Irreversible Protein Adsorption Research Articles

Surface Oxygen Deficiency Enabled Spontaneous Antiprotein Fouling in WO3 Nanosheets for Biosensing in Biological Fluids.

Biofouling deteriorates the performance of sensors operated in biofluids. Protein adsorption is believed to be the first step of biofouling, which also reduces biocompatibility by further inducing cell adhesion, platelet activation, and even inflammation. Current studies of antifouling coatings are focused on polymers and hydrogels, which have succeeded in remaining resistant to protein adsorption, but their application on sensor electrodes is limited due to low conductivity and biocompatibility. Here, we report a spontaneous antibiofouling strategy for sensor electrodes by controlling oxygen vacancies in WO3 nanosheets. Irreversible adsorption of proteins was reduced by 76% in unprocessed human plasma when electrodes were coated with WO3 rich in surface oxygen vacancy. These electrodes maintained 91% of the initial current density after 1 month of incubation in human plasma.

Surface activity of protein extracts from seed oil by-products and wettability of developed bioplastics

Protein concentrates, extracted from the by-products of Hemp (Cannabis sativa), Cardoon (Cynara cardunculus), and Argan (Argania spinosa L.) oilseeds after oil extraction, were utilized to produce sustainable and eco-friendly protein-based bioplastics. The surface wettability and roughness of these bioplastics were investigated due to the pivotal role of these parameters in their application in food packaging sector. Advancing contact angle value revealed that Argan protein-based bioplastic is the most hydrophobic (θ > 90°) while Cardoon protein-based film is the most hydrophilic (θ < 40°). These results are then supported by the roughness of wet film surfaces and their swelling ratio, where Cardoon-based bioplastics and Argan-based bioplastics have also the lowest and the highest roughness average, respectively. The measured hydrophilicity of the produced bioplastics motivates a detailed investigation of the surface activity of protein concentrates used for film formation which can determine the packaging by coating. Adsorption/desorption kinetics, surface tension and dilatational rheology are reported at two different pHs values (10 and 12). The three protein concentrates are surface active and develop stable adsorbed layers at the air-water interface after 1 h. Cardoon proteins showed the same final surface tension (>45 mN m−1) at both pHs, while Argan and Hemp proteins displayed lower values than Cardoon, especially at pH 12 (<40 mN m−1), indicative of higher surface activity. Finally, Argan protein adsorbed more irreversibly, followed by Hemp protein while Cardoon protein provides the largest partial desorption from the surface. Combined analysis of the data features a correlation between the higher advancing contact angle of Hemp protein-based bioplastic and higher hydrophobicity, less swelling, faster adsorption kinetics, lower surface tension and more irreversible adsorption of protein. These apply for Hemp and Cardoon protein concentrates and their driven bioplastics while the presence of free oil in Argan protein concentrate and its bioplastic hinders the correlation between different phenomena. The new interconnections highlighted between film properties and surface adsorption could potentially be employed in food packaging and coating technology.

Protein Desorption Kinetics Depends on the Timescale of Observation.

The presence of so-called reversible and irreversible protein adsorption on solid surfaces is well documented in the literature and represents the basis for the development of nanoparticles and implant materials to control interactions in physiological environments. Here, using a series of complementary single-molecule tracking approaches appropriate for different timescales, we show that protein desorption kinetics is much more complex than the traditional reversible-irreversible binary picture. Instead, we find that the surface residence time distribution of adsorbed proteins transitions from power law to exponential behavior when measured over a large range of timescales (10-2-106 s). A comparison with macroscopic results obtained using a quartz crystal microbalance suggested that macroscopic measurements have generally failed to observe such nonequilibrium phenomena because they are obscured by ensemble-averaging effects. These findings provide new insights into the complex phenomena associated with protein adsorption and desorption.

A Multidisciplinary Experiment to Characterize Antifouling Biocompatible Interfaces via Quantification of Surface Protein Adsorption.

