Environmental-friendly, flexible silk fibroin-based film as dual-responsive shape memory material.

Bio-based shape memory materials have attracted wide attention due to their biocompatibility, degradability and safety. However, designing and manufacturing wearable bio-based shape memory films with excellent flexibility and toughness is still a challenge. In this work, silk fibroin substrate with a ß-sheet structure was combined with a tri-block shape memory copolymer to prepare a transparent composited shape memory film. The silk fibroin-based film showed a dual-responsive shape memory function, which can respond to both temperature and water stimuli. This film has a sensitive water-responsive shape memory, which starts deforming after exposure to water for 3 s and fully recovers in 30 s. In addition, the composite film shows highly stretchable (>300 %) and could maintain its high tensile properties after 5 cycles of regeneration. The films also exhibited rapid degradation ability. This study provides new insights for the design of dual-responsive shape memory materials by combining biocompatible matrix and multi-block SMP to simultaneously enhance the mechanical properties, which can be used for intelligent packaging, medical supplies, soft actuators and wearable devices.

Piezoelectric Interlayer Enabling a Rechargeable Quasisolid-State Sodium Battery at 0 °C.

Solid-state sodium (Na) batteries (SSNBs) hold great promise but suffer from several major issues, such as high interfacial resistance at the solid electrolyte/electrode interface and Na metal dendrite growth. To address these issues, a piezoelectric interlayer design for an Na3Zr2Si2PO12 (NZSP) solid electrolyte is proposed herein. Two typical piezoelectric films, AlN and ZnO, coated onto NZSP function as interlayers designed to generate a local stress-induced field for alleviating interfacial charge aggregation coupling stress concentration and promoting uniform Na plating. The results reveal that the interlayer (ZnO) with matched modulus, high Na-adhesion, and sufficient piezoelectricity can provide a favorable interphase. Low interfacial resistances of 91 and 239 Ω cm2 are achieved for the ZnO layer at 30 and 0 °C, respectively, which are notably lower than those for bare NZSP. Moreover, steady Na plating/stripping cycles are rendered over 850 and 4900 h at 0 and 30 °C, respectively. The superior anodic performance is further manifested in an Na2MnFe(CN)6-based full cell which delivers discharge capacities of 125 mA h g-1 over 1600 cycles at 30 °C and 90 mA h g-1 over 500 cycles at 0 °C. A new interlayer-design insight is clearly demonstrated for SSNBs breaking low-temperature limits.

Preparation and properties of chitin/silk fibroin biocompatible composite fibers.

In the present world chitin is used enormously in various fields, such as biopharmaceuticals, medical and clinical bioproducts, food packaging, etc. However, its development has been curbed by the impaired performance and cumbersome dissolution process when chitin materials are dissolved and regenerated by physical or chemical methods. To further obtain the regenerated chitin fiber material with improved performance, silk fibroin was introduced into the chitin matrix material, and chitin/silk fibroin biocompatible composite fibers were obtained by formic acid/calcium chloride/ethanol ternary system and top-down wet spinning technology. The produced composite fibers outperformed previously reported chitin-silk composites in terms of the tensile strength (160 MPa) and failure strain (25%). The fibers also performed good cell compatibility and strong cellular affinity for non-toxicity. The cell viabilities of the fibers were about 20% greater than those of silk fiber after three days of co-culture with NIH-3T3. Furthermore, no hemolysis occurs in the presence of chitin/silk fibers, demonstrating their superior hemocompatibility. The fibers had a hemolysis index as low as 1%, which is far lower than the acceptable level of 5%. The material offers prospective opportunities for biomaterial applications in anticoagulation, absorbable surgical sutures, etc.

Selective and effective adsorption of cesium ions by metal hexacyanoferrates (MHCF, M = Cu, Co, Ni) modified chitosan fibrous biosorbent.

Selective and effective adsorptive removal of radiocesium is of great importance in terms of nuclear waste management and environmental remediation, but is still challenging because of its radioactive and non-complexing nature. Herein, metal hexacyanoferrates (MHCF, M = Cu, Co, or Ni) modified fibrous chitosan was prepared by multiple sequential adsorption and self-assembly approach, and applied for the selective and effective adsorption of Cs+. The physically supported MHCF in chitosan fibers showed good crystallinity and stability, and the obtained fibrous composite has high specific surface area (18.2-29.4 m2 g-1). Moreover, MHCF crystals endowed the fibrous chitosan-based adsorbent with a high adsorption capacity and selectivity towards Cs+. Its adsorption kinetic and isotherm performance followed the pseudo second-order model and the Sips model. The qm value of three fibrous MHCF/chitosan (M = Cu, Co, or Ni) composites was 24.9-70.3 mg g-1. The fibrous CuHCF/chitosan composite had the highest qm among the three composites. In summary, the modified chitosan can selectively and effectively remove Cs+ from complicated aqueous solutions.

