Facile In Situ Assembly of Nanofibers within Three-Dimensional Porous Matrices with Arbitrary Characteristics for Creating Biomimetic Architectures.

It is challenging to recapitulate the natural extracellular matrix's hierarchical nano/microfibrous three-dimensional (3D) structure with multilevel pores, good mechanical and hydrophilic properties, and excellent bioactivity for designing and developing advanced biomimetic materials. This work reports a new facile strategy for the scalable manufacturing of such a 3D architecture. Natural polymers in an aqueous solution are interpenetrated into a 3D microfibrous matrix with arbitrary shapes and property characteristics to self-assemble in situ into a nanofibrous network. The collagen fiber-like hierarchical structure and interconnected multilevel pores are achieved by self-assembly of the formed nanofibers within the 3D matrix, triggered by a simple cross-linking treatment. The as-prepared alginate/polypropylene biomimetic matrices are bioactive and have a tunable mechanical property (compressive modulus from ∼17 to ∼24 kPa) and a tunable hydrophilicity (water contact angle from ∼94° to 63°). This facile and versatile strategy allows eco-friendly and scalable manufacturing of diverse biomimetic matrices or modification of any existing porous matrices using different polymers.

Strontium-doped mesoporous bioglass nanoparticles for enhanced wound healing with rapid vascularization.

Tissue engineered skin and its substitutes have a promising future in wound healing. However, enabling fast formation of blood vessels during the wound healing process is still a huge challenge to the currently available wound substitutes. In this work, active mesoporous bioglass nanoparticles with a high specific surface area and doped with strontium (Sr) were fabricated for rapid microvascularization and wound healing. The as-prepared bioglass nanoparticles with Sr ions significantly promoted the proliferation of fibroblasts and microvascularization of human umbilical vein endothelial cells in vitro. Silk fibroin sponges encapsulating the nanoparticles accelerated wound healing by promoting the formation of blood vessels and epithelium in vivo. This work provides a strategy for the design and development of active biomaterials for enhancing wound healing by rapid vascularization and epithelial reconstruction.

Manipulating supramolecular gels with surfactants: Interfacial and non-interfacial mechanisms.

Gel is a class of self-supporting soft materials with applications in many fields. Fast, controllable gelation, micro/nano structure and suitable rheological properties are essential considerations for the design of gels for specific applications. Many methods can be used to control these parameters, among which the additive approach is convenient as it is a simple physical mixing process with significant advantages, such as avoidance of pH change and external energy fields (ultrasound, UV light and others). Although surfactants are widely used to control the formation of many materials, particularly nanomaterials, their effects on gelation are less known. This review summarizes the studies that utilized different surfactants to control the formation, structure, and properties of molecular and silk fibroin gels. The mechanisms of surfactants, which are interfacial and non-interfacial effects, are classified and discussed. Knowledge and technical gaps are identified, and perspectives for further research are outlined. This review is expected to inspire increasing research interest in using surfactants for designing/fabricating gels with desirable formation kinetics, structure, properties and functionalities.

NR-MVSNet: Learning Multi-View Stereo Based on Normal Consistency and Depth Refinement.

Multi-view Stereo (MVS) aims to reconstruct a 3D point cloud model from multiple views. In recent years, learning-based MVS methods have received a lot of attention and achieved excellent performance compared with traditional methods. However, these methods still have apparent shortcomings, such as the accumulative error in the coarse-to-fine strategy and the inaccurate depth hypotheses based on the uniform sampling strategy. In this paper, we propose the NR-MVSNet, a coarse-to-fine structure with the depth hypotheses based on the normal consistency (DHNC) module, and the depth refinement with reliable attention (DRRA) module. Specifically, we design the DHNC module to generate more effective depth hypotheses, which collects the depth hypotheses from neighboring pixels with the same normals. As a result, the predicted depth can be smoother and more accurate, especially in texture-less and repetitive-texture regions. On the other hand, we update the initial depth map in the coarse stage by the DRRA module, which can combine attentional reference features and cost volume features to improve the depth estimation accuracy in the coarse stage and address the accumulative error problem. Finally, we conduct a series of experiments on the DTU, BlendedMVS, Tanks & Temples, and ETH3D datasets. The experimental results demonstrate the efficiency and robustness of our NR-MVSNet compared with the state-of-the-art methods. Our implementation is available at https://github.com/wdkyh/NR-MVSNet.

Tuning the microstructure and mechanical properties of lyophilized silk scaffolds by pre-freezing treatment of silk hydrogel and silk solution.

