Surface Of Hollow Fiber Membrane Research Articles

Self-assembly of rare-earth Anderson polyoxometalates on the surface of imide polymeric hollow fiber membranes potentially for organic pollutant degradation

In this study, the self-assembly of rare-earth Anderson polyoxometalates (POMs) on the surfaces of imide polymeric hollow fiber membranes was designed for fabrication of novel POMs-functionalized interfacial composite membranes. The rare-earth Anderson POM ([Gd(H2O)7Cr(OH)6Mo6O18]n) nanoparticles with controllable size and distribution were successfully constructed. Experimental results revealed that the self-assembly was a surface-induced growth process. The silanol groups on the membrane surfaces generated by the (3-aminopropyl)trimethoxysilane pretreatment were essential for the self-assembly process because of the potential hydrogen bonding (OH⋯POMs) and coordination bonding (OHGd) interactions. This work provided a simple but practical method not only for the fabrication of novel POMs-functionalized membranes, but also for the synthesis of POMs nanoarchitectures. In addition, the potential application of the as-prepared POMs-functionalized hollow fiber membranes in degradation of organic pollutant has also been explored. The idea of interfacial membrane contactor has been utilized for the catalytic wet air oxidation of phenol under mild conditions. A three-phase (gas/catalyst/liquid) interface was successfully built up, which enhanced the catalytic efficiency. It is anticipated that these novel POMs-functionalized membranes can promisingly be used as catalytic membrane contactors for wastewater treatment under mild conditions.

Acidic sweep gas with carbonic anhydrase coated hollow fiber membranes synergistically accelerates CO2 removal from blood

The use of extracorporeal carbon dioxide removal (ECCO2R) is well established as a therapy for patients suffering from acute respiratory failure. Development of next generation low blood flow (<500mL/min) ECCO2R devices necessitates more efficient gas exchange devices. Since over 90% of blood CO2 is transported as bicarbonate (HCO3−), we previously reported development of a carbonic anhydrase (CA) immobilized bioactive hollow fiber membrane (HFM) which significantly accelerates CO2 removal from blood in model gas exchange devices by converting bicarbonate to CO2 directly at the HFM surface. This present study tested the hypothesis that dilute sulfur dioxide (SO2) in oxygen sweep gas could further increase CO2 removal by creating an acidic microenvironment within the diffusional boundary layer adjacent to the HFM surface, facilitating dehydration of bicarbonate to CO2. CA was covalently immobilized onto poly (methyl pentene) (PMP) HFMs through glutaraldehyde activated chitosan spacers, potted in model gas exchange devices (0.0151m2) and tested for CO2 removal rate with oxygen (O2) sweep gas and a 2.2% SO2 in oxygen sweep gas mixture. Using pure O2 sweep gas, CA-PMP increased CO2 removal by 31% (258mL/min/m2) compared to PMP (197mL/min/m2) (P<0.05). Using 2.2% SO2 acidic sweep gas increased PMP CO2 removal by 17% (230mL/min/m2) compared to pure oxygen sweep gas control (P<0.05); device outlet blood pH was 7.38 units. When employing both CA-PMP and 2.2% SO2 sweep gas, CO2 removal increased by 109% (411mL/min/m2) (P<0.05); device outlet blood pH was 7.35 units. Dilute acidic sweep gas increases CO2 removal, and when used in combination with bioactive CA-HFMs has a synergistic effect to more than double CO2 removal while maintaining physiologic pH. Through these technologies the next generation of intravascular and paracorporeal respiratory assist devices can remove more CO2 with smaller blood contacting surface areas. Statement of SignificanceA clinical need exists for more efficient respiratory assist devices which utilize low blood flow rates (<500mL/min) to regulate blood CO2 in patients suffering from acute lung failure. Literature has demonstrated approaches to chemically increase hollow fiber membrane (HFM) CO2 removal efficiency by shifting equilibrium from bicarbonate to gaseous CO2, through either a bioactive carbonic anhydrase enzyme coating or bulk blood acidification with lactic acid. In this study we demonstrate a novel approach to local blood acidification using an acidified sweep gas in combination with a bioactive coating to more than double CO2 removal efficiency of HFM devices. To our knowledge, this is the first report assessing an acidic sweep gas to increase CO2 removal from blood using HFM devices.