Adsorption of Co2+ and Sr2+ in aqueous solution by a novel fibrous chitosan biosorbent.

In this study, a novel fibrous chitosan biosorbent was prepared using LiOH/KOH/urea/H2O (4.5:7:8:80.5 by weight) as spinning solvent. The fibrous chitosan exhibited a higher adsorption capacity and a faster adsorption rate for Co2+ and Sr2+, compared with spherical chitosan due to its high specific surface area (16.9 m2 g-1), uniform fineness (24.1 µm), and good mechanical strength. The adsorption capacity of fibrous chitosan for Co2+ and Sr2+ was 31.3 mg g-1 and 20.0 mg g-1, respectively, which was higher than that of spherical chitosan (22.5 mg g-1for Co2+ and 8.9 mg g-1 for Sr2+). The coordination between -NH2/-OH of chitosan and the nuclide ions was the rate-limiting step. The improvement of adsorption performance was due to the higher specific surface area which increased the exposure degree of functional groups (adsorptive sites). This new wet-spun fibrous chitosan biosorbent showed great potential in the adsorptive removal of nuclides ions from aqueous solution.

Facile fabrication of a polyvinyl alcohol-based hydrophobic fluorescent film via the Hantzsch reaction for broadband UV protection.

Excessive exposure to ultraviolet (UV) light is harmful to human health. However, the traditional preparation of anti-UV films through the doping of UV absorbers leads to unstable products. Chemical modification of polyvinyl alcohol (PVA) to fabricate functional derivatives expand the application of these materials. Herein, a 1,4-dihydropyridine (DHP) fluorescent ring with a conjugated structure as a strong UV-absorber group was introduced onto a polyvinyl alcohol acetoacetate (PVAA) film to improve its UV-blocking performance. Firstly, PVAA was prepared via transesterification using tert-butyl acetoacetate (t-BAA). Then, the Hantzsch reaction was carried out on the surface of the PVAA film at room temperature. The resulting film showed high transparency, bright fluorescence emission, good mechanical properties, and outstanding stability. The introduction of the hydrophobic carbon chain reduced the hydrophilicity and swelling capacity of the PVAA film. In addition, the conjugated structure endowed the fluorescent film with excellent UV-blocking performance, where almost 100% UVA and UVB spectra could be shielded. The UV-blocking properties of the prepared films were persistent when they were exposed to UV irradiation, solvents, and subjected to thermal treatment. This work presents a facile and environmentally-friendly strategy by which to fabricate a multifunctional PVA-based film, which holds great potential for application in the anti-counterfeiting and UV-blocking fields.

An Innovative Solvent-Responsive Coiling-Expanding Stent.

Coronary artery disease is the "first killer" in the world, while the classical treatment for this disease is to implant stent. An ideal vascular stent should be nontoxic with self-expanding characteristics, quick expanding speed, and appropriate mechanical supporting property. However, no existing vascular stent covers all properties. Herein, a two-way shape-memory cellulose vascular stent, which can realize shape adjustments by mild solutions such as water and alcohol, is constructed. The shape-memory characteristics, mechanical properties, cell toxicity, and biocompatibility, are systemically investigated by ex vivo experiment as well as molecule simulation and theoretical modeling, revealing that the achieved bilayer two-way shape-memory films (BSMFs) can be used as an artificial vascular stent. In particular, this vascular stent made from BSMFs shows superb biocompatibility according to live/dead cell viability assays. Ex vivo experiments reveal that the novel vascular stent can support arteria coronaria sinistra, or the left main coronary artery, at the opening state while the cross-section of the vessel becomes two times larger than that of the initial state after implantation. Thus, it is believed that effective and scalable BSMFs can make meritorious fundamental contributions to biomaterials science and practical applications such as vascular stents.

Injectable chitin hydrogels with self-healing property and biodegradability as stem cell carriers.

