Fibrous Template Research Articles

Directed Assembly of Elastic Fibers via Coacervate Droplet Deposition on Electrospun Templates.

Elastic fibers provide critical elasticity to the arteries, lungs, and other organs. Elastic fiber assembly is a process where soluble tropoelastin is coacervated into liquid droplets, cross-linked, and deposited onto and into microfibrils. While much progress has been made in understanding the biology of this process, questions remain regarding the timing of interactions during assembly. Furthermore, it is unclear to what extent fibrous templates are needed to guide coacervate droplets into the correct architecture. The organization and shaping of coacervate droplets onto a fiber template have never been previously modeled or employed as a strategy for shaping elastin fiber materials. Using an in vitro system consisting of elastin-like polypeptides (ELPs), genipin cross-linker, electrospun polylactic-co-glycolic acid (PLGA) fibers, and tannic acid surface coatings for fibers, we explored ELP coacervation, cross-linking, and deposition onto fiber templates. We demonstrate that integration of coacervate droplets into a fibrous template is primarily influenced by two factors: (1) the balance of coacervation and cross-linking and (2) the surface energy of the fiber templates. The success of this integration affects the mechanical properties of the final fiber network. Our resulting membrane materials exhibit highly tunable morphologies and a range of elastic moduli (0.8-1.6 MPa) comparable to native elastic fibers.

Carbon nanofibers fabricated via electrospinning to guide crystalline orientation for stable perovskite solar cells with efficiency over 24%

Perovskite solar cell (PerSC) is currently-one of the most promising third-generation photovoltaic technologies. However, the defects derived from the inhomogeneous growth of perovskite film exacerbate the charge recombination and ion migration in the devices, thus restricting their power conversion efficiency (PCE) and stability. In this work, we introduce nitrogen-doped carbon nanofibers (N-CNFs) via electrospinning technology to guide the preferential orientation of perovskite crystals for the first time. N-CNFs with abundant nitrogen-containing functional groups provide plentiful nucleation sites and fibrous templates, which guide the preferential orientation growth of crystals and diminish the defects density in the perovskite film. The PCE of the champion device achieved a remarkable improvement from 21.40 % to 24.08 % and demonstrated less than 5 % degradation after 600 h of continuous exposure to the ambient environment. This study provides a novel strategy to realize efficient and stable PerSCs by controlling the heterogeneous nucleation and preferentially oriented growth of perovskite crystals with electrospinning N-CNFs.

Kinetics and characterization of preparing conductive nanofibrous membrane by In-situ polymerization of Polypyrrole on electrospun nanofibers

Polypyrrole (PPy) is a conductive polymer that can be fabricated into various structures via in-situ polymerization for different applications. However, a kinetics study of its in-situ polymerization is needed for a better understanding of the mechanisms of pyrrole polymerization. This paper develops two different kinetics models based on existing PPy polymerization mechanisms. The most suitable mechanism is first identified by comparing the model results with experimental data. Then, in-situ polymerizations of PPy on electrospun fibrous polyacrylonitrile (PAN) templates were produced at temperatures ranging from 273 to 285 K. The results show that the overall reaction rate of the in-situ polymerization process in the presence of electrospun fibrous template is faster than that without the template. Further investigation confirms that the increase in the overall reaction rate is attributed to the enhanced reactions between oxidized pyrrole oligomers and neutral pyrrole monomers, as the corresponding reaction rate constant and activation entropy increased by 158.2–209.6% and 37.7%, respectively. The reason is that the considerable number of available reaction sites between oxidized oligomers and neutral monomers are created by the fibrous template. In addition, the composite membrane obtained from the in-situ polymerization exhibited well-developed fibrous nanostructure, good electrical conductivity (0.29 ± 0.04 S∙m−1), sufficient mechanical strength (UTS of 8.7 MPa) and relatively stable thermal properties (up to 250 °C).

Porous Alumina Ceramics with Multimodal Pore Size Distributions.

Pore networks with multimodal pore size distributions combining advantages from isotropic and anisotropic shaped pores of different sizes are highly attractive to optimize the physical properties of porous ceramics. Multimodal porous Al2O3 ceramics were manufactured using pyrolyzed cellulose fibers (l = 150 µm, d = 8 µm) and two types of isotropic phenolic resin spheres (d = 30 and 300 µm) as sacrificial templates. The sacrificial templates were homogeneously distributed in the Al2O3 matrix, compacted by uniaxial pressing and extracted by a burnout and sintering process up to 1700 °C in air. The amount of sacrificial templates was varied up to a volume content of 67 Vol% to form pore networks with porosities of 0–60 Vol%. The mechanical and thermal properties were measured by 4-point-bending and laser flash analysis (LFA) resulting in bending strengths of 173 MPa to 14 MPa and heat conductivities of 22.5 Wm−1K−1 to 4.6 Wm−1K−1. Based on µCT-measurements, the representative volume-of-interest (VOI) of the samples digital twin was determined for further analysis. The interconnectivity, tortuosity, permeability, the local and global stress distribution as well as strut and cell size distribution were evaluated on the digital twin’s VOI. Based on the experimental and simulation results, the samples pore network can be tailored by changing the fiber to sphere ratio and the overall sacrificial template volume. The presence pore formers significantly influenced the mechanical and thermal properties, resulting in higher strengths for samples containing fibrous templates and lower heat conductivities for samples containing spherical templates.