This work aims to understand how pre-freezing treatments (-20 °C, -80 °C or -196 °C (liquid nitrogen)) affect the microstructure, mechanical properties and secondary structure of silk scaffolds prepared from lyophilization of silk hydrogels and silk solutions. It is found that in comparison with silk solutions, silk hydrogels at the same silk fibroin concentrations produce scaffolds with more nanofibrous structures when they are pre-frozen at the different temperatures. Although pre-freezing with liquid nitrogen can produce nanofibrous scaffolds from either a silk solution (low concentration of 2%) or silk hydrogel (produced from 2 to 6% silk fibroin solutions), aligned macro-channels can be produced only from silk hydrogels. In addition, scaffolds obtained from silk hydrogels are dominated by ß-sheets due to the crystallization process for gel network formation, while scaffolds prepared from silk solutions are largely amorphous. The findings of this work are important to tune the microstructure and mechanical properties of silk scaffolds.

Enhancing Thermal Conductivity of Polyvinylidene Fluoride Composites by Carbon Fiber: Length Effect of the Filler.

Thermally conductive polyvinylidene fluoride (PVDF) composites were prepared by incorporating carbon fibers (CFs) with different lengths (286.6 ± 7.1 and 150.0 ± 2.3 µm) via cold pressing, followed by sintering. The length effects of the CF on the thermal conductivity, polymer crystallization behaviors, and mechanical properties of the PVDF composites were studied. The through-plane thermal conductivity of the PVDF composites increased significantly with the rise in CF loadings. The highest thermal conductivity of 2.89 W/(m∙K) was achieved for the PVDF composites containing 40 wt.% shorter CFs, ~17 times higher than that of the pure PVDF (~0.17 W/(m∙K)). The shorter CFs had more pronounced thermal conductive enhancement effects than the original longer CFs at higher filler loadings. CFs increased the storage modulus and the glass transition temperature of the PVDF. This work provides a new way to develop thermally conductive, mechanically, and chemically stable polymer composites by introducing CFs with different lengths.

Fabrication of Textile Waste Fibers Aerogels with Excellent Oil/Organic Solvent Adsorption and Thermal Properties.

In recent years, the treatment of textile waste has attracted more and more attention around the world. The reuse of textile waste can contribute to the reduction of carbon emissions and the sustainable development of the economy. Herein, we proposed a facile and cost-effective approach to fabricating aerogel by using textile waste fibers as the matrix and polyvinyl alcohol (PVA) and glutaraldehyde (GA) as crosslinking agents. After being modified with methyltrimethoxysilane (MTMS) via chemical vapor deposition, both the interior and exterior of the textile waste aerogels exhibit a hydrophobic property with a water contact angle of up to 136.9° ± 2.3°. A comprehensive investigation of the structure, thermal properties, mechanical properties and oil absorption capacity of this aerogel shows its potential for building insulation and oil spill cleanup. The textile waste fibers aerogels have low density and high porosity, good thermal stability and outstanding heat insulation properties (Kavg. = 0.049-0.061 W/m·K). With a maximum oil absorption value of 26.9 ± 0.6 g/g and rapid and effective oil/water mixture separation, the aerogel exhibits competitive commercial application value.

Enhanced formation of bioactive and strong silk-bioglass hybrid materials through organic-inorganic mutual molecular nucleation induction and templating.

Materials based on silk fibroin (SF) are important for many biomedical applications due to their excellent biocompatibility and tunable biodegradability. However, the insufficient mechanical strength and low bioactivity of these materials have limited their applications. For silk hydrogels, slow gelation is also a crucial problem. In this work, a simple approach is developed to address these challenging problems all at once. By mixing SF solution with bioglass (BG) sol, instant gelation of silk is induced, the storage modulus of the hydrogel and the compressive modulus of the aerogel are significantly enhanced. The formation of a complex of SF and tetraethyl orthosilicate (TEOS), either through hydrogen bonding or TEOS condensation on SF, facilitated the aggregation of SF and, on the other hand, created active sites for the condensation of TEOS and BG formation on the surface of silk nanofibrils. The resultant hybrid gels have much higher capacity for biomineralization, indicating their higher bioactivity, compared with the pristine silk gels. This organic (SF)-inorganic (BG) mutual nucleation induction and templating can be used for a general approach to produce bioactive silk materials of various formats not limited to gels and may also inspire the formation of other functional protein-BG hybrid materials.

Silk Hydrogel Electrostatically Functionalized with a Polycationic Antimicrobial Peptide: Molecular Interactions, Gel Properties, and Antimicrobial Activity.