Novel biomaterial development is a rapidly growing field that is crucial because biomaterial fouling, due to rapid and irreversible protein adsorption, leads to cellular responses and potentially detrimental consequences such as surface thrombosis, biofilm formation, or inflammation. Therefore, biomaterial technology's fundamentals, like material biocompatibility, are critical in undergraduate education. Exposing undergraduate students to biomaterials and biomedical engineering through interdisciplinary experiments allows them to integrate knowledge from different fields to analyze multidisciplinary results. In this practical laboratory experiment, undergraduate students will characterize surface properties (contact and sliding angle measurements) for the antifouling polydimethylsiloxane (PDMS) polymer using a goniometer and a smartphone, as well as quantify protein adsorption on antifouling surfaces via a colorimetric assay kit to develop their understanding of antifouling surface characteristics, UV-vis spectroscopy, and colorimetric assays. The antifouling PDMS polymer is prepared by silicone oil infusion and compared to untreated control PDMS. The polymer hydrophobicity was demonstrated by static water contact angles of ~99° and 102° for control and antifouling PDMS surfaces, respectively. The control PDMS sliding angle (>90°) was significantly reduced to 9° after antifouling preparation. After 24 h incubation of polymer samples in a 200 mg/mL bovine serum albumin (BSA) solution, the surface adsorbed BSA was quantified using a colorimetric assay. The adsorbed protein on the fouling PDMS controls (29.1 ± 7.0 μg/cm2) was reduced by ~79% on the antifouling PDMS surface (6.2 ± 0.9 μg/cm2). Students will gain experience in materials science, biomedical engineering, chemistry, and biology concepts and better understand the influence of material properties on biological responses for biomaterial interfaces.

Surface-initiated ARGET ATRP of poly(glycidyl methacrylate) from macroporous hydrogels via oil-in-water high internal phase emulsion templates for specific capture of Enterovirus 71

Surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) was applied to graft poly(glycidyl methacrylate) (PGMA) brushes from macroporous hydrogel templating from oil-in-water high internal phase emulsion (O/W HIPE), and the grafted hydrogel was further heparinized as stationary phase of affinity chromatography for Enterovirus 71 (EV71) purification. Acrylate functional monomer containing isobutyl bromide (HEMA-BiBB) was synthesized and introduced into oil phase for macroporous hydrogel with ATRP initiator-anchored surface. With the increase of HEMA-BIBB dosage, the average pore size of hydrogel increased and the specific surface area decreased. Bromine atomic percent of hydrogel reached the maximum of 1.56 % when the HEMA-BiBB dosage was 1.0 g. The corresponding heparinized hydrogel possessed the highest amount of carboxyl group (56.8 μmol per column). Interconnected macropore (1.71 μm) and high porosity (84.2 %) of heparinized hydrogel ensured an excellent permeability (2.1 × 10−13 m2). Meanwhile, grafted PGMA brushes afforded abundant epoxy groups for immobilizing high density of heparin, which endowed hydrogel with outstanding adsorption capability for EV71. Immobilized heparin ligands were competent in specific capture of EV71 by receptor-ligand interaction. Besides, enhanced hydrophilicity of heparinized hydrogel avoided the irreversible and nonspecific adsorption of proteins. As a result, heparinized hydrogel demonstrated superior adsorption selectivity and capability for EV71 (dynamic adsorption capacity: 1275 ng per column, recovery: 86.2 %). The developed heparinized PGMA-grafted macroporous hydrogel was promising to be applied in the large-scale production of EV71 for vaccine industry.

Irreversible Adsorption of Serum Proteins onto Nanoparticles

AbstractWhen a material comes in contact with serum or plasma, proteins will immediately adsorb to its surface. The extent of serum protein adsorption as well as the composition of the protein corona is thought to be decisive for the biological fate. The understanding of the mechanism underlying the concurrent adsorption of multiple proteins and the exact ways by which the adsorbed proteins interact with the biological setting, is still rudimentary. For both cases, a correct estimate of the composition of the protein corona is the key for an improved understanding. The protein corona composition is typically analyzed indirectly through analysis of the supernatant after protein desorption. However, in most cases the particles are not analyzed afterward in order to ensure that all proteins indeed have desorbed. Here, the results related to the analysis of the amounts of proteins in the corona are reported, focusing on the desorbed as well as the fraction of proteins that do not desorb. Irreversible protein adsorption can be observed in some cases. The results show that, in addition of the analysis of the supernatant, analysis of the particles is of critical importance to fully characterize the protein corona formed on nanoparticles.

