Interfiber Separation Research Articles

Can we achieve biomimetic electrospun scaffolds with gelatin alone?

Introduction: Gelatin is a natural polymer commonly used in biomedical applications in combination with other materials due to its high biocompatibility, biodegradability, and similarity to collagen, principal protein of the extracellular matrix (ECM). The aim of this study was to evaluate the suitability of gelatin as the sole material to manufacture tissue engineering scaffolds by electrospinning. Methods: Gelatin was electrospun in nine different concentrations onto a rotating collector and the resulting scaffold's mechanical properties, morphology and topography were assessed using mechanical testing, scanning electron microscopy and white light interferometry, respectively. After characterizing the scaffolds, the effects of the concentration of the solvents and crosslinking agent were statistically evaluated with multivariate analysis of variance and linear regressions. Results: Fiber diameter and inter-fiber separation increased significantly when the concentration of the solvents, acetic acid (HAc) and dimethyl sulfoxide (DMSO), increased. The roughness of the scaffolds decreased as the concentration of dimethyl sulfoxide increased. The mechanical properties were significantly affected by the DMSO concentration. Immersed crosslinked scaffolds did not degrade until day 28. The manufactured gelatin-based electrospun scaffolds presented comparable mechanical properties to many human tissues such as trabecular bone, gingiva, nasal periosteum, oesophagus and liver tissue. Discussion: This study revealed for the first time that biomimetic electrospun scaffolds with gelatin alone can be produced for a significant number of human tissues by appropriately setting up the levels of factors and their interactions. These findings also extend statistical relationships to a form that would be an excellent starting point for future research that could optimize factors and interactions using both traditional statistics and machine learning techniques to further develop specific human tissue.

Design and analysis of hollow core Bragg fibers array for space division multiplexing

The space division multiplexing system is helpful to break through the transmission limitations of traditional optical communication systems. Inter-fiber separation and the number of alternating dielectric layers of Bragg fibers array (BFA) are considered with view to applying BFA to space division multiplexing system. The simulation results indicate that BFA with improper inter-fiber separation will result in topological edge state, thus leading to strong crosstalk and high confinement loss, and its crosstalk is hard to decrease with the increase of alternating dielectric layers. The confinement loss of each Bragg fiber in BFA with proper inter-fiber separation is greatly lower than that of traditional Bragg fiber with the same parameters. Our optimized BFA can be realized with low crosstalk of below −30 dB for 55.4 km propagation. In addition, the arrangement analysis of BFA in this paper provides some constructive suggestions for the application of traditional Bragg fiber in optical devices design such as BFA laser and omnidirectional emitting laser.

Preparation and Electrochemical Properties of the Spongelike Melamine Formaldehyde-Poly(vinyl alcohol)/LiFePO4 Porous Composite as the Lithium-Battery Cathode

The electrospun-based porous nitrogen-enriched carbon-coated olivine LiFePO4 nanocomposites (MF-PVA/LFP) were prepared by employing the practical electrospin technique and using affordable polymers, melamine-formaldehyde (MF) with poly(vinyl alcohol) (PVA), as the nitrogen-containing carbon precursor, followed by carbonization at various temperatures. Uniform and good interfiber separation of electrospun MF-PVA/LFP composite nanofibers with a average diameter of about 150–200 nm were initially obtained and then transformed into the spongelike porous structure after carbonization. The observed conductive pyridinic-N and pyrrolic-N nitrogen functional groups within the carbon coating material combining with the enhanced specific surface and high void volume of the porous structure played a great impact on the rate capability and cycling performance under high current density cycles. The highest obtained discharging capacity of the porous MF-PVA/LFP composite was 105 mAh g–1 at 0.1C. This promising concept c...

Scalable Noninvasive Organic Fiber Lithography for Large‐Area Optoelectronics

The development of precise, chemical‐free, and low‐cost pixel patterning with high resolution and throughput instead of conventional photolithography is very important for large‐area flexible organic light‐emitting diode (OLED) displays or solid‐state lightings with high aperture ratio. Here, a novel scalable and noninvasive lithography is reported as a pixel patterning method for OLEDs using highly aligned printed organic fiber arrays in large area. Use of electrohydrodynamic organic nanowire printing (ONP) enables high‐speed large‐area fabrication and precise positioning of poly(9‐vinylcarbazole) (PVK) fiber pixel separator arrays without chemical damage. Due to circular cross‐section of PVK fibers, clear and effective separation of organic and metal cathode layers by PVK fibers is achieved. Easy control of interfiber separation in ONP also enables the demonstration of green OLED subpixels with different pixel widths (400, 200, 100 μm), which shows almost the same current efficiency and luminance as OLEDs without PVK fibers; i.e., PVK fiber pixel separators in OLEDs do not degrade OLED characteristics because the devices maintain almost the same electroluminescent area. Furthermore, it is demonstrated that individually well‐aligned organic fibers are useful for pixel patterning of large‐area, flexible OLEDs by fabricating a large‐area (3 cm × 3 cm) white OLED and a flexible dot–matrix‐display‐type OLED.

