Search

Anisotropic and super-strong conductive hydrogels were prepared by mechanical stretching combined with the Hofmeister effect. Anisotropic hydrogels exhibit anisotropic mechanical and electrochemical properties.

Underwater adhesion plays an essential role in soft electronics for the underwater interface. Although hydrogel-based electronics are of great interest, because of their versatility, water molecules prevent hydrogels from adhering to substrates, thus bottlenecking further applications. Herein, inspired by the barnacle proteins, MXene/PHMP hydrogels with strong repeatable underwater adhesion are developed through the random copolymerization of 2-phenoxyethyl acrylate, 2-methoxyethyl acrylate, and

Hydrogel-based flexible electronics, especially stretchable human motion sensors, have been intensely investigated in the past few decades. However, challenges remain in the preparation of anti-freezing hydrogels with balanced properties of high sensitivity, large sensing range and suitable mechanical properties in a broad temperature range. In this study, we fabricate a fully-physically crosslinked poly(hydroxyethyl acrylamide)/silk fibroin-LiCl (PHEAA/SF-LiCl) hydrogel with excellent mechanical properties at both room temperature and subzero temperature. Strain sensitivity and durability at both room temperature (25 °C) and low temperature (−30 °C) have been characterized. Strain sensors which can monitor human movements in different situations, including wireless sensing and low temperature sensing have been fabricated, indicating their huge potential in flexible electronics, remote health control and electronic skins.

Traditional adhesives such as cyanoacrylate glue are mostly solvent-based. They are facing the problem of insufficient adhesion to some substrates, and also from the drawback of volatilization and release of small organic molecules in the process of usage. Therefore, a novel adhesive with non-irritating, high adhesive strength, and antibacterial properties is highly required. In this study, a full physically crosslinked zwitterionic poly(betaine sulfonate methacrylate) (PSBMA) hydrogel is proposed. The physical crosslinking interactions endow the hydrogel with good self-healing properties. Furthermore, the pure physical crosslinking hydrogel can form PSBMA powder adhesive after lyophilization and return to the hydrogel state after hydration. The mechanical properties of PSBMA adhesive can be modulated via adjusting the solid content and initiator dosage. Following the cure process similar to that of snail mucus or insect exoskeletons in nature, the adhesion of the PSBMA adhesive is improved at least 100 times than its wet state. In addition, the PSBMA adhesive is easy to be removed due to the dissociation of cross-linked structures in saltwater environments. Moreover, PSBMA adhesive with antifouling properties can effectively prevent the adhesion of proteins and bacteria, which shows potential applications in the assembly of medical devices.

To improve the therapeutic effect of a hydrogel on damaged tissue, a series of hydroxybutyl chitosan (HBC) and poly(sulfobetaine methacrylate) (PSBMA) composite hydrogels (HBC-PSB) with thermosensitivity, self-healing, antibiofouling, and synergistic antibacterial activity are prepared by mechanical blending. The electrostatic interaction among PSBMA and hydrophobic association among HBC are the main drive force to form a full physically crosslinked hydrogel. HBC can avoid the aggregation and precipitation of PSBMA caused by intermolecular strong association. Meanwhile, the existence of the PSBMA network can promote the sol-gel transition of HBC. Due to the reversible physical crosslinking, the HBC-PSB hydrogel shows excellent self-healing behaviors, and can be stored as dry powder. Intriguingly, the composite hydrogel has good synergistic antibacterial performance

Hydrogel-based strain sensors have been widely investigated owing to their intrinsic flexible and extensible properties. However, integrating good mechanical properties and excellent strain sensitivity into one hydrogel remains a challenge. In this work, a dual physical cross-linked carboxymethyl cellulose-Fe3+/polyacrylamide (CMC-Fe3+/PAAm) double network hydrogel was developed by facile two-step method. In this hydrogel, the Fe3+ cross-linked CMC acts as the first network for dissipating energy and hydrophobic association PAAm acts as the second network to maintain the integrity of hydrogel. Owing to these physical interactions, the as-prepared hydrogel shows good mechanical properties (e.g., tensile strength, 1.82 MPa; toughness, 6.52 MJ/m3). Furthermore, these mechanical behaviors can be modulated by adjusting the solid content, CMC/PAAm ratio, Fe3+ concentration and soaking time in Fe3+ solution. Moreover, the obtained hydrogel shows excellent self-recovery and anti-fatigue property due to the reversibility of dual physical cross-linked interactions. Additionally, the CMC-Fe3+/PAAm hydrogel shows good conductivity (1.82 S/m), strain sensitivity (gauge factor = 4.02 at 50–600% strain), and fast response time (260 ms). Based on the high strain sensitivity, the CMC-Fe3+/PAAm hydrogel can fabricate a flexible strain sensor for precisely monitoring various human motions. This study suggests that the CMC-Fe3+/PAAm hydrogel exhibits potential application in the flexible and stretchable strain sensors.

Flexible and stretchable electronics have received tremendous attention for next-generation human-friendly electronic applications. However, fabrication of transparent, fully recyclable and stretchable electronic sensors with low-temperature stability using biocompatible natural polymer-based hydrogels still remains a great challenge. In this study, a green and fully recyclable stretchable electronic sensor with high transparency and ultra-low operating temperature is constructed using ionic conductive gelatin organohydrogels. These gelatin organohydrogels are prepared by a simple strategy of immersing gelatin pre-hydrogels in citrate (Na3Cit) water/glycerol solutions. The existence of Na3Cit in the organohydrogel not only induces the formation of multiple non-covalent cross-linking points, endowing the organohydrogel with high mechanical performances, but also makes the organohydrogel have excellent ionic conductivity. The organohydrogel is also highly transparent and exhibits outstanding antifreezing properties. The mechanical robustness, conductivity and transparency of the organohydrogel can be well maintained even at −60 °C. As a result, a stretchable and transparent electronic sensor based on this organohydrogel is fabricated, which is strain-sensitive with a large linear sensing window and excellent stability. More importantly, the organohydrogel-based electronic sensor can be fully recycled due to the reversible non-covalently crosslinked structure, and the recycled organohydrogel regains its mechanical and sensing properties. The obtained sensors could precisely detect various human activities even below −30 °C, indicating the potential applications of the organohydrogel-based electronic sensor in flexible and stretchable electronics in a broad range of temperature.

