Coagulation Medium Research Articles

THE INFLUENCE OF PEG MOLECULAR WEIGHT ON MORPHOLOGIES AND PROPERTIES OF PVDF ASYMMETRIC MEMBRANES

The preparation and properties of asymmetric poly(vinyldiene fluoride) (PVDF) membranes are described in this study. Membranes were prepared from a casting solution of PVDF, N, N-dimethylacetamide (DMAc) solvent and water-soluble poly(ethylene glycol) (PEG) additives by immersing them in water as coagulant medium. Experiments showed that when PEG molecular weight increased, the changes in the resultant membranes' morphologies and properties showed a transition point at PEG6000. This indicated that PEG with a relatively low molecular weight was used as a pore-forming agent to enhance pure water flux and reduce solute rejection of membranes, but PEG was used as a pore-reducing agent with a further increment of PEG molecular weight to result in pure water flux decreasing and solute rejection increasing. Finally, combined with the precipitation rates of different membrane-forming systems, the membrane formation mechanism describing PEG mobility was discussed extensively basing on the length changes of PEG molecular chains and the affinity between PEG and casting solution. The results offered a better understanding of effects of PEG additives on membrane structure and properties.

Structure and gas permeability of asymmetric polyimide membranes made by dry–wet phase inversion: Influence of alcohol as casting solution

AbstractIn this article, we have reported the influence of alcohol as a casting solution on the structure and the gas permeability of asymmetric polyimide membranes made by dry–wet phase inversion. The apparent skin layer thickness of the asymmetric membrane decreased with an increase in molecular weight of the alcohol, and the thicknesses of the membranes made from methanol, ethanol, propanol, and butanol were 250, 120, 61, and 31 nm, respectively. We found that χ12 as an interaction parameter of solvent–nonsolvent had a significant influence on the phase inversion occurring in the coagulant medium. On the other hand, the gas permeance and the gas selectivity in the asymmetric membranes increased with the increasing molecular weight of the alcohol. We believe that a more packed structure formed in the asymmetric polyimide membrane with a thinner surface skin layer is also responsible for the thickness‐dependence of the gas selectivity obtained in this study. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2739–2746, 2007

Effects of Bipolar Radiofrequency on the Human Meniscus: A Comparative Study Between Patients Younger and Older Than 40 Years Old (SS-45)

Bipolar radiofrequency is frequently used in arthroscopic surgery. It provides excellent intraarticular hemostasis, debridement and shrinkage of soft tissues. Although extensively used in meniscal surgery, there are few studies that report the ultrastructural effect of bipolar radiofrequency on the human meniscus. Furthermore, it is not clear if there is any difference between applying the same amount of energy on younger versus older menisci. The main objective of our study was to evaluate the effects of bipolar radiofrequency applied to the human meniscus in 4 differents intensities and compare the results between patients younger and older than 40 y.o. Our study shows the effects of four different magnitudes of bipolar radiofrequency, commonly used in knee arthroscopic surgery: coagulation medium and high, vaporization intensities 5 and 7. Each magnitude was applied for 3 seconds on 30 human menisci resected from patients between 14 and 84 years old. The menisci were then divided in two groups: younger and older than 40 years old, and studied macroscopically, microscopically and by electronic microscopy. Thermal necrosis was found between m (D.S. 740) andμm from the meniscal surface, with an average of 1700μ0 and 4000 was significantly higher on the vaporization than the coagulation group (p < 0.001). We found significative differences between patients younger or older than 40 years old in groups zone 2 and 3 (zone 2 p=0.038 and zone 3 p=0.044) We concluded that although bipolar radiofrequency can cause deep necrosis (up to m) on the human meniscus, this effect depends on the magnitude of the μ4000 energy applied and is higher when we applied medium intensity in older patients. KEY WORDS: Radiofrequency – Knee arthroscopy – Meniscus.

Preparation of chitosan microfibres using electro-wet-spinning and their electroactuationproperties

Submicron chitosan fibres were prepared using an electro-wet-spinning process. Thechitosan solution was ejected into a coagulation medium containing differentconcentrations of ethyl alcohol in aqueous sodium hydroxide (0, 30, 50 and 70% (v/v)).Submicron chitosan fibres were obtained using a coagulation medium containing 50%(v/v) of ethyl alcohol in an applied electric field of 15 kV with a 10 cm spinningdistance. The density of the coagulation medium controlled the uniformity of theresulting fibres. When a swollen chitosan fibre hydrogel was placed between a pairof electrodes, it contracted in an applied electric field and showed a stepwisecontraction behaviour that depended on the magnitude of the electrical stimulus.Chitosan fibre hydrogels showed a fast and reversible electroactuation under lowapplied potentials. This type of fibre has potential application in artificial muscles.

