High transparency, water vapor barrier and antibacterial properties of chitosan/carboxymethyl glucan/poly(vinyl alcohol)/nanoparticles encapsulating citral composite film for fruit packaging.

Utilizing antibacterial packaging material is an effective approach to delay fruit rotting and spoilage thereby minimizing financial losses and reducing health harm. However, the barrier and mechanical properties of biodegradable antibacterial packaging materials are barely compatible with transparency. Herein, antimicrobial nanoparticles encapsulating citral (ANPs) were first prepared by emulsification under the stabilization of oxidized dextran (ODE) and ethylene diamine. Then, composite films with high transparency, good water vapor barrier, and mechanical and antibacterial properties for fruits packaging were prepared from chitosan (CS), carboxymethyl-glucan (CMG), poly(vinyl alcohol) (PVA), and ANPs by solvent casting strategy. The synergistic effects of electrostatic interaction and hydrogen bonding could regulate crystalline architecture, generating high transparency of the composite films (90 %). The mechanical properties of the composite film are improved with elongation at break up to 167 % and stress up to 32 MPa. The water vapor barrier property of the film is appropriate to the packed fruit for less weight loss and firmness remaining. Simultaneously, the addition of ANPs endowed the film with excellent antimicrobial and UV-barrier capabilities to reduce fruit mildew, thereby extending the shelf life of fruits. More importantly, the composite polymer solution could be sprayed or dipped directly on fruits as a coating for food storage to improve food shelf life, substantially expanding its ease of use and scope of use.

Regulating Electrostatic Interactions toward Thermoresponsive Hydrogels with Low Critical Solution Temperature.

Low critical solution temperature (LCST) of commonly used thermoresponsive polymers in water is basically dominated by hydrophobic interactions. Herein, a novel thermoresponsive system based on electrostatic interactions is reported. By simply loading aluminum chloride (AlCl3 ) into non-responsive poly(2-hydroxyethyl acrylate) (PHEA) hydrogels, PHEA-Al gels turn to have reversible thermoresponsive behavior between transparent and opaque without any volume change. Further investigations by changing metal ion-polymer compositions unravel the necessity of specific electrostatic interactions, namely, cation-dipole bonding interactions between hydroxy groups and trivalent metal ions. The thermoresponsive hydrogel demonstrates high transparency (≈95%), excellent luminous modulation capability (>98%), and cyclic reliability, suggesting great potential as an energy-saving material. Although LCST control by salt addition is widely known, salt-induced expression of thermoresponsiveness has barely been discussed before. This design provides a new approach of easy fabrication, low cost, and scalability to develop stimuli-responsive materials.

Skin-Inspired Patterned Hydrogel with Strain-Stiffening Capability for Strain Sensors.

Flexible materials with ionic conductivity and stretchability are indispensable in emerging fields of flexible electronic devices as sensing and protecting layers. However, designing robust sensing materials with skin-like compliance remains challenging because of the contradiction between softness and strength. Herein, inspired by the modulus-contrast hierarchical structure of biological skin, we fabricated a biomimetic hydrogel with strain-stiffening capability by embedding the stiff array of poly(acrylic acid) (PAAc) in the soft polyacrylamide (PAAm) hydrogel. The stress distribution in both stiff and soft domains can be regulated by changing the arrangement of patterns, thus improving the mechanical properties of the patterned hydrogel. As expected, the resulting patterned hydrogel showed its nonlinear mechanical properties, which afforded a high strength of 1.20 MPa while maintaining a low initial Young's modulus of 31.0 kPa. Moreover, the array of PAAc enables the patterned hydrogel to possess protonic conductivity in the absence of additional ionic salts, thus endowing the patterned hydrogel with the ability to serve as a strain sensor for monitoring human motion.

Evaluation the in vivo behaviors of PM2.5 in rats using noninvasive PET imaging with mimic particles.

Inhaled PM2.5 particles is harmful to human health. However, real-time tracking of PM2.5 particles and dynamic evaluation of the pharmacokinetic behaviors in vivo are still challenging. Here, PET imaging is utilized to noninvasively monitor the in vivo behavior of PM2.5 particles in rats. To mimic aerosol PM2.5 particles suspended in ambient air, 89Zr-labeled melanin nanoparticles (89Zr-MNP) are nebulized into microscopic liquid particles with a mean size of 2.5 µm. Then, the 89Zr-labeled PM2.5 mimic particles (89Zr-PM2.5) are administrated into rats via inhalation. PET imaging showed that 89Zr-PM2.5 mainly accumulated in the lungs for up to 384 h after administration. Besides, we also observe that a small amount of 89Zr-PM2.5 can penetrate the brain through the inhalation. Further PET imaging showed that enhanced uptakes of 18F-FDG and 18F-DPA-714 were found in the brain of rats upon PM2.5 mimic particle exposure, which revealed that pulmonary exposure to PM2.5 could cause potential damages to the brain. Note that abnormal glucose metabolism was reversed, but the neuroinflammation was permanent and could not be alleviated after ceasing PM2.5 exposure. Our results demonstrate that PET is a sensitive and feasible tool for evaluating the in vivo behaviors of PM2.5.

