Binary Protein Solutions Research Articles

Understanding protein adsorption on silica mesoporous materials through thermodynamic simulations

This work presents a molecular thermodynamic theory to study protein interactions within a charge-regulating silica-like nanopore structure. The theory accounts for electrostatic interactions, steric repulsions, finite-size entropic effects, and protonation equilibrium of silanol groups on silica and protein residue side-chains. Coarse-grained representations of proteins based on their 3D crystallographic structures are employed. We evaluate the influence of pH, salt concentration, and pore size on the adsorption of selected proteins (cytochrome c, lysozyme, and myoglobin) in both single- and binary-protein solutions. The surface charge density on the nanopore walls is less negative than on the adjacent planar surface, primarily influenced by pH and salt concentration. Adsorption within the nanopore from single protein solutions exhibits a non-monotonic behavior with pH, increasing with decreasing salt concentration and diminishing pore size. Analysis of the effective interactions between proteins and silica surfaces indicates that adsorption is enhanced when the protein size matches that of the nanopore. Evaluation of various adsorption pathways indicates minimized free energy when the protein enters the nanopore through its edge and contacts its cylindrical walls. In binary solutions, the presence of another protein significantly alters the affinity of a protein for the silica surfaces, potentially preventing its adsorption, and affects its organization on these surfaces upon adsorption.

Facile Preparation of β-Cyclodextrin-Modified Polysulfone Membrane for Low-Density Lipoprotein Adsorption via Dopamine Self-Assembly and Schiff Base Reaction.

A facile method for the immobilization of β-cyclodextrin on polysulfone membranes with the aim of selectively adsorbing low-density lipoprotein (LDL) was established, which is based on the self-assembly of dopamine on the membrane followed by the Schiff base reaction with mono-(6-ethanediamine-6-deoxy)-β-cyclodextrin. The surface modification processes were validated using X-ray photoelectron spectroscopy and attenuated total reflectance Fourier-transform infrared spectroscopy. Surface wettability and surface charge of the membranes were investigated through the water contact angle and zeta potential analysis. The cyclodextrin-modified polysulfone membrane (PSF-CD) showed good resistance to protein solutions, as shown by the measurement of BSA adsorption. The assessment of BSA adsorption revealed that the cyclodextrin-modified polysulfone membrane (PSF-CD) exhibited excellent resistance to protein solutions. To investigate the adsorption and desorption behaviors of the membranes in single-protein or binary-protein solutions, an enzyme-linked immunosorbent assay was employed. The results revealed that the PSF-CD possessed remarkable adsorption capacity and higher affinity for LDL in both single-protein and binary-protein solutions, rendering it a suitable material for LDL apheresis.

Fabrication and Study of Dextran/Sulfonated Polysulfone Blend Membranes for Low-Density Lipoprotein Adsorption.

The abnormal increase in low-density lipoprotein (LDL) in human blood is a main independent risk factor for the pathogenesis of atherosclerosis, whereas a reduced LDL level effectively lowers morbidity. It is important to develop LDL adsorption materials with high efficiency and selectivity, as well as to simplify their fabrication processes. In this paper, polysulfone (PSF), sulfonated polysulfone (SPSF), and sulfonated polysulfone/dextran (SPSF/GLU) membranes were successfully fabricated for LDL adsorption using a solution casting technique. Attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy measurements confirmed the success of the preparation. The water contact angle decreased from 89.7 ± 3.4° (PSF) to 76.4 ± 3.2° (SPSF) and to 71.2 ± 1.9° (SPSF/GLU), respectively. BSA adsorption testing showed that the SPSF/GLU with surface enrichment of sulfonate groups and glycosyl groups possessed higher resistance to protein solution. The adsorption and desorption behaviors of the studied samples in single-protein or binary-protein solutions were systematically investigated by enzyme-linked immunosorbent assay (ELISA), The results showed that SPSF/GLU, which had excellent resistance to protein adsorption, possessed a similar adsorption capacity to that of PSF. SPSF membrane exhibited excellent selective affinity for LDL in single and binary protein solutions, suggesting potential applications in LDL removal.

Protein Adsorption onto Modified Porous Silica by Single and Binary Human Serum Protein Solutions.

Typical porous silica (SBA-15) has been modified with pore expander agent (1,3,5-trimethylbenzene) and fluoride-species to diminish the length of the channels to obtain materials with different textural properties, varying the Si/Zr molar ratio between 20 and 5. These porous materials were characterized by X-ray Diffraction (XRD), N2 adsorption/desorption isotherms at −196 °C and X-ray Photoelectron Spectroscopy (XPS), obtaining adsorbent with a surface area between 420–337 m2 g−1 and an average pore diameter with a maximum between 20–25 nm. These materials were studied in the adsorption of human blood serum proteins (human serum albumin—HSA and immunoglobulin G—IgG). Generally, the incorporation of small proportions was favorable for proteins adsorption. The adsorption data revealed that the maximum adsorption capacity was reached close to the pI. The batch purification experiments in binary human serum solutions showed that Si sample has considerable adsorption for IgG while HSA adsorption is relatively low, so it is possible its separation.