Characterization of Polydioxanone in Near-Field Electrospinning.

Electrospinning is a popular method for creating random, non-woven fibrous templates for biomedical applications, and a subtype technique termed near-field electrospinning (NFES) was devised by reducing the air gap distance to millimeters. This decreased working distance paired with precise translational motion between the fiber source and collector allows for the direct writing of fibers. We demonstrate a near-field electrospinning device designed from a MakerFarm Prusa i3v three-dimensional (3D) printer to write polydioxanone (PDO) microfibers. PDO fiber diameters were characterized over the processing parameters: Air gap, polymer concentration, translational velocity, needle gauge, and applied voltage. Fiber crystallinity and individual fiber uniformity were evaluated for the polymer concentration and translational fiber deposition velocity. Fiber stacking was evaluated for the creation of 3D templates to guide the alignment of human gingival fibroblasts. The fiber diameters correlated positively with polymer concentration, applied voltage, and needle gauge; and inversely correlated with translational velocity and air gap distance. Individual fiber diameter variability decreases, and crystallinity increases with increasing translational fiber deposition velocity. These data resulted in the creation of tailored PDO 3D templates, which guided the alignment of primary human fibroblast cells. Together, these results suggest that NFES of PDO can be scaled to create precise geometries with tailored fiber diameters for biomedical applications.

Confinement-Induced Ordering and Self-Folding of Cellulose Nanofibrils.

Cellulose is a pervasive polymer, displaying hierarchical lengthscales and exceptional strength and stiffness. Cellulose's complex organization, however, also hinders the detailed understanding of the assembly, mesoscopic properties, and structure of individual cellulose building blocks. This study combines nanolithography with atomic force microscopy to unveil the properties and structure of single cellulose nanofibrils under weak geometrical confinement. By statistical analysis of the fibril morphology, it emerges that confinement induces both orientational ordering and self‐folding of the fibrils. Excluded volume simulations reveal that this effect does not arise from a fibril population bias applied by the confining slit, but rather that the fibril conformation itself changes under confinement, with self‐folding favoring fibril's free volume entropy. Moreover, a nonstochastics angular bending probability of the fibril kinks is measured, ruling out alternating amorphous–crystalline regions. These findings push forward the understanding of cellulose nanofibrils and may inspire the design of functional materials based on fibrous templates.

Ultrafine hollow TiO2 nanofibers from core-shell composite fibers and their photocatalytic properties

Abstract The oxidized electrospun polyacrylonitrile (o-PAN) fibers are used as templates and formed core-shell composite fibers by coating a layer of TiO2 sol. After calcination in air, hollow TiO 2 nanofibers (HTONFs) are fabricated by removing the PAN fibrous template for the photocatalyzed degradation of methylene blue (MB). Scanning electron microscopy, transmission electron microscopy , X-ray diffraction and Raman spectra are used to characterize the morphologies and structures of HTONFs. The effects of MB concentration, amount of TiO 2, light intensity, pH and calcination temperatures on the reaction rate constant are investigated. At last, HTONFs is recycled by a simple method, and the reutilization for photocatalyzation is evaluated.

Raw-Cotton-Derived N-Doped Carbon Fiber Aerogel as an Efficient Electrode for Electrochemical Capacitors

The carbon fiber aerogel with a high surface area, as a promising ideal electrode for electrochemical capacitors (ECs), has attracted tremendous attention because it can offer a fast charge–discharge rate and an exceptional rate capability. However, there is still a big challenge to acquire highly porous fiber aerogel with elastic properties and good flexibility. Herein, N-doped porous carbon fiber aerogel (N-CFA) has been successfully fabricated using raw cotton as a fibrous template to obtain shaped aerogels. ZIF-8, in situ fabricated on the surface of cotton, played the role of an active agent and nitrogen source to create a rich porous structure with a certain nitrogen content. Benefiting from the macromonolith morphology with good flexibility, favorable mechanical durability, nitrogen doping, anda high specific surface area, the N-CFA exhibits excellent electrochemical performance with a high capacity of 365 F g–1 at a current of 0.5 A g–1 and a remarkable rate capability of 65.8% from 0.5 to 100 A g...

