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Flexible wearable pressure sensors still face the challenges of complex structure and high manufacturing costs. In this article, we present a simple method for preparing a highly sensitive, flexible wearable pressure sensor based on candle soot and porous PDMS foam. Meanwhile, to enhance the sensor’s robustness and practicality, a fully enclosed packaging design based on PDMS film was developed. The resulting sensor demonstrates excellent sensitivity, attributed to its porous structure, rough surface, and the unique properties of candle soot. Furthermore, the developed sensor can accurately detect movements in various parts of the human body and measure the force applied during finger pressing. This innovative porous PDMS/candle soot pressure sensor shows great potential for applications in wearable electronics.

Sensitive and flexible pressure sensors have invoked considerable interest for a broad range of applications in tactile sensing, physiological sensing, and flexible electronics. The barrier between high sensitivity and low fabrication cost needs to be addressed to commercialize such flexible pressure sensors. A low-cost sacrificial template-assisted method for the capacitive sensor has been reported herein, utilizing a porous Polydimethylsiloxane (PDMS) polymer and a multiwalled carbon nanotube (MWCNT) composite-based dielectric layer. The sensor shows high sensitivity of 2.42 kPa−1 along with a low limit of detection of 1.46 Pa. The high sensitivity originates from adding MWCNT to PDMS, increasing the composite polymer’s dielectric constant. Besides this, the pressure sensor shows excellent stability at a cyclic loading of 9000 cycles, proving its reliability for long-lasting application in tactile and physiological sensing. The high sensitivity of the sensor is suitable for the detection of small deformations such as pulse waveforms as well as tactile pressure sensing. In addition, the paper demonstrates a simultaneous contact and non-contact sensing capability suitable for dual sensing (pressure and proximity) with a single data readout system. The dual-mode sensing capability may open opportunities for realizing compact systems in robotics, gesture control, contactless applications, and many more. The practicality of the sensor was shown in applications such as tactile sensing, Morse code generator, proximity sensing, and pulse wave sensing.

In order to enhance the sensitivity of elastomers, pores were integrated into their structure. These pores facilitate the adjustment of thickness in response to external pressure variations, thereby improving the sensitivity of pressure sensors. Pores were introduced by emulsifying immiscible polydimethylsiloxane (PDMS) and water with a surfactant. By controlling the water content in the PDMS and water emulsion, we controlled the size, density, uniformity, and spatial distribution (2D or 3D) of the pores within the PDMS matrix. The presence of these pores significantly improved the sensitivity of PDMS under low external pressure conditions compared to high pressures. Specifically, porous PDMS exhibited approximately 10-times greater sensitivity under low-pressure conditions than non-porous PDMS. The effectiveness of porous PDMS was demonstrated through dynamic loading and unloading detection of a small Lego toy and monitoring of human heartbeats. These results highlight the efficacy of our pressure sensor based on porous PDMS, which is fabricated through a simple and cost-effective process using a PDMS and water emulsion. This approach is highly suitable for developing the ability to detect applied pressures or contact forces.

In many micro-capacitive pressure sensors, electrostatic forces are weak at larger gaps but strengthen considerably as the gap narrows. Achieving smooth movement and displacement necessitates a low initial mechanical stiffness in the sensor structure. This study introduces a porous polydimethylsiloxane (PDMS) elastomeric filler, which exhibits displacement-dependent porosity, leading to an increase in stiffness with displacement, a characteristic distinct from traditional air-gap designs where stiffness remains constant. This paper investigates the static instability of a micro-capacitive rectangular plate (MCRP), a crucial component in capacitive pressure sensors. The MCRP is supported by a porous PDMS filler and subjected to external pressure and electrostatic bias actuation. ​A novel aspect of this research involves realistically modeling the PDMS filler’s behavior by establishing a power-law relationship between its Young’s modulus and porosity, which is essential for accurately predicting the sensor’s response.​The MCRP is influenced by three primary forces: a downward measurement pressure, an upward mechanical pressure from the deflected PDMS filler, and a downward electrostatic pressure from the bias voltage. Utilizing nonlinear strain effects, the Airy stress function, and the Hamiltonian principle, we derive the governing coupled partial differential equations (PDEs) for static deflection, incorporating new terms that describe the PDMS filler’s behavior. These equations are then simplified using Galerkin’s method into a set of nonlinear algebraic equations and solved numerically. The sensitivity of the designed capacitive pressure sensor exhibits a remarkable increase when the porosity power index is below its critical value of$$\\:{n}_{cr}\\cong\\:1.18$$.​ Moreover, an increased power index value impacts sensitivity in two distinct ways. Firstly, it results in a reduction in the overall sensitivity of the sensor. Secondly, and conversely, it contributed to an expansion of the measurable pressure range. The finding can be beneficial for a variety of target applications as wearable electronics, health monitoring, robotics and human-machine interaction.

