Complex‐Shaped Cellulose Composites Made by Wet Densification of 3D Printed Scaffolds

Cellulose is an attractive material resource for the fabrication of sustainable functional products, but its processing into structures with complex architecture and high cellulose content remains challenging. Such limitation has prevented cellulose‐based synthetic materials from reaching the level of structural control and mechanical properties observed in their biological counterparts, such as wood and plant tissues. To address this issue, a simple approach is reported to manufacture complex‐shaped cellulose‐based composites, in which the shaping capabilities of 3D printing technologies are combined with a wet densification process that increases the concentration of cellulose in the final printed material. Densification is achieved by exchanging the liquid of the wet printed material with a poor solvent mixture that induces attractive interactions between cellulose particles. The effect of the solvent mixture on the final cellulose concentration is rationalized using solubility parameters that quantify the attractive interparticle interactions. Using X‐ray diffraction analysis and mechanical tests, 3D printed composites obtained through this process are shown to exhibit highly aligned microstructures and mechanical properties significantly higher than those obtained by earlier additively manufactured cellulose‐based materials. These features enable the fabrication of cellulose‐rich synthetic structures that more closely resemble the exquisite designs found in biological materials grown by plants in nature.     

Ultrathin Polydopamine Films with Phospholipid Nanodiscs Containing a Glycophorin A Domain

Cellular membranes have long served as an inspiration for nanomaterial research. The preparation of ultrathin polydopamine (PDA) films with integrated protein pores containing phospholipids and an embedded domain of a membrane protein glycophorin A as simplified cell membrane mimics is reported. Large area, ultrathin PDA films are obtained by electropolymerization on gold surfaces with 10–18 nm thickness and dimensions of up to 2.5 cm². The films are transferred from gold to various other substrates such as nylon mesh, silicon, or substrates containing holes in the micrometer range, and they remain intact even after transfer. The novel transfer technique gives access to freestanding PDA films that remain stable even at the air interfaces with elastic moduli of ≈6–12 GPa, which are higher than any other PDA films reported before. As the PDA film thickness is within the range of cellular membranes, monodisperse protein nanopores, so‐called “nanodiscs,” are integrated as functional entities. These nanodisc‐containing PDA films can serve as semi‐permeable films, in which the embedded pores control material transport. In the future, these simplified cell membrane mimics may offer structural investigations of the embedded membrane proteins to receive an improved understanding of protein‐mediated transport processes in cellular membranes.     

Autonomous Ultrafast Self‐Healing Hydrogels by pH‐Responsive Functional Nanofiber Gelators as Cell Matrices

The synthesis of hybrid hydrogels by pH‐controlled structural transition with exceptional rheological properties as cellular matrix is reported. “Depsi” peptide sequences are grafted onto a polypeptide backbone that undergo a pH‐induced intramolecular O–N–acyl migration at physiological conditions affording peptide nanofibers (PNFs) as supramolecular gelators. The polypeptide–PNF hydrogels are mechanically remarkably robust. They reveal exciting thixotropic behavior with immediate in situ recovery after exposure to various high strains over long periods and self‐repair of defects by instantaneous reassembly. High cytocompatibility, convenient functionalization by coassembly, and controlled enzymatic degradation but stability in 2D and 3D cell culture as demonstrated by the encapsulation of primary human umbilical vein endothelial cells and neuronal cells open many attractive opportunities for 3D tissue engineering and other biomedical applications.     

Elaboration and characterization of a refractory based on Algerian kaolin

A refractory material was elaborated from kaolin extracted from the region of Djebel Debbagh (Algeria). Kaolin grog was obtained by calcination at a temperature of 1350 °C during 1 h. It was used as aggregates with granulometric distribution composed of fine fraction (mean grain size: 100–250 μm) and coarse fraction (mean grain size: 1000–2500 μm). Crude kaolin (size < 75 μm) was also used as a binder with an amount representing 15% of the dry material. After a 9.28% moistening and a rotting of 1 day, cylindrical samples were shaped by uniaxial pressure at 80 MPa. The samples were submitted to a natural drying during 24 h, a stoving at 100 °C and a calcination at 600 °C during 1 h. They were fired at high temperatures between 1250 and 1450 °C.

An X-ray diffraction (XRD) analysis showed that the refractory samples are composed of mullite and silica. Silica is a mixture of a vitreous phase and cristobalite at 1300, 1350 and 1400 °C and becomes completely amorphous when the samples are fired at higher temperature (1450 °C). The sample porosity is about 30%. The mechanical tests carried out as a function of temperature revealed different behaviours of the material. From the ambient up to 600 °C, the refractory behaviour is pseudo-plastic caused by micro-cracking. Between 700 and 900 °C, the samples become more rigid. At 1000 °C, the material exhibits a visco-plastic behaviour. The amorphous phase governs the sample properties variation with temperature increasing. Its content varies between 28% and 34% according to the firing temperature. Thermal shock tests realized in water showed that the refractory samples present good thermal shock resistance.     