Deacidification of crude palm oil using PVA-crosslinked PVDF membrane

Over recent years, there has been an explosive growth of interest in the development of alternative approaches for crude palm oil (CPO) refining. During a typical refinery process, free fatty acid (FFA) is one of the key objectionable impurities that need to be reduced if not completely removed from CPO in order to minimize their detrimental effects on the oil quality. Polyvinylidene fluoride (PVDF) membrane shows great potential in removing FFA from CPO owing to its hydrophobic properties, high mechanical strength and good thermal stability. However, low concentration of FFA in CPO, which is normally ranging from 3% to 5%, has hindered the capability of the membranes to separate the trace amount of FFA from the bulk. Thus, modification of PVDF membrane is essential to enhance the interaction between the membrane surface and FFA molecules, facilitating efficient FFA removal. In order to achieve this purpose in the present study, the outer surface of PVDF hollow fiber membranes was crosslinked with polyvinyl alcohol (PVA). Glutaraldehyde (GA) was used as a crosslinking agent to avoid the PVA dissolution. Despite the negligible morphological change observed in the resultant membranes upon PVA crosslinking, the contact angle has been significantly reduced in proportional to the concentration of PVA used for the crosslinking, suggesting the decrease in membrane hydrophobicity. Additionally, the average roughness of the crosslinked PVDF membranes increased with the increasing PVA concentration. The results obtained suggested that the PVDF hollow fiber crosslinked with 100ppm PVA exhibited the highest FFA rejection of 5.93% after 3h of operation. In addition, the membrane also showed good result in reducing the content of phosphorus in the permeate and partial reduction of its color intensity. This study served as the first attempt of CPO deacidification through UF membrane system without the addition of any chemical during the filtration process.

Thermo-responsive poly(N-isopropylacrylamide)-grafted hollow fiber membranes for osteoblasts culture and non-invasive harvest.

Hollow fiber membrane (HFM) culture system is one of the most important bioreactors for the large-scale culture and expansion of therapeutic cells. However, enzymatic and mechanical treatments are traditionally applied to harvest the expanded cells from HFMs, which inevitably causes harm to the cells. In this study, thermo-responsive cellulose acetate HFMs for cell culture and non-invasive harvest were prepared for the first time via free radical polymerization in the presence of cerium (IV). ATR-FTIR and elemental analysis results indicated that the poly(N-isopropylacrylamide) (PNIPAAm) was covalently grafted on HFMs successfully. Dynamic contact angle measurements at different temperatures revealed that the magnitude of volume phase transition was decreased with increasing grafted amount of PNIPAAm. And the amount of serum protein adsorbed on HFMs surface also displayed the same pattern. Meanwhile osteoblasts adhered and spread well on the surface of PNIPAAm-grafted HFMs at 37 °C. And Calcein-AM/PI staining, AB assay, ALP activity and OCN protein expression level all showed that PNIPAAm-grafted HFMs had good cell compatibility. After incubation at 20 °C for 120 min, the adhering cells on PNIPAAm-grafted HFMs turned to be round and detached after being gently pipetted. These results suggest that thermo-responsive HFMs are attractive cell culture substrates which enable cell culture, expansion and the recovery without proteolytic enzyme treatment for the application in tissue engineering and regenerative medicine.

Hollow fiber membrane modification with functional zwitterionic macromolecules for improved thromboresistance in artificial lungs.

