Chain entanglements are one of many parameters that can significantly influence fiber formation during polymer electrospinning. While the importance of chain entanglements has been acknowledged, ...there is no clear understanding of how many entanglements are required to affect/stabilize fiber formation. In this paper, polymer solution rheology arguments have been extrapolated to formulate a semi-empirical analysis to explain the transition from electrospraying to electrospinning in the good solvent, non-specific polymer–polymer interaction limit. Utilizing entanglement and weight average molecular weights (
M
e,
M
w), the requisite polymer concentration for fiber formation may be determined a priori, eliminating the laborious trial-and-error methodology typically employed to produce electrospun fibers. Incipient, incomplete fiber formation is correctly predicted for a variety of polymer/solvent systems at one entanglement per chain. Complete, stable fiber formation occurs at ≥2.5 entanglements per chain.
Electrospun fiber mats are explored as drug delivery vehicles using tetracycline hydrochloride as a model drug. The mats were made either from poly(lactic acid) (PLA), poly(ethylene-co-vinyl acetate) ...(PEVA), or from a 50:50 blend of the two. The fibers were electrospun from chloroform solutions containing a small amount of methanol to solubilize the drug. The release of the tetracycline hydrochloride from these new drug delivery systems was followed by UV–VIS spectroscopy. Release profiles from the electrospun mats were compared to a commercially available drug delivery system, Actisite
® (Alza Corporation, Palo Alto, CA), as well as to cast films of the various formulations.
Solutions of poly(ethylene-co-vinyl alcohol) or EVOH, ranging in composition from 56 to 71
wt% vinyl alcohol, can be readily electrospun at room temperature from solutions in 70% 2-propanol/water ...(rubbing alcohol). The solutions are prepared at 80°C and allowed to cool to room temperature. Interestingly, the solutions are not stable at room temperature and eventually the polymer precipitates after several hours. However, prior to precipitation, electrospinning is extensive and rapid, allowing coverage of fibers on various substrates, including a grounded metal plate, dielectrics interposed between the charged jet and the metal ground, and on the human body. Fiber diameters of ca. 0.2–8.0
μm were obtained depending upon the solution concentration, an attractive range for tissue engineering, wound healing, and related applications. Electrospun EVOH mats have been shown to support the culturing of smooth muscle cells and fibroblasts.
We characterize the infiltration of interstitial cells into tissue engineering scaffolds prepared with electrospun collagen, electrospun gelatin, electrospun poly(glycolic) acid (PGA), electrospun ...poly(lactic) acid (PLA), and an electrospun PGA/PLA co-polymer. Electrospinning conditions were optimized to produce non-woven tissue engineering scaffolds composed of individual fibrils less than 1000 nm in diameter. Each of these materials was then electrospun into a cylindrical construct with a 2 mm inside diameter with a wall thickness of 200–250 μm. Electrospun scaffolds of collagen were rapidly, and densely, infiltrated by interstitial and endothelial cells when implanted into the interstitial space of the rat vastus lateralis muscle. Functional blood vessels were evident within 7 days. In contrast, implants composed of electrospun gelatin or the bio-resorbable synthetic polymers were not infiltrated to any great extent and induced fibrosis. Our data suggests that topographical features, unique to the electrospun collagen fibril, promote cell migration and capillary formation.
Abstract The inability of the adult mammalian retina to regenerate can be partly attributed to the expression of injury-induced inhibitory extracellular matrix (ECM) and cell adhesion molecules. In ...particular, photoreceptor degeneration stimulates deposition of the inhibitory ECM proteins neurocan and CD44 at the outer limits of the dystrophic retina, where they act as a barrier against cellular migration and axonal extension. We have previously shown that degradation of these molecules, via induction of MMP2, promotes host–donor integration and retinal repopulation following transplantation. Here we present a biodegradable/biocompatible polymer scaffold that has the ability to deliver MMP2, in conjunction with retinal progenitor cells, directly to the site of retinal injury in an attempt to enhance cellular integration and promote retinal repopulation. Pre-activated MMP2, loaded into a PLGA polymer, maintained its activity throughout polymer fabrication and hydrolysis. Following delivery, significant degradation of CD44 and neurocan from the outer limits of the dystrophic retina, without further disruption of retinal architecture, was observed. As a result, the number of retinal progenitor cells that migrated beyond the glial barrier into the degenerating host increased significantly. These cells took up residence in the retinal outer nuclear layer, adopted appropriate photoreceptor morphology and expressed the mature photoreceptor markers recoverin and rhodopsin. Thus, we have created a cell delivery platform that upon transplantation provides controlled release of active-MMP2 directly to the site of retinal injury, stimulating inhibitory ECM barrier removal and enhancement of stem cell integration and retinal repopulation.
