Surface Modifying Macromolecules Research Articles

Generation of cell adhesive substrates using peptide fluoralkyl surface modifiers

Previous studies reported on the delivery of vitamin E to the surface of a polycarbonate polyurethane (PCNU) to produce antioxidant surfaces, using a bioactive fluorinated surface modifer (BFSM). In the current report, a cell adhesive peptide sequence was coupled to the BFSM, and when blended into PCNU, generated a cell adhesive substrate. An NH 2-GK*GRGD-CONH 2 peptide sequence (referred to as RGD) with a dansyl label (*) on the lysine residue was coupled via the N-terminal to a BFSM precursor molecule. The resulting RGD BFSM was purified and the pmol peptide/mg BFSM value was assayed by amino acid quantification. The migration of the RGD BFSM in a PCNU blend was confirmed by X-ray photoelectron spectroscopy analysis. U937 macrophage-like cells and human monocytes were seeded onto the PCNU and blends of PCNU with non-bioactive fluorinated surface modifier or the RGD BFSM, in order to study the cell response. Both U937 cells and human monocytes adhered in greater numbers to the RGD BFSM substrate when compared to unmodified PCNU or the blend of PCNU with the non-bioactive fluorinated surface modifying macromolecule substrate. The study demonstrated a novel approach for the introduction of peptides onto the surface of polymers by modifying the surface from within the polymer as opposed to the use of cumbersome post-surface modification techniques. The generation of a peptide substrate points to the possibility of producing complex bioactive surfaces using various peptide BFSMs or pharmaceuticals simultaneously to manipulate cell functions.

Porous hydrophobic/hydrophilic composite membranes: Estimation of the hydrophobic-layer thickness

A porous hydrophobic/hydrophilic composite membrane can be prepared by the phase inversion method in one casting step from a polymer solution containing a hydrophilic polymer and a fluorinated surface modifying macromolecule (SMM). The surface analysis of these membranes indicate that there is a fluorine concentration gradient along the membrane thickness resulting from the migration of fluorinated blocks to the air side surface during membrane formation. In this paper, direct contact membrane distillation (DCMD) process has been applied, together with a new theoretical model, to estimate the hydrophobic-layer thickness of porous composite membranes. The theoretical model involves the structural characteristics of the membranes, the heat transfer mechanism and the physical nature of mass transport through porous composite membranes. The model was validated using two supported commercial poly-tetra-fluoro-ethylene membranes of different pore sizes and known thickness-layers. The effect of the hydrophilic polymer concentration in the casting solution on the formed hydrophobic-layer thickness of the composite membranes has been investigated. Also are studied the effects of stirring rate and temperature in the DCMD system on the determination of the hydrophobic-layer thickness. The results show that the hydrophobic-layer thickness increases with the concentration of the hydrophilic base polymer in the casting solution and is independent on the operational parameters selected to conduct the DCMD experiments. The proposed method can be used to measure the layer thickness of porous composite hydrophobic/hydrophilic membranes within random uncertainties less than 5%. The maximum deviation of each individual thickness from the corresponding average value is less than 9%. The estimated errors due to the different input membrane parameters associated in the mathematical model were discussed. The hydrophobic-layer thickness of the SMM blended membrane was found to be an order of magnitude lower than that of the commercial membranes frequently used in membrane distillation.

Porous hydrophobic/hydrophilic composite membranes: Application in desalination using direct contact membrane distillation

