Tough and Photo-Plastic Liquid Crystal Elastomer with a 2-Fold Dynamic Linker for Artificial Muscles.

Liquid crystal elastomers (LCEs) have been optimized by combining cross-linkers and dynamic bonds to achieve a reversible actuation behavior comparable to living skeletal muscles. In this study, one unique type of segment with 2-fold dynamic properties was introduced into LCEs, which offered not only dynamic diselenide covalent bonds for thermo-/photoplasticity but also H-bond arrays for dynamic cross-linking and mechanical robustness. Besides self-healing, self-welding, and recyclability, the LCEs were reprogrammable with elevated temperature or intensive visible light irradiation. The resultant LCEs gave an actuation blocking stress of 1.96 MPa and an elastic modulus of 14.4 MPa at 80 °C. The actuation work capacity reached 135.2 kJ m-3. When incorporating the Joule electrode or photothermal materials, the LCEs could be programmed as the electricity-driven and photothermal artificial muscles and thereby promised the application both as a biomimetic artificial hand and as an energy collector from sunlight. Thus, the 2-fold dynamic LCEs offered the pathway of enabling the reversible actuation behavior comparable to living skeletal muscles and promising applications in sustainable actuators, artificial muscles, and soft robots.

Mussel-inspired polymeric coatings with the antifouling efficacy controlled by topologies.

Block copolymers with different topologies (linear, loop, 3-armed and 4-armed polymers) containing poly(N-vinylpyrrrolidone) (PVP) antifouling blocks and terminal poly(dopamine-acrylamide) (PDAA) anchoring blocks were synthesized. These polymers can form a robust antifouling nanolayer on various surfaces. The morphologies of the polymer-modified surfaces are strongly dependent on the topologies of the polymers: with the increase of arm numbers, the morphology evolves from the smooth surface to the nanoscale coarse surface. As a result, the hydrophilicity of the coatings increases with the increase of degree of nanoscale roughness, and the 4-armed block copolymer forms a superhydrophilic surface with a water contact angle (WCA) as low as 8.7°. Accordingly, the linear diblock copolymer exhibits the worst antifouling efficiency, while the 4-armed polymer exhibits the best antifouling efficiency. This is the first example systematically showing that the antifouling efficacy could be adjusted simply by the topology of the coatings. Cell viability studies revealed that all of the copolymers exhibit excellent cytocompatibility. These biocompatible polymers with narrowly distributed molecular weight might find niches for antifouling applications in various areas such as anti-protein absorption, anti-bacterial and anti-marine fouling.

Mildly Peeling Off and Encapsulating Large MXene Nanosheets with Rigid Biologic Fibrils for Synchronization of Solar Evaporation and Energy Harvest.

Efficient and nondestructive liquid exfoliation of MXene with large lateral size has drawn growing research interest due to its outstanding properties and diverse potential applications. The conventional sonication method, though enabling a high production yield of MXene nanosheets, broke them down into submicrometric sizes or even quantum dots, and thus sacrificed their size-dependent properties, chemical stability, and wide applications. Herein, rigid biological nanofibrils in combination of mild manual shake were found to be capable of peeling off MXene nanosheets by attaching on MXene surfaces and localizing the shear force. With comparison to sonication, this efficient and nondestructive exfoliation approach produced the MXene nanosheets with the lateral size up to 4-6 µm and a comparable yield of 64% within 2 h. The resultant MXene nanosheets were encapsulated with these biological fibrils, and thus enabled super colloidal and chemical stability. A steam generation efficiency of ∼86% and a high evaporation rate of 3.3 kg m-2 h-1 were achieved on their aerogels under 1-Sun irradiation at ∼25 °C. An evaporation rate of 0.5 kg m-2 h-1 still maintained even at the atmospheric temperature of -5 °C. More importantly, an electricity generation up to ∼350 mV also accompanied this solar evaporation under equivalent 5-Sun irradiation. Thus, this fibrous strategy not only provides an efficient and nondestructive exfoliation method of MXene, but also promises synchronization of solar-thermal evaporation and energy harvest.

Iridescent coating of graphene oxide on various substrates.