Deformation of polyethylene by bidirectional cold rolling was investigated. The objective was to better understand the evolution of the hierarchical structure with thickness reduction and the effect ...on mechanical properties. At a 60% thickness reduction, the thickness recovery after rolling peaked, and the density and crystallinity decreased rapidly resulting in greater optical clarity. Tensile specimens were deformed in uniaxial tension, and it was observed that the yield mechanism shifted from necking and whitening to a diffuse yielding process with extent of rolling. Concomitant greater work hardening, fracture stress, and elastic recovery were also observed upon fracture at both 25 °C and −40 °C. Scanning electron micrographs of the fracture surface revealed discrete buckled microlayers. Furthermore, dynamic mechanical analysis (DMA) revealed the loss tangent peaks associated with the beta and alpha relaxations shifted, suggesting that dilatation rather than compaction was the dominant mode of deformation at 60% thickness reduction.
Display omitted
•Solid HDPE was deformed by shear in compressive stress state by cold roll milling.•Crystallinity from differential scanning calorimetry underestimated biphasic model.•Small-angle x-ray scattering and dynamic analysis suggested lamellar fragmentation.•Wide-angle x-ray scattering, scanning electron micrographs saw planar orientation.•Two deformation regimes defined by plastic deformation of crystals and amorphous.
The first results of electrospinning fibrinogen nanofibers for use as a tissue-engineering scaffold, wound dressing, or hemostatic bandage are reported. Structures composed of fibrinogen fibers with ...an average diameter of 80−700 nm were electrospun from solutions composed of human or bovine fibrinogen fraction I dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol and minimal essential medium (Earle's salts). In summary, the electrospinning process is a simple and efficient technique for the fabrication of 3D structures composed of fibrinogen fibers, as would be present in the physiologic environment.
Electrospinning of Collagen Nanofibers Matthews, Jamil A; Wnek, Gary E; Simpson, David G ...
Biomacromolecules,
03/2002, Letnik:
3, Številka:
2
Journal Article
Recenzirano
Electrospinning is a fabrication process that uses an electric field to control the deposition of polymer fibers onto a target substrate. This electrostatic processing strategy can be used to ...fabricate fibrous polymer mats composed of fiber diameters ranging from several microns down to 100 nm or less. In this study, we describe how electrospinning can be adapted to produce tissue-engineering scaffolds composed of collagen nanofibers. Optimizing conditions for calfskin type I collagen produced a matrix composed of 100 nm fibers that exhibited the 67 nm banding pattern that is characteristic of native collagen. The structural properties of electrospun collagen varied with the tissue of origin (type I from skin vs type I from placenta), the isotype (type I vs type III), and the concentration of the collagen solution used to spin the fibers. Electrospinning is a rapid and efficient process that can be used to selectively deposit polymers in a random fashion or along a predetermined and defined axis. Toward that end, our experiments demonstrate that it is possible to tailor subtle mechanical properties into a matrix by controlling fiber orientation. The inherent properties of the electrospinning process make it possible to fabricate complex, and seamless, three-dimensional shapes. Electrospun collagen promotes cell growth and the penetration of cells into the engineered matrix. The structural, material, and biological properties of electrospun collagen suggest that this material may represent a nearly ideal tissue engineering scaffold.
The structure and proton conductivity of sulfonated styrene−ethylene copolymers have been studied. Conductivities in excess of 0.1 S/cm are obtained depending upon copolymer composition and ...sulfonation level. The dependence of conductivity on humidity has been measured and compared with that of Nafion and a partially sulfonated block copolymer. X-ray and neutron scattering studies suggest the presence of a bicontinuous network of hydrophilic and hydrophobic domains in water-swollen samples.