A new type of composite hydrophobic/hydrophilic porous membrane is proposed for application in membrane distillation. The membranes were prepared by the phase inversion technique in a single casting step from polymer solutions containing surface-modifying macromolecules. Polyetherimide was used as a hydrophilic base polymer. The effects of polyetherimide concentration in the casting solution on the permeate flux and on the membrane characteristics were investigated. The liquid entry pressure of water, mean pore size, effective porosity and mean roughness of the membranes were determined. Direct contact membrane distillation experiments were performed for pure water and aqueous solutions of sodium chloride as feed. The effect of the mean temperature, stirring rate and salt concentration were studied. Similar experiments were carried out for two commercial polytetrafluoroethylene membranes of different pore sizes, often used for membrane distillation purposes. The water vapor permeability of the proposed membranes was determined and compared with that of the commercial membranes. The new membranes seem to be promising in the field of membrane distillation as they combine a low resistance to mass flux achieved by the diminution of the water vapor transport path length through the hydrophobic thin top-layer of the membrane and a low conductive heat loss through the membrane obtained by using thicker hydrophilic sub-layer of the membrane.

Development and characterization of novel hydrophilic surface modifying macromolecule for polymeric membranes

A hydrophiLic Surface Modifying Macromolecule (LSMM) was synthesized, characterized, and blended into the casting solution of polyethersulfone (PES) membranes. Ultra-filtration membranes were prepared by the phase inversion technique. The membranes were then characterized by contact angle measurements and a solute transport study using poly(ethylene glycol) (PEG) and poly(ethylene oxide) (PEO) solutes of different molecular weights. Pore size and pore size distribution of the membranes were determined by using PEG and PEO separation data. The Ottawa River water was treated by the membranes. The LSMM blended PES membranes showed higher fouling resistance and long-term stability than the PES membrane without LSMM.

Impact of Membrane Surface Modification on the Treatment of Surface Water

New polyethersulfone (PES) based membranes for ultrafiltration (UF) were developed by blending a surface-modifying macromolecule (SMM) in the casting solution, in an attempt to minimize the impact of fouling. Fouling was evaluated using concentrated Ottawa River water (CORW), either unfractionated or fractionated via UF. These membranes also included some polyvinylpyrrolidone (PVP), a pore forming additive. A statistical analysis was conducted to evaluate the impact of some variables on the treatment of the surface water. The independent variables included PVP/PES ratio in the casting solution, with and without SMM, and the nature of the feed CORW [low molecular weight (LMW) fraction, unfractionated, high molecular weight (HMW) fraction]. The performance variables studied were total organic carbon (TOC) removal, the foulant accumulation at the membrane surface after filtration, the flux reduction, and the final permeate flux. The most important variable was the feed water. Filtration of LMW had a higher f...

Membrane surface modification and characterization by X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements

Surface modifying macromolecules (SMMs) were used to modify the top surface of polymeric membranes. SMMs are oligomeric fluoropolymers synthesized by polyurethane chemistry and tailored with fluorinated end groups. In this study, the surface of polyetherimide (PEI) flat-sheet membranes prepared by the phase inversion method was modified using 2wt.% of SMM and 15wt.% PEI concentration in the polymer casting solution. The effect of solvent evaporation time on membrane surface modification was investigated. X-ray photoelectron spectroscopy analysis shows enrichment of fluorine on the modified PEI membrane surfaces and their contact angles were higher than those of the unmodified PEI membrane. Both the surface fluorine content and contact angles of the SMM/PEI blended membrane increased when the solvent evaporation time was increased up to 5min. The SMM modified and unmodified PEI membranes were characterized by means of tapping mode atomic force microscopy (TM-AFM). The mean pore size, nodule size, pore density, surface porosity and mean roughness of the modified membranes were determined and compared with those of the unmodified membrane.

Influence of processing conditions on the properties of ultrafiltration membranes

The effect of four processing variables on the final properties of ultrafiltration (UF) membranes was investigated. Flat-sheet polyethersulfone (PES) membranes were prepared by wet phase inversion. The variables of interest were: the concentration of base polymer in the casting solution (dope solution), the solvent evaporation time, the addition of surface modifying macromolecules (SMMs), and the use of the additive polyvinylpyrrolidone (PVP). The membranes were characterized by solute transport and scanning electron microscopy (SEM). No appreciable difference between the structures of surface–modified and unmodified membranes was observed by SEM. Membranes prepared with PVP had pure water permeation rates (PWP) significantly higher than membranes prepared without the PVP additive. However, the average polyethylene glycol (PEG 35 ku (35 kDa)) separation by membranes with PVP was approximately 15% lower than the tightest membranes prepared without PVP. The effect of surface modification with fluorinated additives and solvent evaporation time was observed only with high molecular weight cut-off (MWCO) membranes prepared with 12 wt.% PES casting solution.

