Modular photoorigami-based 4D manufacturing of vascular junction elements.

Four-dimensional (4D) printing, combining three-dimensional (3D) printing with time-dependent stimuli-responsive shape transformation, eliminates the limitations of the conventional 3D printing technique for the fabrication of complex hollow constructs. However, existing 4D printing techniques have limitations in terms of the shapes that can be created using a single shape-changing object. In this paper, we report an advanced 4D fabrication approach for vascular junctions, particularly T-junctions, using the 4D printing technique based on coordinated sequential folding of two or more specially designed shape-changing elements. In our approach, the T-junction is split into two components, and each component is 4D printed using different synthesized shape memory polyurethanes and their nanohybrids, which have been synthesized with varying hard segment contents and by incorporating different weight percentages of photo-responsive copper sulfide-polyvinyl pyrrolidone nanoparticles. The formation of a T-junction is demonstrated by assigning different shape memory behaviors to each component of the T-junction. A cell culture study with human umbilical vein endothelial cells reveals that the cells proliferate over time, and almost 90% of cells remain viable on day 7. Finally, the formation of the T-junction in the presence of near-infrared light has been demonstrated after seeding the endothelial cells on the programmed flat surface of the two components and fluorescence microscopy at day 3 and 7 reveals that the cells adhered well and continue to proliferate over time. Hence, the proposed alternative approach has huge potential and can be used to fabricate vascular junctions in the future.

Fabricating defogging metasurfaces via a water-based colloidal route.

Metamaterials possess exotic properties that do not occur in nature and have attracted significant attention in research and engineering. Two decades ago, the field of metamaterials emerged from linear electromagnetism, and today it encompasses a wide range of aspects related to solid matter, including electromagnetic and optical, mechanical and acoustic, as well as unusual thermal or mass transport phenomena. Combining different material properties can lead to emergent synergistic functions applicable in everyday life. Nevertheless, making such metamaterials in a robust, facile, and scalable manner is still challenging. This paper presents an effective protocol allowing for metasurfaces offering a synergy between optical and thermal properties. It utilizes liquid crystalline suspensions of nanosheets comprising two transparent silicate monolayers in a double stack, where gold nanoparticles are sandwiched between the two silicate monolayers. The colloidally stable suspension of nanosheets was applied in nanometre-thick coatings onto various substrates. The transparent coatings serve as absorbers in the infrared spectrum allowing for the efficient conversion of sunlight into heat. The peculiar metasurface couples plasmon-enhanced adsorption with anisotropic heat conduction in the plane of the coating, both at the nanoscale. Processing of the coating is based on scalable and affordable wet colloidal processing instead of having to apply physical deposition in high vacuum or lithographic techniques. Upon solar irradiation, the colloidal metasurface is quickly (60% of the time taken for the non-coated glass) heated to the level where complete defogging is assured without sacrificing transparency in the visible range. The protocol is generally applicable allowing for intercalation of any nanoparticles covering a range of physical properties that are then inherited to colloidal nanosheets. Because of their large aspect ratio, the nanosheets will inevitably orient parallel to any surface. This will allow for a toolbox capable of mimicking metamaterial properties while assuring facile processing via dip coating or spray coating.

Size-controlled liquid phase synthesis of colloidally stable Co3O4 nanoparticles.

Spinel cobalt(ii,iii) oxide (Co3O4) represents a p-type semiconductor exhibiting promising functional properties in view of applications in a broad range of technological fields including magnetic materials and gas sensors as well as sustainable energy conversion systems based on photo- and electrocatalytic water splitting. Due to their high specific surface area, nanoparticle-based structures appear particularly promising for such applications. However, precise control over the diameter and the particle size distribution is required to achieve reproducible size-dependent properties. We herein introduce a synthetic strategy based on the decomposition of hydroxide precursors for the size-controlled preparation of purified Co3O4 nanoparticles with narrow size distributions adjustable in the range between 3-13 nm. The particles exhibit excellent colloidal stability. Their dispersibility in diverse organic solvents further facilitates processing (i.e. ligand exchange) and opens exciting perspectives for controlled self-assembly of the largely isometric primary particles into mesoscale structures. In view of potential applications, functional properties including absorption characteristics and electrocatalytic activity were probed by UV-Vis spectroscopy and cyclic voltammetry, respectively. In these experiments, low amounts of dispersed Co3O4 particles demonstrate strong light absorbance across the entire visible range and immobilized nanoparticles exhibit a comparably low overpotential towards the oxygen evolution reaction in electrocatalytic water splitting.