Respiratory assist devices seek optimized performance in terms of gas transfer efficiency and thromboresistance to minimize device size and reduce complications associated with inadequate blood biocompatibility. The exchange of gas with blood occurs at the surface of the hollow fiber membranes (HFMs) used in these devices. In this study, three zwitterionic macromolecules were attached to HFM surfaces to putatively improve thromboresistance: (1) carboxyl-functionalized zwitterionic phosphorylcholine (PC) and (2) sulfobetaine (SB) macromolecules (mPC or mSB-COOH) prepared by a simple thiol-ene radical polymerization and (3) a low-molecular weight sulfobetaine (SB)-co-methacrylic acid (MA) block copolymer (SBMAb-COOH) prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. Each macromolecule type was covalently immobilized on an aminated commercial HFM (Celg-A) by a condensation reaction, and HFM surface composition changes were analyzed by X-ray photoelectron spectroscopy. Thrombotic deposition on the HFMs was investigated after contact with ovine blood in vitro. The removal of CO2 by the HFMs was also evaluated using a model respiratory assistance device. The HFMs conjugated with zwitterionic macromolecules (Celg-mPC, Celg-mSB, and Celg-SBMAb) showed expected increases in phosphorus or sulfur surface content. Celg-mPC and Celg-SBMAb experienced rates of platelet deposition significantly lower than those of unmodified (Celg-A, >95% reduction) and heparin-coated (>88% reduction) control HFMs. Smaller reductions were seen with Celg-mSB. The CO2 removal rate for Celg-SBMAb HFMs remained comparable to that of Celg-A. In contrast, the rate of removal of CO2 for heparin-coated HFMs was significantly reduced. The results demonstrate a promising approach to modifying HFMs using zwitterionic macromolecules for artificial lung devices with improved thromboresistance without degradation of gas transfer.

Selective interfacial synthesis of metal-organic frameworks on a polybenzimidazole hollow fiber membrane for gas separation.

Metal-organic frameworks (MOFs) have gained immense attention as new age materials due to their tuneable properties and diverse applicability. However, efforts on developing promising materials for membrane based gas separation, and control over the crystal growth positions on polymeric hollow fiber membranes still remain key challenges. In this investigation, a new, convenient and scalable room temperature interfacial method for growing MOFs (ZIF-8 and CuBTC) on either the outer or inner side of a polybenzimidazole based hollow fiber (PBI-BuI-HF) membrane surface has been achieved in a controlled manner. This was made possible by the appropriate selection of an immiscible solvent pair and the synthetic conditions. The growth of MOFs on the PBI-BuI-HF membrane by the interfacial method was continuous and showed an appreciable gas separation performance, conveying promise for their applicability.

Controllable modification of polymer membranes by LDDLT plasma flow: Antibacterial layer onto PE hollow fiber membrane module

A high-density and uniform network-like antibacterial poly(methacryloxyethyl benzyl dimethyl ammonium chloride) (PDMAE-BC) layer was covalently constructed onto polyethylene (PE) hollow fiber membrane surface in a module scale via long-distance and dynamic low-temperature (LDDLT) plasma flow irradiation and subsequent graft polymerization. After the stepwise construction using this surface plasma chemical engineering method, the hydrophilicity of membrane surface was enhanced greatly due to implantation of numerous oxygen-containing groups. Meanwhile, the surface microstructures and chemical composition distributions were more uniform along with the axial distance from the module inlet and no significant damage/etching in membrane surface was observed. And even more prominent, the obtained PDMAE-BC membrane module can effectively destroy and/or inhibit bacteria by antibacterial layer, thereby preventing the formation of biofilms. It not only exhibited a high antibacterial activity against Gram-negative Escherichia coli, but also had an antifouling property, an increased water flux and an easy-cleanability. The antibacterial efficacy reached about 92.4% in the membrane module with only 10 PE–PDMAE-BC fibers and can be further improved by increasing the fiber packing density. In the long-term running, both original and PDMAE-BC membrane modules showed a 100% rejection ratio for E. coli. Moreover, the PE–PDMAE-BC membrane module can endure general water rinsing with little loss of antibacterial efficacy and exhibited an excellent antibacterial stability. This PE–PDMAE-BC membrane module should prove useful in actual water (mainly drinking water and wastewater) treatment.

