance in comparison with other reports of OECTs on plastic substrates using more complex fabrication methods in terms of OFF current, ON current, transconductance (gm), and contact resistance.

The growth of hexagonal boron nitride (h-BN) and van der Waals (vdW) epitaxy of blue multi-quantum well (MQW) GaN-based LED heterostructures on 6-inch sapphire substrates using metal-organic chemical vapour deposition (MOCVD) is demonstrated. Challenges associated with the growth of large surface h-BN and the subsequent vdW epitaxy of GaN-based LED heterostructures are discussed. To overcome these challenges, the spatial uniformity is controlled of the growth temperature, optimizes the slope of temperature variations during the growth and cooling process, and manages the surface temperature during switching of gas flows. With these adaptations, high quality GaN-based LED heterostructures are grown on h-BN without any spontaneous delamination. The GaN-based LED devices are then fabricated on a 6-inch sapphire wafer, which are lifted off as a membrane and transferred to a flexible copper support. These GaN-based LED devices emitt bright blue illumination with an electroluminescence peak at 437 nm. This scaling up of growth, lift-off, and transfer can lead to the commercialization of GaN-based LEDs on h-BN template on 6-inch sapphire substrates, with a process compatible with current modern equipment for the fabrication of LEDs and electronic devices.

Performance degradation and even loss of function due to mechanical stiffening caused by internal water evaporation and/or freezing significantly limit the application of hydrogel-based electronics. Herein, a high-performance liquid-free electronic skin (e-skin) is assembled based on the dry poly(ethylene glycol)-based gel and conductive Ti3C2 MXenes that is successfully applied in wearable strain sensors. The fabricated liquid-free e-skin exhibits superior mechanical performance, broad sensing ranges (>1000%), good temperature adaptability, and durable environmental stability. Without extra sealed packaging, the e-skin sensor maintains remarkable cycling stability and retains 98.5% conductivity at room temperature after 6 months. Furthermore, the liquid-free e-skin sensors are utilized to provide individuals with proper guidance on body alignment and posture awareness, fostering the development and maintenance of correct exercise techniques, thus mitigating the likelihood of sports-related injuries. This work provides a novel liquid-free electron-conductive electronic integrated with adhesiveness, stretchability, self-healabilitiy, and antifreezing, which can meet wide application needs from artificial skins to smart interfaces.

Exosomes are a type of small extracellular vesicles carrying proteins, nucleic acids, and lipids. Because their expression levels are highly correlated with tumor development, exosomes are regarded as non-invasive biomarkers for cancer diagnosis. Therefore, many exosome detection techniques are developed to provide a new way for cancer diagnosis. However, conventional techniques require the isolation of exosomes from body fluids before analysis, which usually relies on complex equipment and cumbersome operations. In addition, complex procedures may introduce impurities and thus affect the accuracy of the test. As an emerging analysis technology, microfluidic overcomes these shortcomings by integrating a microchannel for sample transport isolation and an exosome analysis module, showing great prospects in cancer diagnosis. This review will provide an overview of microchannel fabrication and analysis methods with outstanding compatibility for different microfluidic types, with a particular focus on microfluidic-based exosome analysis methods that have the potential for clinical application.

Metal materials play an important role in electromagnetic interference (EMI) shielding due to their ultra-high electrical conductivity, but they are rigid and inflexible, as well as of high density, which limits their application in some areas. In this study, a novel and simple method to fabricate the composites of metal foil and polymer is reported. A copper foil (Cuf) with micropores on the surface is used as a shielding matrix, then interpenetrating and interlocking nanostructure as well as reactive groups are introduced on its surface, and then silicone rubber (SiR) is coated on both surfaces to form a sandwich structure, and the obtained Cuf/SiR composites possesses high EMI shielding efficiency (SE), strong interface adhesion, and low density. The average EMI shielding efficiency of the obtained Cuf/SiR composites in the range of 1.13–18 GHz is 111.5 dB, with a high interface adhesion strength of 5.2 N cm−1 and low density of 1.3 g cm−3, and it also possesses bending and splicing properties, which exhibits broad potential application in the field of EMI shielding tents and shielding rooms. This preparation method of the composites is simple and efficient, and provides a guideline for the design and fabrication of metal foil/polymer composites in molding method.

Microfluidic surface chemistry can enable control of capillary-driven flow without the need for bulky external instrumentation. A novel pondered nonhomogeneous coating defines regions with different wetting properties on the microchannel walls. It changes the curvature of the liquid–air meniscus at various channel cross-sections and consequently leads to different capillary pressures, which is favorable in the strive toward automatic flow control. This is accomplished by the deposition of hydrophilic coatings on the surface of multilevel 3D-printed (3DP) microfluidic devices via inkjet printing, thereby retaining the surface hydrophilicity for at least 6 months of storage. To the best of our knowledge, this is the first demonstration of capillary flow control in 3DP microfluidics enabled by inkjet printing. The method is used to create “stop” and “delay” valves to enable preprogrammed capillary flow for sequential release of fluids. To demonstrate further utilization in point-of-care sensing applications, screen printed organic electrochemical transistors are integrated within the microfluidic chips to sense, sequentially and independently from external actions, chloride anions in the (1–100) × 10−3 m range. The results present a cost-effective fabrication method of compact, yet comprehensive, all-printed sensing platforms that allow fast ion detection (<60 s), including the capability of automatic delivery of multiple test solutions.