Effect of surface chemistry on hMSC growth under xeno-free conditions

Human mesenchymal stem/stromal cells (hMSC) are promising therapeutic agents for regenerative medicine. However, therapeutic doses necessary for clinical application require in vitro expansion, ideally under Xeno-Free (XF) conditions to avoid the use of foetal bovine serum (FBS). We previously reported that hMSCs could be expanded using a pharmaceutical-grade human plasma-derived supplement for cell culture (SCC, Plastem®) combined with bFGF and TGFβ1, on fibronectin (Fn)-coated surfaces.hMSCs expansion may also be affected by the chemistry of the culture surface, which modulates protein adsorption at the cell-material interface and, consequently, cell behavior.This work aimed to evaluate the effect of surface chemistry on hMSCs behavior in SCC-based XF media. For that, self-assembled monolayers (SAMs) with hydrophobic (−CH3) and hydrophilic (neutral −OH, positively charged -NH3+ and negatively charged −COO−) groups were used as model surfaces.Under XF conditions, Fn coating showed to be necessary to improve hMSC adhesion (4 h) onto all surfaces, except for OH-SAMs, probably due to a low protein adsorption capacity characteristic of this surface. In terms of cell metabolic activity (5 days) on Fn-coated surfaces, an increase over time under XF conditions was observed in all SAMs except in CH3-SAMs, which can be attributed to strong and irreversible protein adsorption characteristic of hydrophobic surfaces. This trend was also observed under FBS conditions. Nevertheless, none of the surfaces improved hMSC metabolic activity, as compared with tissue-cultured surfaces. Overall, this work describes the role of surface chemistry in XF hMSC expansion.

Ceramic membrane with protein-resistant surface via dopamine/diglycolamine co-deposition

Protein separation and purification is important in biotechnology and food processing industries. Ceramic membranes have shown great potentials for this task. But membrane fouling remains a barrier to their widespread application due to the irreversible adsorption of protein onto the membrane. In this work, one-step co-deposition of dopamine (DA) and diglycolamine (DGA) was conducted on the ceramic membranes for fabricating protein-resistant surfaces. CuSO4/H2O2 was used as a trigger to shorten the deposition time and to improve the deposition efficiency. The effect of DA/DGA mass ratio on the membrane structures and properties was studied by FESEM, FTIR, XPS and contact angle measurements. The results indicate that the optimal DA/DGA mass ratio in the co-deposition solution is 1:4. The modified membranes show improved hydrophilicity and negatively charged property. In dynamic protein filtration, these ceramic membranes exhibit a higher permeate flux, a higher water flux recovery, and a lower water flux reduction compared to the original membrane. Moreover, the antifouling property of the modified membrane is preserved after the membranes are treated with high speed water scouring. As a result, this one-step co-deposition method is a simple and effective way to prepare durable fouling-resistant ceramic membranes for protein removal.

Probing Surface Hydration and Molecular Structure of Zwitterionic and Polyacrylamide Hydrogels.

A hydrogel is a hydrophilic cross-linked polymer network which can contain a large amount of water. Hydrogels with distinguished interfacial physical toughness were analyzed for their potential application as antifouling coating materials, utilizing sum frequency generation (SFG) spectroscopy as the interfacial analytical technique. The surface structures of one sulfobetaine (SBMA) zwitterionic hydrogel (ZWHG) and two polysaccharide hydrogels (PHGs) were probed in air; their interfacial structures with silica were examined using SFG in water and protein solutions, respectively. Both ZWHG and PHGs interfaces in water were dominated by strongly hydrogen-bonded water molecules, but the bonding strength associated with ZWHG was much stronger. Although all hydrogels experienced interfacial change in the presence of protein solutions, after cleaning, the zwitterionic hydrogel interface recovered almost completely while the other two hydrogels were subject to irreversible protein adsorption. Additionally, orientational analysis of ZWHG methyl groups in water was conducted and related to the superior hydrogen-bonding strength of water molecules at the ZWHG interface. The interfacial structures of hydrogel materials probed by SFG can be correlated to their antifouling properties. This research highlighted the critical role that hydrogen-bonding strength of interfacial water molecules play for antifouling applications.

