Search Results (50)

Electroencephalography (EEG) electrodes require low impedance, high biocompatibility, and long-term performance. Conventional Ag/AgCl wet electrodes achieve low impedance but suffer from dehydration and skin irritation, whereas dry electrodes often induce discomfort or exhibit high impedance. To address these limitations, this study engineered a hydrogel-based electrode by incorporating PEDOT:PSS and the nonionic surfactant Triton X-100 into an acrylic acid hydrogel matrix. The flexible acrylic acid backbone, conductive PEDOT:PSS domains, and the nanofibrillar network promoted by Triton X-100 simultaneously enhanced mechanical compliance and electrical stability. In addition, the structural rearrangement of PEDOT:PSS was verified through morphological analyses. The fabricated electrode exhibited a modulus comparable to human soft tissue, demonstrated strong interfacial adhesion in shear tests, and significantly reduced skin–electrode contact impedance. Furthermore, EEG measurements showed that the hydrogel electrode achieved alpha- and beta-band signal power comparable to commercial Ag/AgCl electrodes. These findings establish the PEDOT:PSS–Triton X-100 hydrogel electrode as a promising candidate to replace conventional wet and dry electrodes for reliable EEG applications. Full article

Recent advancements in wearable electronics have significantly enhanced human–device interaction, enabling applications such as continuous health monitoring, advanced diagnostics, and augmented reality. While progress in material science has improved the flexibility, softness, and elasticity of these devices for better skin conformity, their optical properties, particularly transparency, remain relatively unexplored. Transparent wearable electronics offer distinct advantages: they allow for non-invasive health monitoring by enabling a clear view of biological systems and improve aesthetics by minimizing the visual presence of electronics on the skin, thereby increasing user acceptance. Hydrogels have emerged as a key material for transparent wearable electronics due to their high water content, excellent biocompatibility, and tunable mechanical and optical properties. Their inherent softness and stretchability allow intimate, stable contact with dynamic biological surfaces. Furthermore, their ability to support ion-based conductivity is advantageous for bioelectronic interfaces and physiological sensors. Current research is focused on advancing hydrogel design to improve transparency, mechanical resilience, conductivity, and adhesion. The core components of transparent wearable systems include physiological sensors, energy storage devices, actuators, and real-time displays. These must collectively balance efficiency, functionality, and long-term durability. Practical applications span continuous health tracking and medical imaging to next-generation interactive displays. Despite progress, challenges such as material durability, scalable manufacturing, and prolonged usability remain. Addressing these limitations will be crucial for the future development of transparent, functional, and user-friendly wearable electronics. Full article

As conductive materials, ionogels have attracted significant attention for their potential applications in flexible wearable electronics. However, preparing an ionogel with mechanical properties akin to human skin while also achieving transparency, adhesion, and low hysteresis through simple processes remains challenging. Here, we introduce a multifunctional ionogel synthesized via a one-step photopolymerization method. By leveraging the good compatibility between the ionic liquid and the polymer network, as well as the hydrogen bonding and chemical crosslinking within the gel network, we achieved an ionogel with high transparency (>98%), stretchability (fracture strain of 19), low hysteresis (<5.83%), strong adhesion, robust mechanical stability, excellent electrical properties, a wide operating temperature range, and a tunable modulus (1–103 kPa) that matches human skin. When used as a conductor in soft actuators, the ionogel enabled a large area strain of 36% and a fast electromechanical conversion time of less than 1 s. The actuator demonstrated good actuation performance with voltage and frequency dependence, electrochemical stability, and outstanding durability over millions of cycles. This study provides a simple and effective method to produce multifunctional ionogels with tailored mechanical properties that match those of human skin, paving the way for their application in flexible wearable electronics. Full article

