Recent Advances in Biomimetics for the Development of Bio-Inspired Prosthetic Limbs.

Recent advancements in biomimetics have spurred significant innovations in prosthetic limb development by leveraging the intricate designs and mechanisms found in nature. Biomimetics, also known as "nature-inspired engineering", involves studying and emulating biological systems to address complex human challenges. This comprehensive review provides insights into the latest trends in biomimetic prosthetics, focusing on leveraging knowledge from natural biomechanics, sensory feedback mechanisms, and control systems to closely mimic biological appendages. Highlighted breakthroughs include the integration of cutting-edge materials and manufacturing techniques such as 3D printing, facilitating seamless anatomical integration of prosthetic limbs. Additionally, the incorporation of neural interfaces and sensory feedback systems enhances control and movement, while technologies like 3D scanning enable personalized customization, optimizing comfort and functionality for individual users. Ongoing research efforts in biomimetics hold promise for further advancements, offering enhanced mobility and integration for individuals with limb loss or impairment. This review illuminates the dynamic landscape of biomimetic prosthetic technology, emphasizing its transformative potential in rehabilitation and assistive technologies. It envisions a future where prosthetic solutions seamlessly integrate with the human body, augmenting both mobility and quality of life.

A study on the fabrication of metal microneedle array electrodes for ECG detection based on low melting point Bi-In-Sn alloys.

This study describes the fabrication and characteristics of microneedle array electrodes (MAEs) using Bismuth-Indium-Tin (Bi-In-Sn) alloys. The MAEs consist of 57 pyramid-shaped needles measuring 340 µm wide and 800 µm high. The fabrication process involved micromolding the alloys in a vacuum environment. Physical tests demonstrated that Bi-In-Sn MAEs have good mechanical strength, indicating their suitability for successful skin penetration. The electrode-skin interface impedance test confirmed that Bi-In-Sn MAEs successfully penetrated the skin. Impedance measurements revealed the importance of insulating the microneedle electrodes for optimal electrical performance, and a UV-curable Polyurethane Acrylate coating was applied to enhance insulation. Electrocardiogram measurements using the Bi-In-Sn MAEs demonstrated performance comparable to that of traditional Ag/AgCl electrodes, which shows promise for accurate data collection. Overall, the study demonstrates successful, minimally-invasive skin insertion, improved electrical insulation, and potential applications of Bi-In-Sn microneedle array. These findings contribute to advancements in microneedle technology for biomedical applications.

Nature-Inspired Chiral Structures: Fabrication Methods and Multifaceted Applications.

Diverse chiral structures observed in nature find applications across various domains, including engineering, chemistry, and medicine. Particularly notable is the optical activity inherent in chiral structures, which has emerged prominently in the field of optics. This phenomenon has led to a wide range of applications, encompassing optical components, catalysts, sensors, and therapeutic interventions. This review summarizes the imitations and applications of naturally occurring chiral structures. Methods for replicating chiral architectures found in nature have evolved with specific research goals. This review primarily focuses on a top-down approach and provides a summary of recent research advancements. In the latter part of this review, we will engage in discussions regarding the diverse array of applications resulting from imitating chiral structures, from the optical activity in photonic crystals to applications spanning light-emitting devices. Furthermore, we will delve into the applications of biorecognition and therapeutic methodologies, comprehensively examining and deliberating upon the multifaceted utility of chiral structures.

Improving the Performance of Polydimethylsiloxane-Based Triboelectric Nanogenerators by Introducing CdS Particles into the Polydimethylsiloxane Layer.

Energy harvesting and power generation technologies hold significant potential for meeting future energy demands and improving environmental sustainability. A triboelectric nanogenerator (TENG), which harnesses energy from the surrounding environment, has garnered significant attention as a promising and sustainable power source applicable in various fields. In this study, we present a technique to improve the triboelectric performance of a PDMS-based TENG by incorporating nanostructured cadmium sulfide (N-CdS). This study investigates the utilization of CdS nanomaterials in TENG production, where mechanical energy is converted into electrical energy. We conducted a comparative analysis of TENGs utilizing N-CdS/PDMS, commercial CdS/PDMS (C-CdS/PDMS), and pure PDMS substrates. The N-CdS/PDMS substrates demonstrated superior triboelectric performance compared to TENG devices based on pure PDMS and C-CdS/PDMS. The triboelectric open-circuit voltage (Voc) and short-circuit current (Isc) of the N-CdS/PDMS-based TENG device were approximately 236 V and 17.4 µA, respectively, when operated at a 2 Hz frequency. These values were approximately 3 times and 2.5 times higher, respectively, compared to the pure PDMS-based TENGs. They were further studied in detail to understand the effect of different parameters such as contact-separation frequency and contact force on the TENGs' operation. The stability of the TENG devices was studied, and their potential to be integrated into self-powered smart textiles as power sources was demonstrated.