Capillary isoelectric focusing with free or immobilized pH gradient in silica particles packed column

The use of immobilized pH gradient (IPG) capillary isoelectric focusing (CIEF) was confirmed to be possible with packed capillaries. The success of this experiment was due to two key factors: first, the use of surface-confined atom transfer radical polymerization method led to an increase in active reaction sites on the surface of silica particles; second, the subsequent free radical reaction caused carrier ampholytes (CAs) to bond faster and firmer. Based on this scheme, both CIEF with free pH gradient and CIEF with IPG were performed in capillaries packed with 3 μm modified silica particles. In our online CIEF-UV platform, both reversible and irreversible adsorption of proteins was shown to be negligible. Four proteins were focused: cytochrome c (pI 10.2), myoglobin (pI 7.3), carbonic anhydrase (pI 5.9) and trypsin inhibitor (pI 4.5). The comparison of the two CIEF columns showed that the time required for focusing in the packed capillary with IPG is only increased by a factor of 1.5 compared to the packed capillary, giving complete focusing in less than 12 min at 400 V/cm. With the increment of the electric field (the maximum at 600 V/cm), the run time was continually decreasing in these packed capillaries while the peak shape was improving. The four proteins (pH 4.5–10.2) could be successfully separated in our online CIEF platform. Moreover, for the newly online CIEF platform, pressure-driven mobilization without an applied electric field was achieved in the packed capillary with immobilized pH gradient.

Selective cleavage of the polyphosphoester in crosslinked copper based nanogels: enhanced antibacterial performance through controlled release of copper.

Polymeric architectures with controlled and well-defined structural features are required to render a sustainable antibacterial surface - a key requirement in the design of polymeric membranes for water purification. Herein, surface selective crosslinking of copper oxide-polyphosphoester (CuO-PPE) hybrid nanogels on to polyvinylidene fluoride-styrene maleic anhydride (PVDF/SMA) ultrafiltration membranes was developed. The hybrid nanogels, composed of PPE and CuO, with inherent antifouling and antibacterial properties, were crosslinked using a macroinitiator (polyethylene glycol, PEG) and subsequently grafted on to PVDF/SMA by alkyne-anhydride reaction. Partially hydrolysed SMA solubilizes membrane proteins and the phosphatase/phospholipase triggers the cleavage of PPE segments resulting in controlled release of Cu ions. This unique strategy renders the membrane surface antibacterial through sustained and controlled release of Cu ions thereby generating intracellular reactive oxygen species (ROS). In addition, the enhanced antibiofouling performance of these membranes is facilitated by the presence of the hydrophilic macroinitiator (PEG and PPE). The modified membranes designed in this study are durable and possess long-term stability due to strong covalent interaction between CuO-PPE and the PVDF/SMA membrane. Studies on the flux, porosity and protein adsorption of the membranes were performed. An enhanced flux recovery ratio was observed for the modified membrane due to the pendant PPE groups (from CuO-PPE) which prohibit irreversible protein adsorption on the PVDF surface. The cytotoxicity of CuO-PPE is greatly reduced because of an effective coverage of CuO by biocompatible PPEs. This study opens up new avenues of fabricating "smart" inorganic nanoparticles that can be confined in a soft hybrid polymeric gel network with controlled release of Cu ions thereby precluding ubiquitous bacterial treatment in water filtration systems.

Evaluating endoglucanase Cel7B-lignin interaction mechanisms and kinetics using quartz crystal microgravimetry.