Flexible, wearable biomedical sensors based on laser-induced graphene (LIG) have garnered significant attention due to a straightforward fabrication process and exceptional electrical and mechanical properties. However, most relevant studies rely on commercial polyimide precursors, which suffer from inadequate biocompatibility and weak adhesion between the precursor material and the LIG layer. To address these challenges, we synthesized cross-linked polyurethanes (PUs) with good biocompatibility and used them as substrates for LIG-based wearable pulse sensors. During fabrication, we employed two methods of LIG transfer to achieve optimal transfer yield. We adjusted the thickness of PU films and tailored their mechanical and physicochemical properties by varying the soft segment content to achieve optimal sensor performance. Our findings demonstrate that the success of LIG transfer is strongly influenced by the structure and composition of the polymeric substrate. Tensile testing revealed that increasing the soft segment content in PU films significantly improved their tensile strength, elongation at break, and flexibility, with PU based on 50 wt.% soft segment content (PU-50) showing the best mechanical properties. LIG exhibited minimal sensitivity to humidity, while PU films maintained high transparency (>80% at 500 nm), and PU-50 was non-toxic, with less than 5% lactate dehydrogenase (LDH) release in endothelial cell cultures, confirming its biocompatibility. Adhesion tests demonstrated that LIG transferred onto PU-50 exhibited significantly stronger adhesion compared to other tested substrates, with only a 30% increase in electrical resistance after the Scotch tape test, ensuring stability for wearable sensors. The optimal substrate, a semicrystalline PU-50, yielded superior transfer efficiency. Among all tested sensors, the LIG/PU-50, featuring a 77 μm thick substrate with good mechanical properties and improved adhesion, exhibited the highest signal-to-noise ratio (SNR). This study showcases a skin-safe LIG/PU-based pulse sensor that has significant potential for applications as a wearable patch in medical and sports monitoring. Full article

Electronic skin (e-skin) is an innovative technology characterized by its flexibility, stretchability, and self-healing properties, designed to biomimic the functionalities of human or animal skin. This technology is well-suited for applications in robotics, prosthetics, and health monitoring since it can sense a wide range of tactile signals, such as humidity, pressure, temperature, and stress. Developing e-skin for wearable devices faces several challenges. One major challenge is the need for soft and stretchable electronic materials, as conventional materials are brittle. Furthermore, the development of skin-like hydrogel devices for wearable electronics faces challenges such as limited functionality, low ambient stability, poor surface adhesion, and relatively high power consumption. Innovation in this area has the potential to pay off. Organizations that invest in and develop innovative e-skin technologies based on biomimetic hydrogels can secure intellectual property rights through patents. This study is dedicated to reviewing the state of the art by presenting what has been patented concerning biomimetic-hydrogel-based e-skin. At the end, a section presents relevant patents to demonstrate the innovation and formulation of such hydrogels as biomimetic materials for e-skin applications. A market overview of e-skins is also presented. This contextualizes the significance of research in biomimetic-hydrogel-based e-skins within the broader commercial landscape. Full article