Surface modification of polysulfone hollow fiber membrane spun under different air-gap lengths for carbon dioxide absorption in membrane contactor system

Surface modified polysulfone (PSf) hollow fiber membranes (HFMs) using surface modifying macromolecules (SMM) were spun with air-gaps of 0–50cm. Morphological analysis of the prepared fibers were carried out using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The wetting resistances of the membranes were determined by critical water entry pressure (CEPw) and contact angle (CA) measurements. The HMFs were further subjected to CO2 capture by membrane contactor (MC) where water was used as absorbent. The test results indicated that both CEPw and CA showed a maximum value at 15cm air-gap distance. The maximum He permeation was also achieved at 15cm air-gap. The CO2 flux of prepared membranes showed a maximum of 4.79×10−3mol/m2s at the absorbent flow rate of 300ml/min. It was deduced that both He permeation and CO2 absorption flux were governed by the HFM surface porosity. The long-term stability test revealed the reduction of 25% in CO2 flux during the first 55h of operation for the PSf membrane prepared at 15cm air-gap. This study indicated that the surface modified HFMs prepared using an appropriate air-gap could be a promising option to increase membrane performance in MC systems.

Hemocompatibility evaluation of small elastomeric hollow fiber membranes as vascular substitutes.

One of the main challenges for clinical implementation of small diameter vascular grafts (SDVGs) is their limited hemocompatibility. Important design specifications for such grafts include features that minimize the long-term risks of restenosis, fouling, and thrombus formation. In our lab, we have developed elastomeric hollow fiber membranes (HFMs), using a phase inversion method, as candidates for SDVGs. Here, we present our results for in vitro hemocompatibility testing of our HFM under flow and static conditions. Our results showed that the polymer-based HFMs do not damage the integrity of human red blood cells (RBCs) as shown by their low hemolytic extent (less than 2%). When analyzed for blood cell lysis using lactate dehydrogenase (LDH) activity as an indicator, no significant differences were observed between blood exposed to our HFMs and uncoagulated blood. Analysis of protein adsorption showed a low concentration of proteins deposited on the surfaces of HFM after 24 h. Platelet adhesion profiles using human platelet-rich plasma (PRP) showed that a low level of platelets adhered to the HFMs after 24 h, indicating minimal thrombotic potential. Under the majority of conditions, no significant differences were observed between medical-grade polymers and our HFMs. Eventual optimization of hemocompatible elastomeric HFM vessel grafts could lead to improved tissue vascularization as well as vascularized, tissue-engineered scaffolds for organ repair.

Preparation of Sulfobetaine-Grafted PVDF Hollow Fiber Membranes with a Stably Anti-Protein-Fouling Performance.

Based on a two-step polymerization method, two sulfobetaine-based zwitterionic monomers, including 3-(methacryloylamino) propyl-dimethyl-(3-sulfopropyl) ammonium hydroxide (MPDSAH) and 2-(methacryloyloxyethyl) ethyl-dimethyl-(3-sulfopropyl) ammonium (MEDSA), were successfully grafted from poly(vinylidene fluoride) (PVDF) hollow fiber membrane surfaces in the presence of N,N′-methylene bisacrylamide (MBAA) as a cross-linking agent. The mechanical properties of the PVDF membrane were improved by the zwitterionic surface layers. The surface hydrophilicity of PVDF membranes was significantly enhanced and the polyMPDSAH-g-PVDF membrane showed a higher hydrophilicity due to the higher grafting amount. Compared to the polyMEDSA-g-PVDF membrane, the polyMPDSAH-g-PVDF membrane showed excellent significantly better anti-protein-fouling performance with a flux recovery ratio (RFR) higher than 90% during the cyclic filtration of a bovine serum albumin (BSA) solution. The polyMPDSAH-g-PVDF membrane showed an obvious electrolyte-responsive behavior and its protein-fouling-resistance performance was improved further during the filtration of the protein solution with 100 mmol/L of NaCl. After cleaned with a membrane cleaning solution for 16 days, the grafted MPDSAH layer on the PVDF membrane could be maintain without any chang; however, the polyMEDSA-g-PVDF membrane lost the grafted MEDSA layer after this treatment. Therefore, the amide group of sulfobetaine, which contributed significantly to the higher hydrophilicity and stability, was shown to be imperative in modifying the PVDF membrane for a stable anti-protein-fouling performance via the two-step polymerization method.

