Inner Surface Of Hollow Fibers Research Articles

Construction of PDMS@ZIF-8 composite membrane on PVDF hollow fiber inner surface for ultrafast ethanol/water separation

Construction of ultra-thin and defect-free separation membrane on inner surface of hollow fiber supports is significant but challenging for molecular separation. In this study, the highly permeable PDMS@ZIF-8/PVDF composite membranes were successfully fabricated upon the inner-surface of polyvinylidene fluoride (PVDF) hollow fiber membrane for pervaporation (PV) ethanol/water separation. The efficient preparation of hierarchical PDMS@ZIF-8/PVDF composite membranes benefited from the precise regulation of ZIF-8 layer through interfacial synthesis and sequential coating of PDMS matrix. The thickness of the PDMS layer was only 16 ± 2 nm, which admirably eliminated the non-selective defects in ZIF-8 layer. Owning to the optimal combination of MOF layer and ultra-thin polymer layer, the as-prepared membrane exhibited the excellent ethanol flux of 1.34 kg m−2 h−1 with an ethanol concentration in permeate of 31.3 wt% for separating 5 wt% ethanol aqueous solution at 40 °C. The separation performance of the resultant membrane was superior to that of the other ethanol selective PV membranes. These findings herein provided a new way for preparing high-performance hollow fiber composite membranes for PV separation.

Aquaporin-based membranes made by interfacial polymerization in hollow fibers: Visualization and role of aquaporin in water permeability

Aquaporins are water channel proteins with high permeability and solute rejection, making them ideal components for the preparation of desalination biomimetic membranes. In one strategy, E. coli aquaporin Z (AqpZ) proteoliposomes are immobilized in a polyamide layer formed by interfacial polymerization at the inner surface of hollow fibers. However, once polymerization occurs, the system is almost a black box where it is difficult to disentangle the relative contribution to performance of (i) water permeation through AqpZ channels and (ii) the possible modification of the properties or structure of the polymer layer by the mere presence of protein and lipid. Indeed, the fate of protein and lipid once the polymer is formed, and how much of it is actually used, is under debate. Also, the performance of these modules has been reported to be stable over several months. This is intriguing because of the expected degradation of functional AqpZ and lipid with time. Herein, we used lipid and AqpZ, both fluorescently labeled, to unequivocally localize both components only at the inner surface of the hollow fibers. To characterize module performance, we tested about 30 half-inch modules containing five hollow fibers each. Those reconstituted with wild type AqpZ produced higher permeability (∼8.5 ± 0.9 LMH/bar) than those reconstituted with AqpZ mutant (R189A) (∼5.6 ± 1.7 LMH/bar) or lipid-only liposomes (3.7 ± 1.1 LMH/bar). However, while these differences are significant, they are smaller than expected from the comparison of relative permeabilities of membranes incorporating wild-type AqpZ, R189A mutant and only-lipid. In addition, we show that in a five-month long experiment, performance of two of these modules showed only minor deterioration, if any, which is not consistent with the observed rapid degradation of proteoliposomes at room temperature. Overall, these data obtained in this set-up suggests that although both AqpZ and lipid are localized at the inner of the hollow fibers, they mainly behave as additives that modify the properties of the robust polyamide layer. A small contribution of AqpZ channel activity to module performance is possible, but to be significant it would require full coverage and a higher protein density in the proteoliposomes, which at present cannot be achieved in the current protocol.

Polydimethylsiloxane (PDMS) Composite Membrane Fabricated on the Inner Surface of a Ceramic Hollow Fiber: From Single-Channel to Multi-Channel

Abstract The fabrication of a separation layer on the inner surface of a hollow fiber (HF) substrate to form an HF composite membrane offers exciting opportunities for industrial applications, although challenges remain. This work reports on the fabrication of a polydimethylsiloxane (PDMS) composite membrane on the inner surface of a single-channel or multi-channel ceramic HF via a proposed coating/cross-flow approach. The nanostructures and transport properties of the PDMS HF composite membranes were optimized by controlling the polymer concentration and coating time. The morphology, surface chemistry, interfacial adhesion, and separation performance of the membranes were characterized by field-emission scanning electron microscope (FE-SEM), attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, the nano-indentation/scratch technique, and pervaporation (PV) recovery of bio-butanol, respectively. The formation mechanism for the deposition of the PDMS layer onto the inner surface of the ceramic HF was studied in detail. The optimized inner surface of the PDMS/ceramic HF composite membranes with a thin and defect-free separation layer exhibited a high flux of ~1800 g·m−2·h−1 and an excellent separation factor of 35–38 for 1 wt% n-butanol/water mixtures at 60 °C. The facile coating/cross-flow methodology proposed here shows great potential for fabricating inner-surface polymer-coated HFs that have broad applications including membranes, adsorbents, composite materials, and more.