Manufacturing conditions of surface-modified membranes: effects on ultrafiltration performance

The treatment of surface water was studied using different experimental ultrafiltration surface-modified polyethersulfone membranes. They were prepared adjusting three membrane-manufacturing variables: addition of three surface modifying macromolecules (SMMs), the solvent evaporation time and the polyethersulfone concentration in the casting solution. Membrane performance was evaluated in terms of total organic carbon removal, the amount of natural organic matter deposited on top of the membrane after filtration, the permeate flux and the flux reduction. In order to define the manufacturing conditions resulting in the “best membrane”, in addition to the performance results, other considerations such as membrane strength and SMM compatibility were necessary. Membranes prepared with a novel polypropylene diol-based additive proved to have a positive effect on the treatment of this particular surface water. A trade-off between total organic carbon removal and permeate flux, and a logical connection between membrane characteristics and performance were observed. Membranes with small molecular weight cut-off (and pore size) had high total organic carbon removals and low-permeate fluxes, consequently, fouling was small.

Application of surface modifying macromolecules for the preparation of membranes for membrane distillation

The top surface of polyetherimide (PEI) flat sheet membranes was modified using fluorinated surface modifying macromolecule (SMM). The SMM modified and unmodified membranes were prepared by the phase inversion method from casting solutions containing the solvent N, N-dimethylacetamide and the non-solvent y-butyrolactone (GBL). The effect of the base polymer concentration on the membrane properties has been investigated. It was found that SMM actively migrated to the air surface and changed the surface properties of the PEI membranes. Contact angle measurements indicate that the PEI membrane surface becomes more hydrophobic after adding the SMM to the PEI casting solutions, while X-ray photoelectron spectroscopy analysis shows enrichment of fluorine on the PEI membrane surfaces. The SMM modified and unmodified PEI membranes were also characterised by means of liquid entry pressure of water measurements ( LEP w ) and gas permeation test using nitrogen as standard gas. SMM modified PEI membranes have potential to be used in membrane distillation.

Study on surface modification by surface‐modifying macromolecules and its applications in membrane‐separation processes

AbstractSurface‐modifying macromolecules (SMMs) are oligomeric fluoropolymers synthesized by polyurethane chemistry and tailored with fluorinated end groups. In the literature, several formulations of SMMs have been developed and blended with base polymers of polyurethanes and polyethersulfone for surface modification. It has been shown that SMMs migrate to the surface and the fluorine end groups orient themselves toward the air–polymer interface, reducing the surface energy of the hydrophilic base polymer to values close to that of polytetrafluoroethylene (Teflon). Because only a small amount of SMMs was needed, the bulk properties of the base polymer remained relatively unchanged. The properties of the SMM polymers were characterized, including molecular weights, elemental analysis, and thermal transitions. The morphology and surface properties of the SMM‐modified and unmodified membranes were assessed. The use of SMMs has been tested for use in ultrafiltration, pervaporation, and biomedical applications. SMM‐modified membranes offer advantages over unmodified membranes and the use of SMMs will continue to be the focus of future studies. This study reviews the recent development of surface‐modifying macromolecules (SMMs) and SMM‐blended membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2902–2916, 2003

Surface modification of a polycarbonate-urethane using a vitamin-E-derivatized fluoroalkyl surface modifier