The Preparation of Polyamide/Polyacrylonitrile Composite Hollow Fiber Membranes for Pervaporation

This paper prepared polyamide (PA)/polyacrylonitrile (PAN) thin-film composite hollow fiber membranes via interfacial polymerization by using triethylenetetramine (TETA) and trimesoyl chloride (TMC) as the monomers and asymmetric PAN hollow fiber membrane as the substrate. The effect of hydrolysis of asymmetric PAN hollow fiber membranes on the chemical properties was investigated. The results showed that the chemical properties of PAN hollow fiber membranes were affected by hydrolysis. Moreover, the effects of PA thin film polymerized onto the inner and outer surface of asymmetric PAN hollow fiber membranes on pervaporation performances were also investigated. The results also revealed that the interfacial polymerized PA/PAN composite hollow fiber membranes that were polymerized onto the outer surface of asymmetric PAN hollow fiber membranes can be used in the pervaporation of aqueous alcohol solution.

Carbonic anhydrase immobilized on hollow fiber membranes using glutaraldehyde activated chitosan for artificial lung applications

Extracorporeal CO2 removal from circulating blood is a promising therapeutic modality for the treatment of acute respiratory failure. The enzyme carbonic anhydrase accelerates CO2 removal within gas exchange devices by locally catalyzing HCO3 (-) into gaseous CO2 within the blood. In this work, we covalently immobilized carbonic anhydrase on the surface of polypropylene hollow fiber membranes using glutaraldehyde activated chitosan tethering to amplify the density of reactive amine functional groups for enzyme immobilization. XPS and a colorimetric amine assay confirmed higher amine densities on the chitosan coated fiber compared to control fiber. Chitosan/CA coated fibers exhibited accelerated CO2 removal in scaled-down gas exchange devices in buffer and blood (115% enhancement vs. control, 37% enhancement vs. control, respectively). Carbonic anhydrase immobilized directly on hollow fiber membranes without chitosan tethering resulted in no enhancement in CO2 removal. Additionally, fibers coated with chitosan/carbonic anhydrase demonstrated reduced platelet adhesion when exposed to blood compared to control and heparin coated fibers.

The effect of re-generable silver nanoparticles/multi-walled carbon nanotubes coating on the antibacterial performance of hollow fiber membrane

We report a simple and efficient technique to deposit a re-generable coating of silver nanoparticles/multi-walled carbon nanotubes (Ag/MWNTs) on the surface of hollow fiber membrane by filtration. The resultant disinfection layer consists of porous and entangled network of Ag/MWNTs which is sufficiently stable for normal filtration operation. This physical attachment method resulted in insignificant water flux drop since chemical treatment or photon/plasma-assisted sputtering of the membrane was not involved. The composite membrane significantly reduces the formation of biofilm due to the presence of silver nanoparticles on the membrane surface and the leached silver ions. Upon depletion of the silver content due to silver leaching, the coating can be easily detached from the membrane surface and replenished with silver nanoparticles for recycle, while retaining good antimicrobial performances for prolonged use. The technique used in this study can be extended to other types of antimicrobial agents, the support materials and membranes.