Two-dimensional nanomaterials have been incorporated into coating layers for exceptional properties in mechanic toughness, electronics, thermology and optics. Graphene oxide (GO), however, was greatly hindered by its strong adsorption within visible wavelength and hereby the intrinsic dark color at the solid state. Herein, we found a unique aqueous mixture of GO containing sodium dodecyl sulfate and l-ascorbic acid. It enabled to produce iridescent coating layers with tunable thickness of 0.3-50 µm on both hydrophilic and hydrophobic substrates (e.g., glass, aluminum foil, polytetrafluoroethylene), through brushing, liquid-casting, dipping and writing. Their iridescence could be further tuned by incorporating MXene nanosheets. And their mechanical properties could be enhanced by certain synthetic polymers (e.g., polyvinyl alcohol and polyethylene glycol). Their sensitivity to heat, laser and water also benefited to pattern the coating layers. Furthermore, by controlling laser intensity, the domain color could be changed (e.g., green to blue). Thus, this study may pave a new pathway of producing iridescent coatings of graphene oxide in a large scale for practical applications.

Biofibrous nanomaterials for extracting strategic metal ions from water.

Strategic metals play an indispensable role in the related industries. Their extraction and recovery from water are of great significance due to both their rapid consumption and environmental concern. Biofibrous nanomaterials have shown great advantages in capturing metal ions from water. Recent progress in extraction of typical strategic metal ions such as noble metal ions, nuclear metal ions, and Li-battery related metal ions is reviewed here using typical biological nanofibrils like cellulose nanofibrils, chitin nanofibrils, and protein nanofibrils, as well as their assembly forms like fibers, aerogels/hydrogels, and membranes. An overview of advances in material design and preparation, extraction mechanism, dynamics/thermodynamics, and performance improvement in the last decade is provided. And at last, we propose the current challenges and future perspectives for promoting biological nanofibrous materials toward extracting strategic metal ions in practical conditions of natural seawater, brine, and wastewater.

Design of MXene Composites with Biomimetic Rapid and Self-Oscillating Actuation under Ambient Circumstances.

Although responsive actuators have been intensively investigated, it remains challenging to enable rapid and self-oscillating actuation under ambient circumstances without human intervention analogous to living organisms. By hybridizing a unique type of two-dimensional nanomaterials (i.e., MXene) with a particular hydrophilic polymer, a smart and flexible conductive composite was produced with rapid actuation and spontaneous oscillation near a moist surface. Due to the presence of layered microstructures and the moisture-sensitivity improved by surface roughness and intercalated polymeric layers, the composites could reversibly bend up to 180° in 2 s or 210° in 10 s on demand when the circumstantial humidity was varied, being superior or comparable to many actuators in the literature. More importantly, the composite was capable not only of flipping upside down repeatedly on the moist surface but also of self-oscillating ceaselessly under ambient gradient humidity without human intervention, e.g., an oscillation between 30 and 100° with an oscillation frequency of 0.08 Hz. This self-oscillation resulted from the occurrence of rapid asymmetrical hydration and dehydration of the composite between the regions of high and low humidity, which could further be modulated both by different hydrophilic polymers and by photoradiation owing to the photothermal effect of MXene nanosheets. Because of the ubiquitous presence of humidity gradient near the moist surface, this type of smart composite may not only offer a strategy for designing artificial materials that are capable of spontaneous actuation under ambient circumstance without human intervention but also promise potential applications in artificial muscles, autonomous robotics, and energy harvesting from environments.

Liquid Metal Initiator of Ring-Opening Polymerization: Self-Capsulation into Thermal/Photomoldable Powder for Multifunctional Composites.

Liquid metal nanodroplets not only share similar metallic properties and nanoscale effect with solid metal nanoparticles, but also possess the additional uniqueness in nonvolatile fluidity and ambient sintering ability into continuous conductors. In most cases, liquid metal nanodroplets are encapsulated into ultrathin and fragile shells of oxides and amphiphile monolayers, and may be hindered from incorporating homogeneously into various composites through conventional processing methods. In this study, ring-opening polymerization is found to be initiated by sonicating the liquid metal EGaIn in fluidic lactones. By this in situ polymerization, EGaIn nanodroplets are encapsulated into polylactone shells with tunable thickness, which can further be dried into a solid powder. Besides high chemical stability and dispersibility in organic solvents, the powder of the EGaIn capsules combines the exceptional properties of the EGaIn droplets (e.g., photothermal effect) and the polylactone shells (e.g., biocompatibility, biodegradability, and compatibility with different polymer matrixes), being capable of being introduced into thermoplastic composites through liquid casting and thermal- or photomolding for the notch-insensitive tearing property, sintering-induced electric conductivity, and photothermal effect. Thus, the EGaIn initiator of ring-opening polymerization may start a pathway to produce stable andthermal/photomoldable powders of EGaIn capsules and their multifunctionalcomposites, applicable in biomedicines, soft electronics, and smart robots.

