Pressure and multicolor dual-mode detection of mucin 1 based on the pH-regulated dual-enzyme mimic activities of manganese dioxide nanosheets.

Mucin 1 is an essential tumor biomarker, and developing cost-effective and portable methods for mucin 1 detection is crucial in resource-limited settings. Herein, the pH-regulated dual-enzyme mimic activities of manganese dioxide nanosheets were demonstrated, which were integrated into an aptasensor for dual-mode detection of mucin 1. Under acidic conditions, manganese dioxide nanosheets with oxidase mimic activities catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine sulfate, producing visible multicolor signals; while under basic conditions, manganese dioxide nanosheets with catalase mimic activities were used as catalyst for the decomposition of hydrogen peroxide, generating gas pressure signals. The proposed method allows the naked eye detection of mucin 1 through multicolor signal readout and the quantitative detection of mucin 1 with a handheld pressure meter or a UV-vis spectrophotometer. The study demonstrates that manganese dioxide nanosheets with pH-regulated dual-enzyme mimic activities can facilitate multidimensional transducing signals. The use of manganese dioxide nanosheets for the transduction of different signals avoids extra labels and simplifies the operation procedures. Besides, the signal readout mode can be selected according to the available detection instruments. Therefore, the use of manganese dioxide nanosheets with pH-regulated dual-enzyme mimic activities for dual-signal readout provides a new way for mucin 1 detection.

Solvent-Resistant Adhesive Gel with Thermal Post-Tunability.

Adhesives have received extensive attention in flexible bioelectronics, wearable electronic medical devices, and biofuel cells. However, it is a challenge to achieve late regulation of performance once polymer-based gels are formed. Here, a double-network organogel composed of a hydrophilic and hydrophobic polymer network and a polyamide acid network was successfully prepared. In diverse liquid environments (including isopropyl alcohol, glycerol, epichlorohydrin, n-propanol, dichloromethane, triethanolamine, ethanol absolute, hydrogen peroxide, and ethyl acetate), the organogel adhesive demonstrated remarkable properties. It exhibits a strong tensile strength of 200 kPa, a high fracture strain reaching 560%, and an impressive adhesion strength of 38 kPa. In addition, the organogel demonstrates exceptional adhesive properties toward polytetrafluoroethylene, plastics, metals, rubber, and glass. Note that the organogel could also regulate adhesive and tough performance by thermally triggering a cyclization reaction even after the organogel has been formed. The strategy provides a new idea for designing soft materials with post-tunability.

Thermochromic Hydrogels with Opaque-Transparent Gradient Transition for Switchable Window and Temperature Monitor.

In recent years, the thermochromic hydrogel was acted as suitable sandwiching material to adjust light transmission. However, to accurately control the thermochromic temperature in a wide range still was a significant challenge. Here, a simple method was explored to prepare hydrogels with gradient opaque-transparent transition thermochromic temperature from 5 °C to 53 °C, which was regulated by the aggregation state of sodium dodecyl sulfate micelles by adding potassium tartrate hemihydrate and cations. Using Li+ , Na+ , and K+ as cations, the accuracy was controlled at 1 °C. Moreover, the transmittance of the hydrogel was not changed when the thermochromic temperature was adjusted. As a result, an intelligent window was fabricated by utilizing thermochromic hydrogel as a sandwiching layer into the outer glass layers, which could effectively and stably regulate the visible and infrared light. The temperature monitors/detectors were also designed, which showed excellent temperature monitoring/detecting ability. Therefore, this low-cost, high-efficient, large-scale prepared thermochromic hydrogel provided more potential for intelligent temperature devices.

A Novel Self-Pumping Janus Dressing for Promoting Wound Immunomodulation and Diabetic Wound Healing.