Percutaneous implants osseointegrated into the residuum of a person with limb amputation need to provide mechanical stability and protection against infections. Although significant progress has been made in the biointegration of percutaneous implants, the problem of forming a reliable natural barrier at the level of the surface of the implant and the skin and bone tissues remains unresolved. The use of a microporous implant structure incorporated into the Skin and Bone Integrated Pylon (SBIP) should address the issue by allowing soft and bone tissues to grow directly into the implant structure itself, which, in turn, should form a reliable barrier to infections and support strong osseointegration. To evaluate biological interactions between dermal fibroblasts and MC3T3-E1 osteoblasts in vitro, small titanium discs (with varying pore sizes and volume fractions to achieve deep porosity) were fabricated via 3D printing and sintering. The cell viability MTT assay demonstrated low cytotoxicity for cells co-cultured in the pores of the 3D-printed and sintered Ti samples during the 14-day follow-up period. A subsequent Quantitative Real-Time Polymerase Chain Reaction (RT-PCR) analysis of the relative gene expression of biomarkers that are associated with cell adhesion (α2, α5, αV, and β1 integrins) and extracellular matrix components (fibronectin, vitronectin, type I collagen) demonstrated that micropore sizes ranging from 200 to 500 µm of the 3D printed and sintered Ti discs were favorable for dermal fibroblast adhesion. For example, for representative 3D-printed Ti sample S6 at 72 h the values were 4.71 ± 0.08 (α2 integrin), 4.96 ± 0.08 (α5 integrin), 4.71 ± 0.08 (αV integrin), and 1.87 ± 0.12 (β1 integrin). In contrast, Ti discs with pore sizes ranging from 400 to 800 µm demonstrated the best results (in terms of marker expression related to osteogenic differentiation, including osteopontin, osteonectin, osteocalcin, TGF-β1, and SMAD4) for MC3T3-E1 cells. For example, for the representative 3D sample S4 on day 14, the marker levels were 11.19 ± 0.77 (osteopontin), 7.15 ± 0.29 (osteonectin), and 6.08 ± 0.12 (osteocalcin), while for sintered samples the levels of markers constituted 5.85 ± 0.4 (osteopontin), 4.45 ± 0.36 (osteonectin), and 4.46 ± 0.3 (osteocalcin). In conclusion, the data obtained show the high biointegrative properties of porous titanium structures, while the ability to implement several pore options in one structure using 3D printing makes it possible to create personalized implants for the best one-time integration with both skin and bone tissues. Full article

Biomimetic micro-hexagonal-textured surfaces have sparked interest for their application in fields that demand high friction and adhesion, such as micro-robotics and biomedicine. Despite extensive research conducted on this specific microstructure, its friction behavior against soft counterfaces remains a topic that has not been fully investigated yet. This study examines how micro-hexagon textures behave when they come into contact with engineered and biological materials like gelatin and chicken skin in dry and wet conditions. The results show clearly that under dry contact conditions, flat surfaces generate higher friction compared to hexagon micropattern surfaces. Under wet conditions, hexagon micropattern surfaces generate higher friction compared to flat surfaces. In wet conditions specifically, the static coefficient of friction is up to 13 times greater than that of a flat specimen against glass, up to 11 times greater against gelatin, and up to 6 times greater against chicken skin. For the dynamic coefficient of friction, the patterned surface demonstrates a maximum increase by a factor of 28 against glass, 11 against gelatin, and 5 against chicken skin. These results further develop our knowledge of these hexagon micropattern surfaces and pave the way for their utilization in future technological advancements in which soft and wet counterfaces are to be considered, such as in biomedical applications that can benefit from increased friction in wet conditions for better control and stability. Full article

Background: The most problematic complication of external fixation is infection at the pin insertion site. Technology that improves the adhesion of the external fixation pin to the skin, subcutaneous tissue, and bone may prevent infection at the pin site. The purpose of this study is to formulate a calcium phosphate–fibroblast growth factor (Cp-FGF) coating on a stainless-steel external fixation pin and to verify its effectiveness in reducing infection at the pin site and its possible influence on bone fixation in animal experiments. Methods: We compared stainless-steel screws without coating (SS group; n = 32), those with a calcium phosphate coating (Cp group; n = 30), those with a Cp-FGF coating (FGF group; n = 32), and those with a Cp-FGF coating having enhanced biological activity (FGF+ group; n = 32) in male Japanese white domesticated rabbits. Screws were inserted percutaneously into the bilateral proximal tibial diaphysis of the rabbits and implanted for 4 weeks. Screws and periscrew tissue were observed postoperatively for qualitatively assessing infection. Results: Infection assessment by gross findings after 4 weeks (at screw removal) showed no significant differences between the groups. Histopathological evaluation of soft tissue infection and bone tissue infection showed no significant differences between the groups for either soft tissue or bone tissue. Since neither the FGF+ group nor the FGF group showed anti-infective effects, the biological activity of FGF is not the only determining factor. We compared SEM, XRD, coating detaching test, sustained release test, and bioassay to examine physicochemical properties among the coatings but found no sufficient differences. Conclusions: It is suggested that improving the tissue adhesion to and/or biocompatibility of pins is also important to improve the in vivo performance of Cp-FGF-coated external fixation pins. Full article