Comparing the Colloidal Stabilities of Commercial and Biogenic Iron Oxide Nanoparticles That Have Potential In Vitro/In Vivo Applications.

For the potential in vitro/in vivo applications of magnetic iron oxide nanoparticles, their stability in different physiological fluids has to be ensured. This important prerequisite includes the preservation of the particles' stability during the envisaged application and, consequently, their invariance with respect to the transfer from storage conditions to cell culture media or even bodily fluids. Here, we investigate the colloidal stabilities of commercial nanoparticles with different coatings as a model system for biogenic iron oxide nanoparticles (magnetosomes) isolated from magnetotactic bacteria. We demonstrate that the stability can be evaluated and quantified by determining the intensity-weighted average of the particle sizes (Z-value) obtained from dynamic light scattering experiments as a simple quality criterion, which can also be used as an indicator for protein corona formation.

Stretchable Clay Nanocomposite Barrier Film for Flexible Packaging.

The goal of reconciling all packaging requirements, e.g., mechanical resistance, transparency, flexibility, and gas barrier properties, is immensely challenging for packaging materials. Particularly, the combination of flexibility and good gas barrier properties poses a serious problem, especially when barrier requirements can only be met by lamination with a metal foil, metalization, or vapor-deposited ceramic layers, as all of these tend to be nonstretchable. In this work, we produced a stretchable nanocomposite barrier composed of one-dimensional (1D) crystalline (Bragg stack) barrier films composed of alternating layers of poly(ethylene glycol) (PEG) and synthetic sodium fluorohectorite (Hec) nanosheets. By sandwiching the Bragg stack type film between two plasticized poly(vinyl alcohol) (PVOH) layers, a waterborne laminate was obtained that outperforms commercial polymer materials in terms of water vapor permeability (WVP = 2.8 g mm m-2 day-1 bar-1 at 23 °C and 85% relative humidity), which is remarkable for an entirely water-soluble film. Moreover, no deterioration of barrier performance up to 10% elongation was observed, rendering the transparent self-standing laminate promising for thermoformed blister packaging, shrink wrap, or vacuum packaging. Besides the low WVP, the scalable and green processing method makes this technology auspicious for real-world applications.

Fabrication of Bragg stack films of clay nanosheets and polycations via co-polymerization of intercalated monomers and functional interlayer cations.

The fabrication of one-dimensional (1D) crystalline, monodomain nanocomposite films (hybrid Bragg stacks) is still limited to a few combinations of polymers and clay. The main reason is the segregation of clay and polymers driven by the entropic loss faced by the polymer confined in a narrow slit between the nanosheets. By exchanging synthetic sodium-fluorohectorite with vinylbenzyltrimethylammonium chloride, we succeeded in delaminating clay via 1D dissolution in N-methylformamide to obtain a liquid crystalline suspension. By combining this with bisphenol A glycerolate diacrylate, 1D crystalline nanocomposites could be obtained via photopolymerization of doctor bladed wet coatings. Infrared spectroscopy confirmed the co-polymerization of monomers and the organic modifier between the hectorite platelets. This single-phase hybrid material shows very low oxygen and water vapor transmission rates. The incorporation of the modified clay into the polymer leads to an oxygen transmission rate of 0.21 cm3 m-2 day-1 atm-1 at 50% r.h. and 23 °C and a water vapor transmission rate of 0.05 g m-2 day-1 for a coating of 3.7 µm, making this material appropriate for challenging packaging applications.

Extremely low thermal conductivity and high electrical conductivity of sustainable carbon-ceramic electrospun nonwoven materials.

