Investigation of low-pressure adhesion performance of mushroom shaped biomimetic dry adhesives

The effectiveness of biomimetic dry adhesives at different ambient pressures was investigated. Biomimetic dry adhesives have great potential for space applications but there have been few studies on how these adhesives perform in low-pressure environments. The best performing geometry for dry adhesives with respect to normal adhesion has previously been determined to be mushroom shaped fibers, but the pressure sensitivity of these designs has been unclear – with some groups reporting pressure dependent adhesion, and others claiming no effect. We have compared the microscale adhesion of mushroom shaped polymer fibers at different ambient pressures and have determined that suction cup effects are negligible for fibers with caps less than 16.4?μm in diameter. Further investigation in this work showed that a simple suction cup model provided estimates for the geometry requirements for a non-negligible suction cup effect and determined that the minimum cap radius for the 10?μm pillar diameter used in this study should be over 26?μm – past the dimension that can be successfully fabricated using this technology.     

二氧化钛纳米棒自组装纤维的水热一步合成及其光催化性能

本文以TiCl3为原料,采用水热法,在150℃下很方便地制备出了纯金红石型二氧化钛纤维。对样品进行的粉末X射线衍射(XRD),扫描电子显微镜(SEM),高分辨透射电子显微镜(HRTEM)表征显示,该纤维由纳米棒自组装而成,纤维的长度约为1~2mm,直径约为15μm,分散性良好。紫外可见光(UV-vis)吸收谱图显示该样品的能隙能量Eg=3.0eV,降解RhB实验表明该样品在可见光下的催化能力优于商用P25。     

Reduced Graphene Oxide-Encapsulated Microfiber Patterns Enable Controllable Formation of Neuronal-Like Networks

Scaffold-guided formation of neuronal-like networks, especially under electrical stimulation, can be an appealing avenue toward functional restoration of injured nervous systems. Here, 3D conductive scaffolds are fabricated based on printed microfiber constructs using near-field electrostatic printing (NFEP) and graphene oxide (GO) coating. Various microfiber patterns are obtained from poly(l -lactic acid-co-caprolactone) (PLCL) using NFEP and complexity is achieved via modulating the fiber overlay angles (45°, 60°, 75°, 90°), fiber diameters (15 to 148 µm), and fiber spatial organization (spider web and tubular structure). Upon coating GO onto PLCL microfibers via a layer-by-layer (L-b-L) assembly technique and in situ reduction into reduced GO (rGO), the obtained conductive scaffolds, with 25–50 layers of rGO, demonstrate superior conductivity (≈0.95 S cm⁻¹) and capability of inducing neuronal-like network formation along the conductive microfibers under electrical stimulation (100–150 mV cm⁻¹). Both electric field (0–150 mV cm⁻¹) and microfiber diameter (17–150 µm) affect neurite outgrowth (PC-12 cells and primary mouse hippocampal neurons) and the formation of orientated neuronal-like networks. With further demonstration of such guidance to neuronal cells, these conductive scaffolds may see versatile applications in nerve regeneration and neural engineering.     

Necklace‐Like Microfibers with Variable Knots and Perfusable Channels Fabricated by an Oil‐Free Microfluidic Spinning Process

Fiber materials with different structural features, which in many cases endow the fibers extraordinary functions, are drawing considerable attention from biomedical and material researchers. Here, perfusable necklace‐like knotted microfibers are presented for the first time. Additionally, a novel microfluidic spinning method facilitates the production of variable knots and channels. Not only spindle‐, but also hemisphere‐ and petal‐knotted microfibers can be controllably fabricated. Generation and perfusion of both Janus channels and helical channel in the knotted microfibers are also shown. With no need of oil and surfactant, the spinning process is highly cytocompatible. The potential bioengineering and biomedical application of the knotted hollow microfiber is demonstrated by its cell‐encapsulation feasibility and the unique liver acinus‐like diffusion gradient in the knot. The merits of perfusability, cytocompatibility, and structural diversity of the microfibers may open more avenues for further material and biomedical investigation.     

Compound‐Droplet‐Pairs‐Filled Hydrogel Microfiber for Electric‐Field‐Induced Selective Release

The separate co‐encapsulation and selective controlled release of multiple encapsulants in a predetermined sequence has potentially important applications for drug delivery and tissue engineering. However, the selective controlled release of distinct contents upon one triggering event for most existing microcarriers still remains challenging. Here, novel microfluidic fabrication of compound‐droplet‐pairs‐filled hydrogel microfibers (C‐Fibers) is presented for two‐step selective controlled release under AC electric field. The parallel arranged compound droplets enable the separate co‐encapsulation of distinct contents in a single microfiber, and the release sequence is guaranteed by the discrepancy of the shell thickness or core conductivity of the encapsulated droplets. This is demonstrated by using a high‐frequency electric field to trigger the first burst release of droplets with higher conductivity or thinner shell, followed by the second release of the other droplets under low‐frequency electric field. The reported C‐Fibers provide novel multidelivery system for a wide range of applications that require controlled release of multiple ingredients in a prescribed sequence.     