Thermal- and pH-responsive triple-shape memory hydrogel based on a single reversible switch.

Here we provide a novel method for fabricating a pH- and thermal-responsive triple-shape memory hydrogel based on a single reversible switch phase. A high-density quadruple hydrogen-bonding ureido-pyrimidinone (UPy) system was introduced into the hydrogel network, which can occur to varied degrees of dissociation under different pH and temperature conditions. Different degrees of dissociation and reassociation can be viewed as different subsets of memory elements to freeze and unfreeze the temporary shapes. Although this class of hydrogels contains only a single transition phase, they feature a large dissociative differential in response to varied external stimuli to provide multiple windows for programming different temporary shapes.

Correction: One-step mild preparation of tough and thermo-reversible poly(vinyl alcohol) hydrogels induced by small molecules.

Correction for 'One-step mild preparation of tough and thermo-reversible poly(vinyl alcohol) hydrogels induced by small molecules' by Chuang Dong et al., Chem. Commun., 2021, 57, 3789-3792, https://doi.org/10.1039/D1CC00578B.

High-Strength, Degradable and Recyclable Epoxy Resin Based on Imine Bonds for Its Carbon-Fiber-Reinforced Composites.

Carbon fiber (CF) is widely used in the preparation of carbon-fiber-reinforced polymer composites (CFRP) in which it is combined with epoxy resin due to its good mechanical properties. Thermosetting bisphenol A epoxy resin, as one of the most common polymer materials, is a non-renewable resource, leading to a heavy environmental burden and resource waste. To solve the above problems and achieve high mechanical and thermal properties comparable to those of bisphenol A, herein, a high-performance, degradable and recyclable bio-based epoxy resin was developed by reacting the lignin derivative vanillin with 4-amino cyclohexanol via Schiff base. This bio-based epoxy resin showed a Young's modulus of 2.68 GPa and tensile strength of 44 MPa, 36.8% and 15.8% higher than those of bisphenol A epoxy, respectively. Based on the reversible exchange reaction of the imine bond, the resin exhibited good degradation in an acidic environment and was recoverable by heat treatment. Moreover, the prepared epoxy resin could be used to prepare carbon fiber (CF)-reinforced composites. By washing off the epoxy resin, the carbon fiber could be completely recycled. The recovered carbon fiber was well preserved and could be used again for the preparation of composite materials to realize the complete recovery and utilization of carbon fiber. This study opens a way for the preparation of high-performance epoxy resin and the effective recycling of carbon fiber.

A monocarboxylic acid induction strategy to prepare tough and thermo-reversible poly(vinyl alcohol) physical gels with high transparency.

To date, poly(vinyl alcohol) (PVA) gels attract tremendous attention because of their potential applications in a wide variety of fields. Here, a novel monocarboxylic acid induction strategy was developed to fabricate tough and thermo-reversible PVA physical gels by introducing monocarboxylic acids into the PVA/dimethyl sulfoxide (DMSO) system. The obtained PVA gels exhibited appropriate crystalline architectures, leading to superior mechanical properties and high transparency. Furthermore, the role of monocarboxylic acids in the formation of PVA physical gels and the effects of alkyl chain length, concentration, and the induction time of monocarboxylic acids on the properties of PVA physical gels were also investigated.

Injectable Dopamine-Polysaccharide In Situ Composite Hydrogels with Enhanced Adhesiveness.

