Ultra-Tough Waterborne Polyurethane-Based Graft-Copolymerized Piezoresistive Composite Designed for Rehabilitation Training Monitoring Pressure Sensors.

Effective training is crucial for patients who need rehabilitation for achieving optimal recovery and reducing complications. Herein, a wireless rehabilitation training monitoring band with a highly sensitive pressure sensor is proposed and designed. It utilizes polyaniline@waterborne polyurethane (PANI@WPU) as a piezoresistive composite material, which is prepared via the in situ grafting polymerization of PANI on the WPU surface. WPU is designed and synthesized with tunable glass transition temperatures ranging from -60 to 0 °C. Dipentaerythritol (Di-PE) and ureidopyrimidinone (UPy) groups are introduced, endowing the material with good tensile strength (14.2 MPa), toughness (62 MJ-1 m-3 ), and great elasticity (low permanent deformation: 2%). Di-PE and UPy enhance the mechanical properties of WPU by increasing the cross-linking density and crystallinity. Combining the toughness of WPU and the high-density microstructure derived by hot embossing technology, the pressure sensor exhibits high sensitivity (168.1 kPa-1 ), fast response time (32 ms), and excellent stability (10 000 cycles with 3.5% decay). In addition, the rehabilitation training monitoring band is equipped with a wireless Bluetooth module, which can be easily applied to monitor the rehabilitation training effect of patients using an applet. Therefore, this work has the potential to significantly broaden the application of WPU-based pressure sensors for rehabilitation monitoring.

Formation of calcium carbonate nanoparticles through the assembling effect of glucose and the influence on the properties of PDMS.

In order to prepare calcium carbonate nanoparticles in a green and environmentally friendly way, the concept of bio-mineralization has been proposed. Glucose, as a common small molecular organic substance found in organisms, participates in the mineralization process in cells. By adding glucose as a chemical additive, long chains of calcium carbonate form at the initial stage and then break granularly via over-carbonation. The average size of the calcium carbonate nanoparticles is about 40 nm based on the statistical analyses of three hundred particles. The growth mechanism of calcium carbonate under the influence of glucose is obtained. After the calcium carbonate nanoparticles are modified by sodium stearate, they are introduced to the PDMS matrix to achieve the composite material. Compared with pure PDMS, the composite with additional 3% calcium carbonate has its elongation at break and tensile strength increased by 23.96% and 48.15%, respectively.

Wireless Rehabilitation Training Sensor Arrays Made with Hot Screen-Imprinted Conductive Hydrogels with a Low Percolation Threshold.

Herein, we propose a highly sensitive wireless rehabilitation training ball with a piezoresistive sensor array for patients with Parkinson's disease (PD). The piezoresistive material is a low percolation threshold conductive hydrogel which is formed with polypyrrole (PPy) nanofibers (NFs) as a conductive filler derived from a polydopamine (PDA) template. The proton acid doping effect and molecular template of PDA are essential for endowing PPy NFs with a high aspect ratio, leading to a low percolation threshold (∼0.78 vol %) and a low Young's 004Dodulus of 37.69 kPa and hence easy deformation. The piezoresistive sensor exhibited a static and dynamic stability of 10,000 s and 15,000 cycle times, respectively. This stability could be attributed to the increased hydrophilicity of conductive fillers, enhancing the interfacial strength between the conductive filler and the matrix. The interaction between the PDA-PPy NFs and the hydrogel matrix endows the hydrogel with toughness and ensures the stability of the device. Additionally, the microdome structure of the conductive hydrogel, produced by hot screen-imprinting, dramatically improves the sensitivity of the piezoresistive sensor (∼856.14 kPa-1). The microdome conductive hydrogel can distinguish a subtle pressure of 15.40 Pa compared to the control hydrogel without a microstructure. The highly sensitive piezoresistive sensor has the potential to monitor the hand-grip force, which is not well controlled by patients with PD. The rehabilitation training ball assembled with a sensor array on the surface and a wireless chip for communication inside is built and used to monitor the pressure in real time through the WeChat applet. Thus, this work has significantly broadened the application of hydrogel-based flexible piezoresistive sensors for human activity monitoring, which provides a promising strategy to realize next-generation electronics.

In Situ and Intraoperative Detection of the Ureter Injury Using a Highly Sensitive Piezoresistive Sensor with a Tunable Porous Structure.