The kinetics and mechanisms of protein interactions with solid surfaces are important to fields as diverse as industrial biocatalysis, biomedical engineering, food science, and cell biology. The nonproductive adsorption of cellulase enzymes to lignin, a plant cell wall polymer, reduces their effectiveness in saccharifying biomass. Cellulase has been shown to interact with lignin, but the heterogeneity of lignin surfaces, challenges in measuring irreversible components of these interactions, and fast adsorption rates make quantifying the reaction kinetics difficult. This work employs quartz crystal microgravimetry with dissipation monitoring (QCM-D) for real-time measurement of adsorbed mass on a flat lignin surface. We have developed a method for casting homogeneous lignin films that are chemically similar to lignin found in pretreated biomass, and used QCM-D to compare three models of reversible-irreversible binding behavior: a single-site transition model, a transition model with changing adsorbate footprint, and a two-site transition model. Of the three models tested, the two-site transition model provides the only kinetic mechanism able to describe the behavior of Cel7B binding to lignin. While the direct implications of lignin-cellulase interactions may be limited to biomass deconstruction for renewable energy and green chemistry, the analytical and experimental methods demonstrated in this work are relevant to any system in which the kinetics and reaction mechanism of reversible and irreversible protein adsorption at a solid-liquid interface are important.

Investigation of cell behaviors on thermo-responsive PNIPAM microgel films

The use of poly(N-isopropylacrylamide) (PNIPAM) as building blocks for engineering responsive coatings and their potential use as switchable substrates such as biosensors have attracted great attention in recent years. However, few studies have been conducted regarding the cell behaviors and the related mechanism on thermos-responsive surfaces consisting of PNIPAM microgel particles. In this work, monodisperse PNIPAM microgels were synthesized and used to prepare PINPAM microgel films. Uniform microgel surfaces can be fabricated by drop-coating with the precoating of a polyethylenimine (PEI) layer. Cell experiments indicate that unlike PNIPAM polymer brushes reported with controllable detachment ability, HepG2, which is a human liver carcinoma cell line, remains adherent on the microgel films upon cooling. Surface plasmon resonance (SPR) experiments show an irreversible adsorption of serum proteins on the microgel surface upon cooling, whose adsorption is a prerequisite of cell adhesion during cell culture. This fact may account for the irreversible adhesion of HepG2 cells.

Эллипсометрический контроль сорбции белков при использовании PLOT-колонок с дендритной стационарной фазой

The article is related to the investigation of adsorption potential of proteins ( albumin, insulin, lysozyme and myoglobin) on the surface of hyperbranched polymers, specifically, water-soluble oligosaccharide derivatives of polyethyleneimine, which are used as a stationery phase in capillary electrochromatography (CEC). Various protein molecules are known to be markers of different diseases. Detection and quantification of these proteins are of the highest importance for a successful disease diagnostics. However, irreversible adsorption of proteins onto the walls of the silica-fused capillary during the separation process may distort the results of the analysis. A method of ellipsometry is proposed to solve the problem. In the research we suggest to carry out the ellipsometric measurement mode in situ on the surface of a silicon wafer coated with a thin film of hyperbranched polyethyleneimine modified with maltose. According to the data of ellipsometric investigation, hyperbranched polymers are revealed to prevent protein adsorption during their electrophoretic separation. Key words : hyperbranched polyethyleneimine, ellipsometry, protein adsorption, capillary electrochromatography, PLOT-column. (Russian) DOI: http://dx.doi.org/10.15826/analitika.2014.18.1.009 V. Potolitsyna, L. Kartsova, E. Bessonova Saint-Petersburg State University (SPbU), St. Petersburg, Russian Federation

In situ polymerization of PVDF-HEMA polymers: electrospun membranes with improved flux and antifouling properties for water filtration

In situ polymerization of poly (vinylidene fluoride) (PVDF) with hydroxyethylmethacrylate (HEMA) followed by electrospinning was employed to prepare electrospun nanofibrous membranes (ENMs), referred to as PVDF-PHEMA-ENMs. Enhanced hydrophilicity of the ENMs was observed after polymerization. A decrease in the fiber thickness resulted in a decrease in the pore size and 60% improvement in the flux. The fiber mat exhibited excellent microfiltration behavior after being coated with a surface-charged chitosan (CS) polymer, compared with its non-coated counterparts. Porosity, flux and protein adsorption studies were performed for these ENMs. A comparatively less reduced flux and better recovery ratio were observed for the PVDF-PHEMA-ENMs and CS-coated PVDF-PHEMA-ENMs due to hydrophilic pendant hydroxyl groups (from PHEMA) and/or CS groups, which can prohibit irreversible protein adsorption, on the ENM surfaces. One step method for the fabrication of electospun nanofibrous membranes (ENMs) with hydrophilic surfaces and improved flux via in situ polymerization technique is described. The developed membranes also possess enhanced antifouling properties when compared with the virgin PVDF polymer.