Glycopolymers/PEI complexes as serum-tolerant vectors for enhanced gene delivery to hepatocytes.

Serum stability is a crucial factor for ideal polymeric gene vectors. In this work, a series of serum-tolerant and low-toxicity glycopolymers/poly(ethyleneimine) (PEI) complexes were designed for gene delivery. Atomic transfer radical polymerization (ATRP) was used to synthesize the comb-shaped random copolymers dextran-g-poly(2-dimethylaminoethyl methacrylate-co-2-lactobionamidoethyl methacrylate) (DDrL). Then DDrLs/PEI were investigated for their use as plasmid DNA (pDNA) vectors, which can completely condense the pDNA into nanoparticles. The DDrLs/PEI/pDNA complexes in serum-containing media showed better stability than PEI/pDNA complexes. in vitro gene transfection studies showed that DDrLs/PEI exhibited a remarkable transfection efficiency enhancement in the presence of serum compared to that in serum-free conditions. Moreover, the transfection level of DDrLs/PEI were two orders of magnitude higher than that of PEI alone in the presence of 30% serum. DDrLs/PEI complexes with galactose enhanced pDNA delivery to hepatocytes, with higher protein expression in ASGPr-presenting HepG2 than in HeLa cells, which lack the receptor. All of the DDrLs/PEI/pDNA complexes had lower cytotoxicity than PEI/pDNA.

A versatile platform to achieve mechanically robust mussel-inspired antifouling coatings via grafting-to approach.

Although significant progress has been made in mussel-inspired antifouling coatings, most of them suffer from low mechanical stability. Herein, we present a facile and efficient method to fabricate mechanically robust mussel-inspired antifouling coatings. A polyvinyl alcohol (PVA)-based mussel-inspired coating material, which exhibits the highest adhesion capability (always at 5B level in a tape adhesion test based on the ASTM D3359 method) and excellent anti-abrasive properties (little mass loss after 1000 abrasion cycles), is used as a universal platform for further modification to introduce antifouling properties. Intriguingly, the hydroxyl groups in this PVA-based coating material are used as the anchor for the installation of either hydrophilic or hydrophobic segments (or both) via a grafting-to approach. Single modifiers, methoxypolyethylene glycol (MPEG), sodium 2-hydroxyethanesulfonate (SHS) and 1H,1H,2H,2H-perfluorooctan-1-ol (PFO), and complex modifiers, MPEG/PFO, are tethered onto the coating through an effective urethane bond formation reaction to endow the surfaces with antifouling efficacy. The functionalized surfaces are shown to be effective in preventing bovine serum albumin (BSA) adsorption and in reducing bacterial (Gram-positive bacteria S. aureus and Gram-negative bacteria E. coli) adhesion. More importantly, such modification does not influence the strong adhesion and excellent anti-abrasion properties of the coating. To the best of our knowledge, this is the first example of merging excellent mechanical properties and antifouling capability for mussel-inspired coatings, which might find niches in a broad range of applications in the industrial and biomedical fields.

Contribution of the Polarity of Mussel-Inspired Adhesives in the Realization of Strong Underwater Bonding.

Although the role of 3,4-dihydroxyphenyl-L-alanine(DOPA)in mussel foot proteins (mfps) in the realization of underwater bonding has been widely recognized, the role of the polarity of the polymer was largely overlooked. Here, by systematically comparing the underwater bonding properties of four mussel-inspired adhesives with different amide/lactam contents but similar catechol contents and molecular weights, we came to the conclusion that the polarity of the polymers also contributes to the strong underwater bonding. With the increase in the amide/lactam contents, the polarity of the polymeric adhesive increases, which correlates to the improved underwater bonding strength. A dielectric constant is introduced to evaluate the polarity of the polymer, which may be used as a guidance for the design of mussel-inspired adhesives with even better underwater bonding properties.