Functionalization of silk fibroin hydrogel with antimicrobial activity is essential for promoting the applications of this excellent biomaterial. In this work, a simple approach based on electrostatic interaction is adopted to produce antimicrobial silk hydrogel containing an antimicrobial peptide (AMP), polymyxin B, an important last-line antibiotic to treat multidrug-resistant bacterial superbugs. The polycationic property of this peptide and the negative charge of silk fibroin lead to strong interactions between them, as demonstrated by changes in nanofibril structure, gelation kinetics, ζ-potential, fluorescence emission, and rheological properties of the gel. The hydrogels loaded with polymyxin B demonstrated antimicrobial activity against two Gram-negative bacterial strains. A combination of the results from the different characterizations suggests that the optimal molar ratio of polymyxin B to silk fibroin is 1:2.5. As most AMPs are cationic, this electrostatic approach is suitable for the straightforward functionalization of inert silk hydrogel with other AMPs.

Antimicrobial and Bioactive Silk Peptide Hybrid Hydrogel with a Heterogeneous Double Network Formed by Orthogonal Assembly.

Hydrogels mimic the natural extracellular matrix in terms of their nanofibrous structure and large water content. However, the lack of a combination of properties including sufficient heterogeneity in the gel structure, intrinsic antimicrobial activity, and bioactivity limits the efficiency of hydrogels for tissue engineering applications. In this work, a hydrogel with a combination of these properties was fabricated by hybridizing silk fibroin with a low-molecular-weight peptide gelator. It was observed that silk fibroin and the peptide gelator assembled orthogonally in sequence. While the morphology of silk fibroin nanofibrils was not affected by the peptide gelator, silk fibroin promoted the formation of wider nanoribbons of the peptide gelator by modulating its nucleation and growth. Orthogonal assembly maintained the antimicrobial activity of the peptide gelator and the excellent biocompatibility of silk fibroin in the hybrid gel. The hybrid gel also demonstrated improved interactions with cells, an indicator of a higher bioactivity, possibly due to the heterogeneous double network structure.

Ectopic Expression of TRIM25 Restores RIG-I Expression and IFN Production Reduced by Multiple Enteroviruses 3Cpro.

Enteroviruses (EVs) 3C proteins suppress type I interferon (IFN) responses mediated by retinoid acid-inducible gene I (RIG-I), while an E3 ubiquitin ligase, tripartite motif protein 25 (TRIM25)-mediated RIG-I ubiquitination is essential for RIG-I antiviral activity. Therefore, whether the effect of EVs 3C on RIG-I is associated with TRIM25 expression is worth to be further investigated. Here, we demonstrate that 3C proteins of EV71 and coxsackievirus B3 (CVB3) reduced not only RIG-I expression but also TRIM25 expression through protease cleavage activity, while overexpression of TRIM25 restored RIG-I expression and IFN-ß production reduced by 3C proteins. Further investigation confirmed that the two amino acids and functional domains in TRIM25 required for RIG-I ubiquitination and TRIM25 structural conformation were essential for the recovery of RIG-I expression. Moreover, we also observed that TRIM25 could rescue RIG-I expression reduced by 3C proteins of CVA6 and EV-D68 but not CVA16. Our findings provide an insightful interpretation of 3C-mediated host innate immune suppression and support TRIM25 as an attractive target against multiple EVs infection.

Bioactive hierarchical silk fibers created by bioinspired self-assembly.

Artificial recapitulation of the hierarchy of natural protein fibers is crucial to providing strategies for developing advanced fibrous materials. However, it is challenging due to the complexity of the natural environment. Inspired by the liquid crystalline spinning of spiders, we report the development of natural silk-like hierarchical fibers, with bundles of nanofibrils aligned in their long-axis direction, by self-assembly of crystallized silk fibroin (SF) droplets. The formation of self-assembled SF fibers is a process of coalesced droplets sprouting to form a branched fibrous network, which is similar to the development of capillaries in our body. The as-assembled hierarchical SF fibers are highly bioactive and can significantly enhance the spreading and growth of human umbilical vein endothelial cells compared to the natural SF fibers. This work could help to understand the natural silk spinning process of spiders and provides a strategy for design and development of advanced fibrous biomaterials for various applications.

Enhanced Photovoltaic Efficiency via Control of Self-Assembly in Cyanopyridone-Based Oligothiophene Donors.