Polysaccharide bio-adhesives used for non-invasive repair often show weak mechanical strength and tissue adhesion, even when covalently modified with dopamine (DA) from mussel proteins and its derivatives. Low cohesion of the polysaccharide adhesives and easy oxidation of DA may result in the low adhesion properties of the polysaccharide-DA adhesives. In this work, we aimed to prepare a series of injectable hydrogel adhesives to improve their cohesion and adhesion by in situ mixing DA with the polysaccharide without covalent modification. The injectable and rapid curing adhesives were prepared by mixing oxidized dextran (ODE) and chitosan (CS) through a Schiff base reaction in the presence (or absence) of DA. The gelation time of the adhesive was customized to be less than 20 s by controlling the amount of ODE, regardless of the amount of DA. Multi-cross-linked (MC) hydrogels were further prepared by adding cross-linking agents such as sodium periodate (NaIO4) and ferric trichloride (FeCl3), and their sol-gel transitions were easily adjusted by changing the amounts of the cross-linking agents. The MC-FeCl3 hydrogel adhesive displayed good tissue adhesion with a lap shear adhesion strength of 345 kPa, which was 43 times that of fibrin glue. Results from Raman spectra, texture profile analyses, and atomic force microscopy images confirmed the enhanced adhesion induced by a higher cohesion of MC-FeCl3, owing to the coordination of Fe3+ and DA and non-covalent and covalent bonds of DA. Moreover, the adhesives showed good biodegradability and biocompatibility. These results demonstrate that the injectable and sticky hydrogels with good adhesion are promising materials for tissue repair.

High-Sensitivity Flexible Sensor Based on Biomimetic Strain-Stiffening Hydrogel.

Recently, flexible wearable and implantable electronic devices have attracted enormous interest in biomedical applications. However, current bioelectronic systems have not solved the problem of mechanical mismatch of tissue-electrode interfaces. Therefore, the biomimetic hydrogel with tissue-like mechanical properties is highly desirable for flexible electronic devices. Herein, we propose a strategy to fabricate a biomimetic hydrogel with strain-stiffening property via regional chain entanglements. The strain-stiffening property of the biomimetic hydrogel is realized by embedding highly swollen poly(acrylate sodium) microgels to act as the microregions of dense entanglement in the soft polyacrylamide matrix. In addition, poly(acrylate sodium) microgels can release Na+ ions, endowing hydrogel with electrical signals to serve as strain sensors for detecting different human movements. The resultant sensors own a low Young's modulus (22.61-112.45 kPa), high nominal tensile strength (0.99 MPa), and high sensitivity with a gauge factor up to 6.77 at strain of 300%. Based on its simple manufacture process, well mechanical matching suitability, and high sensitivity, the as-prepared sensor might have great potential for a wide range of large-scale applications such as wearable and implantable electronic devices.

A photothermally triggered one-component shape memory polymer material prepared by cross-linking porphyrin-based amphiphilic copolymer self-assemblies.

Photothermally triggered shape memory polymer materials are usually prepared by dispersing photothermally responsive fillers or compounds into shape memory polymer matrixes through physical blending, while the migration and non-biodegradability of the fillers limit their potential applications (e.g., in the biomedical field). Here, we synthesized a new type of porphyrin-based amphiphilic random copolymer bearing a reactive moiety of carbonyl group by co-polymerizing methyl methacrylate (MMA), butyl acrylate (BA), diacetone acrylamide (DAAM), acrylic acid (AA) and double-bonded vinyl porphyrin monomers, followed by induced self-assembly in aqueous solution to give rise to amphiphilic random copolymer nanoparticles. The nanoparticles were further crosslinked by means of adipic dihydrazide (ADH) to fabricate the photothermally triggered one-component shape memory polymer material. Compared with the most-studied multi-phase/multi-component shape memory polymer materials, the porphyrin moiety, playing the role of a photo-to-heat converter, covalently bonded into the polymer structure would certainly make it more homogeneous and more stable in principle.

Mussel-Inspired Epoxy Bioadhesive with Enhanced Interfacial Interactions for Wound Repair.

The balance between high mechanical properties and strong adhesion strength is crucial in designing and preparing a bio-based hydrogel adhesive for wound closure. Although the adhesion performance of bioadhesives has been remarkably improved by modification with catechol groups, their mechanical properties are yet to meet the biomedical requirements. In this study, mussel-inspired epoxy bioadhesives (CSD-PEG) were synthesized based on catechol-modified chitosan oligosaccharide (CSD) and polyethylene glycol diglycidyl ether (PEGDGE) through nucleophilic substitution. Notably, the CSD-PEG adhesive showed high mechanical and adhesion strengths, which were up to 50.7 kPa and 136.7 kPa, respectively. It was confirmed that a certain amount of the epoxy and catechol groups provided multiple interfacial interactions among the adhesives, substrates, and polymer chains for enhancing the performance of adhesives. The adhesives showed good binding and repairing effects for wound closure and favorable biocompatibility in vivo. The prepared CSD-PEG adhesives are expected to be a promising candidate for surgical tissue repair, wound closure, and tissue engineering fields. STATEMENT OF SIGNIFICANCE: Current reported adhesives composed of biopolymers generally suffer from poor mechanical properties or weak tissue adhesiveness. Therefore, to achieve simultaneously high mechanical and adhesion properties in a bio-based adhesive for wound closure is a big challenge. In this study, mussel-inspired adhesive hydrogels (CSD-PEG) were prepared based on catechol-modified chitosan oligosaccharide (CSD) and polyethylene glycol diglycidyl ether (PEGDGE). The tensile strength and adhesive strength of CSD-PEG on porcine skin reached 50.7 kPa and 136.7 kPa, respectively, which were higher than those for most reported biopolymeric adhesives, mainly due to the multiple interfacial interactions between the catechol and epoxy groups. The CSD-PEG bioadhesives also showed good binding and repairing effects for wound closure and tissue regeneration in vivo.

