Porous Porous Polydimethylsiloxane Research Articles

Enhanced stretchability of porous PDMS/CIP composites via weak interfacial bonding and their electromagnetic noise suppression properties

The development of wearable devices operated through massive data communication necessitates the use of lightweight, highly efficient stretchable composites to suppress electromagnetic (EM) noise. In this study, highly stretchable porous polydimethylsiloxane (PDMS)/carbonyl iron powder (CIP) composite-based EM noise suppressors were explored. The porous structure reduced the volume fraction of PDMS in the composites, leading to a reduction in the total weight of the composites. The introduction of CIP to porous PDMS initially degraded stretchability owing to stress concentration at the strongly bonded interfaces between the CIP surface and PDMS. However, reducing the interfacial bonding strength by removing the SiO2 layer on the CIP surface significantly enhanced stretchability, causing the resulting composite to display 1.2–1.6 times higher rupture strain values at the same CIP loading contents than those with high interfacial bonding strength. The EM absorption properties of the porous and nonporous PDMS/CIP composites were characterized, and the porous PDMS/CIP composites exhibited ∼1.5 times higher EM noise suppression performance than the nonporous composites. This improvement is attributed to the vacant space within the porous framework filled with air, which enhances impedance matching and extends the transmission route of EM waves.

Highly Flexible and Sensitive Pressure Sensor: Fabrication of Porous PDMS/Graphene Composite via Laser Thermoforming

AbstractFlexible pressure sensors employing porous polymer materials are renowned for their superior sensing capabilities, attributed to the inherently low stiffness of porous polymers. The practical utilization of such sensors hinges on the development of a straightforward, cost‐effective, and patternable method for preparing porous polymer materials. In this research, a novel laser thermoforming process is introduced to craft a porous Polydimethylsiloxane (PDMS) film, leveraging carbon black (CB) as an endothermic agent and glucose as a porogen. The resulting porous PDMS film serves as the foundation for a remarkably sensitive flexible piezoresistive sensor. Owing to the inherent flexibility endowed by the porous structure, the porous PDMS‐based pressure sensor achieves a remarkable sensitivity of 109.4 kPa−1 within 0–200 Pa, an effective measurement span of 0–100 kPa, rapid response and recovery times of 79 and 55 ms, and impressive stability over 5000 cycles. The sensor's utility extends to applications such as human pulse monitoring, Morse coding, and robot claw sensing, underscoring its promise in the realm of flexible electronics. In summary, the laser thermoforming process realizes the one‐step, economical, and patternable preparation of porous polymer materials, and introduces a novel avenue for the realization of high‐performance flexible sensors based on thermally cured porous polymers.

Enhancing biomedical applications: Modifying porous poly-di-methyl-siloxane (PDMS) structures with magnetite nanoparticles (MNPs) to improve interaction with normal human breast cells (MCF10A cells)

The phenomenon of cell-biomaterial interaction is responsible for adherent cells' adhesion to the biomaterial surface and the corresponding cell activities. The study aimed to enhance biocompatibility and versatility by modification of porous PDMS structures with MNPs for their safe interaction with normal human breast cells, MCF10A cell line. Preparation of the MNP-modified porous PDMS substrate was carried out by mixing a silicone elastomer base with a curing agent at a specific ratio, typically in a 10:1, followed by modification with MNP and the creation of pores of different dimensions. The substrate was subsequently characterized with Fourier-transform infrared spectroscopy. Furthermore, the assessment of cell proliferation and fluorescence imaging was done using the Alamar blue assay and fluorescence microscopy, respectively. The result of the study showed that PDMS + MNP (non-porous) did not significantly differ in percentage Alamar blue reduction at 4 hours when compared to PDMS + MNP_0-150, PDMS + MNP_150-250, and PDMS + MNP_250-500. Additionally, all the groups differed significantly (P>0.05) from one another at 48 and 96 h, except the PDMS+MNP_150-250 group compared to the PDMS+MNP_250-500 group, which did not exhibit any significant differences (P>0.05). The result further showed that when compared to all other groups, the fluorescence imaging result revealed that, after 96 h, there was very little cell attachment and proliferation on the surface of PDMS+MNP (non-porous). Other groups demonstrated discernable cell adhesion and proliferation over time. These outcomes demonstrate the significance of porosity in influencing cellular interactions and highlight its role in cell proliferation on biomaterial.