To meet the demands of various therapeutic tasks, injectable hydrogels with tunable mechanical properties and degradability are highly desired. Herein, we developed an injectable chitin hydrogel system with well-manipulated mechanical properties and degradability through dynamic acylhydrazone crosslinking catalyzed by 4-amino-DL-phenylalanine (Phe-NH2). The mechanical properties and degradability of the hydrogels could be easily adjusted by varying the solid content, while their gelation time could be maintained at a constant level (∼130 s) by altering Phe-NH2 content, thereby ensuring the good injectability of hydrogels. Moreover, the chitin hydrogels showed excellent self-healing capacity with a healing efficiency up to 95 %. Owing to their superior biocompatibility and biodegradability, the chitin hydrogels could support the proliferation and multi-potent differentiations of rat bone marrow-derived stem cells, serving as a beneficial 3D scaffold for stem cell encapsulation and delivery. This work provides a promising injectable delivery vehicle of therapeutic drugs or cells for tissue regenerative medicine.

Robust chitin films with good biocompatibility and breathable properties.

Chitin is the second abundant polysaccharide after cellulose, and has been demonstrated to possess various applications in the fields of the biomaterials, water treatment, etc. Here, mechanically strong chitin films were successfully fabricated from chitin solution in NaOH/urea aqueous system with cooling by chemical crosslinking with epichlorohydrin (ECH). The results indicated that tensile strength and elongation at break of the chitin film prepared by using the weight ratio of ECH to chitin solution of 6:100 enhanced significantly to achieve 139 MPa and 43%, respectively, showing highly strong strength and elongation. The cell assay results confirmed that the chitin films were non-toxicity. Water vapor transmittance rate testing indicated that the chitin films had better breathable properties than commercial product. The robust chitin films with high transmittance, biocompatibility and breathability have great potentials in the wide applications such as biomedical, food packaging, wound healing, garments fields, etc.

Super Strong All-Cellulose Composite Filaments by Combination of Inducing Nanofiber Formation and Adding Nanofibrillated Cellulose.

In this work, super strong all-cellulose multifilaments were obtained from cellulose dissolved in LiOH/urea system by inducing nanofiber formation, and were simultaneously reinforced by the introduction of TEMPO-oxidized nanofibrillated cellulose (NFC) with mean diameter of 20 nm. The all-cellulose composite filaments (CF) containing only 3 wt % NFC exhibits a high orientation that Herman's parameter is 0.89. Importantly, the NFC can simultaneously reinforce and toughen the CF, with a tensile strength and elongation at break of 3.92 cN/dT and 14.6%, respectively, which make the obtained CF to become super strong. The strengthened mechanism of CF is considered as the nanofibril-induced crystallization and orientation, which makes up for the deficits and constructs a flawless structure in the regenerated cellulose filaments. Of note, the stability of spinning dope was also effectively improved by adding small amount of NFC, which is very important for fiber spinning on industry. This finding contributes to the preparation of high performance regenerated cellulose multifilaments by a simple, energy-efficient, and eco-friendly route.

High-Strength Films Consisted of Oriented Chitosan Nanofibers for Guiding Cell Growth.

Chitosan has biocompatibility and biodegradability; however, the practical use of the bulk chitosan materials is hampered by its poor strength, which can not satisfy the mechanical property requirement of organs. Thus, the construction of highly strong chitosan-based materials has attracted much attention. Herein, the high strength nanofibrous hydrogels and films (CS-E) were fabricated from the chitosan solution in LiOH/KOH/urea aqueous system via a mild regenerating process. Under the mild condition (ethanol at low temperature) without the severe fluctuation in the system, the alkaline-urea shell around the chitosan chains was destroyed, and the naked chitosan molecules had sufficient time for the orderly arrangement in parallel manner to form relatively perfect nanofibers. The nanofibers physically cross-linked to form CS-E hydrogels, which could be easily oriented by drawing to achieve a maximum orientation index of 84%, supported by the scanning electron microscopy and two-dimensional wide-angle X-ray diffraction. The dried CS-E films could be bent and folded arbitrarily to various complex patterns and shapes. The oriented CS-E films displayed even ultrahigh tensile strength (282 MPa), which was 5.6× higher than the chitosan films prepared by the traditional acid dissolving method. The CS-E hydrogels possessed hierarchically porous structure, beneficial to the cell adhesion, transportation of nutrients, and removal of metabolic byproducts. The cell assay results demonstrated that the CS-E hydrogels were no cytotoxicity, and osteoblastic cells could adhere, spread, and proliferate well on their surface. Furthermore, the oriented CS-E hydrogels could regulate the directional growth of osteoblastic cells along the orientation direction, on the basis of the filopodia of the cells to extend and adhere on the nanofibers. This work provided a novel approach to construct the oriented high strength chitosan hydrogels and films.