Alginate microparticles prepared by spray–coagulation method: Preparation, drug loading and release characterization

A spray–coagulation method was developed for the preparation of large scale of porous alginate microparticles. The effect of three variables on porosity was evaluated: (1) alginate solution concentration (2) the concentration of CaCl 2 in the coagulation medium and (3) the ratio of guluronic acid to manuronic acid of the alginate. Methylene blue (MB), a highly water-soluble compound and a practically water-insoluble compound, 4-phenylazoaniline (PAA) were used as the model drugs to study drug loading and release characteristics from alginate microparticles. The release of the model compounds from the microparticles was found to depend upon the release medium. Incomplete in vitro release of both model drugs in deionized (DI) water was observed. The release of MB in simulated gastrointestinal fluid (0.1N HCl) was fast and complete, while the release of PAA was slow in 0.1N HCl and fast in phosphate buffer solution (pH 6.8). Interactions between the model drugs and alginate microparticles were identified from scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) analysis. The results indicated that (1) porous alginate microparticles can be produced by the spray–coagulation method; (2) drugs can be loaded by the adsorption method; (3) and the obtained microparticles may be used for delaying the release of drugs of low water solubility in acidic conditions.

Polyetherimide membrane formation by the cononsolvent system and its biocompatibility of MG63 cell line

Polyetherimide (PEI) membrane could be prepared by immersion–precipitation process by using the N-methyl-2-pyrrolidone (NMP)–methylene chloride (MC) cononsolvent as the coagulation medium. The membrane, via scanning electron microscopy (SEM), showed a typically asymmetrical structure consisting of a thin and dense skin layer, sponge morphology in the cross-section and porous bottom surface. Trend expected on the basis of the phase diagram of the use of two solvents serving as a cononsolvent system for the membrane formation, replacing the traditional solvent–nonsolvent pair, was in reasonable agreement with the observed membrane morphology. Therefore, the principles of membrane formation established for the ternary systems with polymer–solvent–nonsolvent can be applied to a polymer–cononsolvent (solvent–solvent) system. Furthermore, the biocompatibility of the PEI membrane top (dense) and bottom (porous) surfaces was assessed in an in vitro model using the human osteoblast-like cell line MG63. Compared to cells grown on tissue culture polystyrene (TCPS), cells cultured on the PEI membranes had lower cell growth, but every single cell on the PEI membrane showed similar viability to control cells. SEM analysis showed comparable adhesion and confluence characteristics on all substrates. In addition, the levels of alkaline phosphotase (ALP), prostaglandin E2 (PGE 2) and transforming growth factor β1 (TGF-β1) cytokines produced by MG63 cells on the prepared PEI membranes, regardless of the top or bottom surface, were similar to those on TCPS. The results of this study suggest that the PEI membrane prepared from a cononsolvent system is a non-toxic, biocompatible substrate for the proliferation of human bone cells in vitro.

Experimental study of the control of pore sizes of porous membranes applying chemicals methods

Poly(vinylidene fluoride) (PVDF), polymethyl methacrylate (PMMA) and cellulose acetate (CA) in the presence of N-methyl pyrrolidone were blended in various combinations by using dimethylformamide (DMF) and glacial acetic acid (CH 3COOH) as solvent and used to prepare flat-sheet membranes by the phase-inversion process. A square-crossing table with four factors and three levels for the PVDF-PMMA-CA system was designed to study the influences of the casting solution composition and gelation conditions on membrane pore size; preparation conditions for the system were optimized. The results showed that the effect of the casting solution composition was stronger than that of the solid content and the content of the coagulation medium on characteristics of the prepared membrane. The suitable composition for the PVDF-PMMA-CA system was found to be a solid content of 18%, an additive content of 4%, DMF/CH 3COOH = 4:1 and a Na 2CO 3 solution with aa concentration of 2% as the coagulation medium. In addition, it was found that carbon dioxide gas produced by the reaction of glacial acetic acid in the cast solution with sodium carbonate in a coagulation bath can be used to control the even distribution of the membrane pore size during the process of coagulation.