χ^2 analysis for estimating the accuracy of optical properties derived from time resolved diffuse-reflectance

Weighted residuals and the reduced chi(2) (chi(R) (2)) value are investigated with regard to their relevance for assessing optical property estimates using the diffusion equation for time-resolved measurements in turbid media. It is shown and explained, for all photon counting experiments including lifetime estimation, why chi(R) (2) increases linearly with the number of photons when there is a model bias. Only when a sufficient number of photons has been acquired, chi(R) (2) is a pertinent value for assessing the accuracy of mu(a) and mu(s)' estimates. It was concluded that chi(R) (2) is of particular interest for cases of small interfiber separation, low-level scattering, strong absorption and incorrect measurement of instrument response function. It was also found that chi(R) (2) is less pertinent for judging mu(a) in case of air boundary effects.

A fiber placement device and methodology for preparing 2-D and 3-D combinatorial microcomposites

A fiber placement device is described and methodology is given for preparing two-dimensional (2-D) and three-dimensional (3-D) combinatorial microcomposites. Although 2-D microcomposites with uniform fiber spacing have been prepared previously, the preparation of uniformly spaced 3-D microcomposites with 6–20 μm diameter fibers is new. The preparation of these combinatorial specimens was motivated by research results from reference [Li et al. (1995) Compos Sci Technol 54:251]. These results showed that the mean fragment length of the broken fibers in an array of fibers of the shear-lag models increases as the inter-fiber separation decreases. It was noted that shear-lag theory predicts the opposite effect. Therefore, specimens of this type are needed to unambiguously verify this trend. In addition, data from this new technology should delineate the factors that influence critical flaw nucleation in unidirectional laminate composites.

Coupling between two collinear air-core Bragg fibers

We characterize coupling between two identical collinear hollow-core Bragg fibers, assuming a TE01 launching condition. Using a multipole method and a finite-element method, we have investigated the dependence of the beat length between supermodes of the coupled fibers and supermode radiation losses as a function of the interfiber separation, the fiber core radius, and the index of the cladding. We established that coupling is maximal when the fibers are touching each other and decreases dramatically during the first hundreds of nanometers of separation. However, residual coupling with the strength proportional to the fiber radiation loss decreased over a long range as an inverse square root of the interfiber separation and exhibited periodic variation with interfiber separation. Finally, we considered coupling between the TE01 modes with a view to designing a directional coupler. We found that for fibers with large enough core radii one can identify broad frequency ranges in which the intermodal coupling strength exceeds supermode radiation losses by 1 order of magnitude, thus opening the possibility of building a directional coupler. We attribute such unusually strong intermode coupling both to the resonant effects in the intermirror cavity and to proximity interaction between the leaky modes localized in the mirror.

Hollow Bragg fiber bundles: when coupling helps and when it hurts.

Coupling between leaky modes of collinear hollow-core Bragg fibers is considered. It is found that coupling is unusually strong because of resonant effects in the interfiber cavity when the fibers are touching each other and decreases dramatically with the first tens of nanometers of fiber separation. However, residual coupling with a strength proportional to the fiber radiation loss is long range, decreasing as an inverse square root of the interfiber separation and exhibiting periodic variation. The possibility of building a directional coupler from touching Bragg fibers is discussed in view of the findings.

On the elastic stress transfer and longitudinal modulus of unidirectional multi-short-fiber composites

An analysis is presented on the elastic stress transfer and longitudinal modulus of unidirectional multi-short-fiber composites. The analysis involves a three-cylinder model consisting of fiber, matrix and composite medium. The fiber axial stress and the interface shear stress are derived as functions of the fiber axial position. The effects of fiber-aspect ratio, fiber-volume fraction, fiber-to-matrix modulus ratio and inter-fiber separation (or fiber end gap) on stress transfer are studied in detail. The influence of neighbouring fibers on stress transfer is considered in a global manner by including the effect of the composite medium. The significance of the influence is clearly shown by comparing the stress transfer in multi-short-fiber composites with that in single-short-fiber composites. The composite modulus can be expressed by a modified rule of mixtures equation by introducing a fiber-length factor. Then, the effects of fiber-aspect ratio, fiber-volume fraction, fiber-to-matrix modulus ratio and inter-fiber separation (or fiber end gap) on the fiber-length factor are investigated. Some interesting findings are obtained. Finally, the present theory is compared with several existing theories.

