Non-hygroscopic ionogel-based humidity-insensitive iontronic sensor arrays for intra-articular pressure sensing.

Implanted pressure sensors can provide pressure information to assess localized health conditions of specific tissues or organs, such as the intra-articular pressure within knee joints. However, the prerequisites for implanted sensors pose greater challenges than those for wearables or for robots: aside from biocompatibility and tissue-like softness, they must also exhibit humidity insensitivity and high-pressure resolution across a broad pressure spectrum. Iontronic sensors can provide superior sensing properties, but they undergo property degradation in wet environments due to the hygroscopic nature of their active component: ionogels.

High-resolution flexible iontronic skins for both negative and positive pressure measurement in room temperature wind tunnel applications.

Flexible skins that can be laminated on curved surfaces are a desired form for wind pressure measurement. Sensors for such applications need to detect both negative and positive wind pressure with ultrahigh pressure resolution over a wide range up to 600 kPa, whereas existing flexible sensors are unsatisfactory to such demands. Here, we report a flexible skin containing two iontronic pressure sensors for negative pressure and positive pressure sensing, respectively, and show the potential of the skin for pressure measurement in room temperature wind tunnels.

Mussel-Bioinspired Lignin Adhesive for Wearable Bioelectrodes.

As a natural "binder," lignin fixes cellulose in plants to foster growth and longevity. However, isolated lignin has a poor binding ability, which limits its biomedical applications. In this study, inspired by mussel adhesive proteins, acidic/basic amino acids (AAs) are introduced in alkali lignin (AL) to form ionic-π/spatial correlation interactions, followed by demethylation to create catechol residues for enhanced adhesion activity.

Data-driven inverse design of flexible pressure sensors.

Artificial skins or flexible pressure sensors that mimic human cutaneous mechanoreceptors transduce tactile stimuli to quantitative electrical signals. Conventional trial-and-error designs for such devices follow a forward structure-to-property routine, which is usually time-consuming and determines one possible solution in one run. Data-driven inverse design can precisely target desired functions while showing far higher productivity, however, it is still absent for flexible pressure sensors because of the difficulties in acquiring a large amount of data.

Tailoring Stress-Strain Curves of Flexible Snapping Mechanical Metamaterial for On-Demand Mechanical Responses via Data-Driven Inverse Design.

By incorporating soft materials into the architecture, flexible mechanical metamaterials enable promising applications, e.g., energy modulation, and shape morphing, with a well-controllable mechanical response, but suffer from spatial and temporal programmability towards higher-level mechanical intelligence.

A bioadhesive pacing lead for atraumatic cardiac monitoring and stimulation in rodent and porcine models.

Current clinically used electronic implants, including cardiac pacing leads for epicardial monitoring and stimulation of the heart, rely on surgical suturing or direct insertion of electrodes to the heart tissue. These approaches can cause tissue trauma during the implantation and retrieval of the pacing leads, with the potential for bleeding, tissue damage, and device failure. Here, we report a bioadhesive pacing lead that can directly interface with cardiac tissue through physical and covalent interactions to support minimally invasive adhesive implantation and gentle on-demand removal of the device with a detachment solution.

Integrated Fibrous Iontronic Pressure Sensors with High Sensitivity and Reliability for Human Plantar Pressure and Gait Analysis.

Flexible sensing systems (FSSs) designed to measure plantar pressure can deliver instantaneous feedback on human movement and posture. This feedback is crucial not only for preventing and controlling diseases associated with abnormal plantar pressures but also for optimizing athletes' postures to minimize injuries. The development of an optimal plantar pressure sensor hinges on key metrics such as a wide sensing range, high sensitivity, and long-term stability.

Displacement-pressure biparametrically regulated softness sensory system for intraocular pressure monitoring.

High intraocular pressure (IOP) is one of the high-risk pathogenic factors of glaucoma. Existing methods of IOP measurement are based on the direct interaction with the cornea. Commercial ophthalmic tonometers based on snapshot measurements are expensive, bulky, and their operation requires trained personnel.

Ultrafast piezocapacitive soft pressure sensors with over 10 kHz bandwidth via bonded microstructured interfaces.