Self-pumping dressings become one of the optimal solutions for the controlled management of chronic diabetic wound exudate and wound healing. However, present self-pumping dressings are not only prone to breakage of the loose hydrophobic layer but also have cumbersome and complicated preparation steps, which hinder the application of self-pumping dressings in diabetic wound treatment. Herein, a novel self-pumping structure of superabsorbent Janus dressing is designed to improve the strength of the hydrophobic layer and promote diabetic wound healing. The Janus dressing consists of a hydrophobic layer with a drainage agent (drainage layer) and a fluffy 3D nanofiber cotton (absorbent layer). Regardless of the thickness of the drainage layer, the drainage agent in the drainage layer provides the fluid to penetrate the drainage layer to the absorbent layer for unidirectional fluid draining. In design proof, the superabsorbent Janus dressing provides unidirectional drainage of inflammatory exudate and regulation of macrophage polarization, resulting in faster diabetic wound healing than single-layer dressings. Thus, the Janus dressing demonstrates important clinical implications to offer a novel design and preparation strategy for accelerating diabetic wound healing.

Gum Arabic-based three-dimensional printed hydrogel for customizable sensors.

Most three-dimensional (3D) printed hydrogel exhibit non-idealized rheological properties in the process of direct ink writing and complicated curing. Therefore, accurate writability and convenient curing for 3D printed hydrogel remain a challenge. In this paper, we developed a typical 3D printed hydrogel which realized direct ink writing (DIW) at temperatures similar to human body. Silicon dioxide (SiO2) and Gum Arabic (GA) formed the Bingham fluid to ensure shape stability. The rapid initiation system of potassium persulfat (KPS) and N,N,N',N' -tetramethylethylenediamine (TMEDA) allowed the 3D printed hydrogel precursor solution to transiently form a hydrophobic conjoined cross-linking network structure of acrylamide (AAM) and lauryl methacrylate (LMA) after printing, resulting in preferable mechanical properties. Hydrogel precursor solution showed better rheological properties with the nature of Bingham fluids, and achieved transient cross-linking at 30 °C for 10 s in the rheological test. A variety of 3D printed hydrogel with individual strain sensing properties are prepared as customizable sensor that could monitor significant strain signals within 0-20 % strain with high sensitivity. Moreover, they were discovered excellent temperature sensitivity over a wide operating range (0-80 °C). The 3D printing hydrogel sensors were expected to have broad application prospects in flexible wearable devices and medical monitoring.

Hierarchical Porous Aerogels With Multiple Adsorptive Interactions for Dye Wastewater Purification.

Aerogels present a huge potential for removing organic dyes from printing and dyeing wastewater (PDW). However, the preparation of aerogels with multiple dye adsorption capabilities remains a challenge, as many existing aerogels are limited to adsorbing only a single type of dye. Herein, a composite aerogel (CG/T-rGO) with the addition of carboxymethyl chitosan, gelatin and tannic acid reduced graphene oxide (T-rGO) was synthesized by freeze-drying technology. The electrostatic interactions between dye molecular and GEL/CMCS (CG) networks, as well as the supramolecular interactions (H-bonds, electrostatic interactions and π-π stacks) between T-rGO, have endowed the aerogel with the ability to adsorb multiple types of dye, such as methylene blue (MB) and methyl orange (MO). Results exhibited that the prepared CG/T-rGO aerogel possessed strong mechanical strength and a porous 3D network structure with a porosity of 96.33 %. Using MB and MO as adsorbates, the adsorption capacity (88.2 mg/g and 66.6 mg/g, respectively) and the mechanism of the CG/T-rGO aerogel were investigated. The adsorption processes of aerogel for MB and MO were shown to follow the pseudo-second-order kinetic model and Langmuir isotherm model, indicating the chemical adsorption of a monolayer. The proposed aerogel in this work has promising prospects for dye removal from PDW.

Multi-Parameter Optimization of Rubidium Laser Optically Pumped Magnetometers with Geomagnetic Field Intensity.