Fluorinated surface-modifying macromolecules (SMMs) have been previously reported on and shown to limit the hydrolytic degradation of polyurethanes. The SMM molecules achieve this effect by allowing for the selective migration of terminal fluorinated groups to the polymer's surface, which may then shield more hydrolytically-sensitive groups in the base polyurethane backbone. A further extension of the SMM concept would be to utilize the migration of the fluorine tails to simultaneously deliver biologically active moieties to the surface. This study explored the synthesis and characterization of a vitamin-E (natural anti-oxidant) coupled surface modifier, as a model for the bioactive SMM concept. The SMM was synthesized using lysine diisocyanate (LDI), polycarbonate diol (PCN), and a fluoroalcohol. By derivatizing the LDI pendant ester, vitamin E was coupled to the SMM. The vitamin-E SMM was physically characterized using gel-permeation chromatography (GPC) and its anti-oxidant activity was assessed in the presence of 0.1 mM NaOCl. Polymer degradation experiments were carried out using 10 mM NaOCl incubation solutions, and the relative material breakdown was assessed using GPC and scanning electron microscopy (SEM). The results indicate that while the fluoro-component reduced damage of the PU, the bioactive component achieved a further deactivating effect. A similar action may also be effective against superoxide anions generated by human macrophages.

Morphological study of fluorinated asymmetric polyetherimide ultrafiltration membranes by surface modifying macromolecules

Phase inversion polyetherimide (PEI) flat sheet membranes were surface modified using fluorinated surface modifying macromolecules (SMMs) additives. Two SMM formulations were used. Each SMM was blended into polyetherimide casting solutions containing the solvent N, N-dimethyleacetamide and the non-solvent hydroxybutyric acid γ-lactone (GBL). The effects of the SMM and the PEI base polymer concentrations on the morphological properties of the prepared membranes have been investigated. Contact angle measurements indicate that PEI membrane surface becomes more hydrophobic after adding the SMMs to the PEI casting solutions, while X-ray photoelectron spectroscopy analysis shows enrichment of fluorine on the PEI membrane surfaces. The SMM modified and unmodified PEI membranes were also characterized by means of atomic force microscopy (AFM), gas permeation tests and ultrafiltration experiments using aqueous solutions of polyethylene glycol (PEG) and polyethylene oxide (PEO) of various molecular weights. Pore sizes and nodule sizes obtained from AFM images were remarkably fitted to the log-normal probability distribution curves. Mean pore sizes, pore size distributions, nodule sizes, nodule size distributions and roughness parameters of the membranes were determined. It was found that SMM actively migrated to the air surface and changed the surface properties of the PEI membranes. The mean pore size and the molecular weight cut-off (MWCO) of the SMM modified PEI membranes were lower than those corresponding to the unmodified membranes, while the nodule sizes were larger. The surface roughness parameters were reduced when SMMs were added.

Surface modification of polyvinylidene fluoride pervaporation membranes

AbstractPolyvinylidene fluoride (PVDF) membranes were surface‐modified using fluorinated surface‐modifying macromolecules (SMMs) additives. The membranes were prepared using the phase‐inversion method. Two novel SMM formulations were used. The effect of some relevant parameters, such as the solvent evaporation time, evaporation temperature, and concentration of SMM in the PVDF casting solution, was considered. The prepared membranes were characterized in terms of the contact angle analysis, the liquid entry pressure of water measurements, and the scanning electron microscopy. Pervaporation experiments were conducted for dilute chloroform/water binary mixtures. Based on the contact angle analysis, the incorporation of SMM into the PVDF casting solution produced membranes with higher surface hydrophobicity. The pervaporative performance of the prepared membranes was investigated, and the relationship between the surface characteristics of the modified PVDF membranes and the chloroform separation discussed.