Generating backwashable carbon nanotube mats on the inner surface of polymeric hollow fiber membranes

Porous carbon nanotube (CNT) mats adsorbed on flat sheet membranes have previously been shown to significantly improve fouling resistance and contaminant removal capabilities. Unfortunately, these CNT mats are easily disrupted by backwashing, severely limiting their value in commercial membranes. In this study, we describe how CNT mats, which are stable to backwashing, can be generated on the inner surface of hollow fiber membranes. Mat stability was determined from electron microscopy and by quantifying the mass of CNTs lost during aggressive backwashing, including hydraulic stress and exposure to harsh chemicals. Stable mats were also formed with powder activated carbon, demonstrating that the mat's stability is not a consequence of CNT properties, but rather the nature and directionality of the forces that these mats experience during backwashing. Compared to virgin membranes, CNT-modified membranes exhibited improved fouling resistance which was sustained through multiple backwashing cycles. Moreover, no measureable quantities of CNTs entered the permeate when natural organic matter was filtered through a CNT-modified membrane, indicating that CNTs will not be released into the permeate during filtration. Collectively, these findings indicate that CNT-modified membranes could positively impact the sustainability and performance of hollow fiber membranes being used in water purification.

The Modification of Polypropylene Hollow Fiber Membrane by Grafting with N,N’-Methylene-Bisac-Rylamide on the Surface

The surface of polypropylene hollow fiber membrane was modified with N,N’-methylene-bisac-rylamide (MBA) by the UV-irradiation, with the benzophenone (BP) as the light initiator. Fourier transform infrared spectrometer (FT-IR) was utilized to characterize copolymer composition. Field emission scanning electron microscopy (FE-SEM) was utilized to observe the fiber surface and section. Results showed that MBA was grafted on the surface of membrane. The influence was researched by changing the concentration of BP, MBA and irradiated time. Results showed that the grafting rate grew rapidly and then declined as the increase the BP concentration. The grafting rate increased at first as the MBA concentration increased, but decreased after the maximum. The grafting rate firstly increased slowly and then increased sharply with the irradiated time extended.

Hydrophilic modification of high-strength polyvinylidene fluoride hollow fiber membrane

The polyvinylidene fluoride (PVDF)/polyvinyl alcohol (PVA) polymer solutions were coated on the outer surface of PVDF matrix hollow fiber membrane. On the principle of the homogeneous-reinforced (HR) membrane technology, the reinforced PVDF/PVA (RFA) hollow fiber membranes prepared through the dry-wet spinning method. The performance of the RFA membranes varies with the PVA concentration in the polymer solution and is characterized in terms of pure water flux (PWF), porosity, a mechanical strength test, and morphology observations by a scanning electron microscopy (SEM). The results of this study indicate that PVA can apparently improve the hydrophilicity of the PVDF hollow fiber membranes. The growing enrichment of the hydrophilic components PVA on the membrane surface is determined by X-ray photoelectron spectroscopy. The RFA membranes have a favorable interfacial bonding between the coating layer (PVDF/PVA) and the matrix membrane (PVDF hollow fiber membrane), as shown by SEM. The elongation at break of the RFA membranes increases much more than that of the matrix membrane that is endowed with the better flexibility of the membrane performance. PWF decreases much more compared with that of the matrix membrane. The RFA membranes have a lower flux decline degree during the process of protein solution and ink solution filtration compared with that of the matrix membrane. POLYM. ENG. SCI., 54:276–287, 2014. © 2013 Society of Plastics Engineers

Interaction of Serum Proteins with Surface of Hemodialysis Fiber Membranes

The poly(vinyl pyrrolidone)-covered hydrophilic surface of hollow-fiber membranes (fiber membrane, hereafter) for hemodialysis was mechanically probed using modified tips on an atomic force microscope (AFM) with covalent crosslinkers and several types of serum protein. The retraction part of many of the force extension (F–E) curves obtained with AFM tips coated with serum albumin had a long and smooth extension up to 200–300 nm indicating forced elongation of poly(vinyl pyrrolidone) chains. When fibrinogen-coated tips were used, long extension F–E curves up to 500 nm with multiple peaks were obtained in addition to smooth curves most likely reflecting the unfolding of fibrinogen molecules. The results indicated that individual polymer chains had a significant affinity toward serum proteins. The adhesion frequency of tips coated with serum proteins was lower on the poly(vinyl pyrrolidone) surface than on the uncoated hydrophobic polysulfone surface.