Analysis of x-ray diffraction patterns from amyloid of biopsied vitreous humor and kidney of transthyretin (TTR) Met30 familial amyloidotic polyneuropathy (FAP) patients: axially arrayed TTR monomers constitute the protofilament

Familial amyloidotic polyneuropathy (FAP) is characterized by deposits of amyloid jbers in which the major protein component is transthyretin (TTR). Nearly fifty mutations have been reported for the TTR in hereditary FAP. Protein crystallography of mutant TTRs has shown that the molecular structures of the variant molecules are similar to those found in the wild type. On this basis, the FAP fibers were initially proposed to consist of native-like TTR tetramers. In the current paper, we used x-ray fiber diffraction to study the structure of FAP fibers from biopsy samples of vitreous humor and kidney. The reflections of the vitreous sample showed a cross-β diffraction pattern. All the meridional reflections were indexed by a one-dimensional, 29 Å-period lattice, and the equatorial reflections were indexed by an apparent one-dimensional 67 Å-period lattice. The x-ray intensity distribution indicated that the unit structure, which is similar to a TTR monomer, is composed of a pair of β-sheets consisting of four hydrogen-bonded β-chains per sheet, with the β-chains oriented approximately normal to the fiber axis. The axial disposition of these units, with a 29 Á-period, constitutes the protofilament; and a tetrameric lateral assembly of the protofilaments containing the core domain of the ∼20 Å-wide β-sheet structure constitutes the FAP amyloid fiber. An inter-fiber separation of 75 Å in these concentrated samples accounts for the apparent one-dimensional lattice perpendicular to the fiber axis. In the delipidated kidney FAP sample, the diffraction pattern indicated a pair of β-sheets, suggesting that the protofilament structure in kidney is similar to that in vitreous humor. In the non-delipidated sample the successive sharp reflections indexed to a one-dimensional, 48.9 Å-lattice, and the electron density projection showed a density elevation at the center of a lipid bilayer. This suggests that lipid may be associated with the monomeric TTR in the kidney FAP protofilament.

Fiber interactions in the multi-fiber composite fragmentation test

The single-fiber fragmentation test has been extended to a multi-fiber fragmentation test that demonstrates the fiber/fiber interactions that are present in real composites. The model composites are of Nicalon fibers embedded in an epoxy resin and have a controlled inter-fiber separation. An important qualitative result is that the interfacial failure in each fiber in an array is correlated with that of its neighbors, even when the individual fiber breaks are not at the same location. The fiber bundle as a whole thus has well defined regions of interfacial failure. Quantitatively, fibers in an array have a larger mean fragment length than a single fiber, and the fragment length increases with smaller inter-fiber separation or more embedded fibers. Shear-lag theory predicts the opposite effect. The results suggest that the presence of neighboring fibers prevent failure at some flaws. The flaw density function changes as a result of fiber/fiber interactions and this affects the fiber fragmentation process. Multi-fiber fragmentation tests show that the embedded single fiber test is insufficient to model fiber behavior within real composites.

OPTIMIZATION OF MULTIFIBER LIGHT DELIVERY FOR THE PHOTODYNAMIC THERAPY OF LOCALIZED PROSTATE CANCER

The understanding of light distribution within the target organ is essential in ensuring efficacy and safety in photodynamic therapy (PDT). A computer simulator of light distribution in prostatic tissue was employed for optimizing dosimetry for PDT in localized prostatic cancer. The program was based on empirically determined light distributions and optical constants and an assumed fluence rate differential from fiber source to necrosis periphery. The diffusion theory approximation to the Boltzmann transport equation was the applicable formulation relevant to prostatic tissue, which has a high albedo with forward-scattering characteristics. Solving this equation of diffusive transfer for the appropriate fiber geometry yielded the energy fluence distributions for cleaved fiber and cylindrical diffuser light delivery. These distributions, confirmed by our measurements, show a 1/r and 1/square root of r dependency (r = distance from light source) of the fluence phi (r) for the cleaved fiber and diffuser, respectively. This manifests itself by the tighter spacing of energy fluence isodoses in the case of the cleaved fiber. It was predicted that for a typical PDT regime a single interstitially placed cleaved fiber would treat 0.05-0.72 cm3. Four parallel fibers improved the uniformity of light distribution and treatment volume, and an interfiber separation of 12 mm would be necessary to provide optimal overlap of PDT necrosis, treating 0.26-3.6 cm3. The cylindrical diffuser, however, could treat larger volumes, and it was predicted that four 3 cm long diffusers at an optimal separation of 25 mm would treat 25-88 cm3 of prostatic tissue.

Dependent scattering by parallel fibers - Effects of multiple scattering and wave interference

The respective contributions of multiple scattering and wave interference on dependent scattering by a collection of closely-spaced, parallel fibers were investigated in this paper. The former is primarily a near field effect, and the latter occurs in the far field. The present analysis first employs the formulation for the full dependent scattering theory which accounts for both the nearand far-field wave interactions. These effects were then successively removed to derive the scattering properties for different approximations. Expressions for the scattering and extinction cross sections, as well as the general form factor for oblique incidence, were obtained when multiple scattering is neglected. The validity of neglecting multiple scattering is evaluated from both physical and analytical considerations. Neglecting multiple scattering is shown to result in incorrect scattering properties, except for small fiber sizes. The error caused by neglecting multiple scattering decreases when the fibers approach the Rayleigh limit and when the interfiber separation is large.