Here, we report an ultrasoft extra long-lasting, reusable hydrogel-based sensor that enables high-quality electrophysiological recording with low-motion artifacts. The developed sensor can be used and stored in an ambient environment for months before being reused. The developed sensor is made of a self-adhesive electrical-conductivity-enhanced ultrasoft hydrogel mounted in an Ecoflex-based frame. The hydrogel’s conductivity was enhanced by incorporating polypyrrole (PPy), resulting in a conductivity of 0.25 S m⁻¹. Young’s modulus of the sensor is only 12.9 kPa, and it is stretchable up to 190%. The sensor was successfully used for electrocardiography (ECG) and electromyography (EMG). Our results indicate that using the developed hydrogel-based sensor, the signal-to-noise ratio of recorded electrophysiological signals was improved in comparison to that when medical-grade silver/silver chloride (Ag/AgCl) wet gel electrodes were used (33.55 dB in comparison to 22.16 dB). Due to the ultra-softness, high stretchability, and self-adhesion of the developed sensor, it can conform to the skin and, therefore, shows low susceptibility to motion. In addition, the sensor shows no sign of irritation or allergic reaction, which usually occurs after long-term wearing of medical-grade Ag/AgCl wet gel electrodes on the skin. Further, the sensor is fabricated using a low-cost and scalable fabrication process. Full article

Silk fibroin (SF) extracted from silk is non-toxic and has excellent biocompatibility and biodegradability, making it an excellent biomedical material. SF-based soft materials, including porous scaffolds and hydrogels, play an important role in accurately delivering drugs to wounds, creating microenvironments for the adhesion and proliferation of support cells, and in tissue remodeling, repair, and wound healing. This article focuses on the study of SF protein-based soft materials, summarizing their preparation methods and basic applications, as well as their regenerative effects, such as drug delivery carriers in various aspects of tissue engineering such as bone, blood vessels, nerves, and skin in recent years, as well as their promoting effects on wound healing and repair processes. The authors expect SF soft materials to play an important role in the field of tissue repair. Full article

For ultrasound diagnosis, a gel is applied to the skin. Ultrasound gel serves to block air exposure and match impedance between the skin and the probe, enhancing imaging efficiency. However, if use of the ultrasound gel exceeds a certain period of time, it may dry out and be exposed to air, causing impedance mismatch and reducing imaging resolution. In such cases, the use of a soft, solid gel proves advantageous, as it can be employed for an extended period without succumbing to the drying phenomenon and can be reused after disinfection. Its soft consistency ensures excellent skin adhesion. Our soft solid gel demonstrated approximately 1.2 times better performance than water, silicone, and traditional ultrasound gels. When comparing the dimensions of grayscale, dead zone, vertical, and horizontal regions, the measurements for the traditional ultrasound gel were 93.79 mm, 45.32 mm, 103.13 mm, 83.86 mm, and 83.86 mm, respectively. In contrast, the proposed soft solid gel exhibited dimensions of 105.64 mm, 34.48 mm, 141.1 mm, and 102.8 mm. Full article

Polyacrylates and polysiloxanes are polymers used in pressure-sensitive adhesive (PSA) patches. Liquid additives are co-solvents of the active substances or permeation enhancers, and their compatibility with the polymeric matrix and the effect on adhesive properties should be considered. The patches were prepared from commercial polyacrylates (three types of Duro-Tak^®) and siloxanes (Bio-PSA^® and Soft Skin Adhesive^®). Propylene glycol, polyoxyethylene glycol, isopropyl myristate, triacetin, triethyl citrate and silicone oil were added (10% w/w). Formulations were evaluated microscopically and with a texture analyzer in terms of in vitro adhesiveness and hardness. Only silicone oil was compatible with the silicone matrices. The best compatibility of acrylic PSA was observed with triethyl citrate; one out of three Duro-Tak matrices was incompatible with every additive. In all compositions, the adhesiveness was impaired by the liquid additives. A significant drop in adhesiveness was noted after immersion of the patches in buffer and drying. The probe tack test was considered as the most useful for evaluation of the effect of the liquid additive on adhesiveness, but the results obtained with a spherical and cylindrical probe were contradictory. The structural changes caused by the additives were also demonstrated by a 90° peel test, considered as complementary to the tack test. Full article