Preparation of porous PVDF hollow fibre membrane via a phase inversion method using lithium perchlorate (LiClO 4) as an additive

Polyvinylidene fluoride (PVDF) hollow fibre membranes were prepared via a phase inversion method, using N, N-dimethylacetamide (DMAc) as solvent, lithium perchlorate (LiClO 4) as inorganic salt additive and water as the coagulation medium. The phase diagram of the LiClO 4/PVDF/DMAc/water quaternary systems was constructed using cloud-point experimental data. With the addition of the LiClO 4, the effect of coagulation bath temperature on the structure of membranes was investigated. The gas permeation method was used to estimate the pore size and pore size distribution of the PVDF hollow fibre membrane prepared. Also, the effect of the composition of internal coagulant on the membrane structure was investigated using different ratio of 1-methyl-2-pyrrolidone (NMP)/water mixtures.

Effect of coagulation media on membrane formation and vapor permeation performance of novel aromatic polyamide membrane

In the present work, a novel aromatic polyamide was prepared by direct polymerization of 4,4′-hexafluoroisopropylidenedibenzoic acid with diamine of 2,2′-dimethyl-4,4′-bis(aminophenoxy)diphenyl by triphenyl phosphite and pyridine in N-methyl-2-pyrrolidinone. The effects of coagulation media on the membrane morphology and the vapor permeation performances of aqueous ethanol solution through wet phase inversion prepared asymmetric polyamide membrane were investigated. The Young’s modulus increases and membrane porosity of the asymmetric polyamide membrane decreases with increasing the molar volume of coagulation medium. The diffusivity of coagulation medium ranks in the following order: water>methanol>ethanol> n-propanol. The membrane morphology and membrane formation properties were characterized by SEM, Fourier transform infrared (FT-IR)–attenuated total reflectance (ATR), light transmission, and DMA, etc. Optimum vapor permeation results, a separation factor of 21 and permeation rate of 657 g/m 2 h, were obtained with the asymmetric polyamide membrane prepared from the ethanol (coagulation medium) system.

Formation of integrally skinned asymmetric polyetherimide nanofiltration membranes by phase inversion process

AbstractIntegrally skinned asymmetric polyetherimide (PEI) membranes were prepared by the phase inversion process from casting solution containing dimethylformamide (DMF) as a solvent and 1,4‐dioxane as a cosolvent. Deionized water was used as a coagulation medium in preparing asymmetric membranes. The effect of 1,4‐dioxane was investigated by measuring casting solution properties, permeation properties, and membrane structures. Various effects of polymer concentration, evaporation time, and coagulation bath temperature were also studied. Low miscibility of 1,4‐dioxane with coagulant (water) resulted in reducing membrane pore size. The molecular weight cutoff values of asymmetric membranes could be controlled by changing the amount of 1,4‐dioxane in the casting solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1300–1307, 2002; DOI 10.1002/app.10452

Preparation of asymmetric polyacrylonitrile membrane with small pore size by phase inversion and post-treatment process

Integrally skinned asymmetric polyacrylonitrile (PAN) membranes were prepared by the phase inversion process and the post-treatment (annealing) from a casting solution containing N-methyl-2-pyrrolidone (NMP)as a solvent. Deionized (DI) water was used as a coagulation medium in preparing asymmetric membranes. The effect of annealing on the membrane performance was investigated by changing the annealing temperature in DI water. The annealing had great influence on reducing pore size of PAN membrane. The membrane surface modification by strong bases such as NaOH and CH 3ONa was also studied. The surface modification of the annealed membrane made the membrane swollen. As a result, the presence of base disrupted the integrity of the annealed membrane. The molecular weight cut-off of the annealed membrane was about polyethylene glycol 1000.

Dehydration of acetic acid by pervaporation through an asymmetric polycarbonate membrane

Dehydration of acetic acid by pervaporation through an asymmetric polycarbonate membrane was investigated. Investigations focused on the effects of feed composition, degree of swelling, and the molar volume of non-solvent additive on the pervaporation performances. The membrane formation systems are discussed in terms of the presence of a nonsolvent in the casting solution, the kinds of coagulation media, and the polymer concentration. The rate of liquid–liquid demixing decreases with increasing alcohol molar volume of the coagulation medium. The durability of the asymmetric polycarbonate membranes with n-hexanol additive was tested for 3 wt.% aqueous acetic acid solution at 25°C for two months and it was found to be stable.