The influence of protein adsorption and surface modifying macromolecules on the hydrolytic degradation of a poly(ether–urethane) by cholesterol esterase

Previous investigations have demonstrated that the inflammatory cell derived enzyme, cholesterol esterase (CE) could degrade polyurethanes (PUs) by hydrolyzing ester and urethane bonds. Studies that have investigated the development of protective coatings for PUs have reported that the polymer degradation of polyester–urethanes (PESUs) can be reduced with the use of fluorine containing surface modifying macromolecules (SMMs). Since these latter studies were carried out in the presence of relatively pure enzyme, it has not been shown if SMMs would still provide an enhanced inhibitory effect if surfaces were pre-exposed to plasma proteins. This would be more representative of the in vivo scenario since protein adsorption would occur before the appearance of monocyte-derived macrophages which would be a primary source of esterase activities. The current investigation has focused on studying the influence of fibrinogen (Fg) as a simple model of protein adsorption in order to assess the effect of CE in combination with protein on polyether–urethane (PEU) surfaces. The materials were prepared with and without SMMs, and were pre-coated with Fg prior to carrying out biodegradation studies. The pre-adsorption of Fg onto the modified and non-modified surfaces provided a significant delay in the hydrolytic action of CE onto the PEU substrates. However, the effect was gone by 70 days and by the 126th day of incubation, both Fg coated and non-Fg coated groups had the same level of degradation. The difference between Fg coated and non-coated substrates was much smaller for materials containing SMMs. In addition, the pre-adsorption of Fg did not alter the SMMs’ ability to provide a more biostable surface over the 4 month incubation period.

Effects of surface modifying macromolecule (SMM) on the properties of polyethersulfone membranes

Surface modifying macromolecules (SMMs) were synthesized and blended into the casting solution of polyethersulfone (PES) membranes. The solution was cast to films on the glass plate. The cast films were placed in a temperature-controlled oven with forced air circulation to remove the solvent, before being immersed into water at 4°C for gelation. The following effects on the properties of the PES membranes were found. 1) Mechanical strength of the PES membrane was enhanced by adding SMMs. 2) According to the contact angle measurement, surface hydrophobicity of the PES membrane increased as solvent evaporation period increased. X-ray Photoelectron Spectroscopy (XPS) detected surface migration of SMMs 3) SMM blended PES membranes have potential to be used for the purpose of membrane distillation.

Surface modification of membranes for the separation of volatile organic compounds from water by pervaporation

Surface modifying macromolecules (SMMs) are oligomeric fluoropolymers synthesized by urethane chemistry and tailored with fluorinated endgroups. Two novel SMM formulations were blended into polyvinylidene fluoride (PVDF) casting solutions containing N,N-dimethylacetamide. Based on the advancing and the receding contact angle measurements, it was found that the SMM modified membranes exhibited higher surface hydrophobicity than the unmodified membranes. The effect of solvent evaporation time and SMM concentration in the PVDF casting solution has been investigated. The membranes were characterized by scanning electron microscopy. Pervaporation experiments were carried out for dilute chloroform/water binary mixtures and the relationship between the membrane characteristics and the pervaporative performance of the membranes is discussed.

Study on the Kinetics of Surface Migration of Surface Modifying Macromolecules in Membrane Preparation

Surface modifying macromolecules (SMM) were synthesized and blended into the casting solution of poly(ether sulfone). The solution was cast to films with thickness of 0.12 and 0.24 mm. The cast films were placed in an oven with forced air circulation for periods of 3, 5, 7, and 2000 min to remove the solvent, before being immersed into water at 4 °C for gelation. The membranes so prepared were further dried and subjected to contact angle measurement and XPS (X-ray photoelectron spectroscopy) analysis. It was found that the contact angle increased as the solvent evaporation period increased. The increase in contact angle was faster when the membrane was thinner. According to the XPS analysis, after an initial time lag the surface fluorine content increased as the evaporation time increased and finally leveled off. The increase in surface fluorine content was also faster when the membrane was thinner. A kinetic model was established for the SMM surface migration.

Fluorinated surface-modifying macromolecules: modulating adhesive protein and platelet interactions on a polyether-urethane.