Investigation of Poly(ethersulfone)/Polyvinylpyrrolidone ultrafiltration membrane degradation by contact with sodium hypochlorite through FTIR mapping and two-dimensional correlation spectroscopy

It is well recognized that chlorine is responsible for aging of membrane materials. The goal of this study is to investigate the modifications of a commercial PES/PVP hollow fiber membrane exposed to hypochlorite solution at pH 7.5 by continuous filtration. Thanks to ATR-FTIR 2D Correlation Spectroscopy (2DCoS) analysis it was confirmed that PVP is oxidized into succinimide compound. 2DCoS analysis revealed the sequence order of PES/PVP membrane degradation: PVP oxidation is followed by the modifications of C-H cyclic structures and finally the formation of succinimide compounds. ATR-FTIR-microscopy mapping unveiled that PVP was mainly situated at the inner surface of hollow fibers exhibiting initially a 67 μm thickness layer. PVP layer disappearance was not homogenous versus the exposure dose suggesting the topochemical character of the PVP-chlorine reaction. Results demonstrate that advanced material characterization are key methodologies to understand membrane aging mechanisms.

Hollow fiber integrated microfluidic platforms for in vitro Co-culture of multiple cell types.

This study demonstrates a rapid prototyping approach for fabricating and integrating porous hollow fibers (HFs) into microfluidic device. Integration of HF can enhance mass transfer and recapitulate tubular shapes for tissue-engineered environments. We demonstrate the integration of single or multiple HFs, which can give the users the flexibility to control the total surface area for tissue development. We also present three microfluidic designs to enable different co-culture conditions such as the ability to co-culture multiple cell types simultaneously on a flat and tubular surface, or inside the lumen of multiple HFs. Additionally, we introduce a pressurized cell seeding process that can allow the cells to uniformly adhere on the inner surface of HFs without losing their viabilities. Co-cultures of lung epithelial cells and microvascular endothelial cells were demonstrated on the different platforms for at least five days. Overall, these platforms provide new opportunities for co-culturing of multiple cell types in a single device to reconstruct native tissue micro-environment for biomedical and tissue engineering research.

The preparation of zeolite NaA membranes on the inner surface of hollow fiber supports

Abstract Zeolite NaA membranes with excellent water/ethanol separation factors are successfully prepared on the inner surface of hollow fibers in a rotating autoclave for the first time. NaA/PES composite hollow fibers (CHF) are first used to investigate the effects of different synthesis conditions such as synthesis composition, synthesis time and synthesis method (static and dynamic) because there are uniform seed crystals on the inner surface of CHF supports. The seeded growth of zeolite NaA membranes on the inner surface of alumina hollow fibers (AHF) supports (1.0 mm i.d.) are carried out at 373 K. The optimal synthesis conditions obtained are applied to AHF supports to investigate the effects of seed suspensions by the dip-coating seeding method. The effects of the synthesis conditions for AHF supports on the membrane morphology and properties are also investigated. The synthesized membranes are characterized by scanning electron microscopy. The separation properties of the membranes are evaluated by pervaporation of 90 wt.% ethanol/water mixture at 348 K. Zeolite membranes with high separation factor up to 10,000 can be obtained under the conditions: synthesis composition of 7.5Na 2 O:2SiO 2 :Al 2 O 3 :600H 2 O, synthesis time of 5 h, using a rotating autoclave (30 rpm).

Atmospheric pressure dielectric barrier microplasmas inside hollow-core optical fibers

An atmospheric glow microplasma is generated in the hollow core of microns-thick optical fibers (>1 m long) when the sinusoidal voltage with a peak voltage of 5 kV and a frequency of 5.0 kHz is applied to these microelectrodes along the outside of optical fibers. Measurements show that the atmospheric glow microdischarge consists of current pulses with amplitudes of tens of amperes and pulse widths of several microseconds. Atmospheric surface barrier discharges are formed along the inner surface of hollow optical fibers between adjacent microelectrodes, which results in the pulsed glow microdischarges. By flowing octafluorocyclobutane (c-C4F8)/helium (He) mixtures through the hollow-core optical fiber, fluorocarbon polymer (FCP) coatings are deposited on the inner surface of the > 1 m long optical fiber. Analysis indicates that the glow microdischarge contributes to the uniform deposition of FCP coatings on the inner surface of hollow fibers. The in situ optical emission measurements show that various carbon-containing species, such as CF2, CN, and C2 are generated in the visually uniform microplasmas. The discharge mechanism is discussed based on the I-V and optical emission measurements and FCP coating characterizations.