The effect of dope solution characteristics on the membrane morphology and gas transport properties: 2. PES/γ-BL system

Macrovoid-free, sponge-like membranes with improved gas permeance were obtained from a heterogeneity-developed polyethersulfone (PES)/γ-butyrolactone (γ-BL) dope solution. The heterogeneity of the dope solution was developed with aging time and such a heterogeneity-developed cast solution film was immersed in a nonsolvent so that it would be coagulated. In this novel procedure, the heterogeneity developed was maintained until the moment of immersion in a coagulation medium. The effect of heterogeneity in dope polymer solution on the membrane morphology as well as on gas transport properties has been studied using light scattering, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Detailed roughness analysis of surface images indicates that nascent PES membranes having a finger-like structure have deep surface valleys, whereas those having a sponge-like structure have a smooth surface. Low fluidity of the dope solution due to the heterogeneity developed resulted in the membrane morphology of a sponge-like structure with a smooth surface layer.

The effect of acetic acid on the structure and filtration properties of poly(vinyl alcohol) membranes

The role played by acetic acid in the formation of poly(vinyl alcohol) (PVA) membranes was investigated. Membranes were prepared from a casting solution of PVA, water, and acetic acid by immersion in Na 2SO 4/KOH/H 2O coagulation bath. Experimental results show that the acetic acid additive exerts an influence on the structure and filtration properties of membranes. Not only the surface morphology but also the structure of cross-section could be modulated by adding the acetic acid in the casting solution. Obviously, the increase of the amount of acetic acid in the casting solution decreased the thickness of skin layer. This could be attributed to the fact that the increase of the amount of acetic acid in the casting solution increases H 3O + ion of the casting solution enhancing the influx rate of coagulant medium for acid-base equilibrium. A mechanism describing the affinity between the PVA solution and the coagulant medium is proposed to estimate the PVA membrane structure by adding the acid. The results presented here offer a better understanding of relationships between the membrane formation mechanism and the skin structure when designing an asymmetric membrane with acetic acid as an additive.

The effect of polymeric additives on the structure and permeability of poly(vinyl alcohol) asymmetric membranes

The manufacture and dextran-rejection properties of asymmetric poly(vinyl alcohol) (PVA) membranes have been described in this study. Membranes were prepared from a casting solution of PVA, water as solvent, and water-soluble polymeric additive by immersing them in Na 2SO 4/KOH/H 2O as coagulant medium. Experiments showed that the dextran and poly(vinyl pyrrolidone) (PVP) additives exerted a different influence on the structure and permeability of membranes. Especially, the structure of skin layer strongly depended on the polymeric additives in the casting solution. The addition of dextran additives in the system could induce pores in the top layer. Conversely, the PVP additives effectively blocked the interstitial cavities within the top layer to generate a more compact structure. A mechanism describing that the affinity between additive and casting solution as well as between additive and coagulant medium was proposed to investigate the effect of dextran and PVP additives in the formation of PVA membranes. The results presented here offer a better understanding of relationships between the membrane formation mechanism and the skin structure when designing an asymmetric membrane by the addition of polymeric additives in the casting solution.

Morphology control of asymmetric membranes by UV irradiation on polyimide dope solution

The membrane morphology was readily controlled by the gelation of dope solution before immersion into a coagulation medium. In particular, macrovoid-free, sponge-like integrally skinned asymmetric polyimide membranes with improved selectivity were obtained by the chemical gelation of cast solution film. Cross-linking was performed by ultraviolet irradiation for benzophenone containing polyimide dope solution. Cross-linking maintained the structure of cast solution film until the moment of immersion into a nonsolvent bath. Macrovoid decreases with irradiation time on the cast solution film. Sponge-like integrally skinned asymmetric membranes were obtained with sufficient irradiation. Gas permselectivity increased significantly with the progress of cross-linking on the cast solution film. Membrane morphology and subsequent transport properties can be controlled both by the extent of cross-linking and by the concentration of dope solution.