Optimizing the dynamic and thermodynamic properties of hybridization in DNA-mediated nanoparticle self-assembly.

DNA-directed nanoparticle (DNA-NP) systems provide various applications in sensing, medical diagnosis, data storage, plasmonics and photovoltaics. Bonding probability and melting properties are helpful to evaluate the selectivity, thermostability and thermosensitivity of these applications. We investigated the influence of temperature, nanoparticle size, DNA chain length and surface grafting density of DNA on one nanoparticle on the DNA dynamic hybridization percentage and melting properties of DNA-NP assembly systems by molecular dynamics simulation. The high degree of consistency of free energy estimations for DNA hybridization via our theoretical deduction and the nearest-neighbor rule generally used in experiments validates reasonably our DNA model. The melting temperature and thermosensitivity parameter are determined by the sigmoidal melting curves based on hybridization percentage versus temperature. The results indicated that the hybridization percentage presents a downward trend with increasing temperature and nanoparticle size. Applications based on DNA-NP systems with bigger nanoparticle size, such as DNA probes, have better selectivity, thermostability and thermosensitivity. There exist optimal DNA chain length and surface grafting density where the hybridization percentage reaches the maximal value. The melting temperature reaches a maximum at the point of optimal grafting density, while the thermosensitivity parameter presents an upward trend with the increase of grafting density. Several physical quantities consisting of the radial density function, root mean square end-to-end distance, contact distance parameter and effective volume fraction are used to analyse DNA chain conformations and DNA-NP packing in the assembly process. Our findings provide the theoretical basis for the improvement and optimization of applications based on DNA-NP systems.

One-step mild preparation of tough and thermo-reversible poly(vinyl alcohol) hydrogels induced by small molecules.

To overcome shortcomings of the traditional freeze-thaw method for PVA hydrogel preparation, we develop a one-step mild method, which induces PVA crystallization to form hydrogels through small molecules containing hydroxyl and carboxyl groups. The obtained hydrogels showed high mechanical properties, untypical plasticity with short gelation time and repeatable sol-gel transformation.

Bio-Based Hotmelt Adhesives with Well-Adhesion in Water.

We suggest a simple idea of bio-based adhesives with strong adhesion even under water. The adhesives simply prepared via polycondensation of 3,4-dihydroxyhydrocinnamic acid (DHHCA) and lactic acid (LA) in one pot polymerization. Poly(DHHCA-co-LA) has a hyperbranched structure and demonstrated strong dry and wet adhesion strength on diverse material surfaces. We found that their adhesion strength depended on the concentration of DHHCA. Poly(DHHCA-co-LA) with the lowest concentration of DHHCA showed the highest adhesion strength in water with a value of 2.7 MPa between glasses, while with the highest concentration of DHHCA it exhibited the highest dry adhesion strength with a value of 3.5 MPa, which was comparable to commercial instant super glue. Compared to underwater glues reported previously, our adhesives were able to spread rapidly under water with a low viscosity and worked strongly. Poly(DHHCA-co-LA) also showed long-term stability and kept wet adhesion strength of 2.2 MPa after steeping in water for 1 month at room temperature (initial strength was 2.4 MPa). In this paper, Poly(DHHCA-co-LA) with strong dry and wet adhesion properties and long-term stability was demonstrated for various kinds of applications, especially for wet conditions.

The compatibilization of poly (propylene carbonate)/poly (lactic acid) blends in presence of core-shell starch nanoparticles.

A novel core-shell starch-based nanoparticles (CSS NPs) with a "hard" starch core and a "soft" poly (methyl acrylate) (PMA) shell was prepared and incorporated into a PPC/PLA blend. The excellent compatibilization of CSS NPs was revealed by atomic force microscope (AFM), differential scanning calorimetry (DSC) and rheological test. More importantly, due to the excellent compatibilization the resulted PPC/PLA/CSS blend exhibited a strikingly improved mechanical and thermal properties. Compared to PPC/PLA (60/40), the elongation at break of PPC/PLA/CSS (60/40/20) increased greatly from 15 % to 272 % without sacrificing the tensile strength. Besides, the heat distortion temperature (HDT) of PPC/PLA/CSS (60/40/20) was improved to 47.3 °C, which was 20.5 °C higher than that of the neat PPC. These results established a novel and efficient strategy to improve the compatibility of polymer blends and to prepare polymer blends with balanced toughness and stiffness.