Development of bioartificial renal tubule devices with lifespan-extended human renal proximal tubular epithelial cells

The bioartificial renal tubule device is a cell therapy system for renal failure. The major obstacle in the development of the bioartificial renal tubule device is the obtainment of a large number of viable renal tubule cells to seed on the inner surface of hollow fibers. Although our previous studies had used a transformed cell line, they may be dangerous for clinical uses. Therefore, different approaches to amplify renal proximal tubular epithelial cells (RPTEC) in culture without oncogenes, vectors and carcinogens have been required. The limitation of the replicative lifespan of human RPTEC, which is ∼12 population doublings (PDs), was extended by invalidating messenger RNA of cell cycle-related genes with antisense oligonucleotide or small interfering RNA (siRNA). Periodic transfection of siRNA to a tumor suppressor p53 or a cyclin-dependent kinase inhibitor p16(INK4a) extended the lifespan by 33 and 63 PDs, respectively, in 3 months of culture. The siRNA-mediated lifespan extension was controllable because cell division ceased within 2 weeks after the transfection was discontinued. Expressions of γ-glutamyltransferase 1 and glucose transporter 1 were recovered in siRNA-transfected RPTEC cultured on porous membranes. Bioartificial renal tubule devices (0.8 m(2)) constructed with these cells showed reabsorption of water (122.3 ± 4.2 mL/30 min), sodium (18.1 ± 0.7 mEq/30 min) and glucose (121.7 ± 4.4 mg/30 min) after 1 week of circulation. Furthermore, β2-microglobulin and pentosidine were metabolized by RPTEC in mini-devices (65 cm(2)) within 48 h of circulation. These approaches enabled us to yield a high enough number of RPTEC for construction of bioartificial renal tubule devices repeatedly. Lifespan-extended RPTEC could recover their specific characteristics by culturing on porous membranes, and bioartificial renal tubule devices constructed with these cells showed good performances of reabsorption and metabolism. A large number of human renal tubular cells required for construction of the bioartificial renal tubule device were prepared by extending the lifespan of the primary cells by invalidating mRNA of cell cycle-related genes. Constructed bioartificial renal tubule devices with lifespan-extended cells showed good performances of in vitro examination of reabsorption and metabolism. Requiring no oncogenes, vectors or cell cloning, the RNAi-mediated lifespan extension can help advance tissue-replacement therapy as well as basic research.

Dynamically formed inner skin hollow fiber polydimethylsiloxane/polysulfone composite membrane for alcohol permselective pervaporation

This work is concerned with the preparation of alcohol permselective inner skin hollow fiber composite membrane using a dynamic cross-flow coating method. The membranes were successfully prepared by dynamically coating polydimethylsiloxane (PDMS) on the inner surface of the polysulfone (PS) hollow fibers under a pressure-driven process. The strategy of alternating PDMS casting solution direction was firstly explored to ensure the formation of a uniform and defect-free selective layer. Subsequently, the effects of coating time, polymer concentration, and crosslink agent concentration on alcohol permselective performance were investigated. The appropriate conditions were: coating time, 60 min; PDMS concentration, 22.8 wt.%; and TEOS concentration, 1.5 wt.%. Under the given conditions, in the case of pervaporation separation of 8 wt.% ethanol–water mixture (50 °C), the membrane had a separation factor of 6.4 and a permeate flux of 265 g/(m 2 h), respectively. The pervaporation separation behavior of various alcohol/water mixtures with the alcohols being t-butanol, 2-propanol was also investigated. SEM, AFM and contact angle analyses confirmed the formation of selective layer on the inner surface of hollow fibers. Therefore, it indicates that the dynamic cross-flow coating technique is a unique approach to the construction of selective layer on porous hollow fiber substrates, which could emerge as a powerful technique for the preparation of a range of separation membranes.

Single-side hydrolysis of hollow fiber polyacrylonitrile membrane by an interfacial hydrolysis of a solvent-impregnated membrane

In this paper, a new method was proposed to improve the mechanical strength and flux of polyacrylonitrile (PAN)-based membrane by a single-side hydrolysis of hollow fiber PAN substrate membrane. A non-water miscible solvent of cyclohexane was firstly incorporated into membrane pores to form cyclohexane-impregnated hollow fiber PAN membrane by stepwise solvent replacement method. Alkaline aqueous solution was then fed into lumen side to introduce interfacial hydrolysis reaction on the inner surface of hollow fiber by using the cyclohexane/water phase interface. After the reaction, the cyclohexane incorporated was displaced by water to remain the pore pathway. The ATR-FTIR and EDX analyses confirmed that the alkaline hydrolysis did not occur in the membrane pores. SEM and AFM were also conducted to further understand the microtopographical changes on membrane surfaces. During the assembly of PAN-based polyelectrolyte pervaporation composite membranes, both flux and mechanical strength was highly improved by using single-side hydrolysis of PAN substrate membrane while the selectivity was still kept at a relatively high level.

