Soft Liquid Metal-Based Conducting Composite with Robust Electrical Durability for a Wearable Electrocardiogram Sensor

Liquid metals not only have the electrical property of conductivity, but they also have a unique characteristic of existing in a liquid state at room temperature, unlike ordinary stiff solid metals. However, in bioelectronics, the modulus matching well between a device and skin or tissue is considered very advantageous, because high-quality biological signals can be recorded. Therefore, it is possible to implement soft electronics with stable and robust electrical characteristics by using LM as a conductive liquid-state filler. In this study, we changed a type of liquid metal, Eutectic Gallium Indium (EGaIn), into a particle form via tip sonication and mixed it with a solution that dissolved Styrene-Ethylene-Butylene-Styrene (SEBS) in toluene to fabricate a composite. The EGaIn-SEBS composite has high conductivity, excellent electrical durability under mechanically harsh conditions, and a degree of modulus similar to that of bare SEBS, which is lower than that of solid-filler-based SEBS composite. Finally, we demonstrated electrocardiogram signal monitoring using an EGaIn-Alginate two-layer electrode (EATE) that was fabricated by simply coating the surface of the composite with alginate hydrogel, which demonstrates excellent performance in bioelectronics.11Nsciescopu

Single Trace Side Channel Analysis on NTRU Implementation

As researches on the quantum computer have progressed immensely, interests in post-quantum cryptography have greatly increased. NTRU is one of the well-known algorithms due to its practical key sizes and fast performance along with the resistance against the quantum adversary. Although NTRU has withstood various algebraic attacks, its side-channel resistance must also be considered for secure implementation. In this paper, we proposed the first single trace attack on NTRU. Previous side-channel attacks on NTRU used numerous power traces, which increase the attack complexity and limit the target algorithm. There are two versions of NTRU implementation published in succession. We demonstrated our attack on both implementations using a single power consumption trace obtained in the decryption phase. Furthermore, we propose a countermeasure to prevent the proposed attacks. Our countermeasure does not degrade in terms of performance

Skin-like transparent polymer–hydrogel hybrid pressure sensor with pyramid microstructures

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.Soft biomimetic electronic devices primarily comprise an electronic skin (e-skin) capable of implementing various wearable/implantable applications such as soft human–machine inter-faces, epidermal healthcare systems, and neuroprosthetics owing to its high mechanical flexibility, tissue conformability, and multifunctionality. The conformal contact of the e-skin with living tissues enables more precise analyses of physiological signals, even in the long term, as compared to rigid electronic devices. In this regard, e-skin can be considered as a promising formfactor for developing highly sensitive and transparent pressure sensors. Specifically, to minimize the modulus mismatch at the biotic–abiotic interface, transparent-conductive hydrogels have been used as electrodes with exceptional pressing durability. However, critical issues such as dehydration and low compatibility with elastomers remain a challenge. In this paper, we propose a skin-like transparent polymer– hydrogel hybrid pressure sensor (HPS) with microstructures based on the polyacrylamide/sodium-alginate hydrogel and p-PVDF-HFP-DBP polymer. The encapsulated HPS achieves conformal contact with skin due to its intrinsically stretchable, highly transparent, widely sensitive, and anti-de-hydrative properties. We believe that the HPS is a promising candidate for a robust transparent epidermal stretchable-skin device.11Nsciescopu

Stretchable Surface Electrode Arrays Using an Alginate/PEDOT:PSS-Based Conductive Hydrogel for Conformal Brain Interfacing

An electrocorticogram (ECoG) is the electrical activity obtainable from the cerebral cortex and an informative source with considerable potential for future advanced applications in various brain-interfacing technologies. Considerable effort has been devoted to developing biocompatible, conformal, soft, and conductive interfacial materials for bridging devices and brain tissue; however, the implementation of brain-adaptive materials with optimized electrical and mechanical characteristics remains challenging. Herein, we present surface electrode arrays using the soft tough ionic conductive hydrogel (STICH). The newly proposed STICH features brain-adaptive softness with Young’s modulus of ~9.46 kPa, which is sufficient to form a conformal interface with the cortex. Additionally, the STICH has high toughness of ~36.85 kJ/mm3, highlighting its robustness for maintaining the solid structure during interfacing with wet brain tissue. The stretchable metal electrodes with a wavy pattern printed on the elastomer were coated with the STICH as an interfacial layer, resulting in an improvement of the impedance from 60 kΩ to 10 kΩ at 1 kHz after coating. Acute in vivo experiments for ECoG monitoring were performed in anesthetized rodents, thereby successfully realizing conformal interfacing to the animal’s cortex and the sensitive recording of electrical activity using the STICH-coated electrodes, which exhibited a higher visual-evoked potential (VEP) amplitude than that of the control device

Injectable and tissue-conformable conductive hydrogel for MRI-compatible brain-interfacing electrodes

The development of flexible and stretchable materials has led to advances in implantable bio-integrated electronic devices that can sense physiological signals or deliver electrical stimulation to various organs in the human body. Such devices are particularly useful for neural interfacing systems that monitor neurodegenerative diseases such as Parkinson’s disease or epilepsy in real time. However, coupling current brain-interfacing devices with magnetic resonance imaging (MRI) remains a practical challenge due to resonance frequency variations from inorganic metal-based devices. Thus, organic conductive materials, such as poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), have recently been considered as promising candidates. Nonetheless, their conformability on curvilinear tissues remains questionable. In this study, we developed an injectable conductive hydrogel (ICH) composed of tyramine-conjugated hyaluronic acid (HATYR) and PEDOT:PSS for MRI-compatible brain-interfacing electrodes. Our ICH produced low impedance around 5 kΩ even under 10 Hz, demonstrating high confidence volumetric capacitance. Due to HATYR’s biocompatibility, histological and cytotoxicity assays showed almost no inflammation and toxicity, respectively; in addition, ICH was able to degrade into 40% of its original volume within four weeks in vivo. An electrocorticogram (ECoG) array was also patternable by syringe injections of ICH on a stretchable and flexible elastomeric substrate layer that conformed to curvy brain tissues and successfully recorded ECoG signals under light stimulation. Furthermore, MRI imaging of implanted devices did not show any artifacts, indicating the potential of the MRI-compatible hydrogel electrodes for advanced ECoG arrays. This study provides a promising solution for MRI-compatible neural electrodes, enabling the advancement of chronic neural interfacing systems for monitoring neurodegenerative diseases. © The Author(s) 2023. Open Access.11Nscopu