Rubidium laser optically pumped magnetometers (OPMs) are widely used magnetic sensors based on the Zeeman effect, laser pumping, and magnetic resonance principles. They measure the magnetic field by measuring the magnetic resonance signal passing through a rubidium atomic gas cell. The quality of the magnetic resonance signal is a necessary condition for a magnetometer to achieve high sensitivity. In this research, to obtain the best magnetic resonance signal of rubidium laser OPMs in the Earth's magnetic field intensity, the experiment system of rubidium laser OPMs is built with a rubidium atomic gas cell as the core component. The linewidth and amplitude ratio (LAR) of magnetic resonance signals is utilized as the optimization objective function. The magnetic resonance signals of the magnetometer experiment system are experimentally measured for different laser frequencies, radio frequency (RF) intensities, laser powers, and atomic gas cell temperatures in a background magnetic field of 50,765 nT. The experimental results indicate that optimizing these parameters can reduce the LAR by one order of magnitude. This shows that the optimal parameter combination can effectively improve the sensitivity of the magnetometer. The sensitivity defined using the noise spectral density measured under optimal experimental parameters is 1.5 pT/Hz1/2@1 Hz. This work will provide key technical support for rubidium laser OPMs' product development.

A hydrogel sensor driven by sodium carboxymethyl starch with synergistic enhancement of toughness and conductivity.

Conductive hydrogels are potential materials for fabricating wearable strain sensors owing to their excellent mechanical properties and high conductivity. However, it is a challenge to simultaneously enhance the mechanical properties and conductivity of hydrogels. Herein, a simple strategy was proposed for concurrently enhancing the mechanical properties and conductivity of the wearable hydrogel sensors by introducing carboxymethyl starch sodium (CMS). The introduction of CMS not only dramatically enhanced the mechanical performance of the hydrogel due to hydrogen bonding and electrostatic interaction, but also improved the conductivity of the hydrogel owing to the existence of sodium ions. As a result, the hydrogel sensors with excellent durability and stability could repeatedly detect and distinguish various human activities, including walking, chewing and speaking. Meanwhile, multiple sensors are also assembled into a 3D sensor array for detecting the three-dimensional distribution of stress and strain. Moreover, the peaks of EMG signals and the waveforms of ECG signals could be recorded because the hydrogel sensor presented super sensitivity and fast response. Therefore, the multifunctional hydrogel presented remarkable potential for applications in human medical diagnosis, health monitoring and artificial intelligence.

Muscle-Inspired Anisotropic Hydrogel Strain Sensors.

Hydrogel strain sensors have attracted tremendous attention in medical monitoring, flexible wearable devices, and human-machine interfaces. However, traditional hydrogels exhibit isotropic sensing performance based on their isotropic structure. Therefore, it is challenging to fabricate a hydrogel with an anisotropic structure similar to human tissues for achieving anisotropic sensing characteristics. Herein, we proposed a simple and effective method for preparing anisotropic poly(vinyl alcohol) (PVA) conductive hydrogels, which demonstrated anisotropic mechanical properties and anisotropic ion conductivity. The anisotropic hydrogel was successfully constructed through first thermal stretching and then directional freezing. The mechanical strength of hydrogels along the parallel stretching direction (stress of 1596 kPa and toughness of 3.69 MJ/m3) was higher than that of the hydrogels along the vertical stretching direction (stress of 883.1 kPa and toughness of 1.96 MJ/m3). Moreover, the hydrogel showed anisotropic conductivity on the advantage of the different ion channels. The prepared hydrogel sensor exhibited anisotropic sensing for multidirectional stress in the strain range from 0.5 to 100%. The gauge factors (GF) parallel to the stretching direction were greater than the GF vertical to the stretching direction. The anisotropic hydrogel sensors are expected to have broad application prospects in flexible wearable devices and medical monitoring.

Adhesive and tough hydrogels promoted by quaternary chitosan for strain sensor.

