The effect of distant mutations on the catalytic reaction of dihydrofolate reductase (DHFR) is reexamined by empirical valence bond simulations. The simulations reproduce for the first time the ...changes in the observed rate constants (without the use of adjustable parameters for this purpose) and show that the changes in activation barriers are strongly correlated with the corresponding changes in the reorganization energy. The preorganization of the polar groups of enzymes is the key catalytic factor, and anticatalytic mutations destroy this preorganization. Some anticatalytic mutations in DHFR also increase the distance between the donor and acceptor, but this effect is not directly related to catalysis since the native enzyme and the uncatalyzed reaction in water have similar average donor−acceptor distances. Insight into the effect of a mutation is provided by constructing the relevant free energy surfaces in terms of the generalized solute−solvent coordinates. It is shown how the mutations change the reaction coordinate and the activation barrier, and it is clarified that the corresponding changes do not reflect dynamical effects. It is also pointed out that all reactions in a condensed phase involve correlated motions (both in enzymes and in solution) and that the change of such motions upon mutations is a result of the change in the shape of the multidimensional reaction path on the solute−solvent surface, rather than the reason for the change in rate constant. Thus, as far as catalysis is concerned, the change in the activation barrier is due to the change in the electrostatic preorganization energy.
The first example of dually synergetic network hydrogel, which has integrated mechanical stretchability, thermal responsiveness, and electrical conductivity, has been constructed by a versatile and ...topological co-cross-linking approach. Poly(N-isopropylacrylamide) (PNIPAAm) is introduced as the thermally responsive ingredient, and polyaniline (PANI) is selected as the electrically conductive ingredient. PNIPAAm network is cross-linked by double-bond end-capped Pluronic F127 (F127DA). PANI network is doped and cross-linked by phytic acid. These two ingredients are further mechanically interlocked. Due to the integrated multiple functionalities, the topologically co-cross-linked hydrogels, as will be mentioned as F-PNIPAAm/PANI hydrogels, can be fabricated into resistive-type strain sensors. The strain sensors can achieve a gauge factor of 3.92, a response time of 0.4 s, and a sensing stability for at least 350 cycles and can be further applied for monitoring human motions, including motion of two hands, bending of joints, and even swallowing and pulse rate. Moreover, F-PNIPAAm/PANI hydrogels are utilized to construct efficient temperature alertors based on the disconnection of circuits induced by volume shrinkage at high temperature.
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•Pressure/strain sensors are fabricated from PVA/HPS hydrogels.•Strain sensor achieves a tensile strength of 9.3 MPa and a gauge factor of 7.4.•Pressure sensor achieves a gauge factor ...of 3.6 kPa−1.•The sensors are applied in monitoring strain and pressure in daily life.
Flexible sensors based on conductive hydrogels have found potential applications in many emerging electronic devices, but they often suffer from poor mechanical properties, single response mode and low sensitivity. Herein, robust and sensitive pressure/strain sensors are designed and fabricated utilizing novel composite hydrogels composed of hollow polyaniline spheres (HPS), poly(vinyl alcohol) (PVA) and phytic acid (PA). By taking advantages of structure-derived elasticity of hollow spheres, conductivity of doped conducting polymers, flexibility of polymer matrix and physically cross-linked structure, the composite hydrogels exhibit outstanding mechanical properties, strain sensitivity, piezoresistivity and solution processability. The optimized composite hydrogel possesses high tensile strength (9.3 MPa), stretchability (>493%) and toughness (2.6 MJ/m3). Resistive-type strain sensors assembled from the composite hydrogel can achieve a gauge factor (GF) of 2.9 in the strain range of 0%~300%, a GF of 7.4 in the strain range of 300%–450%, a response time of 0.22 s and high reliability (1000 cycles). Capacitive-type pressure sensor with ultrahigh sensitivity of GF = 3.6 kPa−1 is fabricated by sandwiching a dielectric layer between two composite hydrogel films. Interestingly, piezoresistivity of such composite hydrogels makes them promising materials for piezoresistive-type pressure sensors and visualization of pressure. On the basis of their high performances, flexible sensors of the composite hydrogels are applied in monitoring various human motions, physiological activities and bending/vibration deformations in daily life.