Flexible pressure sensors can convert mechanical stimuli to electrical signals to interact with the surroundings, mimicking the functionality of the human skins. Piezocapacitive pressure sensors, a class of most widely used devices for artificial skins, however, often suffer from slow response-relaxation speed (tens of milliseconds) and thus fail to detect dynamic stimuli or high-frequency vibrations. Here, we show that the contact-separation behavior of the electrode-dielectric interface is an energy dissipation process that substantially determines the response-relaxation time of the sensors.

Mechanical Tester Driven by Surface Tension.

The measurement of in-plane mechanical properties, such as Young's modulus and strength, of thin and stretchable materials has long been a challenge. Existing measurements, including wrinkle instability and nano indentation, are either indirect or destructive, and are inapplicable to meshes or porous materials, while the conventional tension test fails to measure the mechanical properties of nanoscale films. Here, we report a technique to test thin and stretchable films by loading a thin film afloat via differential surface tension and recording its deformation.

Creep-free polyelectrolyte elastomer for drift-free iontronic sensing.

Artificial pressure sensors often use soft materials to achieve skin-like softness, but the viscoelastic creep of soft materials and the ion leakage, specifically for ionic conductors, cause signal drift and inaccurate measurement. Here we report drift-free iontronic sensing by designing and copolymerizing a leakage-free and creep-free polyelectrolyte elastomer containing two types of segments: charged segments having fixed cations to prevent ion leakage and neutral slippery segments with a high crosslink density for low creep. We show that an iontronic sensor using the polyelectrolyte elastomer barely drifts under an ultrahigh static pressure of 500 kPa (close to its Young's modulus), exhibits a drift rate two to three orders of magnitude lower than that of the sensors adopting conventional ionic conductors and enables steady and accurate control for robotic manipulation.

A robotic sensory system with high spatiotemporal resolution for texture recognition.

Humans can gently slide a finger on the surface of an object and identify it by capturing both static pressure and high-frequency vibrations. Although modern robots integrated with flexible sensors can precisely detect pressure, shear force, and strain, they still perform insufficiently or require multi-sensors to respond to both static and high-frequency physical stimuli during the interaction. Here, we report a real-time artificial sensory system for high-accuracy texture recognition based on a single iontronic slip-sensor, and propose a criterion-spatiotemporal resolution, to corelate the sensing performance with recognition capability.

Arteriosclerosis Assessment Based on Single-Point Fingertip Pulse Monitoring Using a Wearable Iontronic Sensor.

Arteriosclerosis, which appears as a hardened and narrowed artery with plaque buildup, is the primary cause of various cardiovascular diseases such as stroke. Arteriosclerosis is often evaluated by clinically measuring the pulse wave velocity (PWV) using a two-point approach that requires bulky medical equipment and a skilled operator. Although wearable photoplethysmographic sensors for PWV monitoring are developed in recent years, likewise, this technique is often based on two-point measurement, and the signal can easily be interfered with by natural light.

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.

Embedment of sensing elements for robust, highly sensitive, and cross-talk-free iontronic skins for robotics applications.

Iontronic pressure sensors are promising in robot haptics because they can achieve high sensing performance using nanoscale electric double layers (EDLs) for capacitive signal output. However, it is challenging to achieve both high sensitivity and high mechanical stability in these devices. Iontronic sensors need microstructures that offer subtly changeable EDL interfaces to boost sensitivity, while the microstructured interfaces are mechanically weak.

A Tough Hydrogel Adhesive for the Repair of Archeological Pottery.

Pottery is the oldest art and plays a landmark role in human civilization. The repair of ceramic relics often uses acrylic resins and cyanoacrylate adhesives. However, existing adhesives often take hours to get cured, and wet adhesion is not possible.

Partial Liquid Alloy Microdroplet Sedimentation Induced a Gradient Porous Structured Elastomer with a Tunable Property for an Anisotropic Robotic Bulk.

With the confrontation of ever increasing complicated working objects and unstructured environments, it is necessary for soft robots to be equipped with diverse intelligent mechanical structures, for example, anisotropically motorial bulk and timely proprio/exteroceptive sensing with programmable morphologies. Owing to abundant pores inside, porous media are promising to host various intelligent functions as interfaces/structures of robots yet challenging because of a limited anisotropic response inherited from a random hierarchical pore distribution. Here, an electron competition between Ga, N, and Pt is found and used to tune the polymerization of a gradient liquid alloy and NHHCO-suspended silicone precursor mixture and, thus, decompose gas movements in gradient pore formation under high-temperature heating (120 °C).