Flexible Force Sensors

Engineered grafts constitute an alternative to autologous transplant for repairing severe peripheral nerve injuries. However, current clinically available solutions have substantial limitations and are not suited for the repair of long nerve defects. A novel design of nerve conduit is presented here, which consists of a chitosan porous matrix embedding a 3D-printed poly-ε-caprolactone mesh. These materials are selected due to their high biocompatibility, safe degradability, and ability to support the nerve regeneration process. The proposed design allows high control over geometrical features, pores morphology, compression resistance, and bending stiffness, yielding tunable and easy-to-manipulate grafts. The conduits are tested in chronic animal experiments, aiming to repair a 15-mm long gap in the sciatic nerve of rats, and the results are compared with an autograft. Electrophysiological and nociception tests performed monthly during a 4-month follow-up show that these conduits allow a good degree of muscle functional recovery. Histological analyses show abundant cellularization in the wall and in the lumen of the conduits and regenerated axons within all rats treated with these grafts. It is suggested that the proposed conduits have the potential to repair nerves over the limiting gap length and can be proposed as strategy to overcome the limitations of autograft.

Printed electronic paper identifies its interest in flexible organic electronics and sustainable and clean energy applications because of its straightforward production method, cost-effectiveness, and positive environmental impact. However, current limitations include restricted material thickness and the use of supporting substrate for printing. Here, 2D and 3D electronic patterned paper are fabricated from direct ink writing (DIW) nanocellulose and PEDOT:PSS-based materials using syringe deposition and 3D printing. The conductor patterns are integrated in the bulk of the paper, while non-conductive sections are used as support to form free-standing paper. The strong interface between the patterns of electronic patterned paper gives mechanical stability for practical handling. The conductive paper-based electrode has 202 S cm−1 and is capable of handling electric current up to 0.7 A, which can be used for high-power devices. Printed supercapacitor papers show high specific energy of 4.05 Wh kg−1, specific power of 4615 W kg−1 at 0.06 A g−1, and capacitance retention above 95% after 2000 cycles. The new design structure of electronic patterned papers presents a solution for additive manufacturing of paper-based composites for supercapacitors, wearable electronics, or sensors for smart packaging.

This work details the triboelectric characteristics of diamond-like carbon (DLC) film where a proportioned sp3:sp2 bond ratio is engineered through a patented pulsed DC magnetron sputtering process to achieve a durable commercial energy harvesting material. A triboelectric nanogenerator (TENG) is fabricated by creating the triboelectric interface between DLC and PTFE. The presence and synchronization of σ – σ and σ – π bonds between DLC-PFTE contact surface amplify the electronic cloud overlap between their atoms leading to an enhancement of the triboelectric surface charge density. The inherent hardness and reduced friction achieved through DLC and PTFE respectively prevent the mass transfer, and consequent power loss upon consecutive mechanical contact and achieves a stable electric power output of 141 mW m−2. The DLC durability achieved with PTFE in TENG demonstrates its significant potential as low frequency (1 – 10 Hz) energy harvesting devices and self-/low-power electronic devices and sensors. The paper uniquely contributes to a better understanding of the triboelectrification mechanism by insightfully detailing the band-to-band transition of electrons between the PTFE and DLC tribo-interface, as well as discussing gap and frequency limitation of the tribo-pair on the triboelectric charge yield, storage, transfer, and on the friction layer electric field.

Intelligent humidity-programmed hydrogel patches with high stretchability and tunable water-uptake and -release are prepared by copolymerization and crosslinking of N-isopropylacrylamide and oligo(ethylene glycol) comonomers. These intelligent elastomeric patches strongly respond to different humidities and temperatures in terms of mechanical properties which makes them applicable for soft robotics and smart skin applications where autonomous adaption to environmental conditions is a key requirement. It is shown that beyond using the hydrogel in the conventional state in aqueous media, new patches can be controlled by relative humidity. This humidity programming of the patches allows to tune drug release kinetics, opening potential application fields such as skin wound therapy and personalized medication. In situ dynamic-mechanical measurements show a huge dependence on temperature and humidity. The glass transition temperature Tg shifts from around 60 °C at dry conditions to below 0 °C for 75% r.h. and higher. The storage modulus is tunable over more than four orders of magnitude from 0.6 up to 400 MPa. Time-temperature superposition in master curves allows to extract relaxation times over 14 orders of magnitude. With strains at break of over 200% the patches are compliant with human skin and therefore patient-friendly in terms of adapting to movements.

The fabrication of a fully printed, lead-free, polymer piezoelectric transducer is presented and the characterization of its structural, dielectric, and ferroelectric properties at different processing stages is demonstrated. The performance of poly(vinylidene fluoride-trifluoroethylene) transducers with resonance frequency analyses, acoustic power measurements, and pulse-echo experiments is evaluated. Notably, for the first time for a fully printed transducer, an optimal performance in the medical ultrasound range (1 W cm−2, which is promising for applications in epidermal and wearable electronics. Overall, the findings provide a strong foundation for future research in the area of flexible ultrasound transducers.