Skin has a dynamic surface and offers essential information through biological signals originating from internal organs, blood vessels, and muscles. Soft and stretchable bioelectronics can be used in wearable machines for long-term stability and to continuously obtain distinct bio-signals in conjunction with repeated expansion and contraction with physical activities. While monitoring bio-signals, the electrode and skin must be firmly attached for high signal quality. Furthermore, the signal-to-noise ratio (SNR) should be high enough, and accordingly, the ionic conductivity of an adhesive hydrogel needs to be improved. Here, we used a chitosan-alginate-chitosan (CAC) triple hydrogel layer as an interface between the electrodes and the skin to enhance ionic conductivity and skin adhesiveness and to minimize the mechanical mismatch. For development, thermoplastic elastomer Styrene-Ethylene-Butylene-Styrene (SEBS) dissolved in toluene was used as a substrate, and gold nanomembranes were thermally evaporated on SEBS. Subsequently, CAC triple layers were drop-casted onto the gold surface one by one and dried successively. Lastly, to demonstrate the performance of our electrodes, a human electrocardiogram signal was monitored. The electrodes coupled with our CAC triple hydrogel layer showed high SNR with clear PQRST peaks. Full article

In wearable bioelectronics, various studies have focused on enhancing prosthetic control accuracy by improving the quality of physiological signals. The fabrication of conductive composites through the addition of metal fillers is one way to achieve stretchability, conductivity, and biocompatibility. However, it is difficult to measure stable biological signals using these soft electronics during physical activities because of the slipping issues of the devices, which results in the inaccurate placement of the device at the target part of the body. To address these limitations, it is necessary to reduce the stiffness of the conductive materials and enhance the adhesion between the device and the skin. In this study, we measured the electromyography (EMG) signals by applying a three-layered hydrogel structure composed of chitosan–alginate–chitosan (CAC) to a stretchable electrode fabricated using a composite of styrene–ethylene–butylene–styrene and eutectic gallium-indium. We observed stable adhesion of the CAC hydrogel to the skin, which aided in keeping the electrode attached to the skin during the subject movement. Finally, we fabricated a multichannel array of CAC-coated composite electrodes (CACCE) to demonstrate the accurate classification of the EMG signals based on hand movements and channel placement, which was followed by the movement of the robot arm. Full article

Flexible bioelectronics exhibit promising potential for health monitoring, owing to their soft and stretchable nature. However, the simultaneous improvement of mechanical properties, biocompatibility, and signal-to-noise ratio of these devices for health monitoring poses a significant challenge. Hydrogels, with their loose three-dimensional network structure that encapsulates massive amounts of water, are a potential solution. Through the incorporation of polymers or conductive fillers into the hydrogel and special preparation methods, hydrogels can achieve a unification of excellent properties such as mechanical properties, self-healing, adhesion, and biocompatibility, making them a hot material for health monitoring bioelectronics. Currently, hydrogel-based bioelectronics can be used to fabricate flexible bioelectronics for motion, bioelectric, and biomolecular acquisition for human health monitoring and further clinical applications. This review focuses on materials, devices, and applications for hydrogel-based bioelectronics. The main material properties and research advances of hydrogels for health monitoring bioelectronics are summarized firstly. Then, we provide a focused discussion on hydrogel-based bioelectronics for health monitoring, which are classified as skin-attachable, implantable, or semi-implantable depending on the depth of penetration and the location of the device. Finally, future challenges and opportunities of hydrogel-based bioelectronics for health monitoring are envisioned. Full article