Flexible pressure sensors have received wide attention due to their potential applications in wearable electronics and electronic skins. It is still a challenge to manufacture high-sensitivity flexible pressure sensors in a low-cost and efficient way. In this study, a low-cost and simple method for preparing a flexible pressure sensor with porous structure based on physical foaming is proposed. The sensitivity of the flexible pressure sensor is 0.796 kPa−1 (applied pressure ≤ 2 kPa). In addition, the flexible pressure sensor has a low limit of detection of 4 Pa and a fast response time of 65 ms, and its performance remains unchanged after 1000 loading/unloading tests. This high performance enables flexible pressure sensors to detect touch and limb movement. Considering the good performance of the device, we expect that the sensor will provide broad application prospects in the fields of smart electronics and artificial intelligence.

Water, alcohols, diols, and glycerol are low-cost blowing agents that can be used to create the desired silicone foam structures. Although their combined use can be beneficial, it remains unclear how it affects the physical properties of the resulting materials. We conducted a comparative study of these hydroxyl-bearing blowing agents in fumed silica- and mica-filled polymer composite systems for simultaneous blowing and crosslinking to obtain a low-density, uniform porosity and superior mechanical properties. The foams were optimized for a uniform open-pore structure with densities ranging from 75 to 150 kg‧m−3. Varying the diol chain length (Cn) from one to seven carbons can alter the foam density and structure, thereby enhancing the foam tensile strength while maintaining a low density. Replacing 10 mol% of water with 1,4-butanediol decreased the density by 26%, while increasing the specific strength by 5%. By combining glycerol and water blowing, the resulting foams exhibited a 30% lower apparent density than their water-blown analogs. The results further showed that Cn > 4 alkane chain diols had an odd–even effect on the apparent density and cell wall thickness. All foamable compositions had viscosities of approximately 7000 cSt and curing times below 2 min, allowing for quick dispensing and sufficient time for the foam to cure in semi-industrial volumes.

Flexible electronic films need to be applied in different ambient temperatures. The porous substrate of the composite film enhances air permeability. The lifespan of these composite films is significantly affected by variations in temperature and substrate porosity. To explore the impact of temperature and porosity on the performance of composite films, we developed a 3D deformation detection system utilizing the advanced three-dimensional digital image correlation (3D-DIC) method. This system enabled us to observe and analyze the 3D deformation behaviors of porous polydimethylsiloxane (PDMS) flexible composite films when they are subjected to uniaxial stretching at different temperatures. We proposed employing two parameters, namely the strain fluctuation coefficient (M) and off-plane displacement (w), to characterize the 3D deformation of the films. This holistic characterization of deformation through the combined utilization of parameters M and w held greater significance for composite films compared to the conventional practice of solely measuring mechanical properties like the elastic modulus. Through experimental analysis, we discovered that as the temperature increased, the M value of the film decreased while the w value increased for the same stretching distance. Furthermore, the porosity of the composite film depended on the doping mass ratio of PDMS to deionized water during the fabrication process. Specifically, when the ratio was set at 6:1, the composite film exhibited the smallest M value and w value, and the highest air permeability. Additionally, the 3D deformation behavior remained stable across different temperatures for this specific ratio. Moreover, our findings unveiled a remarkable association between the parameter w and the resistance value of the device. These findings provide valuable insights for optimizing the fabrication process of porous PDMS flexible electronic composite films.