Structure–mechanical property relationships of 3D-printed porous polydimethylsiloxane films

Abstract Complex microstructures can be produced from different base materials by combining three-dimensional (3D) printing technology and ink formulations. The surface wettability of the 3D-printed porous polydimethylsiloxane (PDMS), particularly its superhydrophobic property, strongly depends on its physical structure. However, the mechanism underlying the effect of the microporous structure on the mechanical properties is not understood, which seriously constrains the structural–functional integration design of the 3D-printed superhydrophobic porous PDMS. To solve this problem, we studied the influence of the printing parameters on the mechanical properties in the compression and tension directions using a finite element method. The results showed that the load transfer path of the 3D-printed porous PDMS was along the overlapping area of the adjacent filaments. As the filament spacing decreased or the filament diameter increased, the elastic modulus of the porous PDMS was enhanced, improving its resistance to tensile and compressive deformation. A quantitative relationship was established between the relative densities of the porous PDMS films and their relative elastic moduli. This study provides theoretical guidance for the structural–functional integration design of 3D-printed superhydrophobic porous PDMS.

Solid Reservoir Reference Electrode

Potentiometric sensing requires a stable sensing electrode that is selectively responsive to an analyte, and a reference electrode (RE) that provides a stable and well-defined reference potential in a liquid electrolytic environment. In sensor applications where compactness and ease of integration are essential characteristics, pseudo-REs in the form of doped polymer semiconductors, bare metal films, or a bare chlorinated silver film are typically used. Bulk glass electrodes, such as the Ag/AgCl electrode, are incompatible with sensor integration.We report here a solid reservoir reference electrode (SRRE) that achieves the performance of traditional immersed wire Ag/AgCl REs in a compact, layered structure. The SRRE is a solid, layered analogue of the Ag/AgCl RE, with a chlorinated silver film as metallic electrode, a solid KCl layer serving as a saturated reservoir of chloride, and a porous polydimethylsiloxane (PDMS) layer acting as membrane for exchange of water and ions. We demonstrate two different method to fabricate the porous PDMS in figure A and B. The characteristics of the SRRE, including impedance, noise, and long-term drift, can be tuned by adjustment of the PDMS membrane permeance and KCl solid reservoir size.We have demonstrated temporal stability of the RE open circuit potential (OCP), with drift less than 0.37 mV over 17 hours in deionized water. When compared against bare chlorinated silver, the SRRE exhibits superior stability of OCP versus changes in electrolyte ion-concentration, including solutions of potassium chloride, sodium chloride and pH buffers. The ease of fabrication enables SRRE integration with graphene ion-sensitive field effect transistors (ISFETs) to achieve entirely solid-contact micro ion sensors. The solid-contact micro ion sensor can simultaneously measure pH and Na+, in volumes as low as 20 μL. Using the same layered structure, we further demonstrated fabricated electrocardiogram (ECG) and electroencephalogram (EEG) electrodes with significantly lower impedance and noise when compared to disposable gel electrodes. Finally, we have shown that the SRRE can function in non-aqueous solventssuch as acetonitrile, demonstrating the wide range of SRRE applications. Figure 1

A Study on the 3D Deformation Behavior of Porous PDMS Flexible Electronic Composite Films Stretched under Different Temperatures.

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.

Porous polydimethylsiloxane films with specific surface wettability but distinct regular physical structures fabricated by 3D printing.

Porous polydimethylsiloxane (PDMS) films with special surface wettability have potential applications in the biomedical, environmental, and structural mechanical fields. However, preparing porous PDMS films with a regular surface pattern using conventional methods, such as chemical foaming or physical pore formation, is challenging. In this study, porous PDMS films with a regular surface pattern are designed and prepared using 3D printing to ensure the formation of controllable and regular physical structures. First, the effect of the surface wettability of glass substrates with different surface energies (commercial hydrophilic glass and hydrophobic glass (F-glass) obtained by treating regular glass with 1H,1H,2H,2H-perfluorooctyl-trichlorosilane) on the structural characteristics of the 3D printed PDMS filaments is investigated systematically. Additionally, the effect of the printing speed and the surface wettability of the glass substrate on the PDMS filament morphology is investigated synchronously. Next, using the F-glass substrate and an optimized printing speed, the effects of the number of printed layers on both the morphologies of the individual PDMS filaments and porous PDMS films, and the surface wettability of the films are studied. This study reveals that regularly patterned porous PDMS films with distinct structural designs but the same controllable surface wettability, such as anisotropic surface wettability and superhydrophobicity, can be easily fabricated through 3D printing. This study provides a new method for fabricating porous PDMS films with a specific surface wettability, which can potentially expand the application of porous PDMS films.