Parameter estimation for a model of fibronectin adsorption onto hydroxylapatite, oxidised polystyrene and nanostructured silica

Fibronectin is a protein present in blood and the extracellular matrix which has important roles in cell adhesion and migration, wound healing and blood clotting. Three models of fibronectin adsorption, on various substrates of interest to biochemists, are compared. The first model (of Langmuir) is expressed explicitly as a time dependent function for the mass of protein adsorbed. The second model is a modification of the scaled particle theory of Reiss et al. [J. Chem. Phys., 31:369--380, 1959] and takes into account the probability of a molecule finding a sufficiently large vacant area on the adsorbing substrate surface. The third model extends the second model to the case in which molecules may expand the radius of their contact with the substrate upon adsorption. We used datasets obtained from experiments to compare the models. The Langmuir model is straightforward to fit to a dataset. The remaining models are fitted using a steepest descent method to minimise least squares error. We describe initial estimates for parameters for this procedure and compare the quality of fit of the models. References M. A. Brusatori and P. R. van Tassel. A kinetic model of protein adsorption/surface-induced transition kinetics evaluated by the scaled particle theory. J. Colloid Interface Sci. , 219(2):333--338, 1999. doi:10.1006/jcis.1999.6496 D. E. MacDonald, B. Markovic, M. Allen, P. Somasundaran, A. L. Boskey. Surface analysis of human plasma fibronectin adsorbed to commercially pure titanium materials. J. Biomed. Mater. Res. , 41:120--130, 1998. http://www.ncbi.nlm.nih.gov/pubmed/9641632 E. Helfand, H. Reiss, H. L. Frisch, J. L. Lebowitz. Scaled particle theory of fluids. J. Chem. Phys. , 33(5):1379--1385, 1960. doi:10.1063/1.1731417 H. P. Erikson and N. A. Carrell. Fibronectin in extended and compact conformations: Electron microscopy and sedimentation analysis. J. Biol. Chem. , 258(23):14539--14544, 1983. http://www.jbc.org/content/258/23/14539 H. Reiss, H. L. Frisch and J. L. Lebowitz. Statistical mechanics of rigid spheres. J. Chem. Phys. , 31(2):369--380, 1959. doi:10.1063/1.1730361 I. Langmuir. The adsorption of gases on plane surfaces of glass, mica and platinum. J. Am. Chem. Soc. , 40(9):1361--1403, 1918. doi:10.1021/ja02242a004 P. R. van Tassel, L. Guemouri, J. J. Ramsden, G. Tarjus, P. Viot and J. Talbot. A particle--level model of irreversible protein adsorption with a postadsorption transition. J. Colloid Interface Sci. , 207(2):317--323, 1998. doi:10.1006/jcis.1998.5781 P. Schaaf and J. Talbot. Surface exclusion effects in adsorption processes. J. Chem. Phys. , 91(7):4401--4409, 1989. doi:10.1063/1.456768 B. Widom. Random sequential addition of hard spheres to a volume. J. Chem. Phys. , 44(10):3888--3894, 1966. doi:10.1063/1.1726548

Synthesis and characterization of poly(arylene ether ketone) copolymers with pendant carboxylic acid groups for antifouling ultrafiltration membrane

This work focused on the synthesis of a series of poly(arylene ether ketone) random copolymers with various controlled pendant carboxylic acid groups (PEAK-COOH) by direct copolymerization method and the preparation of antifouling ultrafiltration membranes via the conventional immersion precipitation phase inversion method. The morphologies of the PEAK-COOH membranes were investigated by scanning electron microscopy. In addition, the surface hydrophilicity and charged property of the PEAK-COOH membranes were studied by water contact angle and membrane potential measurements, and the results indicated that the introduction of COOH on the polymer chains of membrane materials was really an effective way to negatively charge the membrane and enhance the hydrophilicity. The pure water flux and protein solution permeation through the prepared membranes were increased with the increase in the content of carboxylic acid groups. The cycle ultrafiltration experiments for protein solution revealed that nonspecific protein adsorption, especially irreversible protein adsorption, for the PEAK-COOH membranes, was significantly reduced, suggesting superior antifouling performance.