A hybrid sequential additive manufacturing process combined an extrusion syringe and a fused deposition modeling is developed to fabricate a porous PDMS based triboelectric sensor easily and environmentally. The porosity of the PDMS is controlled by using wet sugar particle sizes, and we fabricate a porous PDMS plate with a pore-to-volume ratio of 46%, which has 11 times larger internal contact area and 52.4% softer mechanical strength compared to a non-porous one. So, two key factors for high performance triboelectric sensor is obtained using the proposed method. A cylinder-shaped triboelectric sensor impregnated carbon black particles on the porous PDMS matrix, which is wearable on a finger, is fabricated for evaluation of its characteristics on detecting finger joint movements. From the experimental results, the sensor shows the ability to help quantitatively analyze finger movements, therefore, the proposed flexible triboelectric sensor can apply to athletes or patients around their knees, wrists, or other joints to analyze their physical behavior. Also, we believe that it can be utilized to measure various physical signals such as contact force, gripping force, and pressure with small values.

Flexible pressure sensors have many potential applications in the monitoring of physiological signals because of their good biocompatibility and wearability. However, their relatively low sensitivity, linearity, and stability have hindered their large-scale commercial application. Herein, a flexible capacitive pressure sensor based on an interdigital electrode structure with two porous microneedle arrays (MNAs) is proposed. The porous substrate that constitutes the MNA is a mixed product of polydimethylsiloxane and NaHCO3. Due to its porous and interdigital structure, the maximum sensitivity (0.07 kPa-1) of a porous MNA-based pressure sensor was found to be seven times higher than that of an imporous MNA pressure sensor, and it was much greater than that of a flat pressure sensor without a porous MNA structure. Finite-element analysis showed that the interdigital MNA structure can greatly increase the strain and improve the sensitivity of the sensor. In addition, the porous MNA-based pressure sensor was found to have good stability over 1500 loading cycles as a result of its bilayer parylene-enhanced conductive electrode structure. Most importantly, it was found that the sensor could accurately monitor the motion of a finger, wrist joint, arm, face, abdomen, eye, and Adam's apple. Furthermore, preliminary semantic recognition was achieved by monitoring the movement of the Adam's apple. Finally, multiple pressure sensors were integrated into a 3 × 3 array to detect a spatial pressure distribution. Compared to the sensors reported in previous works, the interdigital electrode structure presented in this work improves sensitivity and stability by modifying the electrode layer rather than the dielectric layer.

Severe to profound sensorineural hearing loss seriously affects the communication and cognitive ability of the patients. Cochlear implantation (CI) is currently the most effective treatment, while it may damage the remaining inner ear function due to its poor biocompatibility and the resultant fibrosis. Herein, a porous methacrylated poly(dimethylsiloxane) (MA‐PDMS)‐coated cochlear electrode is presented for CI and hearing protection. The porous MA‐PDMS is filled with a hybrid hydrogel system made of dexamethasone sodium phosphate (Dex), Ti3C2Tx MXene (MXene), and methacrylate gelatin (GelMA). The coating shows good biocompatibility and drug loading and release capacity in vitro, protective effects on hair cells (HCs) and spiral ganglion neurons (SGNs) of the inner ear, as well as the residual hearing protection and the effective fibrosis reduction in vivo. It is anticipated that this porous electrode drug‐loading coating may provide a valuable reference strategy for the future cochlear electrode transplantation system. This study presents a novel porous drug‐loading coating for cochlear electrodes, utilizing MA‐PDMS infused with GelMA hydrogel containing dexamethasone and MXene nanoparticles. The coating enhances biocompatibility, enables sustained drug release, reduces fibrosis, and preserves residual hearing post‐CI. This approach offers a promising strategy for improving cochlear electrode design and clinical outcomes.