Bio-inspired mineral fluorescent hydrogels cross-linked by amorphous rare earth carbonates.

The bio-inspired mineral plastic hydrogel based on calcium carbonate and polyacrylic acid has been recently investigated as a promising sustainable material. Here we report that rare earth carbonates can act as cross-linkers to fabricate analogous hydrogels and provide remarkable optical properties.

Poly(amino acid) Multilayers Modified Dendritic Mesoporous Silica Nanoparticles Achieve Effective Enzyme Stability for Ultrasensitive Immunoassay.

Enzyme-linked immunosorbent assay (ELISA) is one of the most common techniques in biomedical detection; however, the poor sensitivity in early diagnosis for some diseases seriously limits its application. In this work, we developed an ultrasensitive ELISA system that is based on horseradish peroxidase (HRP)-loaded dendritic mesoporous silica nanoparticles (DMSN) modified with poly(amino acid) multilayers (defined as DSHP). A large amount of HRP adsorption was achieved in center-radial mesoporous channels of DMSN because of the high specific surface area and large pore size, leading to significant signal amplification. Additionally, DSHP could not only effectively maintain HRP activity for at least 10 days but also provide preferable protection for HRP activity even at high temperatures or a wide pH range. Moreover, the DSHP system exhibited admirable signal amplification performance with a limit of detection of 0.667 fM and a wide detectable range from 6.67 × 10-4 to 6.67 × 105 pM, whose sensitivity was 104 times higher than that of the conventional ELISA. We believe that the DSHP will offer a new strategy for signal amplification of the ELISA system in clinical diagnosis.

Self-Standing Hydrogels Composed of Conducting Polymers for All-Hydrogel-State Supercapacitors.

Conducting polymer hydrogels that are capable of contacting with electrolytes at the molecular level, represent an important electrode material. However, the fabrication of self-standing hydrogels merely composed of conducting polymers is still challenging owing to the absence of reliable methods. Herein, a novel and facile macromolecular interaction assisted route is reported to fabricate self-standing hydrogels consisting of polyaniline (PANi: providing high electrochemical activity) and poly(3,4-ethylenedioxythiophene) (PEDOT: enabling high electronic conductivity). Owing to the synergistic effect between them, the self-standing hydrogels possess good mechanical properties and electronic/electrochemical performances, making them an excellent potential electrode for solid-state energy storage devices. A proof-of-concept all-hydrogel-state supercapacitor is fabricated, which exhibits a high areal capacitance of 808.2 mF cm-2 , and a high energy density of 0.63 mWh cm-3 at high power density of 28.42 mW cm-3 , superior to many recently reported conducting polymer hydrogels based supercapacitors. This study demonstrates a novel promising strategy to fabricate self-standing conducting polymer hydrogels.

Mussel inspired bio-adhesive with multi-interactions for tissue repair.

Bio-adhesives based on biopolymers have been widely researched for tissue repair. However, the adhesive properties are still insufficient to meet the practical applications. Introducing functional groups into the polymer chains that have multi-interactions among inter/intra-molecules and with substrates is an efficient way to increase cohesion force and further improve the adhesive properties. In this study, 3,4-dihydroxyphenyl propionic acid (DPA) and dopamine (DA) containing adhesion functional catechol groups were employed to modify chitosan (CS) and γ-polyglutamic acid (γPGA), respectively. The substituted degrees of the catechol groups were controlled by the catechol compositions. DPA modified chitosan/DA modified γPGA (CS-DPA/γPGA-DA) adhesives prepared by mixing CS-DPA and γPGA-DA. Effects of the substituted degrees and substrates on the adhesion strength were measured by tensile testing machine. The results showed good adhesion property of the CS-DPA/γPGA-DA adhesive on many surfaces of the substrates. Especially on the arthrodial cartilage, the adhesive strength reached around 150 kPa, much higher than commercially available tissue adhesives. The high adhesion property might be due to the adhesion interactions between the catechol groups and substrates and the high cohesion forces induced by the crosslinking interactions formation among the catechol groups and the electrostatic interactions between the CS and γPGA polymers. In vitro experiments demonstrated that the adhesive had good biocompatibility. These results suggested the catechol-based adhesive is a very suitable and promising biomaterial in the clinical medicine field.