Using 2-acrylamide-2-methyl propane sulfonic acid (AMPS), itaconic acid (IA), and N-vinyl-2-pyrrolidone (NVP) as monomers, a new retader terpolymer AMPS/IA/NVP (PAIN) was synthesized by free radical ...aqueous solution copolymerization and characterized by FTIR and H-NMR. Through the orthogonal experiment, the optimum reaction conditions of copolymerization were obtained: NVP 7.5 wt (mass fraction) %; regulator V 4%; reaction temperature 60°C; initiator 1 wt %. The intrinsic viscosity number of PAIN synthesized with different amount of regulator (isopropanol) was determined, finding that the regulator can change the molecular weight and distribution of PAIN. Through the thickening experiment in high temperature and high pressure, it was found that PAIN had an excellent retardation property in high temperature, and the thickening times of the cement slurries with 1% (BOWC) PAIN were up to 256 min at 110°C and 234 min at 130°C, respectively. The PAIN was even stable when the temperature below 350°C proved by TG-SDTA analysis. Moreover, the retarding mechanism of PAIN was analyzed and discussed.
Highly sensitive capacitive-type pressure sensor has been achieved by fabricating reliefs on solution-processable hydrogel electrodes. Hybrid PVA/PANI hydrogels (PVA, poly(vinyl alcohol); PANI, ...polyaniline) with a fully physically cross-linked binary network are selected as the electrodes of the pressure sensors. On the basis of the solution processability, reliefs are fabricated on the surface of PVA/PANI hydrogel electrodes by a template method. The gauge factor (GF) is enhanced by introducing reliefs and regulated by controlling the composition and relief dimension of hydrogel electrodes. The optimized pressure sensor containing reliefs achieves the highest GF of 7.70 kPa
and a sensing range of 0-7.4 kPa. Furthermore, the freezing and drying problems of the hydrogel sensors are overcome by introducing a binary solvent of water/glycerol and the pressure sensing ability at -18 °C has been achieved. Finally, monitoring of various pressures in daily life, such as joint bending, blowing, and brush writing, is demonstrated using such pressure sensors.
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Polydopamine (PDA)-based self-adhesive hydrogel sensors are extensively explored but it is still a challenge to construct PDA-based hydrogels by free radical polymerization. Herein, a ...new approach to construct self-adhesive hydrogels by conducting free radical polymerization in both aqueous phase and micelle phase is developed. The following two-phase polymerization processes account for the formation of the self-adhesive hydrogels. The first one is the polymerization of acrylamide (AM) and dopamine (DA) in aqueous phase to form adhesive component PAM-PDA (PAM, polyacrylamide; PDA, polydopamine). The second one is the polymerization of hydrophobic monomer 2-methoxyethyl acrylate (MEA) in micelles of an amphiphilic block copolymer Pluronic F127 diacrylate (F127DA). The poly(2-methoxyethyl acrylate) (PMEA) networks help to maintain the high robustness of the hydrogel. Because PMEA and PDA form in relatively separated phases, the inhibition effect of PDA on the free radical polymerization process of PMEA is weakened. Based on this mechanism, mechanically strong and adhesive hydrogels are achieved. The introduced ions during preparation process, such as Na+, OH– and K+, endow the resulting hydrogels ionic conductivity. Resistive strain sensor of the hydrogel achieves a high gauge factor (GF) of 5.26, a response time of 0.25 s and high sensing stability. Because of the adhesiveness, such hydrogel sensor can be applied as wearable sensors in monitoring various human motions. To further address the freezing and drying problems of the hydrogels, organohydrogels are constructed in glycerol-water mixed solvent. The organohydrogels exhibit outstanding anti-freezing property and moisture retention ability, and their adhesiveness is well maintained in subzero conditions. Capacitive pressure sensors of the organohydrogels possessing a GF of 2.05 kPa−1, high sensing stability and reversibility, are demonstrated and explored in monitoring diverse human motions.
