Microfiber Structures Research Articles

Microstructured silk fiber scaffolds with enhanced stretchability.

Despite extensive research, current methods for creating three-dimensional (3D) silk fibroin (SF) scaffolds lack control over molecular rearrangement, particularly in the formation of β-sheet nanocrystals that severely embrittle SF, as well as hierarchical fiber organization at both micro- and macroscale. Here, we introduce a fabrication process based on electrowriting of aqueous SF solutions followed by post-processing using an aqueous solution of sodium dihydrogen phosphate (NaH2PO4). This approach enables gelation of SF chains via controlled β-sheet formation and partial conservation of compliant random coil structures. Moreover, this process allows for precise architecture control in microfiber scaffolds, enabling the creation of 3D flat and tubular macro-geometries with square-based and crosshatch microarchitectures, featuring inter-fiber distances of 400 μm and ∼97% open porosity. Remarkably, the crosslinked printed structures demonstrated a balanced coexistence of β-sheet and random coil conformations, which is uncommon for organic solvent-based crosslinking methods. This synergy of printing and post-processing yielded stable scaffolds with high compliance (modulus = 0.5-15 MPa) and the ability to support elastic cyclic loading up to 20% deformation. Furthermore, the printed constructs supported in vitro adherence and growth of human renal epithelial and endothelial cells with viability above 95%. These cells formed homogeneous monolayers that aligned with the fiber direction and deposited type-IV collagen as a specific marker of healthy extracellular matrix, indicating that both cell types attach, proliferate, and organize their own microenvironment within the SF scaffolds. These findings represent a significant development in fabricating organized stable SF scaffolds with unique microfiber structures and mechanical and biological properties that make them highly promising for tissue engineering applications.

Long-term maintenance of functional primary human hepatocytes in 3D gelatin matrices produced by solution blow spinning

Solution blow spinning (SBS) has recently emerged as a novel method that can produce nano- and microfiber structures suitable for tissue engineering. Gelatin is an excellent precursor for SBS as it is derived mainly from collagens that are abundant in natural extracellular matrices. Here we report, for the first time the successful generation of 3D thermally crosslinked preforms by using SBS from porcine gelatin. These SBS mats were shown to have three-dimensional fibrous porous structure similar to that of mammalian tissue extracellular matrix. In pharma industry, there is an urgent need for adequate 3D liver tissue models that could be used in high throughput setting for drug screening and to assess drug induced liver injury. We used SBS mats as culturing substrates for human hepatocytes to create an array of 3D human liver tissue equivalents in 96-well format. The SBS mats were highly cytocompatible, facilitated the induction of hepatocyte specific CYP gene expression in response to common medications, and supported the maintenance of hepatocyte differentiation and polarization status in long term cultures for more than 3 weeks. Together, our results show that SBS-generated gelatin scaffolds are a simple and efficient platform for use in vitro for drug testing applications.

Bamboo-like microfiber structures fabricated by one-step-tapering a fiber preform.

The microfiber-based optical structures have been attracting increasing research interests in communications and sensing fields. However, the fabrication of forming structures on fragile microfibers requires delicate operations, which limits the developments of their practical applications. In this work, a one-step-tapering technique is proposed to manufacture structures on microfibers. As a demonstration, the fiber preform, consisting of sawtooth shaped solid-air interfaces with designed dimensions, is obtained using a femtosecond laser milling technique. By one-step tapering the preform, periodic bumps are formed, resulting in a bamboo-like microfiber device. The fabricated structure shows spectral characteristics of a long-period grating, of which extinction ratio is up to 18.2 dB around 1553.3 nm. The response to refractive index is measured to be ∼875.02 nm/RIU and the temperature coefficient is ∼5.78 pm/°C. The theoretical analysis shows good agreement with the experimental results. The microfiber-based structure fabricated using the one-step-tapering-preform technique is featured with flexibility of design, reproducibility, and structural stability.

A facile design of EGF conjugated PLA/gelatin electrospun nanofibers for nursing care of in vivo wound healing applications

Nano (or) microfiber structures made from biodegradable polymers offer many benefits for biomedical applications, including the tissue engineering system. In this study, a mixture of poly (lactic acid) (PLA)/gelatin (GEL) conjugated epidermal growth factor (EGF) electrospun nanofiber scaffolds, which may have potential applications for nursing care of diabetic wound healing. The amount of EGF conjugation on the PLA/GEL nanofibers was quantitated by X-ray photoelectron spectroscopy. A morphological examination of the electrospun nanofibers was performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which has bead-free morphology nanofibers. After characterizing, the PLA/GEL and PLA/GEL/EGF scaffolds were selected for further investigation based on their superior mechanical properties, including tensile strength, maximum elongation, and tensile modulus. We evaluated the antibacterial activity, cell proliferation and the efficiency of diabetic wound healing in vivo. The antibacterial effect of EGF present in the PLA/GEL nanofibers was assessed using the zone inhibition test against S. aureus and E. coli. In vitro cell proliferation activity was well maintained after the PLA/GEL conjugation and was compared to that of EGF with L929 fibroblast cells. The nanofiber PLA/GEL conjugated with EGF exerted greater curative activities in vivo compared to the control groups or EGF solutions. This study showed that the nanofiber PLA/GEL in combination with EGF could potentially be used as a novel material for nursing care of wound healing by antibacterial, increasing inflammatory cell, and re-epithelialization.