The optoelectronic properties of functional π-conjugated organic materials are affected by their ability to self-assemble within thin films of devices. There are limited reports that demonstrate the positive impact of self-assembly on the photovoltaic performance of organic solar cells. Here, we demonstrate that hydrogen-bonded supramolecular arrays of a cyanopyridone-based oligothiophene donor, CP6, show notable improvement in photovoltaic performance upon self-assembly into a nanofibrous network. The honeycomb-like blend network exhibited higher hole mobility, leading to efficient charge generation and transport. The photovoltaic performance of CP6 was superior to that of two structural analogues, CP5 and CP1, and was attributed to the enhanced capability of CP6 to self-assemble into a film morphology favorable for BHJ devices. The BHJ devices comprising CP6 and the conventional fullerene acceptor (PC71BM) exhibited an efficiency of 7.26%, which is greater than that of CP5 (5.19%) and CP1 (3.11%) and is among the best-performing, cyanopyridone-based oligothiophene donors described to date.

Fibrous-Structured Freestanding Electrodes for Oxygen Electrocatalysis.

Electrocatalysts used for oxygen reduction and oxygen evolution reactions are critical materials in many renewable-energy devices, such as rechargeable metal-air batteries, regenerative fuel cells, and water-splitting systems. Compared with conventional electrodes made from catalyst powders, oxygen electrodes with a freestanding architecture are highly desirable because of their binder-free fabrication and effective elimination of catalyst agglomeration. Among all freestanding electrode structures that have been investigated so far, fibrous materials exhibit many unique advantages, such as a wide range of available fibers, low material and material-processing costs, large specific surface area, highly porous structure, and simplicity of fiber functionalization. Recent advances in the use of fibrous structures for freestanding electrocatalytic oxygen electrodes are summarized, including electrospun nanofibers, bacterial cellulose, cellulose fibrous structures, carbon clothes/papers, metal nanowires, and metal meshes. After detailed discussion of common techniques for oxygen electrode evaluation, freestanding electrode fabrication, and their electrocatalytic performance, current challenges and future prospects are also presented for future development.

Outer Membranes of Polymyxin-Resistant Acinetobacter baumannii with Phosphoethanolamine-Modified Lipid A and Lipopolysaccharide Loss Display Different Atomic-Scale Interactions with Polymyxins.

Resistance to the last-line polymyxins is increasingly reported in multidrug-resistant Gram-negative pathogens, including Acinetobacter baumannii, which develops resistance via either lipid A modification (e.g., with phosphoethanolamine [pEtN]) or even lipopolysaccharide (LPS) loss in the outer membrane (OM). Considering these two different mechanisms, quantitative membrane lipidomics data were utilized to develop three OM models representing polymyxin-susceptible and -resistant A. baumannii strains. Through all-atom molecular simulations with enhanced sampling techniques, the effect of lipid A-pEtN modification and LPS loss on the action of colistin (i.e., polymyxin E) was examined for the first time, with a focus on the dynamics and energetics of colistin penetration into these OMs. Lipid A-pEtN modification improved the OM stability, impeding the penetration of colistin into the OM; this differed from the current literature that lipid A-pEtN modification confers resistance by diminishing the initial interaction with polymyxins. In contrast, the LPS deficiency significantly reduced the negative charges on the OM surface, diminishing the binding of colistin. Moreover, both lipid A-pEtN modification and LPS loss also constituted colistin resistance through disturbing the conformational transitions of the colistin molecule. Collectively, atomic-scale interactions between polymyxins and different bacterial OMs are very different and the findings may facilitate the discovery of new-generation polymyxins against Gram-negative 'superbugs'.

Molecular dynamics simulations informed by membrane lipidomics reveal the structure-interaction relationship of polymyxins with the lipid A-based outer membrane of Acinetobacter baumannii.

BACKGROUND: MDR bacteria represent an urgent threat to human health globally. Polymyxins are a last-line therapy against life-threatening Gram-negative 'superbugs', including Acinetobacter baumannii. Polymyxins exert antimicrobial activity primarily via permeabilizing the bacterial outer membrane (OM); however, the mechanism of interaction between polymyxins and the OM remains unclear at the atomic level. METHODS: We constructed a lipid A-based OM model of A. baumannii using quantitative membrane lipidomics data and employed all-atom molecular dynamics simulations with umbrella sampling techniques to elucidate the structure-interaction relationship and thermodynamics governing the penetration of polymyxins [B1 and E1 (i.e. colistin A) representing the two clinically used polymyxins] into the OM. RESULTS: Polymyxin B1 and colistin A bound to the A. baumannii OM by the initial electrostatic interactions between the Dab residues of polymyxins and the phosphates of lipid A, competitively displacing the cations from the headgroup region of the OM. Both polymyxin B1 and colistin A formed a unique folded conformation upon approaching the hydrophobic centre of the OM, consistent with previous experimental observations. Polymyxin penetration induced reorientation of the headgroups of the OM lipids near the penetration site and caused local membrane disorganization, thereby significantly increasing membrane permeability and promoting the subsequent penetration of polymyxin molecules into the OM and periplasmic space. CONCLUSIONS: The thermodynamics governing the penetration of polymyxins through the outer leaflet of the A. baumannii OM were examined and novel structure-interaction relationship information was obtained at the atomic and membrane level. Our findings will facilitate the discovery of novel polymyxins against MDR Gram-negative pathogens.