As a flexible material, hydrogels have attracted considerable attention in the exploration of various wearable sensor devices. However, the performance of the existing hydrogels is often too single, which limits its further application. Here, a conductive hydrogel with adhesiveness, toughness, self-healing and anti-swelling properties was successfully prepared by adding 2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC) to the polyacrylic acid/ferric ionic (PAA/Fe3+) cross-linking system. Based on the existence of three types of non-covalent interactions in the hydrogel system, including electrostatic interaction, coordination interaction and hydrogen bonds, the hydrogel possessed excellent mechanical properties (tensile stress and strain were 827 kPa and 1652 %, respectively), self-healing properties (self-healing efficiency reached 83.3 % at room temperature) and anti-swelling properties. In addition, the introduction of HACC also successfully gave the hydrogel outstanding adhesiveness. Moreover, the existence of iron ions provided sensitive conductivity to the hydrogel, which could be used as a flexible sensor for directly monitoring various motions. Therefore, this simple strategy for preparation of multifunctional hydrogels would expand the application of a new generation of hydrogel-based sensors.

Durable and Controllable Smart Windows Based on Thermochromic Hydrogels.

In recent years, the use of smart windows to adjust sunlight to achieve energy conversion has received increasing attention. In this paper, a novel smart window was easily prepared by using thermochromic hydrogels as an interlayer and indium tin oxide films as an electric heating layer. The shielding transmission rates of visible and near-infrared light reached 88.3 and 85.4% at the temperature of 25 °C, respectively. However, the transmittance at a light wavelength of 550 nm was greater than 70% after applying voltage. The smart windows with different components could possess thermochromic temperature ranging from 28 to 35 °C, which was suitable for daily life. The smart window could maintain a stable reversible thermochromic transition. Importantly, the time of light transition and the demand of energy efficiency could be adjusted by controlling the magnitude of the output voltage, which benefited the development of energy-efficient materials.

Alginate fiber toughened gels similar to skin intelligence as ionic sensors.

The stretchable hydrogels provide potential alternatives to bionic skins. However, skin simulation remains seriously challenging due to its complex nature, including mechanical property, protective effect, and sensory capability. Herein, conductive gels toughened by sodium alginate fibers in oil-water system were developed for preparation of skin-like ionic sensors. The dynamic network was constructed by polyvinyl alcohol and sodium alginate fibers, providing a wide scope of mechanical properties, such as high toughness, anti-fatigue fracture and remodelability. Moreover, salts imparted good conductivity to gels. As a result, gels exhibited sensory capability toward stress and strain, so they were considered sensors to monitor various movements of human body. In particular, gels demonstrated temperture tolerance ranging from -20 °C to 40 °C and non-drying for 6 days at 25 °C. In this study, gels showed complex intelligence similar to natural skin, and might find applications in artificial intelligence, human-mechanial interactions, and smart wearable devices.

High strength, anti-freezing and strain sensing carboxymethyl cellulose-based organohydrogel.

The gel-based sensor was extensively investigated due to the flexible and extensible properties. Here, a flexible, excellent mechanical (fracture energy of 5238 kJ/m3) and anti-freezing ionic conductive carboxymethyl cellulose-based organohydrogel sensor was prepared via Fe3+ cross-linked sodium carboxymethyl cellulose (CMC) as the first network and covalently cross-linked polyacrylamide as the second network in the co-solvents of water and ethylene glycol. Owing to the clipping transportation of Fe3+ in the water channels, the gel sensor had good sensitivity (GF = 1.4, 0˜30% strain) and fast strain-responsiveness (0.98 s) to monitor the subtle motions of human body. The CMC-based organohydrogel with high strain-sensitivity exhibited more potential applications of next-generation bioelectronic materials and devices.

Skin-Inspired Gels with Toughness, Antifreezing, Conductivity, and Remoldability.