Materials with an extremely low thermal and high electrical conductivity that are easy to process, foldable, and nonflammable are required for sustainable applications, notably in energy converters, miniaturized electronics, and high-temperature fuel cells. Given the inherent correlation between high thermal and high electrical conductivity, innovative design concepts that decouple phonon and electron transport are necessary. We achieved this unique combination of thermal conductivity 19.8 ± 7.8 mW/m/K (cross-plane) and 31.8 ± 11.8 mW/m/K (in-plane); electrical conductivity 4.2 S/cm in-plane in electrospun nonwovens comprising carbon as the matrix and silicon-based ceramics as nano-sized inclusions with a sea-island nanostructure. The carbon phase modulates electronic transport for high electrical conductivity, and the ceramic phase induces phonon scattering for low thermal conductivity by excessive boundary scattering. Our strategy can be used to fabricate the unique nonwoven materials for real-world applications and will inspire the design of materials made from carbon and ceramic.

Long-Term Stability, Biocompatibility, and Magnetization of Suspensions of Isolated Bacterial Magnetosomes.

Magnetosomes are magnetic nanoparticles biosynthesized by magnetotactic bacteria. Due to a genetically strictly controlled biomineralization process, the ensuing magnetosomes have been envisioned as agents for biomedical and clinical applications. In the present work, different stability parameters of magnetosomes isolated from Magnetospirillum gryphiswaldense upon storage in suspension (HEPES buffer, 4 °C, nitrogen atmosphere) for one year in the absence of antibiotics are examined. The magnetic potency, measured by the saturation magnetization of the particle suspension, drops to one-third of its starting value within this year-about ten times slower than at ambient air and room temperature. The particle size distribution, the integrity of the surrounding magnetosome membrane, the colloidal stability, and the biocompatibility turn out to be not severely affected by long-term storage.

Delamination by Repulsive Osmotic Swelling of Synthetic Na-Hectorite with Variable Charge in Binary Dimethyl Sulfoxide-Water Mixtures.

Swelling of clays is hampered by increasing layer charge. With vermiculite-type layer charge densities, crystalline swelling is limited to the two-layer hydrate, while osmotic swelling requires ion exchange with bulky and hydrophilic organic molecules or with Li+ cations to trigger repulsive osmotic swelling. Here, we report on surprising and counterintuitive osmotic swelling behavior of a vermiculite-type synthetic clay [Na0.7]inter[Mg2.3Li0.7]oct[Si4]tetO10F2 in mixtures of water and dimethyl sulfoxide (DMSO). Although swelling in pure water is restricted to crystalline swelling, with the addition of DMSO, osmotic swelling sets in at some threshold composition. Finally, when the DMSO concentration is increased further to 75 vol %, swelling is restricted again to crystalline swelling as expected. Repulsive osmotic swelling thus is observed in a narrow composition range of the binary water-DMSO mixture, where a freezing point suppression is observed. This suppression is related to DMSO and water molecules exhibiting strong interactions leading to stable molecular clusters. Based on this phenomenological observation, we hypothesize that the unexpected swelling behavior might be related to the formation of different complexes of interlayer cations being formed at different compositions. Powder X-ray diffraction and 23Na magic angle spinning-NMR evidence is presented that supports this hypothesis. We propose that the synergistic solvation of the interlayer sodium at favorable compositions exerts a steric pressure by the complexes formed in the interlayer. Concomitantly, the basal spacing is increased to a level, where entropic contributions of interlayer species lead to a spontaneous thermodynamically allowed one-dimensional dissolution of the clay stack.

Nematic suspension of a microporous layered silicate obtained by forceless spontaneous delamination via repulsive osmotic swelling for casting high-barrier all-inorganic films.