Carbon-decorated iron oxide hollow granules formed using a silk fibrous template: lithium-oxygen battery and wastewater treatment applications

Hierarchical nanoarchitecture and phase control of iron oxides are important approaches for achieving multi-functionality for various applications. Herein, rice-grain-shaped iron oxide hollow structures were synthesized via a hydrothermal process using a silk fibrous template, and the crystalline phases (α-Fe2O3, Fe3O4) were controlled by annealing. These structures were applied in a lithium-oxygen battery cathode and as adsorbents for wastewater treatment. The porosity, hollow interior, surface area, surface chemical composition and efficient carbon matrix of the C/Fe3O4 hollow granules obtained by annealing under Ar atmosphere were favorable for enhancing the oxygen reduction and evolution kinetics when applied as an electrocatalyst for lithium-oxygen batteries, and also led to superior adsorption of organic pollutants (Rhodamine B) from an aqueous medium. The C/Fe3O4 hollow granules were uniformly distributed and confined in the 3D nanoarchitecture; this morphology can offer rapid ion transport with improved electronic and chemical kinetics as well as superior adsorption of organic pollutants.

Microfibrous PEDOT scaffold for neural recordings

Event Abstract Back to Event Microfibrous PEDOT scaffold for neural recordings Jason Marroquin1, Kun Zhou1, Bjorn Winther-Jensen1, Harry Coleman2, Helena Parkington2 and John S. Forsythe1 1 Monash University, Materials Engineering, Australia 2 Monash University, Physiology, Australia Current neural interfaces used for both recording and stimulating neurons have great potential in neurophysiological research to help understand processes, and in biomedical applications to restore some functions in the nervous system, e.g. prostheses, bionic implants. However, there presently exist serious limitations in obtaining stable, consistent and long-term stimulation or recording, mainly due to an unwanted glial response. The scar increases resistance to current flow as well as the distance between the neurons and the current source [1]. Consequently, higher electrical currents or voltages are required, which result in damage to neural tissue due to Faradaic reactions. Additionally, most neural interfaces have limited proximity to neurons (due to their 2D recording sites), which is greatly compromised once a glial response occurs [2]. In the present study, a microfibrous 3D neural electrode is under development using a PLLA electrospun template. The fibrous template was imbued with electroactive properties by coating with PEDOT, a conductive polymer, via vapour phase polymerization. The electrical properties of the PEDOT-coated substrates were studied in terms of sheet resistance measured by a 4-point probe, and scaffold morphology was investigated by scanning electron microscopy. Scaffold biocompatibility was assessed through in vitro assay of rat primary hippocampal neurons using patch clamp electrophysiology, calcium imaging (using fluorescent indicator Fluo-4) and immunocytochemistry. Importantly, the in vitro assays demonstrated normal spontaneous neural activity, indicating robust neural networking, up to 40 days in culture on PEDOT scaffolds.

Preparation and characterization of electrospun copoly (phthalazinone biphenyl ether ketone) superfine fibrous membrane served as plating template of Pd

Novel copoly (phthalazinone biphenyl ether ketone) (PPBEK) superfine fibrous membrane was successfully fabricated through electrospinning, and characterized by SEM, DSC, TGA and tensile test. The solution concentration of PPBEK suited for electrospinning was 0.10–0.30gmL−1, and the average diameter of PPBEK fibers increased obviously with the increase of solution concentration. The electrospun PPBEK superfine fibrous membrane had very high glass transition temperature (>242°C), excellent tensile strength (4.94–18.66MPa) and superior chemical resistance, which were critical advantages for the membrane as plating template applied in fuel cells. Pd was deposited on the PPBEK fibrous template by electroless plating with a layer thickness of ~250nm. TEM shows that Pd nanoparticles dispersed well on PPBEK fibers and the diameter was about 4nm. The as-prepared Pd/PPBEK superfine fibrous membrane had good conductivity and was successfully applied as free-standing electrocatalytic electrode for methanol oxidation without using any conductive support.

Layer-by-layer self-assembly of Cibacron Blue F3GA and lipase on ultra-fine cellulose fibrous membrane

Cibacron Blue F3GA (CB) dye and lipase from Candida rugosa were assembled into multiple alternating bilayers on ultra-fine cellulose (Cell) fiber surfaces via electrostatic layer-by-layer (LBL) deposition. The presence and even coverage of CB and lipase molecules on the fibers were clearly evident by FTIR spectra and microprobe element mapping. The average thickness of each CB/lipase bilayer was ∼11 nm and the total LBL thickness increased with increasing numbers of bilayers up to 5 bilayers. The CB and lipase loadings on the Cell fibrous membrane also increased with the increasing bilayers. While CB was loaded at ∼8.1 mg/g Cell from layers 2–4, lipase loading was ∼3.3 mg/g Cell for the first 2 then became more varied, i.e., between 1.5 and 6.5 mg/g Cell, from layers 3–5. The maximum catalytic activities of lipase bound in the CB/lipase bilayers were 97.0, 90.4, 85.2, 76.1, and 55.6 U/mg of lipase with 1–5 bilayers, respectively. The catalytic activity of lipase bound in all 5-bilayer LBL was equivalent to 45% of that of free lipase. The successful assembling of alternating layers of CB and lipase as shown by incrementally increasing thickness and loading demonstrate that LBL is a promising approach to immobilize enzymes as nano-films on 3D fibrous templates.