Patterning Techniques in Coplanar Micro/Nano Capacitive Sensors.

Rapid technological advancements have led to increased demands for sensors. Hence, high performance suitable for next-generation technology is required. As sensing technology has numerous applications, various materials and patterning methods are used for sensor fabrication. This affects the characteristics and performance of sensors, and research centered specifically on these patterns is necessary for high integration and high performance of these devices. In this paper, we review the patterning techniques used in recently reported sensors, specifically the most widely used capacitive sensors, and their impact on sensor performance. Moreover, we introduce a method for increasing sensor performance through three-dimensional (3D) structures.

Amplifying the Output of a Triboelectric Nanogenerator Using an Intermediary Layer of Gallium-Based Liquid Metal Particles.

The production of energy has become a major issue in today's world. Triboelectric nanogenerators (TENGs) are promising devices that can harvest mechanical energy and convert it into electrical energy. This study explored the use of Galinstan particles in the production of TENGs, which convert mechanical energy into electrical energy. During the curing process, the evaporation of the hexane solvent resulted in a film with varying concentrations of Galinstan particles. The addition of n-hexane during ultrasonication reduced the viscosity of the polydimethylsiloxane (PDMS) solution, allowing for the liquid metal (LM) particles to be physically pulverized into smaller pieces. The particle size distribution of the film with a Galinstan concentration of 23.08 wt.% was measured to be within a few micrometers through ultrasonic crushing. As the amount of LM particles in the PDMS film increased, the capacitance of the film also increased, with the LM/PDMS film with a 23.08% weight percentage exhibiting the highest capacitance value. TENGs were created using LM/PDMS films with different weight percentages and tested for open-circuit voltage, short-circuit current, and charge amount Q. The TENG with an LM/PDMS film with a 23.08% weight percentage had the highest relative permittivity, resulting in the greatest voltage, current, and charge amount. The use of Galinstan particles in PDMS films has potential applications in wearable devices, sensors, and biomedical fields.

Eco-Friendly Keratin-Based Additives in the Polymer Matrix to Enhance the Output of Triboelectric Nanogenerators.

A triboelectric nanogenerator (TENG) is an energy generator that converts mechanical energy into electrical energy using triboelectricity at a nanoscale. Given their potential application as power sources in electronic devices, various attempts have been made to improve their output performance. Here, we present an eco-friendly, low-cost, and facile fabrication method to enhance TENG characteristics with keratin protein additives. Keratin sources, human and cat hair, are processed into powder and added to the friction layer, which increases their positive charge affinity, thereby boosting the output performance of the TENG. The output performances of the keratin-added TENG (K-TENG) are measured in the vertical contact-separation mode, with both additives having the highest output values at 5 wt % load. The K-TENG generates more output voltage and current values than the pristine TENG by 90 and 208%, respectively. Hence, we conclude that this method would potentially promote TENG as a strong candidate for a competitive "green" energy harvesting device in future electronics applications.

Simple Fabrication of Photodetectors Based on MoS2 Nanoflakes and Ag Nanoparticles.

Low-dimensional transition-metal dichalcogenides (TMDs) have recently emerged as promising materials for electronics and optoelectronics. In particular, photodetectors based on mono- and multilayered molybdenum disulfide (MoS2) have received much attention owing to their outstanding properties, such as high sensitivity and responsivity. In this study, photodetectors based on dispersed MoS2 nanoflakes (NFs) are demonstrated. MoS2 NFs interact with Ag nanoparticles (NPs) via low-temperature annealing, which plays a crucial role in determining device characteristics such as good sensitivity and short response time. The fabricated devices exhibited a rapid response and recovery, good photo-responsivity, and a high on-to-off photocurrent ratio under visible light illumination with an intensity lower than 0.5 mW/cm2.

Intaglio Contact Printing of Versatile Carbon Nanotube Composites and Its Applications for Miniaturizing High-Performance Devices.