Structure-Interaction Relationship of Polymyxins with the Membrane of Human Kidney Proximal Tubular Cells.

Multidrug-resistant Gram-negative bacteria are a serious global threat to human health. Polymyxins are increasingly used in patients as a last-line therapy to treat infections caused by these life-threatening 'superbugs'. Unfortunately, polymyxin-induced nephrotoxicity is the major dose-limiting factor and understanding its mechanism is crucial for the development of novel, safer polymyxins. Here, we undertook the first all-atom molecular dynamics simulations of the interaction between four naturally occurring polymyxins A1, B1, M1 and colistin A (representative structural variations of the polymyxin core structure) and the membrane of human kidney proximal tubular cells. All polymyxins inserted spontaneously into the hydrophobic region of the membrane where they were retained, although their insertion abilities varied. Polymyxin A1 completely penetrated into the hydrophobic region of the membrane with a unique folded conformation, whereas the other three polymyxins only inserted their fatty acyl tails into this region. Furthermore, local membrane defects and increased water penetration were induced by each polymyxin, which may represent the initial stage of cellular membrane damage. Finally, the structure-interaction relationship of polymyxins was investigated based on atomic interactions at the cell membrane level. The hydrophobicity at positions 6/7 and stereochemistry at position 3 regulated the interactions of polymyxins with the cell membrane. Collectively, our results provide new mechanistic insights into polymyxin-induced nephrotoxicity at the atomic level and will facilitate the development of new-generation polymyxins.

The key structural features governing the free radicals and catalytic activity of graphite/graphene oxide.

The presence of unpaired electrons (radicals) due to structural defects is believed to contribute to the catalytic reactivity of carbon materials. Graphite oxide and graphene oxide (GO) consist of significant structural defects and hence are considered more reactive than graphite and graphene. However, the relationship between their radical content/reactivity and their physical and chemical structures remains unknown, which limits the fabrication of high efficiency carbon-based catalysts. In this work, we progressively oxidize graphite to achieve graphite oxide and GO with different levels of oxidation and different sizes. It is observed that a maximal radical content can be achieved on graphite oxide with a C/O ratio of ca. 3.0 and a thickness of around 50 nm. Such a graphite oxide contains about 45% of π bonds and 38% of oxygenated bonds, respectively. Thinner or thicker sheets have lower radical contents due to over or insufficient oxidation, respectively. Single GO sheets with high radical contents can only be produced through a combination of oxidation and reduction. The catalytic activity of the graphite/graphene oxide for phenol degradation was found to be linearly correlated to their radical contents. The observations are significant for the advancement of carbon-based metal-free catalysis.

Nanoscale optical and structural characterisation of silk.

The nanoscale composition of silk defining its unique properties via a hierarchial structural anisotropy needs to be analysed at the highest spatial resolution of tens of nanometers corresponding to the size of fibrils made of ß-sheets, which are the crystalline building blocks of silk. Nanoscale optical and structural properties of silk have been measured from 100 nm thick longitudinal slices of silk fibers with ca. 10 nm resolution, the highest so far. Optical sub-wavelength resolution in hyperspectral mapping of absorbance and molecular orientation were carried out for comparison at IR wavelengths of 2-10 µm using synchrotron radiation. A reliable distinction of transmission changes by only 1-2% as the anisotropy of amide bands was obtained from nanometer-thin slices of silk.

Infrared Polariscopy Imaging of Linear Polymeric Patterns with a Focal Plane Array.

Polariscopy is demonstrated using hyperspectral imaging with a focal plane array (FPA) detector in the infrared (IR) spectral region under illumination by thermal and synchrotron light sources. FPA Fourier-transform IR (FTIR) imaging microspectroscopy is useful for monitoring real time changes at specific absorption bands when combined with a high brightness synchrotron source. In this study, several types of samples with unique structural motifs were selected and used for assessing the capability of polariscopy under this FPA-FTIR imaging technique. It was shown that the time required for polariscopy at IR wavelengths can be substantially reduced by the FPA-FTIR imaging approach. By using natural and laser fabricated polymers with sub-wavelength features, alignment of absorbing molecular dipoles and higher order patterns (laser fabricated structures) were revealed. Spectral polariscopy at the absorption peaks can reveal the orientation of sub-wavelength patterns (even when they are not spatially resolved) or the orientation of the absorbing dipoles.