Advances in materials and devices for mimicking sensory adaptation

Adaptive Processing Enabled by Sodium Alginate Based Complementary Memristor for Neuromorphic Sensory System

Adaptive processing allows sensory systems to autonomically adjust their sensitivity with exposure to a constant sensory stimulus and thus organisms to adapt to environmental variations. Bioinspired electronics with adaptive functions are highly desirable for the development of neuromorphic sensory systems (NSSs). Herein, the functions of desensitization and sensitivity changing with background intensity (i.e., Weber's law), as two fundamental cues of sensory adaptation, are biorealistically demonstrated in an Ag nanowire (NW)-embedded sodium alginate (SA) based complementary memristor. In particular, Weber's law is experimentally emulated in a single complementary memristor. Furthermore, three types of adaptive NSS unit are constructed to realize a multiple perceptual capability that processes the stimuli of illuminance, temperature, and pressure signals. Taking neuromorphic vision as an example, scotopic and photopic adaptation functions are well reproduced for image enhancement against dark and bright backgrounds. Importantly, an NSS system with multisensory integration function is demonstrated by combining light and pressure spikes, where the accuracy of pattern recognition is obviously enhanced relative to that of an individual sense. This work offers a new strategy for developing neuromorphic electronics with adaptive functions and paves the way toward developing a highly efficient NSS.

Memory effect and coexistence of negative and positive photoconductivity in black phosphorus field effect transistor for neuromorphic vision sensors

Black phosphorus (BP) field-effect transistors with ultrathin channels exhibit unipolar p-type electrical conduction over a wide range of temperatures and pressures. Herein, we study a device that exhibits mobility up to 100 cm2 V-1 s-1 and a memory window up to 1.3 μA. Exposure to a supercontinuum white light source reveals that negative photoconductivity (NPC) and positive photoconductivity (PPC) coexist in the same device. Such behavior is attributed to the chemisorbed O2 molecules, with a minor role of physisorbed H2O molecules. The coexistence of NPC and PPC can be exploited in neuromorphic vision sensors, requiring the human eye retina to process the optical signals through alerting and protection (NPC), adaptation (PPC), followed by imaging and processing. Our results open new avenues for the use of BP and other two-dimentional (2D) semiconducting materials in transistors, memories, and neuromorphic vision sensors for advanced applications in robotics, self-driving cars, etc.

Biomimetic dual sensing polymer nanocomposite for biomedical applications

There is a growing need for sensing materials that can provide multiple sensing capabilities for wearable devices, implantable sensors, and diagnostics tools. As complex human physiology requires materials that can simultaneously detect and respond to slow and fast pressure fluctuations. Mimicking the slow adaptive (SA) and fast adaptive (FA) mechanoreceptors in skin can lead to the development of dual sensing electrospun polymer nanocomposites for biomedical applications. These dual sensing nanocomposites can provide simultaneous sensing of both slow and fast pressure fluctuations, making them ideal for applications such as monitoring vital signs, detecting a wider range of movements and pressures. Here we develop a novel dual sensing PVDF-HFP-based nanocomposite that combines the advantages of capacitive and piezoelectric properties through controling electrospinning environment and processing parameters, polymer solution composition, and addition of nucleating agents such as Carbon Black (CB) to enhance the crystalline development of β-phase, fibre thickness, and morphology. The developed PVDF-HFP/CB nanocomposite presents and response to both slow and fast pressure fluctuations with high capacitance (5.37 nF) and output voltage (1.51 V) allowing for accurate and reliable measurements.

Enhancing the Uniformity of Organic Field-Effect Transistors by a Single-Crystalline Layer-Controlled Active Channel

Despite remarkable improvement in the mobility of the organic field-effect transistors (OFETs) being achieved in past decades, the uniformity in electrical performance remains ambiguous, impeding their implantation in organic integrated circuits. The coefficient of variance (CV) in mobility of reported OFETs is typically larger than 8%, which is not adequate for building medium-to-large scale integrated circuits. In this work, it is shown that utilizing single-domain molecular monolayer crystals as the active channel can largely enhance the uniformity of OFETs. Benefiting from the sole molecular layer with long-range ordering, the OFETs exhibit uniformities in both channel transport and charge injection, thereby giving rise to a high average mobility of 11.64 cm2 V-1 s-1 and CV of only 2.57%. Statistical transmission length method evaluation is conducted, covering channel length from 3 to 21 µm, channel width from 90 to 170 µm, and a total OFET number of 370. The low contact resistance of 79.00 ± 7.00 Ω cm and high intrinsic mobility of 12.36 ± 0.45 cm2 V-1 s-1 are acquired with very high accuracy and reliability. As such, this work provides a practical way to enhance the uniformity of OFETs by a single-crystalline layer-controlled active channel toward their applications in integrated circuits.

Effects of textured insoles and elastic braces on dynamic stability in patients with functional ankle instability

BACKGROUND

Functional ankle instability (FAI) is a common condition that affects individuals who have experienced previous ankle sprains. Textured insoles and elastic ankle braces have been previously used as interventions to improve stability in FAI patients. However, the optimal combination of these interventions has not been fully explored. The objective of this study was to investigate the effects of different types of textured insoles and elastic ankle braces on the dynamic stability of individuals diagnosed with FAI.

METHODS

The study involved 18 FAI patients who performed single-leg landing tasks with and without wearing an eight-band elastic ankle brace while wearing textured insoles with protrusion heights of 0 mm, 1 mm, and 2 mm. The dynamic posture stability index (DPSI) and its components in the anterior-posterior (APSI), mediolateral (MLSI) and vertical (VSI) directions were calculated from the ground reaction force collected from the Kistler force plate during the first three seconds of the landing tasks.

RESULTS

A significant interaction was found between textured insole type and ankle brace for DPSI (P = 0.026), APSI (P = 0.001), and VSI (P = 0.021). However, no significant interaction was observed for MLSI (P = 0.555). With elastic ankle braces, textured insoles with 1-mm protrusions significantly enhanced anterior-posterior, mediolateral, vertical, and overall stability compared to textured insoles with no and 2 mm protrusions (P < 0.05). Without elastic ankle braces, textured insoles with 1-mm protrusions significantly improved the anterior-posterior (P = 0.012) and overall stability (P = 0.014) of FAI patients compared to smooth insoles.

CONCLUSIONS

The combination of textured insoles with 1-mm protrusion heights and an elastic ankle brace could enhance the dynamic stability of individuals with FAI, potentially mitigating the risk of ankle sprains.

Technology Roadmap for Flexible Sensors

Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Progress of Materials and Devices for Neuromorphic Vision Sensors

The latest developments in bio-inspired neuromorphic vision sensors can be summarized in 3 keywords: smaller, faster, and smarter. (1) Smaller: Devices are becoming more compact by integrating previously separated components such as sensors, memory, and processing units. As a prime example, the transition from traditional sensory vision computing to in-sensor vision computing has shown clear benefits, such as simpler circuitry, lower power consumption, and less data redundancy. (2) Swifter: Owing to the nature of physics, smaller and more integrated devices can detect, process, and react to input more quickly. In addition, the methods for sensing and processing optical information using various materials (such as oxide semiconductors) are evolving. (3) Smarter: Owing to these two main research directions, we can expect advanced applications such as adaptive vision sensors, collision sensors, and nociceptive sensors. This review mainly focuses on the recent progress, working mechanisms, image pre-processing techniques, and advanced features of two types of neuromorphic vision sensors based on near-sensor and in-sensor vision computing methodologies.