Iatrogenic ureteral injury, as a commonly encountered problem in gynecologic, colorectal, and pelvic surgeries, is known to be difficult to detect in situ and in real-time. Consequently, this injury may be left untreated, thereby leading to serious complications such as infections, renal failure, or even death. Here, high-performance tubular porous pressure sensors were proposed to identify the ureter in situ intraoperatively. The electrical conductivity, mechanical compressibility, and sensor sensitivity can be tuned by changing the pore structure of porous conductive composites. A low percolation threshold of 0.33 vol % was achieved due to the segregated conductive network by pores. Pores also lead to a low effective Young's modulus and high compressibility of the composites and thus result in a high sensitivity of 448.2 kPa-1 of sensors, which is consistent with the results of COMSOL simulation. Self-mounted on the tip of forceps, the sensors can monitor tube pressures with different frequencies and amplitudes, as demonstrated using an artificial pump system. The sensors can also differentiate ureter pulses from aorta pulses of a Bama minipig in situ and in real-time. This work provides a facile, cost-effective, and nondestructive method to identify the ureter intraoperatively, which cannot be effectively achieved by traditional methods.

Self-Adhesive, Stretchable, Biocompatible, and Conductive Nonvolatile Eutectogels as Wearable Conformal Strain and Pressure Sensors and Biopotential Electrodes for Precise Health Monitoring.

Conductive stretchable hydrogels and ionogels consisting of ionic liquids can have interesting application as wearable strain and pressure sensors and bioelectrodes due to their soft nature and high conductivity. However, hydrogels have a severe stability problem because of water evaporation, whereas ionogels are not biocompatible or even toxic. Here, we demonstrate self-adhesive, stretchable, nonvolatile, and biocompatible eutectogels that can always form conformal contact to skin even during body movement along with their application as wearable strain and pressure sensors and biopotential electrodes for precise health monitoring. The eutectogels consist of a deep eutectic solvent that has high conductivity, waterborne polyurethane that is an elastomer, and tannic acid that is an adhesive. They can have an elongation at a break of 178%, ionic conductivity of 0.22 mS/cm, and adhesion force of 12.5 N/m to skin. They can be used as conformal strain sensors to accurately monitor joint movement and breath. They can be even used as pressure sensors with a piezoresistive sensitivity of 284.4 kPa-1 to precisely detect subtle physical movements like arterial pulses, which can provide vital cardiovascular information. Moreover, the eutectogels can be used as nonvolatile conformal electrodes to monitor epidermal physiological signals, such as electrocardiogram (ECG) and electromyogram (EMG).

Magnetic-Assisted Transparent and Flexible Percolative Composite for Highly Sensitive Piezoresistive Sensor via Hot Embossing Technology.

A highly transparent and flexible percolative composite with magnetic reduced graphene oxide@nickel nanowire (mGN) fillers in EcoFlex matrix is proposed as a sensing layer to fabricate high-performance flexible piezoresistive sensors. Large excluded volume and alignment of mGN fillers contribute to low percolation threshold (0.27 vol %) of mGN-EcoFlex composites, leading to high electrical conductivity of 0.003 S m-1, optical transmittance of 71.8%, and low Young's modulus of 122.8 kPa. Large-scale microdome templates for sensors are prepared by hot embossing technology cost-effectively and COMSOL Multiphysics is utilized to optimize the sensor performances. Piezoresistive sensors fabricated experimentally show superior average sensitivity of 1302.1 kPa-1 with a low device-to-device variation of 3.74%, which provides a new way to achieve transparent, highly sensitive, and large-scale electronic skin.

Multimode Signal Processor Unit Based on the Ambipolar WSe2-Cr Schottky Junction.

A Schottky barrier is a double-edged sword in electronic and optoelectronic devices, especially devices based on two-dimensional materials. It may restrict the carrier transport in devices, but it can also realize multifunctional devices by architecture design. We designed a simple but novel device structure based on theWSe2-Cr Schottky junction with an asymmetric Schottky contact area of the source and drain. A significant rectification ratio over 105 and multiple rectifying states (e.g., full pass, forward pass, off, and backward pass) were achieved in the single Schottky junction tuned by gate voltage. Furthermore, switching characteristic, rectification characteristic, and amplitude of a sin wave can be effectively modulated by the electrical field or light illumination in a signal process circuit based on the WSe2-Cr Schottky junction. The highly tunable Schottky junction working as a multimode signal processor unit has great potential in future optoelectronic-integrated chips.

