Electrospun Liquid-Infused Membranes for Emulsified Oil/Water Separation.

From an environmental perspective, microfiltration membranes are attractive for the separation of emulsified oils from contaminated water. However, fouling of the membrane is a major drawback of the technology. "Liquid-infused membranes" (LIMs) have the potential to eliminate membrane fouling. Here, we demonstrate the practical application of LIMs for the separation of oil from a stable oil-in-water emulsion and characterize their resistance to fouling. The base membrane is an electrospun nonwoven fibrous layer of the fluorinated copolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP). The surface energy of the PVDF-co-HFP fibers was lowered by the covalent attachment of a fluorinated silane (PFOCTS), and then, the membrane was infused with a perfluoropolyether. The membrane was then challenged with model emulsions of dodecane in water in a cross-flow configuration. This PFOCTS-modified LIM showed better infused liquid stability, permeation selectivity, higher permeate flux than the unmodified LIM, and better anti-fouling properties than the bare membrane without infused liquid. We also examine the mechanism for transport of the dispersed oil phase through the liquid-infused membrane. We find a linear relationship between the dodecane flux and dodecane concentration in the feed and a higher dodecane flux through the PFOCTS-modified membrane than the unmodified one, which suggests that the capture of dodecane droplets from the feed plays an important role in determining the overall rate of permeation. Other factors such as lower viscosity of the infused liquid, larger pore size, and higher operating pressure also improved the permeate flux through the LIMs. Overall, this work provides some guidelines on the design of composite membranes comprising infused liquids and the choice of operating conditions for the filtration process.

Conductive, Acid-Doped Polyaniline Electrospun Nanofiber Gas Sensing Substrates Made Using a Facile Dissolution Method.

A novel dissolution method that allows for the total solvation of high-concentration, high-molecular-weight polyaniline (PANi) doped with (+)-camphor-10-sulfonic acid (CSA) is reported. Preparation of 12-16 wt % 65,000 Da PANi solutions in N,N-dimethylformamide is achievable using a simple one-pot method. Doped polyaniline solutions in common organic solvents were processed into nanofibers using a convenient single-nozzle electrospinning technique. The electrospinning of PANi-CSA into nanofibrous membranes generated substrates that were subsequently employed in colorimetric gas sensing. These substrates demonstrated linearity of response upon exposure to 50-5500 ppm ammonia at ambient (50 ± 10% RH) and high (80% RH) humidity.

Rheology of Crystallizing LLDPE.

Polymer crystallization occurs in many plastic manufacturing processes, from injection molding to film blowing. Linear low-density polyethylene (LLDPE) is one of the most commonly processed polymers, wherein the type and extent of short-chain branching (SCB) may be varied to influence crystallization. In this work, we report simultaneous measurements of the rheology and Raman spectra, using a Rheo-Raman microscope, for two industrial-grade LLDPEs undergoing crystallization. These polymers are characterized by broad polydispersity, SCB and the presence of polymer chain entanglements. The rheological behavior of these entangled LLDPE melts is modeled as a function of crystallinity using a slip-link model. The partially crystallized melt is represented by a blend of linear chains with either free or crosslinked ends, wherein the crosslinks represent attachment to growing crystallites, and a modulus shift factor that increases with degree of crystallinity. In contrast to our previous application of the slip-link model to isotactic polypropylene (iPP), in which the introduction of only bridging segments with crosslinks at both ends was sufficient to describe the available data, for these LLDPEs we find it necessary to introduce dangling segments, with crosslinks at only one end. The model captures quantitatively the evolution of viscosity and elasticity with crystallization over the whole range of frequencies in the linear regime for two LLDPE grades.

A photoactivated nanofiber graft material for augmented Achilles tendon repair.