Polyurethane membrane prepared via a dry/wet phase inversion method for protein adsorption

Hydroxyl-terminated polybutadiene (HTPB)- and 4,4′-dicyclohexyl-methane (H12MDI)-based polyurethanes (PUs) were synthesized by solution polymerization. PU membranes were prepared by a dry/wet phase inversion method. Protein adsorption ratio of fibrinogen to albumin (F/A molar ratio) was measured. Low F/A molar ratio was found on these PUs. It was found that surface composition of these PUs has a subtle effect on F/A adsorption molar ratio. The F/A molar ratio was increased as the increase of hard segment content distributed on the surface. The variation of surface composition of these membranes and the effect on the F/A molar ratio were investigated by the difference in surface energy between nonpolar HTPB soft segment and polar hard segment, concentration, and temperature of coagulation medium, polymer content, and alcohol type. The CO/CC ratio, frequency shift, and difference (Δν) as a measure of polymer homogeneity and the average strength of interpolymer hydrogen bonds were utilized to study the surface composition. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1334–1340, 1999

The effect of dope solution characteristics on the membrane morphology and gas transport properties: PES/γ-BL/NMP system

The effect of heterogeneity of a dope polymer solution on membrane morphology has been investigated. Heterogeneity was developed in polyethersulfone solutions of either γ-butyrolactone (γ-BL) or a mixed solvent of γ-BL/ N-methyl-2-pyrrolidone, which exhibit gelation and/or phase separation with aging time. Two different processes for membrane preparation have been employed; Process I, heterogeneity-developed dope solution was cast on a glass plate with a knife for uniform thickness, and immediately immersed into a nonsolvent form of the membrane. Process II, a dope solution was cast on a glass plate and then aged in a closed environment. After a certain aging time, it was immersed into a nonsolvent to be coagulated. The developed heterogeneity was destroyed markedly during casting in Process I, whereas the heterogeneity was maintained until the moment of immersion into a coagulation medium in Process II. Membranes prepared by Process I were finger-like regardless of the aging time, whereas Process II yielded macrovoid-free and sponge-like membranes having enhanced gas permeance and mechanical strength at long aging times. From these results, it was concluded that the morphology and transport properties of a membrane were able to be controlled by the solution structure, in particular, the solution heterogeneity in the cast film.

Polyurethane membrane prepared via a dry/wet phase inversion method for protein adsorption

Hydroxyl-terminated polybutadiene (HTPB)- and 4,4′-dicyclohexyl-methane (H12MDI)-based polyurethanes (PUs) were synthesized by solution polymerization. PU membranes were prepared by a dry/wet phase inversion method. Protein adsorption ratio of fibrinogen to albumin (F/A molar ratio) was measured. Low F/A molar ratio was found on these PUs. It was found that surface composition of these PUs has a subtle effect on F/A adsorption molar ratio. The F/A molar ratio was increased as the increase of hard segment content distributed on the surface. The variation of surface composition of these membranes and the effect on the F/A molar ratio were investigated by the difference in surface energy between nonpolar HTPB soft segment and polar hard segment, concentration, and temperature of coagulation medium, polymer content, and alcohol type. The CO/CC ratio, frequency shift, and difference (Δν) as a measure of polymer homogeneity and the average strength of interpolymer hydrogen bonds were utilized to study the surface composition. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1334–1340, 1999

Porous chitosan microsphere for controlling the antigen release of Newcastle disease vaccine: preparation of antigen-adsorbed microsphere and in vitro release.

Porous chitosan microspheres suitable for the delivery of antigen were prepared using a wet phase-inversion method. The pore structure of the chitosan microsphere could be modified by the change of pH value of the coagulation medium, which is the aqueous tripolyphosphate (TPP) solution. High porosity of chitosan microsphere with an open porous structure on its surface was prepared by coagulation in TPP aq. solution of pH 8.9. The porous chitosan microspheres were modified chemically with reagents to introduce three types of functional groups; carboxyl, hydrophobic acyl and quaternary ammonium groups. Antigen of ND vaccine was immobilized into the pores of porous chitosan microspheres and the adsorbed antigen was assayed by the Hemoglobin Aggregation (HA) analytical method. Sustained-release of ND vaccine's antigen could be achieved through an adsorption-desorption release test. The chemical modifications of the porous chitosan microspheres have a strong large influence on the adsorption efficiency or release rates of the antigen investigated. The porous microspheres have a higher adsorption efficiency and the slower release rate of antigen when modified chemically with 3-chloro-2-hydroypropyltrimethylamonium chloride.