As a new member of the 2D material family, MXene integrates high metallic conductivity and hydrophilic property simultaneously. It shows tremendous potential in fields of energy storage, sensing, electromagnetic shielding, and so forth. Due to the abundant surface functional groups, the physical and chemical properties of MXene can be tuned by the formation of MXene-polymer composites. The introduction of polymers can expand the interlayer spacing, reduce the distance of ion/electron transport, improve the surface hydrophilicity, and thus guide the assembly of MXene-polymer structures. Herein, the preparation strategies of MXene-polymer composites including physical mixing, surface modification, such as anchoring through TiN and Ti-O-C bonds, bonding through esterification, grafting functional groups through TiOSi/TiOP bonds, photograft reaction, as well as in situ polymerization are highlighted. In addition, the possible mechanisms for each strategy are explained. Furthermore, the applications of MXene-polymer composites obtained by different preparation strategies are summarized. Finally, perspectives and challenges are presented for the designs of MXene-polymer composites.

Conductive hydrogels have consistently attracted researchers' interests in the past few years. However, challenges still remain in the preparation of hydrogels with self-healing ability and underwater sensing capacity. In this work, we fabricate a novel fully-physically crosslinked nanocomposite hydrogel by incorporating gelatin dispersed carbon nanotubes (CNTs) into poly (sulfobetaine methacrylate) (PSBMA) network. The fully physically crosslinked PSBMA backbone and the nano reinforcement of CNTs endow hydrogel with fast self-healing ability (about 30 s) and good mechanical properties. Additionally, PSBMA/CNTs hydrogels exhibit high strain sensitivity (gauge factor up to 10.35) and pressure sensitivity (up to 0.256 kPa−1) and they can be fabricated as strain and pressure sensors to precisely monitor human movements. Moreover, the PSBMA/CNTs hydrogel sensor can detect human motions underwater owing to the anti-swelling feature. This work provides a feasible method to construct self-healing hydrogel sensors with strain and pressure sensing capacity and paves a way for underwater human motion sensors.

Prokaryotes possess CRISPR-Cas systems to exclude parasitic predators, such as phages and mobile genetic elements (MGEs). These predators, in turn, encode anti-CRISPR (Acr) proteins to evade the CRISPR-Cas immunity. Recently, AcrVA4, an Acr protein inhibiting the CRISPR-Cas12a system, was shown to diminish Lachnospiraceae bacterium Cas12a (LbCas12a)-mediated genome editing in human cells, but the underlying mechanisms remain elusive. Here we report the cryo-EM structures of AcrVA4 bound to CRISPR RNA (crRNA)-loaded LbCas12a and found AcrVA4 could inhibit LbCas12a at several stages of the CRISPR-Cas working pathway, different from other characterized type I/II Acr inhibitors which target only 1 stage. First, it locks the conformation of the LbCas12a-crRNA complex to prevent target DNA-crRNA hybridization. Second, it interacts with the LbCas12a-crRNA-dsDNA complex to release the bound DNA before cleavage. Third, AcrVA4 binds the postcleavage LbCas12a complex to possibly block enzyme recycling. These findings highlight the multifunctionality of AcrVA4 and provide clues for developing regulatory genome-editing tools.

With the development of high spatial resolution, high spectral resolution, high radiant resolution and high temporal resolution remote sensing satellites being put into use widely, the adaptive intelligent observation becomes an important function of a new generation of satellite remote sensing system. In order to realize the adaptive intelligent observation function, the first step is to construct the land cover priori knowledge and prejudge the land cover types and its reflectance values of the imaging areas. During the satellite imaging, the setting parameters of optimal camera including the on-orbit CCD integral time, electrical gain and image compression ratio are estimated according to the relationship of apparent radiance with sun illumination condition and land surface reflectance. In the paper, Medium Resolution Imaging Spectrometer (MERIS) bimonthly mean land surface reflectance imagery and 2009 GlobCover map are used to build the global land cover and its reflectance knowledge database. The land cover types include the cropland, urban, grassland, forest, desert, soil, water and ice land cover classes and the mean reflectance values in blue, green, red and near infrared spectral band were calculated in various seasons. The global land cover and reflectance values database has been integrated into the Beijing-1 small satellite mission programming system as the priori landscape knowledge of imaging areas to estimate the proper electrical gain of multispectral camera. After the intelligent observation mode was used in Beijing-1 small satellite, the entropy and SNR of multispectral imagery acquired by the Beijing-1 satellite had been increased greatly.

The obvious vertical strip and chromatic aberration exist in the raw images obtained from the linear push-broom CCD, due to the different response among CCD detectors, the odd/even effect raised in signal transfer and the inconsistency of electronic link outside CCD array. In this paper, one relative radiometric correction method based on dark target image to calculate the bias coefficient and stable light target image to calculate the gain coefficient is discussed, taking the Beijing-1 small satellite panchromatic image as an example. This method is independent of the statistic characteristics of the corrected image, not only can remove the strip noise and the eliminate chromatic aberration, but also can make the color balance of the image, and is suitable for the relative radiometric calibration of linear push-broom CCD remote sensing image without calibration device onboard.