Composites based on carbon nanotubes (CNTs) are promising patternable materials that can be engineered to incorporate the outstanding properties of CNTs into various applications via printing technologies. However, conventional printing methods for CNTs require further improvement to overcome the major drawbacks that limit the patterning resolution and target substrate. Herein, an intaglio contact printing method based on a CNT/paraffin composite is presented for realizing highly precise CNT network patterns without restrictions on the substrate. In this method, the CNT/paraffin composite can be patterned with a high resolution (<10 µm) and neatly transferred onto various substrates with a wide range of surface energies, including human skin. The patterned composite exhibits high durability against structural deformations, and structural damage caused by fatigue accumulation can be cured in a few seconds. In addition, miniaturized sensing and energy-harvesting applications are demonstrated with high performances. The present method facilitates the rapid fabrication of highly precise interdigitated electrodes via one-step printing, enabling high-performance operation and miniaturization of the devices. It is anticipated that these results will not only spur the further development of various applications of CNTs but also contribute to advances in soft lithography methods applicable to many fields of science and engineering.

Flexible and Stretchable Liquid Metal Electrodes Working at Sub-Zero Temperature and Their Applications.

We investigated characteristics of highly flexible and stretchable electrodes consisting of Galinstan (i.e., a gallium-based liquid metal alloy) under various conditions including sub-zero temperature (i.e., <0 °C) and demonstrated solar-blind photodetection via the spontaneous oxidation of Galinstan. For this work, a simple and rapid method was introduced to fabricate the Galinstan electrodes with precise patterns and to exfoliate their surface oxide layers. Thin conductive films possessing flexibility and stretchability can be easily prepared on flexible substrates with large areas through compression of a dried suspension of Galinstan microdroplets. Furthermore, a laser marking machine was employed to facilitate patterning of the Galinstan films at a high resolution of 20 µm. The patterned Galinstan films were used as flexible and stretchable electrodes. The electrical conductivity of these electrodes was measured to be ~1.3 × 106 S m-1, which were still electrically conductive even if the stretching ratio increased up to 130% below 0 °C. In addition, the surface oxide (i.e., Ga2O3) layers possessing photo-responsive properties were spontaneously formed on the Galinstan surfaces under ambient conditions, which could be solely exfoliated using elastomeric stamps. By combining Galinstan and its surface oxide layers, solar-blind photodetectors were successfully fabricated on flexible substrates, exhibiting a distinct increase of up to 14.7% in output current under deep ultraviolet irradiation (254 nm wavelength) with an extremely low light intensity of 0.1 mW cm-2, whereas no significant change was observed under visible light irradiation.

Fabrication of a Flexible Photodetector Based on a Liquid Eutectic Gallium Indium.

A fluidic gallium-based liquid metal (LM) is an interesting material for producing flexible and stretchable electronics. A simple and reliable method developed to facilitate the fabrication of a photodetector based on an LM is presented. A large and thin conductive eutectic gallium indium (EGaIn) film can be fabricated with compressed EGaIn microdroplets. A solution of LM microdroplets can be synthesized by ultrasonication after mixing with EGaIn and ethanol and then dried on a PDMS substrate. In this study, a conductive LM film was obtained after pressing with another substrate. The film was sufficiently conductive and stretchable, and its electrical conductivity was 2.2 × 106 S/m. The thin film was patterned by a fiber laser marker, and the minimum line width of the pattern was approximately 20 µm. Using a sticky PDMS film, a Ga2O3 photo-responsive layer was exfoliated from the fabricated LM film. With the patterned LM electrode and the transparent photo-responsive film, a flexible photodetector was fabricated, which yielded photo-response-current ratios of 30.3%, 14.7%, and 16.1% under 254 nm ultraviolet, 365 nm ultraviolet, and visible light, respectively.

Multiplex lithography for multilevel multiscale architectures and its application to polymer electrolyte membrane fuel cell.

The production of multiscale architectures is of significant interest in materials science, and the integration of those structures could provide a breakthrough for various applications. Here we report a simple yet versatile strategy that allows for the LEGO-like integrations of microscale membranes by quantitatively controlling the oxygen inhibition effects of ultraviolet-curable materials, leading to multilevel multiscale architectures. The spatial control of oxygen concentration induces different curing contrasts in a resin allowing the selective imprinting and bonding at different sides of a membrane, which enables LEGO-like integration together with the multiscale pattern formation. Utilizing the method, the multilevel multiscale Nafion membranes are prepared and applied to polymer electrolyte membrane fuel cell. Our multiscale membrane fuel cell demonstrates significant enhancement of performance while ensuring mechanical robustness. The performance enhancement is caused by the combined effect of the decrease of membrane resistance and the increase of the electrochemical active surface area.

Microfluidic platforms with monolithically integrated hierarchical apertures for the facile and rapid formation of cargo-carrying vesicles.