Computed fiber evaluation of SEM images using DiameterJ

Abstract Fiber materials offer a high potential for improving the surface characteristics of medical implants. For quality assurance of nano- and microfiber structures the morphology is inspected by Scanning Electron Microscopy (SEM) as a standard method. Vast quantities of image data have to be evaluated. Usual practice for obtaining the fiber diameters is the manually setting of measurement points. The software DiameterJ which runs as plugin in ImageJ automatically computes fiber diameters. Here we investigated its capabilities and limitations by comparing the evaluation of selected sample SEM images of electrospun fibers. In this study the fibers of three examplary images specified by different contrast and fiber morphology were analyzed by using varied segmentation algorithms. The results are displayed in bar charts of frequency distribution. Additionally the computed fiber diameters were compared to manual measurements. Depending on various image properties the segmentation process works more or less reliable, and fault data of incomplete segmented fibers are computed. Often the results are eligible, but frequently DiameterJ generates data resembling to thin fibers, which are not present in the image. In some cases the peaks of fault data are much higher than peaks of real fibers. In consequence misinterpretation of data cannot be avoided. DiameterJ is a validated tool with the ability to generate reliable results. Future work on improving the segmentation algorithms can refine computed evaluation.

Identification of sagging in melt-electrospinning of microfiber scaffolds

Melt-electrospinning is a cost-effective and flexible process to fabricate micro-scaled polymeric fibers. Melt-electrospun microfiber structures have been receiving considerable attention from various fields due to their numerous advantages. However, the application of melt-electrospinning is limited by various factors, such as the sagging behavior and unstable whipping motion of microfibers. Here, we presented an experimental approach called beam bridge test to identify the sagging behavior of melt-electrospun microfibers for preparing 3D lattice structures with controllable architecture and well-defined pores in transverse direction. Consequently, the sagging behavior of melt-electrospun microfibers could be identified in a systematic manner. Moreover, the melt-electrospun 3D microfiber lattice structures with various grid sizes had sagging, which agreed well with the beam bridge test results. In addition, fibroblast cells (NIH-3T3) were cultured on the fabricated 3D microfiber lattice structures with various grid sizes. Cell culture results indicated that the cell growth was considerably influenced by microfiber sagging and the grid size of lattice structures. Also it was shown that the cell population for location could be controlled.

Star-Like Glycosaminoglycans with Superior Bioactivity Assemble with Proteins into Microfibers.

Here it is shown that glycosaminoglycans (GAGs) with high molecular weight can be grafted via their reducing end on hyperbranched synthetic cores by oxime condensation without the need of any previous functionalisation of the polysaccharide. The versatility of this reaction is demonstrated by the use of hyaluronan, chondroitin sulfate and heparin with up to 60 sugar units. The isothermal calorimetry analysis demonstrated that the generated star-like glycopolymers have superior bioactivity. Moreover, when mixed with positively charged proteins (e.g., fibroblast growth factor-2, FGF-2) they form microfiber structures instead of the spherical nanocomplexes described for linear GAGs. The results suggest that the described star-like GAG are closer mimics of the proteoglycans at the structural and functional level and therefore have huge potential in the development of tissue engineering platforms and therapeutics by modulating the activity and presentation of various proteins such as growth factors.

TiO2/BiVO4, a Heterojuncted Microfiber with Enhanced Photocatalytic Performance for Methylene Blue under Visible Light Irradiation

Novel TiO2/BiVO4 microfiber heterojunctions were constructed using cotton as biomorphic templates. The as-synthesized samples were characterized by scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectra and photocatalytic experiment. The morphology of the as-synthesized TiO2/BiVO4 composites was consisted of a large quantity of microfiber structures with diameter from 2.5 µm to 5 µm, and the surface of samples became more coarse and compact with the increase of weight ratio of TiO2. The TiO2/BiVO4 samples with proper content (10.00wt%) showed the highest photocatalytic degradation activity for methylene blue (MB) degradation among all the samples under visible light, and 88.58%MB could be degraded within 150 min. The enhancement of photocatalytic activity was mainly attributed to the formation of n-n heterojunction at the contact interface of TiO2 and BiVO4, which not only narrowed the band gap of BiVO4 for extending the absorption range of visible light, but also promoted the transfer of charge carriers across interface. A possible photodegradation mechanism of MB in the presence of TiO2/BiVO4 microfibrous photocatalyst was proposed.