Exploiting the full potential of layered materials for a broad range of applications requires delamination into functional nanosheets. Delamination via repulsive osmotic swelling is driven by thermodynamics and represents the most gentle route to obtain nematic liquid crystals consisting exclusively of single-layer nanosheets. This mechanism was, however, long limited to very few compounds, including 2:1-type clay minerals, layered titanates, or niobates. Despite the great potential of zeolites and their microporous layered counterparts, nanosheet production is challenging and troublesome, and published procedures implied the use of some shearing forces. Here, we present a scalable, eco-friendly, and utter delamination of the microporous layered silicate ilerite into single-layer nanosheets that extends repulsive delamination to the class of layered zeolites. As the sheet diameter is preserved, nematic suspensions with cofacial nanosheets of ≈9000 aspect ratio are obtained that can be cast into oriented films, e.g., for barrier applications.

Ultralight Heat-Insulating, Electrically Conductive Carbon Fibrous Sponges for Wearable Mechanosensing Devices with Advanced Warming Function.

Ultralight highly porous sponges are attractive for electronic devices due to superelasticity, outstanding resilience, and thermal insulation. However, fabricating an ultralight conductive sponge with low thermal conductivity, mechanical flexibility, and piezoresistivity, as well as adjustable heating behavior, is still a challenge. Here, an ultralight carbon nanofibrous sponge fabricated by pyrolyzing a graphene oxide coated polyimide sponge is reported. The resulting carbon sponge demonstrates a high electrical conductivity of 0.03-4.72 S m-1 and a low thermal conductivity of 0.027-0.038 W m-1 K-1 (20 °C, in ambient air), as well as a low density to ∼6 mg cm-3. Additionally, the sponge exhibits mechanical flexibility, stability, excellent piezoresistivity, and an adjustable heating behavior. Hence, it could be utilized as a sensing device, including thermal management, making them promising for use in smart sportswear, human-machine interfaces, and wearable healthcare devices.

Glycyrrhizin-Based Hydrogels Accelerate Wound Healing of Normoglycemic and Diabetic Mouse Skin.

Efficient wound repair is crucial for mammalian survival. Healing of skin wounds is severely hampered in diabetic patients, resulting in chronic non-healing wounds that are difficult to treat. High-mobility group box 1 (HMGB1) is an important signaling molecule that is released during wounding, thereby delaying regenerative responses in the skin. Here, we show that dissolving glycyrrhizin, a potent HMGB1 inhibitor, in water results in the formation of a hydrogel with remarkable rheological properties. We demonstrate that these glycyrrhizin-based hydrogels accelerate cutaneous wound closure in normoglycemic and diabetic mice by influencing keratinocyte migration. To facilitate topical application of glycyrrhizin hydrogels on cutaneous wounds, several concentrations of glycyrrhizinic acid in water were tested for their rheological, structural, and biological properties. By varying the concentration of glycyrrhizin, these hydrogel properties can be readily tuned, enabling customized wound care.

Disorder-Order Transition-Improving the Moisture Sensitivity of Waterborne Nanocomposite Barriers.

Systematic studies on the influence of crystalline vs disordered nanocomposite structures on barrier properties and water vapor sensitivity are scarce as it is difficult to switch between the two morphologies without changing other critical parameters. By combining water-soluble poly(vinyl alcohol) (PVOH) and ultrahigh aspect ratio synthetic sodium fluorohectorite (Hec) as filler, we were able to fabricate nanocomposites from a single nematic aqueous suspension by slot die coating that, depending on the drying temperature, forms different desired morphologies. Increasing the drying temperature from 20 to 50 °C for the same formulation triggers phase segregation and disordered nanocomposites are obtained, while at room temperature, one-dimensional (1D) crystalline, intercalated hybrid Bragg Stacks form. The onset of swelling of the crystalline morphology is pushed to significantly higher relative humidity (RH). This disorder-order transition renders PVOH/Hec a promising barrier material at RH of up to 65%, which is relevant for food packaging. The oxygen permeability (OP) of the 1D crystalline PVOH/Hec is an order of magnitude lower compared to the OP of the disordered nanocomposite at this elevated RH (OP = 0.007 cm3 µm m-2 day-1 bar-1 cf. OP = 0.047 cm3 µm m-2 day-1 bar-1 at 23 °C and 65% RH).