BACKGROUND AND OBJECTIVE: Suture repair of Achilles tendon rupture can cause infection, inflammation and scarring, while prolonged immobilization promotes adhesions to surrounding tissues and joint stiffness. Early mobilization can reduce complications provided the repair is strong enough to resist re-rupture. We have developed a biocompatible, photoactivated tendon wrap from electrospun silk (ES) to provide additional strength to the repair that could permit early mobilization, and act as a barrier to adhesion formation. STUDY DESIGN/MATERIAL AND METHODS: ES nanofiber mats were prepared by electrospinning. New Zealand white rabbits underwent surgical transection of the Achilles tendon and repair by: (a) SR: standard Kessler suture + epitendinous suture (5-0 vicryl). (b) ES/PTB: a single stay suture and a section of ES mat, stained with 0.1% Rose Bengal (RB), wrapped around the tendon and bonded with 532 nm light (0.3 W/cm(2) , 125 J/cm(2) ). (c) SR + ES/PTB: a combination of (a) and (b). Gross appearance, extent of adhesion formation and biomechanical properties of the repaired tendon were evaluated at Days 7, 14, or 28 post-operatively (n = 8 per group at each time point). RESULTS: Ultimate stress (US) and Young's modulus (E) in the SR group were not significantly different from the ES/PTB group at Days 7 (US, P = 0.85; E, P = 1), 14 (US, P = 0.054; E, P = 1), and 28 (US, P = 0.198; E, P = 0.12) post-operatively. Adhesions were considerably greater in the SR group compared to the ES/PTB group at Days 7 (P = 0.002), 14 (P < 0.0001), and 28 (P < 0.0001). The combination approach of SR + ES/PTB gave the best outcomes in terms of E at 7 (P < 0.016) and 14 days (P < 0.016) and reduced adhesions compared to SR at 7 (P < 0.0001) and 14 days (P < 0.0001), the latter suggesting a barrier function for the photobonded ES wrap. CONCLUSION: Photochemical sealing of a ES mat around the tendon repair site provides considerable benefit in Achilles tendon repair. Lasers Surg. Med. 44: 645-652, 2012. © 2012 Wiley Periodicals, Inc.

Free surface electrospinning of fibers containing microparticles.

Many materials have been fabricated using electrospinning, including pharmaceutical formulations, superhydrophobic surfaces, catalysis supports, filters, and tissue engineering scaffolds. Often these materials can benefit from microparticles included within the electrospun fibers. In this work, we evaluate a high-throughput free surface electrospinning technique to prepare fibers containing microparticles. We investigate the spinnability of polyvinylpyrrolidone (PVP) solutions containing suspended polystyrene (PS) beads of 1, 3, 5, and 10 µm diameter in order to better understand free surface electrospinning of particle suspensions. PS bead suspensions with both 55 kDa PVP and 1.3 MDa PVP were spinnable at 1:10, 1:5, and 1:2 PS:PVP mass loadings for all particle sizes studied. The final average fiber diameters ranged from 0.47 to 1.2 µm and were independent of the particle size and particle loading, indicating that the fiber diameter can be smaller than the particles entrained and can furthermore be adjusted based on solution properties and electrospinning parameters, as is the case for electrospinning of solutions without particles.

Electrospinning Bombyx mori silk with poly(ethylene oxide).

Electrospinning for the formation of nanoscale diameter fibers has been explored for high-performance filters and biomaterial scaffolds for vascular grafts or wound dressings. Fibers with nanoscale diameters provide benefits due to high surface area. In the present study we explore electrospinning for protein-based biomaterials to fabricate scaffolds and membranes from regenerated silkworm silk, Bombyx mori, solutions. To improve processability of the protein solution, poly(ethylene oxide) (PEO) with molecular weight of 900,000 was blended with the silk fibroin. A variety of compositions of the silk/PEO aqueous blends were successfully electrospun. The morphology of the fibers was characterized using high-resolution scanning electron microscopy. Fiber diameters were uniform and less than 800 nm. The composition was estimated by X-ray photoelectron spectroscopy to characterize silk/PEO surface content. Aqueous-based electrospining of silk and silk/PEO blends provides potentially useful options for the fabrication of biomaterial scaffolds based on this unique fibrous protein.