PMMA microfiber coated with ZnO nanostructure for the measurement of relative humidity

PMMA microfibers coated with zinc oxide (ZnO) nanostructure are demonstrated for relative humidity monitoring. The fabrication of two different microfiber structures, namely the straight PMMA microfiber and the PMMA microfiber loop resonator (PMLR) were performed by using the direct drawing technique. The sensitivities of the PMMA microfibers were compared and analyzed. The results implied that the PMLR is more sensitive than the straight PMMA microfiber and the sensitivity of the sensors were further increased with the additional coating of ZnO nanostructure on the surface of the PMMA fiber.

Fabrication of highly stable microfiber structures via high-substituted hydroxypropyl cellulose coating for device and sensor applications.

We demonstrate a cost-effective approach to fabricate stable microfiber structures taking advantage of high-substituted hydroxypropyl cellulose (H-HPC) coating. The microfibers are bent, twisted, or coiled to form desired geometries, and then the segments in contact are coated to resist the existing bending or twisting stresses to stabilize the structures. Coated devices including a twisted Sagnac interferometer, a ring resonator, and a Fabry-Perot cavity have been exhibited. Measured result suggests that the coated structures are highly stable over 20 days. The thin, low-index coating material allows for a strong evanescent-field interaction between the mode field and ambient solution. As an example, the coated twisted Sagnac interferometer can act as a refractive-index sensor with a sensitivity as high as 2600nm/RIU. The present technique is greatly beneficial for long-term working of microfiber devices and sensors and offers a possible approach for the development of integrated microphotonic devices and platforms.

Preparation of graphene oxide/polyvinyl alcohol microcomposites and their thermal conducting properties

In this article, we report the fabrication of graphene oxide (GO)/polymer composite structures that may be candidates for use as effective heat dissipation materials. GO was well dispersed in aqueous polyvinyl alcohol (PVA) solutions; anisotropic fiber structures of GO/PVA composites were then prepared by freeze-drying under controlled freezing conditions. GO was well dispersed in the microfiber structures of PVA, and morphologies of the GO/PVA composite structures could be controlled through the concentration of the starting solution, the freezing temperature, freezing rate, and direction of the freeze. Thermal conducting properties were found to depend on the morphology of the composite structures and the content of GO. Anisotropic thermal conductivity was found for some structures.

General approach to splicing optical microfibers via polymer nanowires

We demonstrate a general approach to splicing microfibers via polymer nanowires. Chloroform dissolved polystyrene nanowires are used to splice silica, tellurite glass, and semiconductor microfibers or nanowires, with splicing loss down to 0.51 dB. Using spliced microfiber structures, we also demonstrate microfiber ring resonators and Mach-Zehnder interferometers with high robustness. The splicing technique demonstrated here promises high potentials for robust optical integration of microfibers or nanowires for functional circuits or devices.

Fabrication and characterization of 3-dimensional PLGA nanofiber/microfiber composite scaffolds

Novel three-dimensional (3-D) nano-/microfibrous poly(lactic- co-glycolic acid) (PLGA) scaffolds were fabricated by hybrid electrospinning, involving a combination of solution electrospinning and melt electrospinning. The scaffolds consisted of a randomly oriented structure of PLGA microfibers (average fiber diameter = 28 μm) and PLGA nanofibers (average fiber diameter = 530 nm). From mercury porosimetry, the PLGA nano-/microfiber (10/90) scaffolds were found to have similar pore parameters to the PLGA microfiber scaffolds. PLGA nano-/microfibrous scaffolds were examined and compared with the PLGA microfiber scaffolds in terms of the attachment, spreading and infiltration of normal human epidermal keratinocytes (NHEK) and fibroblasts (NHEF). The cell attachment and spreading of both cell types were several times higher in the nano-/microfiber composite scaffolds than in the microfibrous scaffolds without nanofibers. This shows that the presence of nanofibers enhanced the attachment and spreading of the cells on the nano-/microfiber composite scaffolds. Moreover, the nanofibers helped the cells infiltrate easily into the scaffolds. Overall, this novel nano-/microfiber structures has great potential for the 3-D organization and guidance of cells provided for tissue engineering.

Formation of charged particle tracks in glass-fiber microstructures

Glass-fiber disks intended for the image transfer in electrooptical transducers can be used as targets in microchannel Cerenkov track detectors. Calculated values of the coefficient of Cerenkov radiation trapping in the glass-fiber discs well agree with experiment, which confirms the hypothesis concerning a Cerenkov-type mechanism of the charged particle track formation in non-scintillating microfiber structures.