Novel Graphene Transfer Method to Silicone and its Sensing Application on Porous PDMS

In this work, we demonstrate a simple and sensitive parallel-plate capacitive pressure sensor fabricated on biocompatible, weather durable, elastic composite silicone and polyurethane substrate with porous polydimethylsiloxane (PDMS) dielectric made through a mixture of water as spacers. This sensor comprised a graphene electrode, which was developed through novel chemical vapor deposition on copper with hot press transfer process. The sensitivity of the sensor exhibits a positive correlation with the dielectric porosity. In addition, this device exhibits fast response time and wide dynamic window for applications. The highest sensitivity of 3.01 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> at 20% water concentration in PDMS for the dynamic range of 0–40 kPa was achieved with a response time of 0.25 s and detection resolution of 0.4 pF.

Fabrication and characterization of porous tissue-mimicking optical phantoms as a tool for optical sensor validation.

This paper presents porous polydimethylsiloxane (PDMS) optical phantoms with tunable microstructural and optical properties to mimic porous biological tissues (e.g., fruit) during the design and optimization of novel optical setups. A well connected salt network formed using salt particles of various size distributions was used to obtain porous PDMS phantoms of different porous features including porosity, pore size distribution, pore number density and pore connectivity. These microstructural features are strongly related to the light scattering from the phantom where a higher reduced scattering coefficient ( ) was observed from the porous PDMS phantom with a higher number of small pores compared to the optical phantom with a lower number of larger pores. The prepared phantoms were used to validate GASMAS (gas in scattering media absorption spectroscopy) H2 O and O2 sensors by quantifying the optical path length through the pores and the O2 concentration inside the pores.

Facile Approach to Fabricate Oriented Porous PDMS Composites for Movements Monitoring and Identifying Motion Patterns.

The facile and rapid fabrication of oriented porous polymers is crucial for flexible pressure sensors. Herein, a pressure sensor is developed based on oriented porous polydimethylsiloxane (PDMS) composites for detecting human motion and identifying joint motion patterns. The oriented porous PDMS composite is first constructed through thiol-ene click chemistry and directional freezing within only 30min, then fabricated by interfacial in situ polymerization of dopamine and pyrrole to generate robust interfaces. As a result, the as-prepared oriented porous PDMS composite is assembled into a pressure sensor that shows potential applications in pressure and human motion detection. Interestingly, a sensor assembled by orthogonally stacking the PDMS composites can be used for joint motion pattern recognition with potential monitoring of football motion due to their directional structures. This facile strategy coupled with the oriented porous structure is expected to help design advanced wearable electronic devices.

A flexibly hierarchical porous polydimethylsiloxane film for Passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) is a technology without requiring additional energy that cools objects by reflecting sunlight and radiating heat into outer space. However, the design process of PDRC films is relatively complicated or costly, which is not conducive to large-scale fabrication. For this, we fabricated a flexibly hierarchical porous polydimethylsiloxane (PDMS) radiative cooling film, which is simple and fast to fabricate and can be used for efficient large-scale production. It can reach the average emissivity of 0.95 in the transparent atmospheric window (8–13 μm). The average reflectance is above 0.7 in the solar wavelength band (0.3–2.5 μm), which is nearly 9 times of the non-porous structure. Thus, the porous PDMS films realize excellent sub-ambient temperature drop of 14.9 °C at the solar intensity of 910 W/m2.