Pd−Promoted Ni−P Electroless Deposition on a Hydrogen-Bonded Molecular Surface of a Supramolecular Fibrous Template

A nickel−phosphorus (Ni−P) hollow microfiber was obtained by simply immersing a recyclable hydrogen-bonded supramolecular fibrous template made of amphoteric azopyridine carboxylic acid in an HCl-acidic PdCl2 aqueous solution and in a Ni−P electroless plating bath, followed by template removal in an alkaline aqueous solution. The Ni−P hollow microfiber had an inner pore diameter of 0.5 μm and a wall thickness of about 50 nm. The mechanism of the Pd-promoted Ni−P electroless deposition on the template surface was revealed by XPS analysis and TEM observation. Coordination of the [PdCl4]2- species and its subsequent hydrolysis and condensation polymerization to a tubular Pd2+ nanosheet and formation of the Pd0 nanoparticle as plating catalyst were brought about on the molecular surface of successive head-to-tail COOH···NC5H4 hydrogen bonds, which comprised the supramolecular fibrous template. The hydrogen-bonded surface ordered at a molecular level leading to the tubular Pd2+ nanosheet played an important role in homogeneous Pd-promoted Ni−P electroless deposition and allowed us to fabricate a uniform Ni−P hollow microfiber.

Piezoelectric Lead Zirconate Titanate Ceramic Fiber/Polymer Composites

Piezoelectric lead zirconate titanate (PZT) ceramic fiber/polymer composites were fabricated by a novel technique referred to as “relic” processing. Basically, this involved impregnating a woven carbon‐fiber template material with PZT precursor by soaking the template in a PZT stock solution. Careful heat treatment pyrolized the carbon, resulting in a PZT ceramic relic that retained the fibrous template form. After sintering, the densified relic was backfilled with polymer to form a composite. Optimized relic processing consisted of soaking activated carbon‐fiber fabric twice in an intermediate concentration (405‐mg PZT/(1‐g solution)) alkoxide PZT solution and sintering at 1285°C for 2 h. A series of piezoelectric composites encompassing a wide range of dielectric and piezoelectric properties was prepared by varying the PZT‐fiber orientation and polymer‐matrix material. In PZT/Eccogel polymer composites with PZT fibers orientated parallel to the electrodes, K= 75, d33= 145 pC/N, dh= 45 ± 5 pC/N, and dhgh= 3150 × 10−15 m2/N were measured. Furthermore, in composites with a number of PZT fibers arranged perpendicular to the electroded surfaces, K= 190, d33= 250 pC/N, dh= 65 ± 2 pC/N, and dh gh= 2600 × 10−15 m2/N.

Structure, crystallography, and morphogenesis of the cryptic shell of the terrestrial slug Limax maximus (Mollusca, gastropoda).

The structure and crystallography of the internal shell of the pulmonate gastropod slug Limax maximus were studied at the levels of light and scanning electron microscopy, revealing patterns of shell ontogeny and morphogenesis. The calcified portion of the slightly convex ovoid shell is composed of a single palisade layer of calcitic crystals. Numerous projections, 100 μm in width at the dorsal tip, are found on the dorsal surface of the shell and coincide with local nucleation sites of primordial calcium salt deposition onto the periostracum. With continued calcification these projections coalesce ventrally, forming the single crystalline shell layer. The organic portion of the shell includes the periostracum and an extensive PAS-staining conchiolin. In EDTA-etched preparations, conchiolin appears as a spongy network of fibers throughout the shell. Both horizontal and vertical components of the conchiolin are present, the former of variable thickness and occurring in an intercrystalline manner, the latter always occurring normal to the horizontal set. Macromorphogenic growth is characterized by three distinct temporal stages. Primary growth occurs radially from the umbonal region. Secondary growth is synonymous with shell thickening. Tertiary growth is characterized by both a lateral component, in which the shell extends beyond the primary growth boundaries, and a ventral component, in which the shell continues to grow in thickness. SEM of the ventral shell surface reveals a pattern of growth at the crystalmatrix interface. Proteinaceous fibers of the conchiolin occur unidirectionally in horizontal rows. Zones of incipient calcitic crystallization onto these hypostracal fiber bundles are contrasted by zones of increasing crystallization until the fibrous template (reduced hypostracum) is completely covered by crystals.