Interaction of Serum Proteins with Surface of Hemodialysis Fiber Membranes

The poly(vinyl pyrrolidone)-covered hydrophilic surface of hollow-fiber membranes (fiber membrane, hereafter) for hemodialysis was mechanically probed using modified tips on an atomic force microscope (AFM) with covalent crosslinkers and several types of serum protein. The retraction part of many of the force extension (F–E) curves obtained with AFM tips coated with serum albumin had a long and smooth extension up to 200–300 nm indicating forced elongation of poly(vinyl pyrrolidone) chains. When fibrinogen-coated tips were used, long extension F–E curves up to 500 nm with multiple peaks were obtained in addition to smooth curves most likely reflecting the unfolding of fibrinogen molecules. The results indicated that individual polymer chains had a significant affinity toward serum proteins. The adhesion frequency of tips coated with serum proteins was lower on the poly(vinyl pyrrolidone) surface than on the uncoated hydrophobic polysulfone surface.

Two-step ultrafiltration of rhamnolipids using PSU-g-PEG membrane

Abstract The practical application of two-step ultrafiltration in industry has been limited by severe membrane fouling and the need for a large ethanol dose. To develop an antifouling membrane in two-step ultrafiltration of rhamnolipids from cell-free culture broth, this study evaluated the possibility of using polysulfone-g-polyethylene glycol (PSU-g-PEG), a polysulfone (PSU) hollow-fiber membrane surface modified by polyethylene glycol (PEG). Compared with the commercially available ultrafiltration hollow-fiber membrane PSU, PSU-g-PEG sustained a higher efficiency and maintained better antifouling property in operation. After further optimization of operation conditions (pH and ethanol concentration), over 98% of rhamnolipids were retained in the first ultrafiltration step by the PSU-g-PEG membrane and 87% of the retained rhamnolipids permeated the membrane in the second ultrafiltration. Moreover, the water flux of a treated membrane could be restored to 93% of its initial flux by a regular flush and could be completely recovered by a subsequent overnight immersion. Interestingly, the PSU-g-PEG membrane sustained its high separation efficiency and good antifouling property after extremely long operation (7 h) and seven consecutive operations. These results indicate that the PSU-g-PEG membrane has a large potential for industrial application in recovering rhamnolipids from cell-free culture broth.

Immobilized carbonic anhydrase on hollow fiber membranes accelerates CO2 removal from blood

Current artificial lungs and respiratory assist devices designed for carbon dioxide removal (CO(2)R) are limited in their efficiency due to the relatively small partial pressure difference across gas exchange membranes. To offset this underlying diffusional challenge, bioactive hollow fiber membranes (HFMs) increase the carbon dioxide diffusional gradient through the immobilized enzyme carbonic anhydrase (CA), which converts bicarbonate to CO(2) directly at the HFM surface. In this study, we tested the impact of CA-immobilization on HFM CO(2) removal efficiency and thromboresistance in blood. Fiber surface modification with radio frequency glow discharge (RFGD) introduced hydroxyl groups, which were activated by 1M CNBr while 1.5M TEA was added drop wise over the activation time course, then incubation with a CA solution covalently linked the enzyme to the surface. The bioactive HFMs were then potted in a model gas exchange device (0.0084 m(2)) and tested in a recirculation loop with a CO(2) inlet of 50mmHg under steady blood flow. Using an esterase activity assay, CNBr chemistry with TEA resulted in 0.99U of enzyme activity, a 3.3 fold increase in immobilized CA activity compared to our previous method. These bioactive HFMs demonstrated 108 ml/min/m(2) CO(2) removal rate, marking a 36% increase compared to unmodified HFMs (p < 0.001). Thromboresistance of CA-modified HFMs was assessed in terms of adherent platelets on surfaces by using lactate dehydrogenase (LDH) assay as well as scanning electron microscopy (SEM) analysis. Results indicated HFMs with CA modification had 95% less platelet deposition compared to unmodified HFM (p < 0.01). Overall these findings revealed increased CO(2) removal can be realized through bioactive HFMs, enabling a next generation of more efficient CO(2) removal intravascular and paracorporeal respiratory assist devices.