We fabricated a simple yet robust microfluidic platform with monolithically integrated hierarchical apertures. This platform showed efficient diffusive mixing of the introduced lipids through approximately 8000 divisions with tiny pores (~5 µm in diameter), resulting in massive, real-time production of various cargo-carrying particles via multi-hydrodynamic focusing.

Replication of flexible polymer membranes with geometry-controllable nano-apertures via a hierarchical mould-based dewetting.

Membranes with nano-apertures are versatile templates that possess a wide range of electronic, optical and biomedical applications. However, such membranes have been limited to silicon-based inorganic materials to utilize standard semiconductor processes. Here we report a new type of flexible and free-standing polymeric membrane with nano-apertures by exploiting high-wettability difference and geometrical reinforcement via multiscale, multilevel architecture. In the method, polymeric membranes with various pore sizes (50-800 nm) and shapes (dots, lines) are fabricated by a hierarchical mould-based dewetting of ultraviolet-curable resins. In particular, the nano-pores are monolithically integrated on a two-level hierarchical supporting layer, allowing for the rapid (<5 min) and robust formation of multiscale and multilevel nano-apertures over large areas (2 × 2 cm(2)).

Multiscale transfer printing into recessed microwells and on curved surfaces via hierarchical perfluoropolyether stamps.

A simple method for the formation of multiscale metal patterns is presented using hierarchical polymeric stamps with perfluoropolyether (PFPE). A dual-scale PFPE structure is made via two-step moulding process under partial photocrosslinking conditions. The hierarchical PFPE stamp enables multiscale transfer printing (MTP) of metal pattern in one step within microwells as well as on curved surfaces.

One-step fabrication of nanowire-grid polarizers using liquid-bridge-mediated nanotransfer molding.

Ag nanowire-grid polarizers (NWGPs) were prepared by a one-step fabrication method, called liquid-bridge-mediated nanotransfer molding (LB-nTM). LB-nTM is a new direct nano-patterning method based on the direct transfer of various materials from a mold to a substrate via liquid layer. We fabricated NWGPs with Ag nanowire arrays (81 nm parallel lines and 119 nm spaces) on 2.5 in. transparent substrates by LB-nTM using an Ag nanoparticle solution. The maximum and minimum transmittances of the Ag NWGP at 800 nm were 80% and 10%, respectively.

Efficiency improvement of organic solar cells by tuning hole transport layer with germanium oxide.

Improving optical property is critical for optimizing the power conversion efficiency of organic solar cells. In the present research, we show that modification of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layer with GeO2 leads to 15% improvement of power conversion efficiency in a polymer solar cells through enhancement of short circuit currents. Modified PEDOT:PSS layer with optimized concentration of GeO2 assists active layer absorbing much light by playing a role of optical spacer. Using AFM and grazing incidence X-ray diffraction (GIXD) data, we also present the evidence that an addition of GeO2 does not affect crystallinity of active layer.

Epithelial cell patterns on a PDMS polymer surface using a micro plasma structure.

We developed a simple and reproducible epithelial cell-patterning tool on a PDMS (polydimethylsiloxane) polymer surface using a micro plasma structure that did not require chemical or biological treatment. The concept behind this novel approach was based on the fact that cells should easily adhere to the plasma-treated PDMS surface and not the inherent PDMS surface. The micro plasma structure consisted of copper and SU-8 photoresist on a glass substrate. A predetermined space (micro plasma chamber) was formed between the copper electrode layer on the upper part and the PDMS plate surrounded by the SU-8 photoresist structure. The single cell pattern was achieved by introducing a micro-plasma structure of 30 µm in width. Using this approach, a closed cell pattern was successfully developed using a micro chamber structure that was 200 µm in diameter with a microchannel that was 10 µm in width.

The fabrication of protein nano arrays using 3-dimensional plastic nanopillar patterns.

A plastic nanopillar array was used as the basis for development of a cheap, spatially patterned immobilization method that was applied to nano biochips. A plastic nanopillar array (diameter: 500 nm, height: 1.2 microm) was fabricated using poly(urethane acrylate) (PUA) by simple and fast UV-curable soft lithography. Antibodies were immobilized on top of the nanopillar structure due to the 'lotus effect'; the aqueous solution containing proteins could only contact the top portion of the nanopillar array due to the hydrophobicity of the surface. This phenomenon was verified by atomic force microscopy and confocal microscopy. Optimal conditions were investigated to effectively generate a clear protein pattern on the nanopillar array. The immunoreaction capability of captured antibodies immobilized on the nano pattern was validated using various concentrations of complimentary antibodies.