A Water-Resistant, Self-Healing Encapsulation Layer for a Stable, Implantable Wireless Antenna

Polymers for implantable devices are desirable for biomedical engineering applications. This study introduces a water-resistant, self-healing fluoroelastomer (SHFE) as an encapsulation material for antennas. The SHFE exhibits a tissue-like modulus (approximately 0.4 MPa), stretchability (at least 450%, even after self-healing in an underwater environment), self-healability, and water resistance (WVTR result: 17.8610 g m−2 day−1). Further, the SHFE is self-healing in underwater environments via dipole–dipole interactions, such that devices can be protected from the penetration of biofluids and withstand external damage. With the combination of the SHFE and antennas designed to operate inside the body, we fabricated implantable, wireless antennas that can transmit information from inside the body to a reader coil that is outside. For antennas designed considering the dielectric constant, the uniformity of the encapsulation layer is crucial. A uniform and homogeneous interface is formed by simply overlapping two films. This study demonstrated the possibility of wireless communication in vivo through experiments on rodents for 4 weeks, maintaining the maximum communication distance (15 mm) without chemical or physical deformation in the SHFE layer. This study illustrates the applicability of fluoroelastomers in vivo and is expected to contribute to realizing the stable operation of high-performance implantable devices

Resealable Antithrombotic Artificial Vascular Graft Integrated with a Self-Healing Blood Flow Sensor

Coronary artery bypass grafting is commonly used to treat cardiovascular diseases by replacing blocked blood vessels with autologous or artificial blood vessels. Nevertheless, the availability of autologous vessels in infants and the elderly and low long-term patency rate of grafts hinder extensive application of autologous vessels in clinical practice. The biological and mechanical properties of the resealable antithrombotic artificial vascular graft (RAAVG) fabricated herein, comprising a bioelectronic conduit based on a tough self-healing polymer (T-SHP) and a lubricious inner coating, match with the functions of autologous blood vessels. The self-healing and elastic properties of the T-SHP confer resistance against mechanical stimuli and promote conformal sealing of suturing regions, thereby preventing leakage (stable fixation under a strain of 50%). The inner layer of the RAAVG presents antibiofouling properties against blood cells and proteins, and antithrombotic properties, owing to its lubricious coating. Moreover, the blood-flow sensor fabricated using the T-SHP and carbon nanotubes is seamlessly integrated into the RAAVG via self-healing and allows highly sensitive monitoring of blood flow at low and high flow rates (10- and 100 mL min-1, respectively). Biocompatibility and feasibility of RAAVG as an artificial graft were demonstrated via ex vivo, and in vivo experiment using a rodent model. The use of RAAVGs to replace blocked blood vessels can improve the long-term patency rate of coronary artery bypass grafts.11Nsciescopu

Soft Bio-Integrated Multifunctional Devices Using an Intrinsically Stretchable Conducting Nanomembrane

Soft bioelectronic systems with a unique mechanical property, namely modulus matching between human skin (or tissue) and the device, have gained widespread attention. This is because of their closed-loop strain-insensitive electrical performance ranging from application in the long-term stable measurements of physiological signals and feedback modulation to human skin (or organs). Various materials and integration/fabrication strategies such as buckled, rigid islands, and wavy designs addressed for soft bioelectronic systems require complex device fabrication with time-consuming packaging and integration processes. In this study, we developed a soft bio-integrated multifunctional device (SBMD) fabricated through the simple thermal evaporation and transfer processes. The intrinsically stretchable Au–SEBS film composed of thermally evaporated gold (Au) nanomembranes and an elastomeric substrate was applied to various functional modules that are capable of sensing the strain (up to ~300%), temperature (with a thermal sensitivity of ~0.6 Ω/°C), chemicals (at a concentration of NaCl of ~0.5 wt%), and even electrophysiological cardiac/muscle signals and showing thermal actuations (80 °C at 9 V). Specifically, such multifunctions of the SBMD were stably performed even on skin. Thus, we believe the SBMD would be a promising candidate for realizing soft bioelectronic systems

A soft pressure sensor array based on a conducting nanomembrane

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.Although skin-like pressure sensors exhibit high sensitivity with a high performance over a wide area, they have limitations owing to the critical issue of being linear only in a narrow strain range. Various strategies have been proposed to improve the performance of soft pressure sensors, but such a nonlinearity issue still exists and the sensors are only effective within a very narrow strain range. Herein, we fabricated a highly sensitive multi-channel pressure sensor array by using a simple thermal evaporation process of conducting nanomembranes onto a stretchable substrate. A rigid-island structure capable of dissipating accumulated strain energy induced by external mechanical stimuli was adopted for the sensor. The performance of the sensor was precisely controlled by optimizing the thickness of the stretchable substrate and the number of serpentines of an Au membrane. The fabricated sensor exhibited a sensitivity of 0.675 kPa−1 in the broad pressure range of 2.3–50 kPa with linearity (~0.990), and good stability (>300 Cycles). Finally, we successfully demonstrated a mapping of pressure distribution.11Nsciescopu