Sacrificial Template Method to Fabricate Highly Sensitive Porous Capacitive Pressure Sensor for Full Pulse Waveform Detection

Due to the recent advancements in sensing technology, skin mountable wearable devices have gained much attention due to their non-invasive usage and wearer comfort for health care monitoring. For instance, monitoring pulse waveform from the wrist arterial sites bears tremendous information about cardiovascular health and can show abnormalities such as hypertension or arterial fibrosis. Acquiring a high-quality pulse waveform from the wrist artery requires high-pressure sensitivity and fast response time. However, the need for building highly sensitive and low-cost fabrication of the sensors for subtle physiological monitoring is still challenging. Targeting these issues, this study presents a facile and cost-effective approach to realizing a flexible capacitive pressure sensor by sandwiching porous polydimethylsiloxane (PDMS) polymer functionalized by multi-walled carbon nanotubes (MWCNTs) fabricated by sacrificial template method for physiological monitoring. The fabrication steps for the dielectric layer involve mixing sucrose as the porogens and MWCNTs as the functionalizing material with PDMS followed by casting the mixture in a mold and curing of the PDMS. Subsequently, the sucrose particles are dissolved in water. The sucrose particles are easily dissolved in water leaving a highly uniform and porous structure behind. The dielectric layer is then sandwiched between two conductive textile based electrodes for physiological monitoring. The electromechanical tests were performed for different concentration of MWCNTs content in porous PDMS to obtain the best sensing performance. The champion sensor exhibits ultrahigh-pressure sensitivity of 2.41kPa-1 and a minimum detection limit of 1.4Pa in contrast to the sensor exhibiting only 0.31kPa-1 without addition of any MWCNTs. In addition, the pressure sensor shows a fast response time of 0.18s and excellent cyclic stability over 6000 cycles. The ultrahigh-pressure sensitivity comes from the addition of conductive MWCNTs filler that increases the dielectric permittivity. The highly porous structure of the polymer reduces the typical viscoelastic effects of polymer resulting in fast response time. The pressure sensor could detect arterial pulse waveform from the wrist artery with all the key characteristic points showing its promises for low-cost physiological monitoring. The detailed results will be discussed during the presentation.

Porous Elastomer Based Wide Range Flexible Pressure Sensor for Autonomous Underwater Vehicles

This work presents the design and implementation of a porous polydimethylsiloxane (PDMS)-based wide-range flexible pressure sensor for autonomous underwater vehicles. The capacitive sensor, with porous PDMS as dielectric, is encapsulated in bulk PDMS polymer. The fabricated sensor was evaluated over a wide pressure range (0-230 kPa), which is similar to pressures experienced up to approx. 23 m below the sea level. The sensors showed linear response when tested in air and near-linear response (98%) when submerged in water. The sensor showed much higher sensitivity (0.375 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) in water than in the air environment. However, the sensor exhibited the performance and sensitivity similar to the air condition (0.005 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) when the readout electronics (encapsulated inside a watertight enclosure) was also submerged inside the water along with the sensor. The fabricated sensor also exhibited fast response and recovery time (190 ms), as well as excellent repeatability and stability (no drift) over tested range of 50 loading and unloading cycles. These results demonstrate the suitability of presented sensors for potential use in applications requiring a wide range of pressure, particularly the underwater robotics where real-time pressure monitoring is critical for autonomous operation.

Removal of carbol fuchsin from aqueous solution by using three-dimensional porous, economic, and eco-friendly polymer.

In this study, a three-dimensional (3D) porous polydimethylsiloxane (PDMS) was prepared using a cheap material with a highly simple and different method. PDMS was firstly applied for the removal of carbol fuchsin (CF) cationic organic dye pollution in this study. Besides, the adsorption capacity of 3D PDMS for removal of the CF was found quite high compared to other materials in already published results. The synthesized PDMS was characterized using several spectroscopic and imaging techniques such as FTIR, Raman, SEM, stereomicroscope, EDX, UV/Vis, and TGA. The optimal conditions were found as 10mgL-1 initial concentration, 20mg of adsorbent dose, 2h contact time, pH 10, and 25°C temperature. The removal % of CF and the maximum adsorption capacity were calculated at approximately 89% and 88.8mgg-1 , respectively. Furthermore, the equilibrium studies showed that the Langmuir isotherm model fitted well with the removal of CF. Moreover, according to the kinetic results, the second-order kinetic model was found suitable (qe,cal 89.3mgg-1 and qe,exp 88.8mgg-1 close to each other) for the adsorption of CF. Also, the thermodynamic studies indicated that adsorption occurs spontaneously, and the adsorption process was physical adsorption. Besides, the reusability of the adsorbent was studied. PRACTITIONER POINTS: Water treatment technology should be low cost, economically viable and in the meantime, eco-friendly. The 3D porous PDMS was prepared by using cheap material with a highly simple method and eco-friendly This unique material was firstly applied for the removal of organic dye in water in this study.