High-throughput fabrication of soft magneto-origami machines.

Soft magneto-active machines capable of magnetically controllable shape-morphing and locomotion have diverse promising applications such as untethered biomedical robots. However, existing soft magneto-active machines often have simple structures with limited functionalities and do not grant high-throughput production due to the convoluted fabrication technology. Here, we propose a facile fabrication strategy that transforms 2D magnetic sheets into 3D soft magneto-active machines with customized geometries by incorporating origami folding.

Strong Interfaces Enable Efficient Load Transfer for Strong, Tough, and Impact-Resistant Hydrogel Composites.

Many biological hydrogels are mechanically robust to bear quasi-static and impact loads. In contrast, the mechanical properties of synthetic hydrogels against impact loads remain substantially unexplored, albeit their mechanical robustness under quasi-static loads has been extensively developed. Here, we report on the design and synthesis of strong, tough, and impact-resistant hydrogel composites by reinforcing Ca-alginate/polyacrylamide hydrogels with glass fabrics and conferring strong interfaces between the hydrogel matrix and the fibers.

A strain-programmed patch for the healing of diabetic wounds.

Diabetic foot ulcers and other chronic wounds with impaired healing can be treated with bioengineered skin or with growth factors. However, most patients do not benefit from these treatments. Here we report the development and preclinical therapeutic performance of a strain-programmed patch that rapidly and robustly adheres to diabetic wounds, and promotes wound closure and re-epithelialization.

Fabrication of patterned solid surfaces with highly controllable wettability.

Precisely controlling the wettability of a solid surface is vital for a wide range of applications such as control of liquid droplet motion, water collection and the directional transport of fluids. However, fabricating a large-area solid surface with highly controllable wettability in a low-cost way is still challenging. Here we present a cost-effective method to fabricate patterned solid surfaces with highly controllable wettability by combining chemical etching technique, chemical vapor deposition technique and laser direct writing technique.

Current and Future Trends for Polymer Micro/Nanoprocessing in Industrial Applications.

Polymers are widely used in optical devices, electronic devices, energy-harvesting/storage devices, and sensors, owing to their low weight, excellent flexibility, and simple fabrication process. With advancements in micro/nanoprocessing techniques and more demanding application requirements, it is becoming necessary to realize high-resolution fabrication of polymers to prepare miniaturized devices. This is particularly because conventional processing technologies suffer from high thermal stress and strong adhesion/friction, which can irreversibly damage the micro/nanostructures of miniaturized devices.

Highly stable flexible pressure sensors with a quasi-homogeneous composition and interlinked interfaces.

Electronic skins (e-skins) are devices that can respond to mechanical stimuli and enable robots to perceive their surroundings. A great challenge for existing e-skins is that they may easily fail under extreme mechanical conditions due to their multilayered architecture with mechanical mismatch and weak adhesion between the interlayers. Here we report a flexible pressure sensor with tough interfaces enabled by two strategies: quasi-homogeneous composition that ensures mechanical match of interlayers, and interlinked microconed interface that results in a high interfacial toughness of 390 J·m.

Graded Interlocks for Iontronic Pressure Sensors with High Sensitivity and High Linearity over a Broad Range.

Flexible pressure sensors that have high sensitivity, high linearity, and a wide pressure-response range are highly desired in applications of robotic sensation and human health monitoring. The challenge comes from the incompressibility of soft materials and the stiffening of microstructures in the device interfaces that lead to gradually saturated response. Therefore, the signal is nonlinear and pressure-response range is limited.

Highly Conducting and Stretchable Double-Network Hydrogel for Soft Bioelectronics.

Conducting polymer hydrogels are promising materials in soft bioelectronics because of their tissue-like mechanical properties and the capability of electrical interaction with tissues. However, it is challenging to balance electrical conductivity and mechanical stretchability: pure conducting polymer hydrogels are highly conductive, but they are brittle; while incorporating the conducting network with a soft network to form a double network can improve the stretchability, its electrical conductivity significantly decreases. Here, the problem is addressed by concentrating a poorly crosslinked precursor hydrogel with a high content ratio of the conducting polymer to achieve a densified double-network hydrogel (5.