In recent years, nature-inspired conductive hydrogels have become ideal materials for the design of bioactuators, healthcare monitoring sensors, and flexible wearable devices. However, conductive hydrogels are often hindered by problems such as the poor mechanical property, nonreusability, and narrow operating temperature range. Here, a novel skin-inspired gel is prepared via one step of blending polyvinyl alcohol, gelatin, and glycerin. Due to their dermis-mimicking structure, the obtained gels possess high mechanical properties (fracture stress of 1044 kPa, fracture strain of 715%, Young's modulus of 157 kPa, and toughness of 3605 kJ m-3). Especially, the gels exhibit outstanding strain-sensitive electric behavior as biosensors to monitor routine movement signals of the human body. Moreover, the gels with low temperature tolerance can maintain good conductivity and flexibility at -20 °C. Interestingly, the gels are capable of being recovered and reused by heating injection, cooling molding, and freezing-thawing cycles. Thus, as bionic materials, the gels have fascinating potential applications in various fields, such as human-machine interfaces, biosensors, and wearable devices.

Ultrastretchable Wearable Strain and Pressure Sensors Based on Adhesive, Tough, and Self-healing Hydrogels for Human Motion Monitoring.

Currently, flexible wearable hydrogel-based sensors have attracted considerable attention due to their promising applications in a variety of fields. However, concurrently integrating toughness, adhesiveness, self-healing ability, and conductivity into the hydrogel is still a great challenge. Here, casein sodium salt from bovine milk (sodium casein, SC) and polydopamine (PDA, inspired by mussels) were successfully introduced into the polyacrylamide (PAAm) hydrogel system to fabricate a tough and adhesive SC-PDA hydrogel. The hydrogel exhibits splendidly reversible adhesive behavioral bonding toward various materials and even human skin. Moreover, based on the dynamic cross-linking of SC and PDA in the system, the hydrogel has superstretching ability, excellent fatigue resistance, and rapid self-healing ability. In addition, the existence of sodium ions also endowed the SC-PDA hydrogel with sensitive deformation-dependent conductivity to act as a flexible strain and pressure sensor for directly monitoring large-scale human motions (e.g., joint bending) and tiny physiological signals (e.g., speaking and breathing). Therefore, the strategy would broaden the path of a new generation of hydrogel-based sensors for wide applications.

Tough, adhesive and conductive polysaccharide hydrogels mediated by ferric solution.

In general, chitosan should be dissolved in strong acidic media (such as acetic acid) before it could be applied as hydrogels. However, it was found that chitosan could also be dissolved in the ferric solution to form ferric-chitosan complex via coordination interaction. Subsequently, the ferric-chitosan complex was successfully introduced into the hydrogel system to obtain tough, adhesive and conductive chitosan-polyacrylamide double network (CS-PAAm DN) hydrogels. Surprisingly, CS-PAAm DN hydrogel could repeatedly adhere to various solid materials and biological tissues through physical interactions. The maximum peeling force was 256 N/m on the aluminum surface. Moreover, the hydrogel exhibited adequate mechanical performance (135 kPa, 2332%). And the introduction of ferric chloride could also endow the hydrogel with conductive performance. As a result, the strategy based on tough, adhesive and conductive polysaccharide hydrogels mediated by ferric solution would broaden the path to fabricate a new generation of soft materials for wide applications.

Effect of size of latex particles on the mechanical properties of hydrogels reinforced by latex particles.

Herein, cationic latex particles (CL) of different particle sizes were introduced as a cross-linking center to enhance the mechanical properties of the hydrophobically-associated hydrogels (P(AAm-co-HMA)-CL). Firstly, cationic polymethylmethacrylate (PMMA) latex particles were synthesized via soap-free emulsion polymerization. Subsequently, P(AAm-co-HMA)-CL hydrogels with outstanding mechanical properties were prepared using acrylamide as the monomer, hexadecyl methacrylate as the hydrophobic molecule, and CL as the cross-linking center. The size of CL had a significant effect on the mechanical properties and self-recovery properties of the P(AAm-co-HMA)-CL hydrogels. The hydrogel with larger CL size exhibited low mechanical properties due to weak hydrophobic interactions. In contrast, the hydrogel with small CL size displayed excellent mechanical properties due to an effective entanglement of the hydrophobic chains with the smaller size CL, which significantly affects the mechanical properties of the hydrogel. As a result, the maximum fracture stress and fracture strain of the hydrogel were up to 1.47 MPa and 2847%, respectively. This study can have a profound impact on the development of the technology of toughening hydrogels with latex particles.