Synthesis and controlled morphology of Ni@Ag core shell nanowires with excellent catalytic efficiency and recyclability.

Ni@Ag core shell nanowires (NWs) were prepared by in situ chemical reduction of Ag+ around NiNWs as the inner core. Different Ni@Ag NWs with controllable morphologies were achieved through the layer-plus-island growth mode and this mechanism was confirmed by scanning electron microscopy, X-ray fluorescence, and X-ray photoelectron spectroscopy analyses. When used as a catalyst, the synthesized Ni@Ag NWs exhibited high reduction efficiency by showing a high reaction rate constant k of 0.408 s-1 in reducing 4-nitrophenol at room temperature. Besides, combining the magnetic property, including high saturation magnetization and low coercivity, the magnetic NiNW core contributes to excellent recyclability and long-term stability with only a 2.2% performance loss after 10 recycles by magnets. The Ni@Ag NWs proposed here show unprecedentedly high potential in applications requiring high efficiency and a recyclable catalyst.

A tri-phase percolative ceramic composite with high initial permeability and composition-independent giant permittivity.

The drastic change of properties near the percolation threshold usually limits the practical applications of percolative composite materials. In this work, a tri-phase system, i.e. a BaTiO3 (BTO)/Ni0.5Zn0.5Fe2O4 (NZFO)/BaFe12O19 (BFO) ceramic composite, is proposed and investigated in detail. The BFO phase was in situ formed during a hybrid process of sol-gel and self-combustion methods. The content of the BFO phase could be tuned conveniently by controlling the preparation conditions. The as-prepared BTO/NZFO/BFO tri-phase composite exhibited unprecedented stable dielectric properties that were distinct from those of conventional percolative composites above the percolation threshold due to the existence of a third phase. When the volume fraction of the NZFO phase exceeds 55%, the electrical conductivity and effective permittivity of the composite remain at a stable value of about 10-5 S cm-1 and 10 000, respectively, which is almost independent of the composition. Such behavior is the result of the synergistic control effect of the percolation effect and specific phase composition in the system. It is evident that the stability of the dielectric properties of the composite is chiefly contributed by the introduction of the BFO phase. Meanwhile, the composite exhibited a relatively high permeability of ∼17 with 90% NZFO loading, and its saturated magnetization is larger than 73 emu g-1, approximately 95% of the pure NZFO phase. The finding of our BTO/NZFO/BFO tri-phase ceramic composite with stable giant permittivity and extremely high permeability paves a new way to solve the difficulty of property instability above the percolation threshold in the utilization of percolative materials.

A ferroelectric relaxor polymer-enhanced p-type WSe2 transistor.

WSe2 has attracted extensive attention for p-FETs due to its air stability and high mobility. However, the Fermi level of WSe2 is close to the middle of the band gap, which will induce a high contact resistance with metals and thus limit the field effect mobility. In this case, a high work voltage is always required to achieve a large ON/OFF ratio. Herein, a stable WSe2 p-doping technique of coating using a ferroelectric relaxor polymer P(VDF-TrFE-CFE) is proposed. Unlike other doping methods, P(VDF-TrFE-CFE) not only can modify the Fermi level of WSe2 but can also act as a high-k gate dielectric in an FET. Dramatic enhancement of the field effect hole mobility from 27 to 170 cm2 V-1 s-1 on a six-layer WSe2 FET has been achieved. Moreover, an FET device based on bilayer WSe2 with P(VDF-TrFE-CFE) as the top gate dielectric is fabricated, which exhibits high p-type performance over a low top gate voltage range. Furthermore, low-temperature experiments reveal the influence of the phase transition of P(VDF-TrFE-CFE) on the channel carrier density and mobility. With a decrease in temperature, field effect hole mobility increases and approaches up to 900 cm2 V-1 s-1 at 200 K. The combination of the p-doping and gating with P(VDF-TrFE-CFE) provides a promising solution for obtaining high-performance p-FET with 2D semiconductors.

Excellent absorption properties of BaFe12-xNbxO19 controlled by multi-resonance permeability, enhanced permittivity, and the order of matching thickness.