Mechanical adaptation of brachiopod shells via hydration-induced structural changes.

The function-optimized properties of biominerals arise from the hierarchical organization of primary building blocks. Alteration of properties in response to environmental stresses generally involves time-intensive processes of resorption and reprecipitation of mineral in the underlying organic scaffold. Here, we report that the load-bearing shells of the brachiopod Discinisca tenuis are an exception to this process. These shells can dynamically modulate their mechanical properties in response to a change in environment, switching from hard and stiff when dry to malleable when hydrated within minutes. Using ptychographic X-ray tomography, electron microscopy and spectroscopy, we describe their hierarchical structure and composition as a function of hydration to understand the structural motifs that generate this adaptability. Key is a complementary set of structural modifications, starting with the swelling of an organic matrix on the micron level via nanocrystal reorganization and ending in an intercalation process on the molecular level in response to hydration.

Tuning Sugar-Based Chiral and Flower-Like Microparticles.

Unique supermolecular structures as chiral and flower-like microparticles and the precise tuning of the morphologies hold immense promise for a variety of applications. Examples of such structures deriving from monosaccharides are still rare, and a general understanding is also lacking. Herein, it is shown that chiral, flower-like, or solid microparticles can be tuned by only using monosaccharide esters without external stimuli. Chiral "left-handed" (counterclockwise) and "right-handed" (clockwise) morphologies can be induced by d- and l-glucose stearoyl esters. In comparison, other monosaccharides, i.e., galactose, mannose, and xylose, cannot formed chiral particles and generated diverse other morphologies of the supermolecular microparticles based on their distinct molecular configurations. Due to the numbers of side chains and the bond orientations, microparticles with solid and porous flower-like morphologies can be obtained. While glucose and xylose esters only lead to solid microparticles, mannose and galactose generate porous flower-like particles. These findings suggest a general method to design and control the superstructures by using monosaccharide backbones with diverse molecular configurations.

Stable Mesoscale Nonwovens of Electrospun Polyacrylonitrile and Interpenetrating Supramolecular 1,3,5-Benzenetrisamide Fibers as Efficient Carriers for Gold Nanoparticles.

The immobilization of metal nanoparticles without agglomeration and leaching within composite nonwovens is often challenging and of great importance, for example, for catalytic applications. In this study, we prepared composite nonwovens based on electrospun polyacrylonitrile (PAN) short fibers and supramolecular terpyridine-functionalized benzene-1,3,5-tricarboxamide (BTA1) nanofibers by a sheet-forming wet-laid process. The formation of an interpenetrating and entangled network of supramolecular BTA1 nanofibers and PAN short fibers results in mechanically stable mesoscale nonwovens. Because of the peripheral terpyridine substituents of the BTA1, nonaggregated gold nanoparticles (AuNPs) could be immobilized efficiently in the composite nonwovens. The functionality of the resulting AuNPs-loaded composite nonwovens was verified by catalytic reduction of 4-nitrophenol to 4-aminophenol as a standard model reaction. The AuNPs-loaded PAN/BTA1 composite nonwovens showed high catalytic activity, reusability, and excellent stability.

High-Yield Production, Characterization, and Functionalization of Recombinant Magnetosomes in the Synthetic Bacterium Rhodospirillum rubrum "magneticum".

Recently, the photosynthetic Rhodospirillum rubrum has been endowed with the ability of magnetosome biosynthesis by transfer and expression of biosynthetic gene clusters from the magnetotactic bacterium Magnetospirillum gryphiswaldense. However, the growth conditions for efficient magnetite biomineralization in the synthetic R. rubrum "magneticum", as well as the particles themselves (i.e., structure and composition), have so far not been fully characterized. In this study, different cultivation strategies, particularly the influence of temperature and light intensity, are systematically investigated to achieve optimal magnetosome biosynthesis. Reduced temperatures ≤16 °C and gradual increase in light intensities favor magnetite biomineralization at high rates, suggesting that magnetosome formation might utilize cellular processes, cofactors, and/or pathways that are linked to photosynthetic growth. Magnetosome yields of up to 13.6 mg magnetite per liter cell culture are obtained upon photoheterotrophic large-scale cultivation. Furthermore, it is shown that even more complex, i.e., oligomeric, catalytically active functional moieties like enzyme proteins can be efficiently expressed on the magnetosome surface, thereby enabling the in vivo functionalization by genetic engineering. In summary, it is demonstrated that the synthetic R. rubrum "magneticum" is a suitable host for high-yield magnetosome biosynthesis and the sustainable production of genetically engineered, bioconjugated magnetosomes.

