Dual-Scale Porous Composite for Tactile Sensor with High Sensitivity over an Ultrawide Sensing Range.

Porous structures have been utilized in tactile sensors to improve sensitivity owing to their excellent deformability. Recently, tactile sensors using porous structures have been used in practical applications, such as bio-signal monitoring. However, highly sensitive responses are limited to the low-pressure range, and their sensitivity significantly decreases in a higher-pressure range. Several approaches for developing tactile sensors with high sensitivity overing a wide pressure range have been proposed; however, achieving high sensitivity and wide sensing range remains a crucial challenge. This report presents a carbon nanotube (CNT)-coated CNT-polydimethylsiloxane (PDMS) composite having dual-scale pores for tactile sensors with high sensitivity over a wide pressure range. The porous polymer frame formed with dense pores of dual sizes facilitates the closure of large and small pores at low and high pressures, respectively. This results in an apparent increase in the number of contact points between the CNT-CNT at the pores even under a wide pressure range. Furthermore, the piezoresistivity of the CNT-PDMS composite contributes to achieving a high sensitivity of the tactile sensor over a wide pressure range. Based on these mechanisms, various human movements over a broad pressure spectrum are monitored to investigate the practical usefulness of the sensor.

Location-specific fabrication of suspended nanowires using electrospun fibers on designed microstructure.

While there have been remarkable improvements in the fabrication of suspended nanowires, placing a single nanowire at the desired location remains to be a challenging task. In this study, a simple method is proposed to fabricate suspended nanowires at desired locations using an electrospinning process and a designed microstructure. Using electrospun polymer fibers on the designed microstructure as a sacrificial template, various materials are deposited on it, and the electrospun fibers are selectively removed, leaving only nanowires of the deposited material. After the polymer fibers are removed, the remaining metal fibers agglomerate into a single nanowire. Throughout this process, including the removal of the polymer fibers, the samples are not exposed to high temperatures or chemicals, thereby allowing the formation of nanowires without oxidation or contamination. The diameter of the nanowire can be controlled in the electrospinning process, and a suspended Pd nanowire with a minimum diameter of 100 nm is fabricated. Additionally, a suspended single Pd nanowire-based H2gas sensor fabricated using the proposed process exhibits a highly sensitive response to H2gas.

Ultrasensitive Strain Sensor Based on Separation of Overlapped Carbon Nanotubes.

Although there have been remarkable improvements in stretchable strain sensors, the development of strain sensors with scalable fabrication techniques and which both high sensitivity and stretchability simultaneously is still challenging. In this work, a stretchable strain sensor based on overlapped carbon nanotube (CNT) bundles coupled with a silicone elastomer is presented. The strain sensor with overlapped CNTs is prepared by synthesizing line-patterned vertically aligned CNT bundles and rolling and transferring them to the silicone elastomer. With the sliding and disconnection of the overlapped CNTs, the strain sensor performs excellently with a broad sensing range (≥145% strain), ultrahigh sensitivity (gauge factor of 42 300 at a strain of 125-145%), high repeatability, and durability. The performance of the sensor is also tunable by controlling the overlapped area of CNT bundles. Detailed mechanisms of the sensor and its applications in human motion detection are also further investigated. With the novel structure and mechanism, the sensor can detect a wide range of strains with high sensitivity, demonstrating the potential for numerous applications including wearable healthcare devices.

Humidity-resistant triboelectric energy harvester using electrospun PVDF/PU nanofibers for flexibility and air permeability.

We present a triboelectric energy harvester fabricated with a simple electrospinning process of polyvinylidene fluoride/polyurethane polymers on conductive fabric. This electrospinning process provides higher electrical power output and hydrophobicity driven humidity resistance compared to flat polymer energy harvesters. By using conductive fabric as collector and electrode, the device could retain air permeability and flexibility. The triboelectric energy harvester exhibits a high open-circuit voltage of 45.1 V (at a compressive contact force of 20 N and relative humidity (RH) of 20%), humidity resistance (maintains about 40% of the open-circuit voltage at RH of 80%) and air permeability without deteriorating the air permeability of the fabric. Its durability was tested and shows no significant degradation of electrical output throughout 324,000 cycles of operation. This work suggests an approach for human energy harvesting in textile form with electrospun nanofibers as the contact surfaces of a triboelectric energy harvester.

Heterogeneous Integration of Carbon-Nanotube-Graphene for High-Performance, Flexible, and Transparent Photodetectors.

Low-dimensional carbon materials, such as semiconducting carbon nanotubes (CNTs), conducting graphene, and their hybrids, are of great interest as promising candidates for flexible, foldable, and transparent electronics. However, the development of highly photoresponsive, flexible, and transparent optoelectronics still remains limited due to their low absorbance and fast recombination rate of photoexcited charges, despite the considerable potential of photodetectors for future wearable and foldable devices. This work demonstrates a heterogeneous, all-carbon photodetector composed of graphene electrodes and porphyrin-interfaced single-walled CNTs (SWNTs) channel, exhibiting high photoresponse, flexibility, and full transparency across the device. The porphyrin molecules generate and transfer photoexcited holes to the SWNTs even under weak white light, resulting in significant improvement of photoresponsivity from negligible to 1.6 × 10-2 A W-1 . Simultaneously, the photodetector exhibits high flexibility allowing stable light detection under ≈50% strain (i.e., a bending radius of ≈350 µm), and retaining a sufficient transparency of ≈80% at 550 nm. Experimental demonstrations as a wearable sunlight sensor highlight the utility of the photodetector that can be conformally mounted on human skin and other curved surfaces without any mechanical and optical constraints. The heterogeneous integration of porphyrin-SWNT-graphene may provide a viable route to produce invisible, high-performance optoelectronic systems.

A Novel Conductive and Micropatterned PEG-Based Hydrogel Enabling the Topographical and Electrical Stimulation of Myoblasts.

In this study, we designed a cell-adhesive poly(ethylene glycol) (PEG)-based hydrogel that simultaneously provides topographical and electrical stimuli to C2C12 myoblasts. Specifically, PEG hydrogels with microgroove structures of 3 µm ridges and 3 µm grooves were prepared by micromolding; in situ polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) was then performed within the micropatterned PEG hydrogels to create a microgrooved conductive hydrogel (CH/P). The CH/P had clear replica patterns of the silicone mold and a conductivity of 2.49 × 10-3 S/cm, with greater than 85% water content. In addition, the CH exhibited Young's modulus (45.84 ± 7.12 kPa) similar to that of a muscle tissue. The surface of the CH/P was further modified via covalent bonding with cell-adhesive peptides to facilitate cell adhesion without affecting conductivity. An in vitro cell assay revealed that the CH/P was cytocompatible and enhanced the cell alignment and elongation of C2C12 myoblasts. The microgrooves and conductivity of the CH/P had the greatest positive effect on the myogenesis of C2C12 myoblasts compared to the other PEG hydrogel samples without conductivity or/and microgrooves, even in the absence of electrical stimulation. Electrical stimulation studies indicated that the combination of topographical and electrical cues maximized the differentiation of C2C12 myoblasts into myotubes, confirming the synergetic effect of incorporating microgroove surface features and a conductive PEDOT component into hydrogels.