Avoiding heating interference and guided thermal conduction in stretchable devices using thermal conductive composite islands

The miniaturization and high integration of devices demand significant thermal management materials. Current technologies for the thermal management of electronics show some limitations in the case of multiple chip arrays. A device in multiple chip array is affected by heat from adjacent devices, along with thermal conductive composite. To address this problem, we present a nano composite of aligned boron nitride (BN) nanosheet islands with porous polydimethylsiloxane (PDMS) foam to have mechanical stability and non-thermal interference. The islands of tetrahedrally-structured BN in the composite have a high thermal conductivity of 1.219 W·m−1·K−1 in the through-plane direction (11.234 W·m−1·K−1 in the in-plane direction) with 16 wt.% loading of BN. On the other hand, porous PDMS foam has a low thermal conductivity of 0.0328 W·m−1·K−1 in the through-plane direction at 70% porosity. Heat pathways are then formed only in the structured BN islands of the composite. The porous PDMS foam can be applied as a thermal barrier between structured BN islands to inhibit thermal interference in multiple device arrays. Furthermore, this composite can maintain selective thermal dissipation performance with 70% tensile strain. Another beauty of the work is that it could have guided heat dissipation by assembling of multiple layers which have high vertical thermal conductive islands, while inhibiting thermal interference. The selective heat dissipating composite can be applied as a heatsink for multiple chip arrays electronics.

Highly Sensitive Porous PDMS-Based Capacitive Pressure Sensors Fabricated on Fabric Platform for Wearable Applications.

A novel porous polydimethylsiloxane (PDMS)-based capacitive pressure sensor was fabricated by optimizing the dielectric layer porosity for wide-range pressure sensing applications in the sports field. The pressure sensor consists of a porous PDMS dielectric layer and two fabric-based conductive electrodes. The porous PDMS dielectric layer was fabricated by introducing nitric acid (HNO3) into a mixture of PDMS and sodium hydrogen bicarbonate (NaHCO3) to facilitate the liberation of carbon dioxide (CO2) gas, which induces the creation of porous microstructures within the PDMS dielectric layer. Nine different pressure sensors (PS1, PS2,..., PS9) were fabricated in which the porosity (pore size, thickness) and dielectric constant of the PDMS dielectric layers were varied by changing the curing temperature, the mixing proportions of the HNO3/PDMS concentration, and the PDMS mixing ratio. The response of the fabricated pressure sensors was investigated for the applied pressures ranging from 0 to 1000 kPa. A relative capacitance change of ∼100, ∼323, and ∼485% was obtained by increasing the curing temperature from 110 to 140 to 170 °C, respectively. Similarly, a relative capacitance change of ∼170, ∼282, and ∼323% was obtained by increasing the HNO3/PDMS concentration from 10 to 15 to 20%, respectively. In addition, a relative capacitance change of ∼94, ∼323, and ∼460% was obtained by increasing the PDMS elastomer base/curing agent ratio from 5:1 to 10:1 to 15:1, respectively. PS9 exhibited the highest sensitivity over a wide pressure sensing range (low-pressure ranges (<50 Pa), 0.3 kPa-1; high-pressure ranges (0.2-1 MPa), 3.2 MPa-1). From the results, it was observed that the pressure sensors with dielectric layers prepared at relatively higher curing temperatures, higher HNO3 concentrations, and higher PDMS ratios resulted in increased porosity and provided the highest sensitivity. As an application demonstrator, a wearable fit cap was developed using an array of 16 pressure sensors for measuring and mapping the applied pressures on a player's head while wearing a helmet. The pressure mapping aids in observing and understanding the proper fit of the helmet in sports applications.