Fast electrostatic halftoning

Electrostatic halftoning is a high-quality method for stippling, dithering, and sampling, but it suffers from a high runtime. This made the technique difficult to use for most real-world applications. A recently proposed minimisation scheme based on the non-equispaced fast Fourier transform (NFFT) lowers the complexity in the particle number M from $\mathcal{O}(M^2)$ to $\mathcal{O}(M \log M).$ However, the NFFT is hard to parallelise, and the runtime on modern CPUs lies still in the orders of an hour for about 50,000 particles, to a day for 1 million particles. Our contributions to remedy this problem are threefold: we design the first GPU-based NFFT algorithm without special structural assumptions on the positions of nodes, we introduce a novel nearest-neighbour identification scheme for continuous point distributions, and we optimise the whole algorithm for n-body problems such as electrostatic halftoning. For 1 million particles, this new algorithm runs 50 times faster than the most efficient technique on the CPU, and even yields a speedup of 7,000 over the original algorithm.     

Synthesis of iron(II) complexes with asymmetric N<Subscript>2</Subscript>O<Subscript>2</Subscript> coordinating Schiff base-like ligands and their spin crossover properties

The synthesis of new Schiff base-like ligands with asymmetric substituents pattern and their iron complexes with pyridine as axial ligand is described. Two of the ligands and one of the iron(II) complexes were characterized by single crystal X-ray structure analysis. One of the the iron(II) complexes shows spin crossover behavior while the others remain in the high spin state. The influence of the reduced symmetry of the ligand on the properties of the complexes is discussed.

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Lithium Tin Sulfide—a High‐Refractive‐Index 2D Material for Humidity‐Responsive Photonic Crystals

Extending the portfolio of novel stimuli‐responsive, high‐refractive‐index (RI) materials besides titania is key to improve the optical quality and sensing performance of existing photonic devices. Herein, lithium tin sulfide (LTS) nanosheets are introduced as a novel solution processable ultrahigh RI material (n = 2.50), which can be casted into homogeneous thin films using wet‐chemical deposition methods. Owing to its 2D morphology, thin films of LTS nanosheets are able to swell in response to changes of relative humidity. Integration of LTS nanosheets into Bragg stacks (BSs) based on TiO₂, SiO₂, nanoparticles or H₃Sb₃P₂O₁₄ nanosheets affords multilayer systems with high optical quality at an extremely low device thickness of below 1 µm. Owing to the ultrahigh RI of LTS nanosheets and the high transparency of the thin films, BSs based on porous titania as the low‐RI material are realized for the first time, showing potential application in light‐managing devices. Moreover, the highest RI contrast ever realized in BSs based on SiO₂ and LTS nanosheets is reported. Finally, exceptional swelling capability of an all‐nanosheet BS based on LTS and H₃Sb₃P₂O₁₄ nanosheets is demonstrated, which bodes well for a new generation of humidity sensors with extremely high sensitivity.     

Controlling Cellular Uptake and Toxicity of Polyphenylene Dendrimers by Chemical Functionalization

Polyphenylene dendrimers (PPDs) represent a unique class of macromolecules based on their monodisperse and shape‐persistent nature. These characteristics have enabled the synthesis of a new genre of “patched” surface dendrimers, where their exterior can be functionalized with a variety of polar and nonpolar substituents to yield lipophilic binding sites in a site‐specific way. Although such materials are capable of complexing biologically relevant molecules, show high cellular uptake in various cell lines, and low to no toxicity, there is minimal understanding of the driving forces to these characteristics. We investigated whether it is the specific chemical functionalities, relative quantities of each moiety, or the “patched” surface patterning on the dendrimers that more significantly influences their behavior in biological media.     

Structural equation modeling of multitrait-multimethod data: Different models for different types of methods.

The question as to which structural equation model should be selected when multitrait-multimethod (MTMM) data are analyzed is of interest to many researchers. In the past, attempts to find a well-fitting model have often been data-driven and highly arbitrary. In the present article, the authors argue that the measurement design (type of methods used) should guide the choice of the statistical model to analyze the data. In this respect, the authors distinguish between (a) interchangeable methods, (b) structurally different methods, and (c) the combination of both kinds of methods. The authors present an appropriate model for each type of method. All models allow separating measurement error from trait influences and trait-specific method effects. With respect to interchangeable methods, a multilevel confirmatory factor model is presented. For structurally different methods, the correlated trait-correlated (method-1) model is recommended. Finally, the authors demonstrate how to appropriately analyze data from MTMM designs that simultaneously use interchangeable and structurally different methods. All models are applied to empirical data to illustrate their proper use. Some implications and guidelines for modeling MTMM data are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)