Conductive Organohydrogels with Ultrastretchability, Antifreezing, Self-Healing, and Adhesive Properties for Motion Detection and Signal Transmission.

Conductive hydrogels had demonstrated significant prospect in the field of wearable devices. However, hydrogels suffer from a huge limitation of freezing when the temperature falls below zero. Here, a novel conductive organohydrogel was developed by introducing polyelectrolytes and glycerol into hydrogels. The gel exhibited excellent elongation, self-healing, and self-adhesive performance for various materials. Moreover, the gel could withstand a low temperature of -20 °C for 24 h without freezing and still maintain good conductivity and self-healing properties. As a result, the sample could be applied for motion detection and signal transmission. For example, it can respond to finger movements and transmit network signals like network cables. Therefore, it was envisioned that the effective design strategy for conductive organohydrogels with antifreezing, toughness, self-healing, and self-adhesive properties would provide wide applications of flexible wearable devices.

Highly tough, anti-fatigue and rapidly self-recoverable hydrogels reinforced with core-shell inorganic-organic hybrid latex particles.

The introduction of SiO2 particles as crosslinking points into hydrogels has been recognized as a suitable way for toughening hydrogels, due to their versatile functionalization and large specific surface area. However, chemically linked SiO2 nanocomposite hydrogels often exhibited negligible fatigue resistance and poor self-recoverable properties due to the irreversible cleavage of covalent bonds. Here, we proposed a novel strategy to improve stretchability, fatigue resistance and self-recoverable properties of hydrogels by using SiO2-g-poly(butyl acrylate) core-shell inorganic-organic hybrid latex particles as hydrophobic crosslinking centers for hydrophobic association. The obtained hydrogel could distribute the surrounding applied stress by disentanglement of the hybrid latex particles from hydrophobic segments. Based on this strategy, the formulated hydrogels showed an excellent tensile strength of 1.48 MPa, superior stretchability of 2511% and remarkable toughness of 12.62 MJ m-3. Moreover, the hydrogels owned extraordinary anti-fatigue, rapid self-recovery and puncture resistance properties. Therefore, this strategy provided a novel pathway for developing advanced soft materials with potential applications in biomedical engineering, such as tendons, muscles, cartilages, etc.

Super-tough, ultra-stretchable and strongly compressive hydrogels with core-shell latex particles inducing efficient aggregation of hydrophobic chains.

Toughness, strechability and compressibility for hydrogels were ordinarily balanced for their use as mechanically responsive materials. For example, macromolecular microsphere composite hydrogels with chemical crosslinking exhibited excellent compression strength and strechability, but poor tensile stress. Here, a novel strategy for the preparation of a super-tough, ultra-stretchable and strongly compressive hydrogel was proposed by introducing core-shell latex particles (LPs) as crosslinking centers for inducing efficient aggregation of hydrophobic chains. The core-shell LPs always maintained a spherical shape due to the presence of a hard core even by an external force and the soft shell could interact with hydrophobic chains due to hydrophobic interactions. As a result, the hydrogels reinforced by core-shell LPs exhibited not only a high tensile strength of 1.8 MPa and dramatic elongation of over 20 times, but also an excellent compressive performance of 13.5 MPa at a strain of 90%. The Mullins effect was verified for the validity of core-shell LP-reinforced hydrogels by inducing aggregation of hydrophobic chains. The novel strategy strives to provide a better avenue for designing and developing a new generation of hydrophobic association tough hydrogels with excellent mechanical properties.