The development of high-performance protein-imprinted materials is vital to meet the requirements of proteomics research but remains a challenge. Herein, a new type of raspberry-like cytochrome ...C-imprinted nanoparticle was first designed and fabricated via surface imprinting technology combined with a template immobilization strategy. In particular, the state-of-the-art metal–organic framework (MOF)/carbon nanoparticle (CN) composites were selected as protein immobilization carriers for two advantages: (1) the composites reflected the intrinsic characteristics of MOFs including flexible design, facile preparation, and extensive interactions with proteins and (2) the utilization of composites also overcame the issue associated with the severe agglomeration of individual MOFs during the post-use process. Therefore, the as-prepared composites exhibited a regular raspberry-like shape with good dispersion (polydispersity index (PDI) < 0.25), high specific surface area (551.4 m2 g–1), and outstanding cytochrome C immobilization capacity (900 mg g–1). Furthermore, a zwitterionic monomer was chosen to participate in the synthesis of an imprinting layer to reduce the nonspecific binding with proteins. As a result, the unique design presented here in both the protein immobilization carrier and the selected polymer composition endowed the imprinted material (noted as CN@UIO-66@MIPs) with the excellent ability for cytochrome C enrichment with extremely high recognition ability (imprinting factor (IF) = 6.1), rapid adsorption equilibrium time (40 min), and large adsorption capacity (815 mg g–1). Furthermore, encouraged by the experimental results, we successfully used CN@UIO-66@MIPs to specifically capture cytochrome C in mixed protein solutions and biological samples, which proved them to be a potential candidate for protein separation and purification.
Flexible strain sensors are highly used in soft robotics, human–machine interfaces and health monitoring devices. However, it is still a big challenge to construct strain sensors with excellent ...mechanical properties and broad sensing ranges. In this study, a class of extremely stretchable and electrically conductive hydrogels with dually synergistic networks are fabricated for wearable resistive-type strain sensors. Dually synergistic networks are composed of a soft poly(acrylic acid) (PAA) network and a rigid conductive polyaniline (PANI) network. The PAA network is crosslinked by amphiphilic block copolymers, and the PANI network is chemically doped and ionically crosslinked by phytic acid and these two networks are further interlocked by physical entanglements, hydrogen bonds and ionic interactions. The resulting hydrogels have high tensile strength, controllable conductivity and large tensile deformation (1160%). Moreover, these hydrogels are utilized for fabricating strain sensors with good sensitivity and a wide sensing range (0–1130%). The high performances of hydrogels make such strain sensors suitable for wearable devices monitoring both subtle and large strains induced by human motions, including moving of two hands, bending of joints, conducting of gestures and swallowing.
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•A cyclic freezing-thawing approach to layered Janus hydrogel tapes with single-sided adhesiveness is developed.•The interfacial peeling force of the Janus hydrogel tapes reaches ...114.6 N/m.•Strain sensors of Janus hydrogel tapes achieve a GF of 3.4.•Wireless wearable sensors based on Bluetooth signal transmission system are demonstrated.
Hydrogel strain sensors, which have potential applications in wearable devices, soft robots and human–machine interfaces, etc., are increasingly investigated. But it remains challenging to fabricate hydrogel strain sensors with integrated wearability and high sensing performances. To address this issue, we herein propose a cyclic freezing-thawing approach to layered Janus hydrogel tapes for wearable strain sensors. The hydrogel tapes are composed of an adhesive poly(vinyl alcohol)/phytic acid (PVA/PA) layer and a non-adhesive poly(vinyl alcohol)/polyaniline (PVA/PANI) layer and exhibit controllable flexibility and approximate elastic modulus to soft tissues. A robust interface forms between the two layers and the interfacial peeling force reaches 114.6 N/m. Strain sensors assembled from the Janus hydrogel tapes achieve low response time (loading: 60 ms, unloading: 62 ms), reversible response and high sensitivity (gauge factor: 3.4). Interestingly, such strain sensors can be further integrated with a Bluetooth system to fabricate wireless wearable sensors for convenient monitoring of physiological activities such as walking, squatting, stair climbing, etc. Overall, this work will provide not only a new approach to Janus hydrogels, but also a new clue for developing functional flexible devices.
It is a challenge to fabricate low-cost and flexible electronic devices with degradable materials. In this work, a flexible and degradable strain sensor was fabricated on a paper substrate by ...dip-coating in an aqueous suspension of carbon black (CB) and carboxymethyl cellulose (CMC). The composition of CB and CMC in the suspension was first studied for producing a uniform conducting layer on the paper. Then the strain sensor was obtained by assembling the coated paper and wires with silver paste. The sensor exhibits gauge factor of 4.3 and responsive time of approximately 240 ms, demonstrating the capability of monitoring various human motions with high stability >1000 cycles. The microgaps between CB particles and cracks on the surface of the CB layer can account for this resistive-type sensitivity. The degradation test shows that the sensor can be degraded soon under gentle rubbing in wet state, implying it is an environmentally friendly “green” electronic device. Furthermore, the cost of the sensor is quite low (<$0.001/sensor) due to the cheap raw materials used, which provides an opportunity for its future utilization in various intelligent systems.