Interface-mediated formation of basic cobalt carbonate/polyethyleneimine composite microscrolls by strain-induced self-rolling.

Polyethyleneimine aids the gas diffusion precipitation of nano-structured basic cobalt carbonate sheets at the air/solution interface. Upon drying, these mineral films undergo self-rolling into 3D coiled structures. Exploring this principle for the design of self-supported functional materials, porous Co3O4 spirals composed of interconnected nanoparticles are obtained by thermal conversion.

Towards standardized purification of bacterial magnetic nanoparticles for future in vivo applications.

Bacterial magnetosomes (MS) are well-defined membrane-enveloped single-domain iron oxide (magnetite) nanoparticles, which are susceptible to genetic and chemical engineering. Additionally, the possibility to manipulate these particles by external magnetic fields facilitates their application in biomedicine and biotechnology, e.g. as magnetic resonance imaging probes or for drug delivery purposes. However, current purification protocols are poorly characterized, thereby hampering standardized and reproducible magnetosome production and thus, reliable testing for in vivo applications. In that context, the establishment of reproducible particle isolation procedures as well as the identification of high quality control parameters and the evaluation of potential cytotoxic effects of purified particles are of major importance. In this study, we characterize a multi-step purification protocol for MS with regard to purity, iron content, size and polydispersity of magnetite particles. In addition, we address potential cytotoxic effects of isolated MS when incubated with mammalian cells. Overall, we provide a detailed overview of the process-structure relationship during the isolation of MS and thus, identify prerequisites for high-yield MS production and their future application in the biomedical and biotechnological field. STATEMENT OF SIGNIFICANCE: Magnetic nanoparticles are of increasing interest for a variety of biomedical and biotechnological applications. Due to their unprecedented material characteristics, bacterial magnetosomes represent a promising alternative to chemically synthesized iron oxide nanoparticles. As applications require well-defined, highly purified and fully characterized nanoparticles, reliable protocols are necessary for efficient and reproducible magnetosome isolation. In our study, we evaluate an improved magnetosome extraction procedure and monitor quality parameters such as particle size distribution, membrane integrity and purity of the suspension by a combination of physicochemical and biochemical methods. Furthermore, the cytotoxicity of the isolated magnetosomes is assessed using different cell lines. In summary, our study helps to establish prerequisites for many real-world applications of magnetosomes in the field of biotechnology and biomedicine.

Osmotic Delamination: A Forceless Alternative for the Production of Nanosheets Now in Highly Polar and Aprotic Solvents.

Repulsive osmotic delamination is thermodynamically allowed "dissolution" of two-dimensional (2D) materials and therefore represents an attractive alternative to liquid-phase exfoliation to obtain strictly monolayered nanosheets with an appreciable aspect ratio with quantitative yield. However, osmotic delamination was so far restricted to aqueous media, severely limiting the range of accessible 2D materials. Alkali-metal intercalation compounds of MoS2 or graphite are excluded because they cannot tolerate even traces of water. We now succeeded in extending osmotic delamination to polar and aprotic organic solvents. Upon complexation of interlayer cations of synthetic hectorite clay by crown ethers, either 15-crown-5 or 18-crown-6, steric pressure is exerted, which helps in reaching the threshold separation required to trigger osmotic delamination based on translational entropy. This way, complete delamination in water-free solvents like aprotic ethylene and propylene carbonate, N-methylformamide, N-methylacetamide, and glycerol carbonate was achieved.