For the sol-gel-derived BaFe12-xNbxO19 (x = 0-0.6), coercivity (Hc) and saturation magnetization (Ms) vary from 3.53-0.85 kOe and 70.3-53.8 emu g-1 to 1.02-0.22 kOe and 69.6-59.5 emu g-1, respectively, with an increase in sintering temperature from 1250 °C to 1350 °C. Moreover, ε' and ε'' increase from 4.13-4.04 and 0.0049-0.0045 to 7.64-6.93 and 1.50-0.97 over 26.5-40 GHz, and the multi-resonance peaks in permeability shift from ∼40+ GHz to ∼27 GHz. The bandwidth (BW) and reflection loss peak intensity (RLp) are broadened and enhanced from 0.8 GHz and -10.3 dB of the sample with x = 0.2 sintered at 1250 °C under 0.92 mm to 11.9+ GHz and -54 dB, respectively, of the sample with x = 0.6 sintered at 1350 °C under 0.86 mm around a millimeter-wave atmospheric window of 35 GHz. The effects of Nb5+ content (x) and sintering temperature on grain size, phase compositions, formations of Fe2+ and oxygen vacancy, and thus on static magnetism and EM parameters are investigated. The correlations of multi-resonance permeability, enhanced permittivity, and the order of matching thickness with absorption properties are also discussed in detail.

Coherent and incoherent phonon transport in a graphene and nitrogenated holey graphene superlattice.

The transition between coherent and incoherent phonon transport in a graphene (GRA) and nitrogenated holey graphene (C2N) superlattice is investigated by non-equilibrium molecular dynamics (NEMD) simulation. We find that the thermal conductivity of the GRA-C2N superlattice is much lower than those of graphene and C2N, and exhibits a positive correlation with the system length. Owing to three mechanisms, i.e., phonon wave interference, phonon confinement and phonon interface scattering, the calculated thermal conductivity shows a decreasing trend at small period length scales and gradually increases at large period length scales. The coherence length of the superlattice at 300 K is 4.43 nm, which is independent of the total length. In addition, the effects of temperature and uniaxial tensile strain on phonon transport are investigated. At 100 K, the coherent phonons play a more dominating role in the superlattice and the responding coherence length is enlarged to 7.38 nm. On the other hand, tensile strain can effectively reduce the thermal conductivity, which results from the phonon softening.

High Sensitivity, Wearable, Piezoresistive Pressure Sensors Based on Irregular Microhump Structures and Its Applications in Body Motion Sensing.

A pressure sensor based on irregular microhump patterns has been proposed and developed. The devices show high sensitivity and broad operating pressure regime while comparing with regular micropattern devices. Finite element analysis (FEA) is utilized to confirm the sensing mechanism and predict the performance of the pressure sensor based on the microhump structures. Silicon carbide sandpaper is employed as the mold to develop polydimethylsiloxane (PDMS) microhump patterns with various sizes. The active layer of the piezoresistive pressure sensor is developed by spin coating PEDOT: PSS on top of the patterned PDMS. The devices show an averaged sensitivity as high as 851 kPa(-1) , broad operating pressure range (20 kPa), low operating power (100 nW), and fast response speed (6.7 kHz). Owing to their flexible properties, the devices are applied to human body motion sensing and radial artery pulse. These flexible high sensitivity devices show great potential in the next generation of smart sensors for robotics, real-time health monitoring, and biomedical applications.

A Low-Operating-Power and Flexible Active-Matrix Organic-Transistor Temperature-Sensor Array.

An organic flexible temperature-sensor array exhibits great potential in health monitoring and other biomedical applications. The actively addressed 16 × 16 temperature sensor array reaches 100% yield rate and provides 2D temperature information of the objects placed in contact, even if the object has an irregular shape. The current device allows defect predictions of electronic devices, remote sensing of harsh environments, and e-skin applications.

High performance organic transistor active-matrix driver developed on paper substrate.

The fabrication of electronic circuits on unconventional substrates largely broadens their application areas. For example, green electronics achieved through utilization of biodegradable or recyclable substrates, can mitigate the solid waste problems that arise at the end of their lifespan. Here, we combine screen-printing, high precision laser drilling and thermal evaporation, to fabricate organic field effect transistor (OFET) active-matrix (AM) arrays onto standard printer paper. The devices show a mobility and on/off ratio as high as 0.56 cm(2)V(-1)s(-1) and 10(9) respectively. Small electrode overlap gives rise to a cut-off frequency of 39 kHz, which supports that our AM array is suitable for novel practical applications. We demonstrate an 8 × 8 AM light emitting diode (LED) driver with programmable scanning and information display functions. The AM array structure has excellent potential for scaling up.