Robust mussel-inspired coatings for controlled zinc ion release.

Although mussel-inspired coatings have been extensively studied, most of them suffer from high-cost preparation, poor mechanical strength and low abrasion resistance, which impede them from practical applications. In this study, we report the synthesis of low-cost but robust mussel-inspired coatings based on polyvinyl alcohol (PVA), which could continuously release zinc ions at a high release rate when immersed into artificial seawater (ASW). The coating exhibits high mechanical strength, strong adhesion to stainless steel (SS), and excellent anti-abrasion properties. Moreover, a complicated fabrication process is not required for the coating, which makes it a potential candidate for marine antifouling coating.

Quantum dots encapsulated glycopolymer vesicles: synthesis, lectin recognition and photoluminescent properties.

Biomimetic star-shaped glycopolymer poly(ɛ-caprolactone)-b-poly(2-aminoethyl methacrylate-b-poly(gluconamidoethylmethacrylate) (SPCL-PAMA-PGAMA) was synthesized by the combination of ring opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. The glycopolymer self-assembled into vesicles with low critical aggregation concentration (CAC) (0.0075 mg/mL). Then, the carboxylic capped CdTe QDs were encapsulated within the glycopolymer vesicles. The QDs encapsulated glycopolymer vesicles (Gly@QDs vesicles) could specifically bind Concanavalin A (Con A) without changing the photoluminescent properties of the Gly@QDs vesicles. Cell viability studies revealed that the cytotoxicity of the Gly@QDs vesicles was remarkably improved as compared to that of the original QDs. The Gly@QDs vesicles were internalized by Hep G2 cells and then emitted green fluorescence in the cells. Consequently, these Gly@QDs vesicles provided a multifunctional platform for targeted delivery and imaging.

Biomimetic glycopolymers tethered gold nanoparticles: preparation, self-assembly and lectin recognition properties.

Biomimetic glycopolymers poly(gluconamidoethylmethacrylate)-b-poly(ɛ-caprolactone)-b-poly(gluconamidoethylmethacrylate) with degradable disulfide groups in the backbone (PGAMA-PCL-SS-PCL-PGAMA) were synthesized by the combination of ring opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The internal disulfide bonds were cleaved by reduction with dl-dithiothreitol to yield the corresponding thiol terminated glycopolymers. The thiol terminated glycopolymers were effectively anchored on the surface of gold nanoparticles to prepare the biomimetic glycopolymers modified gold nanoparticles (Gly@Au NPs). Moreover, the properties of the Gly@Au NPs in aqueous solution were investigated. Transmission electron microscopy (TEM) analysis revealed that the self-assembly morphology of the Gly@Au NPs can be fine-tuned, from irregular clusters to spherical aggregates, by changing the weight fraction of the hydrophobic PCL block. Furthermore, the Gly@Au NPs had specific recognition with Concanavalin A (Con A).

Synthesis and properties of novel biomimetic and thermo-responsive dextran-based biohybrids.

A new class of biodegradable, biomimetic and thermo-responsive dextran/synthetic glycopolymer biohybrids (dextran-graft-poly(lactobionamidoethyl methacrylate)-block-poly(di(ethylene glycol) methyl ether methacrylate), dextran-g-(PLAMA-b-PDEGMA)), was synthesized by the direct atom transfer radical polymerization (ATRP) of unprotected lactobionamidoethyl methacrylate (LAMA) glycomonomer and di(ethylene glycol) methyl ether methacrylate (DEGMA) monomer. The dextran macroinitiator for ATRP was prepared by partial esterification of the hydroxyl groups of the polysaccharide with 2-bromo-2-methylpropionic acid (BrMPA). The biohybrids containing PDEGMA segments exhibited a lower critical solution temperature (LCST) behavior, which changed from unimers to aggregates in solutions. Moreover, it was demonstrated that these biohybrids had specific biomolecular recognition with ricinus communis agglutinin 120 (RCA120) in comparison with bovine serum albumin (BSA). Furthermore, these biohybrids showed good biocompatibility in the cytotoxicity assays. This hopefully provides a platform for targeted drug delivery and studying the biomolecular recognition between sugar and lectin.