The Current Challenges for Drug Discovery in CNS Remyelination

The myelin sheath wraps around axons, allowing saltatory currents to be transmitted along neurons. Several genetic, viral, or environmental factors can damage the central nervous system (CNS) myelin sheath during life. Unless the myelin sheath is repaired, these insults will lead to neurodegeneration. Remyelination occurs spontaneously upon myelin injury in healthy individuals but can fail in several demyelination pathologies or as a consequence of aging. Thus, pharmacological intervention that promotes CNS remyelination could have a major impact on patient’s lives by delaying or even preventing neurodegeneration. Drugs promoting CNS remyelination in animal models have been identified recently, mostly as a result of repurposing phenotypical screening campaigns that used novel oligodendrocyte cellular models. Although none of these have as yet arrived in the clinic, promising candidates are on the way. Many questions remain. Among the most relevant is the question if there is a time window when remyelination drugs should be administrated and why adult remyelination fails in many neurodegenerative pathologies. Moreover, a significant challenge in the field is how to reconstitute the oligodendrocyte/axon interaction environment representative of healthy as well as disease microenvironments in drug screening campaigns, so that drugs can be screened in the most appropriate disease-relevant conditions. Here we will provide an overview of how the field of in vitro models developed over recent years and recent biological findings about how oligodendrocytes mature after reactivation of their staminal niche. These data have posed novel questions and opened new views about how the adult brain is repaired after myelin injury and we will discuss how these new findings might change future drug screening campaigns for CNS regenerative drugs.     

Fabrication and characterization of silver nanoparticle-incorporated bilayer electrospun–melt-blown micro/nanofibrous membrane

In this study, we fabricated an antifouling bilayered fibrous filter media having micro-nonwoven by melt blowing and nano-nonwoven by electrospinning process. Silver nanoparticle-incorporated polyurethane nanofibers were electrospun on the meltblown fiber of polypropylene. Silver nanoparticles were synthesized in situ in the polyurethane electrospun nanofibers through reduction of silver nitrate. The filter media were characterized by field emission scanning electron microscope, transmission electron microscopy, and X-ray diffraction and energy-dispersive X-ray spectroscopy analyses. The composite membrane showed that a thin layer of electrospun nanofibers improved the filtration efficiency without substantial increase in pressure drop. In situ synthesis of Ag NPs imparted the antibacterial and antifouling characteristics to the membrane.     

Redox‐Active Iron‐Citrate Complex Regulated Robust Coating‐Free Hydrogel Microfiber Net with High Environmental Tolerance and Sensitivity

Stretchable hydrogel microfibers as a novel type of ionic conductors are promising in gaining skin‐like sensing applications in more diverse scenarios. However, it remains a great challenge to fabricate coating‐free but water‐retaining conductive hydrogel microfibers with a good balance of spinnability and mechanical strength. Here the old yet significant redox chemistry of Fe‐citrate complex is employed to solve this issue in the continuous draw‐spinning process of poly(acrylamide‐co‐sodium acrylate) hydrogel microfibers and microfiber nets from a water/glycerol solution. The resultant microfibers are ionically conductive, highly stretchable, and uniform with tunable diameters. Furthermore, the presence of redox‐reversible Fe‐citrate complex and glycerol endows the fibers with good anti‐freezing, water‐retaining, and environmentally intelligent properties. Humidity and UV light can finely mediate the stiffness of hydrogel microfibers; conversely, the ionic conductance of microfibers is also responsive to light, humidity, and strain, which enables the highly sensitive perception of environmental changes. The present draw‐spinning strategy provides more possibilities for coating‐free conductive hydrogel microfibers with a variety of responsive and sensing applications.     

Transparent,Flexible, and Highly Sensitive Piezocomposite Capable of Harvesting and Monitoring Kinetic Movements of Microbubbles in Liquid

In this study, a zinc oxide (ZnO)-decorated nickel microfiber (ZNMF)-based piezoelectric nanogenerator (ZNMF-PENG) using electrospinning, metal electroplating, electrospraying, and ceramic growing techniques is fabricated. The combination of these techniques enables the ZNMF-PENG to possess high transparency and flexibility that are difficult to achieve through the existing piezoceramic-based PENGs. In particular, the presence of innumerable piezoceramic ZnO nanowires inside the ZNMF-PENG allows for detecting microbubble movements having an extremely low buoyancy force of 0.009 N, which is beneficial for detecting cavitation. Moreover, in comparison to previously reported PENGs fabricated using an electrospinning technique, the ZNMF-PENG demonstrates the highest energy-harvesting efficiency of 8750 V N⁻¹ m⁻². The novel approach in materials and methods proposed in this study is expected to contribute to the further advancement in developing transparent, flexible, and performance-improved PENGs applicable to various industrial applications.     

Controllable Aligned Nanofiber Hybrid Yarns with Enhanced Bioproperties for Tissue Engineering

Electrospun nanofibers have large surface area, high porosity, and controllable orientation while conventional microfibers have appropriate mechanical properties such as stiffness, strength, and elasticity. Therefore, the combination of nanofibers and microfibers can provide building elements to engineer biomimetic scaffolds for tissue engineering. In this study, a core–shell structured fibrous structure with controllable surface topography is created by electrospinning polycaprolactone (PCL) nanofibers onto polyglycolic acid (PGA) microfibers. The surface morphology, surface wettability, and mechanical properties of the resultant core–shell structure are characterized. FE‐SEM images reveal that the orientation of PCL nanofibers on the yarn surface can be tuned by a fiber collector and rotating disks. Benefiting from the introduction of a shell of aligned PCL nanofibers on the core of PGA yarn, the uniaxially aligned PCL nanofiber–covered yarns (A‐PCLs) exhibit higher hydrophilicity, porosity, and mechanical properties than the core PGA yarns. Moreover, A‐PCLs promote the adhesion and proliferation of BALB/3T3 (mouse embryonic fibroblast cell line), and guide cell growth along the biotopographic cues of the PCL nanofibers with controllable alignment. The developed core–shell yarn having both the desired surface topography of PCL nanofibers and mechanical properties of PGA microfibers demonstrates great potential in constructing various tissue scaffolds.