Investigation of porous polydimethylsiloxane structures with tunable properties induced by the phase separation technique

AbstractThis article reports the fabrication and characterization of porous polydimethylsiloxane (PDMS) structures developed by the solvent evaporation‐induced phase separation technique. Ternary systems containing water/tetrahydrofuran (THF)/PDMS with various concentrations are produced to form a stable solution. The porous PDMS structures are formed by removing the solvent (THF) and nonsolvent (water) phases during the stepping heat treatment procedure. The analytical ternary phase diagram is constructed based on the thermodynamic equilibrium state in the polymer solution to explain the stable/unstable formulations and the possible composition change path. The results show that the isolated pores with the adjustable pore size ranging from 330 to 1900 μm are obtained by tuning the water to the THF ratio. The mechanical properties of the porous PDMS structures are determined by conducting the tensile tests on the prepared dog bone‐shaped specimens. A wide range of elastic modulus ranging between 0.49 and 1.05 MPa was achieved without affecting the density of the porous sample by adjusting the solvent and non‐solvent content in the solution. It is shown that the flexibility of the porous structures can be improved by reducing the ratio of water to THF and decreasing the PDMS content. The porosity measurements reveal that the PDMS concentration is the major phase controlling the porosity of the structure, while the effect of water/THF is negligible.

Wearable porous PDMS layer of high moisture permeability for skin trouble reduction

The present research proposes the present porous polydimethylsiloxane (PDMS) layer for the skin trouble reduced daily life skin attachable devices. The present research proposes the new pores forming method in the PDMS by crystallization and dissolution of the citric acid in the PDMS for fabricating high uniform and small size pores. The present porous PDMS layer (i) decreases the pore size 93.2%p and increases the pore size uniformity 425%p compared to the conventional porous PDMS layer of mixing sugars and PDMS; (ii) is able to be fabricated in the thickness of 21–101 µm by spin-coating; (iii) has the 2.2 times higher water vapor transmission rate (947 ± 10.8 g/day•m2) compared to the human skin water vapor transmission rate. The present porous PDMS layer reduces the skin trouble effectively by having the high water vapor permeability, therefore is applicable to the human daily-life skin attachable devices.

A porous PDMS pulsewave sensor with haircell structures for water vapor transmission rate and signal-to-noise ratio enhancement.

We present a porous polydimethylsiloxane (PDMS) pulsewave sensor with haircell structures that improves both water vapor transmission rate (WVTR) and signal-to-noise ratio (SNR). The conventional planar PDMS pulsewave sensors have the problems of low WVTR and low SNR for real-time and long-term pulsewave monitoring. In order to improve WVTR, we fabricated a porous PDMS layer with the thickness of 40 μm and high porosity of 45% by crystallizing and dissolving citric acid powders in PDMS. On the porous PDMS layer, we form haircell structures to increase the skin contact area, thus enhancing SNR. The porous PDMS pulsewave sensor with haircell structures achieved an enhanced WVTR of 486.17 g−1 d−1 m−2 and an SNR of 22.89, respectively, 72% and 757% higher than those of the conventional PDMS pulsewave sensors without haircell structures. Furthermore, the enhanced WVTR is 13% higher than the human skin sweat rate of 432 g−1 d−1 m−2. The present pulsewave sensor shows strong potential for applications in real-time and long-term pulsewave monitoring with the lower skin irritation and the enhanced SNR.

Wearable pressure sensor for athletes’ full-range motion signal monitoring

In order to real-time grasp of various physiological signals of athletes during sports, a high-performance flexible pressure sensor that can monitor various physiological signals and human motion was designed. Porous polydimethylsiloxane (PDMS) foam prepared by the sacrificial template method and graphene as raw materials were used to prepare a flexible pressure sensor with wide working range (0–100 kPa), ultra-high sensitivity (the average sensitivity in the range of 0–30 kPa is 17.9 kPa−1, the sensitivity in the range of 30–100 kPa reaches 79 kPa−1), fast response ability (response time is 20 ms) and long-term work stability (more than 10 000 cycles). The excellent performance of this pressure sensor depends on the use of PDMS foam with a high elastic modulus and the graphene loading level is controlled to an appropriate ratio. Finally, we used the conductive porous PDMS foam based flexible pressure sensor to demonstrate accurate and real-time monitoring of athletes’ tiny physiological signals (including pulse and electrocardiograph signals), vocalization and facial emotions, as well as violent joint and limb movements (including joint bending, walking, squats, jogging, and jumping), showing the potential in coaching athletes.