Bilayer hydrogel actuators with tight interfacial adhesion fully constructed from natural polysaccharides.

Smart hydrogel actuators with excellent biocompatibility and biodegradation are extremely desired for biomedical applications. Herein, we have constructed bio-hydrogel actuators inspired by the bilayer structures of plant organs from chitosan and cellulose/carboxymethylcellulose (CMC) solution in an alkali/urea aqueous system containing epichlorohydrin (ECH) as a crosslinker, and demonstrated tight adhesion between two layers through strong electrostatic attraction and chemical crosslinking. The bilayer hydrogels with excellent mechanical properties could carry out rapid, reversible, and repeated self-rolling deformation actuated by pH-triggered swelling/deswelling, and transformed into rings, tubules, and flower-, helix-, bamboo-, and wave-like shapes by effectively designing the geometric shape and size. The significant difference in the swelling behavior between the positively charged chitosan and the negatively charged cellulose/CMC layers generated enough force to actuate the performance of the hydrogels as soft grippers, smart encapsulators, and bioinspired lenses, showing potential applications in a wide range of fields including biomedicine, biomimetic machines, etc.

Ultra-Stretchable and Force-Sensitive Hydrogels Reinforced with Chitosan Microspheres Embedded in Polymer Networks.

An ultra-stretchable and force-sensitive hydrogel with surface self-wrinkling microstructure is demonstrated by in situ synthesizing polyacrylamide (PAAm) and polyaniline (PANI) in closely packed swollen chitosan microspheres, exhibiting ultra-stretchability (>600%), high sensitivity (0.35 kPa-1 ) for subtle pressures (<1 kPa), and can detect force in a broad range (102 Pa-101 MPa) with excellent electrical stability and rapid response speed, potentially finding applications for E-skin.

An approach for prominent enhancement of the quality of konjac flour: dimethyl sulfoxide as medium.

In this paper, an approach to improve several konjac flour (KF) qualities by dimethyl sulfoxide (DMSO) addition using various concentrations at different temperature levels was proposed. Also, various properties of native and refined KF, including transparency, chemical composition and rheological properties have been investigated. The results showed that the KF refined by 75% DMSO achieved 27.7% improvement in transparency, 99.7% removal of starch, 99.4% removal of soluble sugar, and 98.2% removal of protein as well as more satisfactory viscosity stability. In addition, the morphology structure of refined KF showed a significant difference compared with the native one as observed using the SEM, which is promising for further industrial application. Furthermore, the rheological properties of both native and refined konjac sols were studied and the results showed that DMSO refinement is an effective and alternative approach to improve the qualities of KF in many aspects.

Homogeneous synthesis of chitin-based acrylate superabsorbents in NaOH/urea solution.

A modified freezing-thawing cyclic (FTC) process was applied to dissolve the chitin in NaOH/urea solution. A transparent homogeneous solution was obtained. It was utilized directly for preparing the superabsorbent polymers (SAPs) by grafting copolymerization under static solution conditions without nitrogen protection. The acrylic acid was used conveniently without prior neutralization. The final products existed as hydrogels without excess reagent emissions. The adsorption capacity and yield of SAP that was prepared in the optimum conditions was 2833 g/g and 81.65%, respectively, higher than one-time FTC program prepared with 2527 g/g and 15.44%. Furthermore, it formed a uniform and transparent gel without any residual chitin particles. The regenerated chitin and SAPs were characterized by SEM, FTIR, XRD, and TG. The samples prepared by the new method presented a more amorphous state with good thermal stability, suggesting that this convenient preparation method for a potential industrial application's pathway.

Nanogels fabricated by lysozyme and sodium carboxymethyl cellulose for 5-fluorouracil controlled release.

Lysozyme (Ly) and sodium carboxymethyl cellulose (CMC) were used to fabricate nanogels by a convenient method without using any chemical treatment except simple heating to achieve the denaturation temperature of Ly. The prepared nanogels were characterized by dynamic laser scattering (DLS), rheological analysis, transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS). The nanogels are of spherical shape with average hydrodynamic diameter of 241 nm and the swelling ratio of nanogels is about 5. Then 5-fluorouracil was used as a model drug to investigate the entrapment efficiency and release ability in nanogels. It turned out to be that the release in simulated gastric fluid (SGF) was more slowly compared with that in simulated intestinal fluid (SIF), which could protect the 5-Fu in stomach and ensure it released in intestines.