CD133+Endothelial Progenitor Cells as a Potential Cell Source for a Bioartificial Glomerulus

Development of a bioartificial glomerulus, a hemofilter in which the inner surface of hollow fibers is endothelialized, requires expandable, nonimmunogenic, antithrombogenic, and highly permeable endothelial cells. We used human umbilical cord blood CD133(+) endothelial progenitor cells (EPCs) to evaluate the feasibility of application of EPCs for bioartificial glomerulus. Numbers of adhered CD133(+) EPCs (adhered EPCs) was approximately 25 to 30 times as great in the expansion culture group as in the non-expansion group. Adhered EPCs had endothelial cell features, including the expression of CD31, Kinase domain region, von Willebrand factor, vascular endothelial-cadherin, positive for Ulex europeus agglutinin I staining, and up-take of acetylated low-density lipoprotein. Adhered EPCs secreted 6-keto-prostaglandin F(1alpha) identically to that secreted by human umbilical vein endothelial cells (HUVECs). The cells also expressed messenger RNA for phospholipase A(2), cyclooxygenase (COX)-1, COX-2, prostaglandin I(2) synthase, tissue plasminogen activator, and thrombomodulin (TM). TM protein in adhered EPCs properly activated protein C. Scanning electron microscopy revealed the suppression of platelet adhesion and aggregation on the surface of cell monolayer. Adhered EPCs treated with 50 microg/mL of cytochalasin B induced a larger diameter and a greater number of fenestrae, subsequently producing significantly more ultrafiltration than the non-treated cell. These results suggest that CD133(+) EPCs would potentially be applicable in bioartificial glomerulus.

Enhancement of permeability in endothelial cells for the development of an antithrombogenic bioartificial hemofilter

For the development of an antithrombogenic bioartificial hemofilter, in which the inner surface of hollow fibers is lined by endothelial cells, it is essential to increase the permeability of the cells in order to achieve a sufficient ultrafiltrate. We tried to increase it by using an actin microfilament polymerization inhibitor, cytochalasin B (CyB). Fifty microg/mL CyB was added for 2 h to the culture medium of confluent rat glomerular endothelial cells (RGEC) and human umbilical vein endothelial cells (HUVEC). Under the 130 mmHg hydrostatic pressure, the CyB-treated group produced significantly more ultrafiltration than the non-treated control group and this increase was maintained for at least 7 days. Horseradish peroxidase (HRP) permeability acutely and reversibly increased in the CyB-treated group compared with the non-treated control group. Scanning electron microscopy revealed a larger average diameter and increased number of fenestrae on the CyB-treated endothelial cells, compared with the non-treated cells. This phenomenon also lasted for at least 7 days. The platelet adherence test showed that CyB did not deteriorate the antithrombogenic property of endothelial cells. These results indicate that CyB is potentially applicable for the enhancement of endothelial cell permeability in an antithrombogenic bioartificial hemofilter.

High-intensity pulse compression with plasma nonlinearity

Ultrashort pulses are very important in the research of high field physics. The scheme of extracavity compression in gas-filled hollow fibers has been used to generate 0.1TW/5fs laser pulses successfully. However, the ionization of medium limits the energy of pulses to be compressed in hollow fibers filled with noble gases. Gabriel Tempea et al suggested that plasma nonlinearity can be used to compress the pulse. In this paper, we investigate the possibility of compressing a 50fs, 10mJ pulse with this scheme. We discuss the pulse compression when the ionization of the inner surface of a hollow fiber occurs. Based on numerical simulation, we find that the pulse can be compressed to 5fs after its propagation through the hollow fiber filled with noble gases. The spectral width of the pulse exceeds 200THz and its phase distribution is near the quadratic curve, which can be phase-compensated easily by using chirped mirrors. Also we find that the pulse compression is very sensitive to the gas density in the hollow fiber. The ionization of the inner surface of the large hollow fiber is dominant (about 20∼30%) for the energy loss comparing with the phase modulation due to neutral atoms. We find that a lower gas density is enough for the phase modulation, so the energy loss due to gas ionization is less pronouced.

Techsighting. Test tube kidneys.

Techsighting. Test tube kidneys.