Polyether-urethanes (PEUs) have been the materials of choice for the manufacture of conventional blood-contacting devices. Nevertheless, biostability and blood compatibility are still among the principal limitations in their long-term application. Studies investigating the development of protective coatings for PEUs have shown that degradation can be reduced with the use of fluorinated surface-modifying macromolecules (SMMs). It has also been hypothesized that SMM-modified PEU surfaces may exhibit improved blood compatibility because other studies have shown a modulation in fibrinogen adsorption onto these surfaces. To determine the blood compatibility of a PEU-containing fluorinated SMMs, a series of in vitro experiments were designed to study the pattern of protein adsorption from plasma and then to assess the nature of platelet adhesion and activation on each substrate. Western blot analysis as well as single protein studies revealed that the dominant "adhesive proteins" [fibrinogen (Fg), fibronectin (Fnc), and vitronectin (Vnc)] were adsorbed on two of the SMM-containing PEUs in lower amounts relative to unmodified base. Platelet adhesion and activation data further highlighted the differences among the various substrates. It was shown that the unmodified base had a higher number of adhered platelets relative to the SMM-modified surfaces, and that of the SMM-containing substrates, which showed the lowest levels of adhesive proteins also, exhibited significantly lower platelet densities. Close morphological examination further revealed that platelets residing on these latter substrates were not appreciably activated. Based on the current evidence, it is believed that the fluorinated SMMs demonstrate good potential for the development of surfaces with minimal thrombogenic character in in vivo applications.

Effect of Fluorinated Surface-Modifying Macromolecules on the Molecular Surface Structure of a Polyether Poly(urethane urea)

Fluorinated surface-modifying macromolecules (SMMs) have been developed to preferentially migrate to the surface of poly(urethane urea)s (PEUs), thereby modifying the surface features of the polymer. In the current study, four specific SMMs based on different chemistries were synthesized and incorporated at a 4 wt % concentration in the PEU. The domain structure at the surface was altered, and the nature of the interactions between the SMM and the base polymer was dependent on the defined SMM chemistry. The surface features were characterized by several microscopy techniques. Attenuated total reflectance infrared spectroscopy showed that, in blending with the PEU, some SMMs disrupted the existing hydrogen-bonded hard segment domain structure at the surface. However, this was not a necessity for good dispersion into the base polymer, as one SMM demonstrated good mixing within the PEU, forming SMM−PEU interactions while simultaneously maintaining the hydrogen bonding within the PEU hard segment domains. The...

The effect of fluorinated surface modifying macromolecules on the surface morphology of polyethersulfone membranes

Polyethersulfone (PES) has been recently adopted for membrane materials in applications such as ultrafiltration and haemodialysis. As a biomaterial, the factors which affect the blood compatibility of PES membranes include surface energetics, hydrophobicity, and surface morphology. Surface fluorination of materials has been found to create surfaces with improved blood compatibility and chemical stability. One novel approach to generating fluorinated polymer surfaces has included the use of fluorinated surface modifying macromolecules (SMMs). These macromolecules have been reported to establish fluorinated functional groups at surfaces of polymeric materials without significantly affecting the physical properties of the base polymer. However, to date there has been relatively little information published on the nature of the surface structure for PES materials containing these SMMs. In this study, synthesized SMMs with varying chemical compositions were characterized and blended with PES, and fabricated into flat sheet membranes. The bulk thermal transitions of PES materials were not significantly altered by the addition of 4 wt% SMMs. Contact angle data showed that the addition of SMMs in PES created more hydrophobic surfaces, accompanied by an increase in surface heterogeneity. X-ray photoelectron spectroscopy studies confirmed the presence of elemental fluorine at the surface. Through microscopy studies, it was shown that surface modification was achieved by the migration of SMM concentrated microdomains to the air-membrane interface. The generated microdomains (approximately 1-2 μm in diameter) are dispersed within the top 8 μm of the surface. The concentration of microdomains was gradually depleted from the surface to the bulk of the membrane. A schematic of the morphology for SMMs within the PES membrane surface was proposed.