The preparation of antifouling ultrafiltration membrane by surface grafting zwitterionic polymer onto poly(arylene ether sulfone) containing hydroxyl groups membrane

This work describes the polymerization of a zwitterionic polymer, poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] onto the poly(arylene ether sulfone) containing hydroxyl groups (PES-OH) membrane via redox graft polymerization using ceric (IV) ammonium nitrate (CAN) as initiator. Due to the presence of the activated hydroxyl groups which were used for the immobilization of MPC monomer, the grafting process is facile and effective which avoid the complex and unfavorable pretreatment process and/or hydroxylated treatment. Attenuated total reflectance Fourier transform infrared spectrometer (FTIR-ATR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterize the chemical compositions and surface morphologies of the unmodified (PES-OH) and modified membrane, respectively. Static water contact angle measurement indicated that the introduction of poly(MPC) promoted remarkably the surface hydrophilicity of the PES-OH membrane. The cycle ultrafiltration experiments for protein solution revealed that nonspecific protein adsorption, especially irreversible protein adsorption, for the zwitterionic membrane was significantly reduced, suggesting superior antifouling performance. This work not only introduces a modification approach to obtain a PES-OH membrane grafting hydrophilic poly(MPC) chains, but also gives the zwitterionic membrane a long time life and excellent ultrafiltration performance.

Synthesis of sulfonated polyphenylsulfone as candidates for antifouling ultrafiltration membrane

This work focused on the synthesis of a series of sulfonated polyphenylsulfone (SPPSU) random copolymers with various controlled sulfonation levels by using sulfonated monomer in direct copolymerization method and the preparation of antifouling SPPSU ultrafiltration membranes via the conventional immersion precipitation phase inversion method. The chemical structures of the SPPSU copolymers were confirmed by using Fourier transform infrared spectrometer (FTIR) and their thermal properties were thoroughly characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The morphologies of the SPPSU membranes were investigated by scanning electron microscopy (SEM), and the morphology changes of these resultant membranes had been detailedly explained and verified by Hansen solubility parameters (HSPs) from thermodynamic theory. In addition, the surface hydrophilicity and charged property of the SPPSU membranes were studied by water contact angle and membrane potential measurements, and the results indicated that the sulfonation of membrane material is really an effective way to enhance the hydrophilicity and negatively charge the membrane. The pure water flux and protein solution permeation through the prepared membranes were increased with the increase of the degree of sulfonation. The cycle ultrafiltration experiments for protein solution revealed that nonspecific protein adsorption, especially irreversible protein adsorption, for the SPPSU membranes was significantly reduced, suggesting superior antifouling performance.

Mechanistic Understanding of Protein-Silicone Oil Interactions

To investigate interactions between protein and silicone oil so that we can provide some mechanistic understanding of protein aggregation in silicone oil lubricated syringes and its prevention by formulation additives such as Polysorbate 80 and Poloxamer 188. Interfacial tension values of silicone oil/water interface of abatacept solutions with and without formulation additives were obtained under equilibrium conditions using Attension Theta optical tensiometer. Their adsorption and desorption profiles were measured using Quartz Crystal Microbalancing with Dissipation monitoring (QCM-D). The degree of aggregation of abatacept was assessed based on size exclusion measurement. Adsorption of abatacept at the oil/water interface was shown. Polysorbat 80 was more effective than Poloxamer 188 in preventing abatacept adsorption. Moreover, it was noted that some of the adsorbed abatacept molecules were not desorbed readily upon buffer rinse. Finally, no homogeneous aggregation was observed at room temperature and a slight increase of aggregation was only observed for samples measured at 40°C which can be prevented using Polysorbate 80. Interfacial adsorption of proteins is the key step and maybe responsible for the phenomenon of soluble-protein loss when contacting silicone oil and the irreversible adsorption of protein may be associated with protein denaturation/aggregation.