The influence of ion identity and ionic strength on membrane biofouling of a binary protein solution

Studying biofouling is important for increased implementation of membrane-based water purification technologies. A binary protein solution (bovine serum albumin (BSA) and hemoglobin (Hb)) was used to study biofouling of hydrophilic and hydrophobic PVDF membranes. By fitting normalized plots of flux vs time to an exponential decay, the rate of fouling and long-term steady-state flux were compared in the presence of different ions and at different ionic strengths. The presence of ions causes a lower steady-state flux but rate effects are ion identity dependent. Equally important is membrane type. For the hydrophobic membrane, the charge of the cation dictates different mechanisms affecting the rate or steady-state flux. With the hydrophilic membrane, the presence of cations results in a direct correlation between the rate of fouling and steady-state flux while the presence of different anions leads to no apparent trends. Thus, the Hofmeister series does not explain the influence of ions on the fouling of the binary protein solution. Finally, studies at higher ionic strengths (150–600 mM) show that fouling rates decrease likely due to charge shielding. The ionic strength where this effect is apparent depends on ion identity. The limited flux model supports these conclusions, though membrane type is important. Therefore, while protein-protein interactions are crucial, ion-membrane interactions cannot be ignored either. Conclusions about the role of ions and ionic strength on fouling must be made with care as multiple factors contribute to the rate and extent of fouling of a binary protein solution.

Single and binary protein electroultrafiltration using poly(vinyl-alcohol)-carbon nanotube (PVA-CNT) composite membranes.

Electrically conductive composite ultrafiltration membranes composed of carbon nanotubes have exhibited efficient fouling inhibition in wastewater treatment applications. In the current study, poly(vinyl-alcohol)-carbon nanotube membranes were applied to fed batch crossflow electroultrafiltration of dilute (0.1 g/L of each species) single and binary protein solutions of α-lactalbumin and hen egg-white lysozyme at pH 7.4, 4 mM ionic strength, and 1 psi. Electroultrafiltration using the poly(vinyl-alcohol)-carbon nanotube composite membranes yielded temporary enhancements in sieving for single protein filtration and in selectivity for binary protein separation compared to ultrafiltration using the unmodified PS-35 membranes. Assessment of membrane fouling based on permeate flux, zeta potential measurements, and scanning electron microscopy visualization of the conditioned membranes indicated significant resulting protein adsorption and aggregation which limited the duration of improvement during electroultrafiltration with an applied cathodic potential of -4.6 V (vs. Ag/AgCl). These results imply that appropriate optimization of electroultrafiltration using carbon nanotube-deposited polymeric membranes may provide substantial short-term improvements in binary protein separations.

Efficient adsorptive extraction materials by surface protein‐imprinted polymer over silica gel for selective recognition/separation of human serum albumin from urine

ABSTRACTIn this study, we report the development of adsorptive extraction materials by surface protein‐imprinted polymers (MIPs) over silica gel for selective recognition/separation of human serum albumin (HSA) from urine. The HSA‐imprinted polymers prepared on silica particle had at interface between the silica gel and different MIPs greatly produced enrichment for the binding of protein from the urine. The solid‐phase extraction of the optimized polymer layer was prepared by copolymerization of methacrylic acid (MAA), acrylamide (AAm), and dimethylaminoethylmethacrylate (DMAEMA) and a crosslinker methylenebisacrylamide (MBA) at the mole ratio of 1:158:88 (T:M:C) and showed moderate affinity (<104 order M−1) toward target protein HSA and selectivity. Four analogues, egg white albumin (EWA), bovine serum albumin (BSA), lysozyme (Lyz), and creatinine (Cre) were selected to study the binding efficiency of MIPs in single and binary protein solutions. We studied the influence on recognition ability for HSA and found that prepolymer mixture and matrix flexibility of the optimized thin polymer layer (35 ± 10 nm) on the submicrosilica particles. The high‐binding affinity (QMIP, 86.7 mg g−1) and fast kinetics (180 min) were observed for this synthesized HSA‐MIP when compared with other reported HSA‐MIPs in surface imprinting (5.9 and 11.3 mg g−1) and epitope surface imprinting (46.6 mg g−1) methods. We demonstrated the application in real and synthetic urine samples that the approach allowed the efficient adsorption of HSA in real urine (129.48 mg g−1) is almost double to the binding of HSA in synthetic urine (67.84 mg g−1). Apart from this, only minor interference of Cre (2.74 mg g−1) was observed, eventhough Cre is the final metabolite in urine. These adsorptive submicrosilica materials have potential in the pharmaceutical industry and clinical analysis applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46894.

Conformational and Organizational Insights into Serum Proteins during Competitive Adsorption on Self-Assembled Monolayers.

Physicochemical interactions of proteins with surfaces mediate the interactions between the implant and the biological system. Surface chemistry of the implant is crucial as it regulates the events at the interface. The objective of this study was to explore the performance of modified surfaces for such interactions relevant to various biomedical applications. Because of a wide range of surface wettability, we aimed to study protein behavior (i.e., conformational changes and their packing) during competitive protein adsorption. Three serum proteins (bovine serum albumin, BSA; fibrinogen, FB; and immunoglobulin G, IgG) were tested for their conformational changes and orientation upon adsorption on hydrophilic (COOH and amine), moderately hydrophobic (mixed and hybrid), and hydrophobic (octyl) surfaces generated via silanization. Modified surfaces were characterized using Fourier-transform infrared spectroscopy, contact angle, and atomic force microscopy (AFM) techniques. Adsorbed masses of proteins from single and binary protein solutions on different surfaces were quantified along with their secondary structure analyses. Maximum adsorbed protein masses were found to be on negatively charged and hydrophobic (octyl) surfaces because of ionic and hydrophobic interactions between protein molecules and surfaces, respectively. Side-on and end-on orientations of adsorbed protein molecules were analyzed using theoretical and AFM analyses. We observed compact and elongated forms of BSA molecules on hydrophilic and hydrophobic surfaces, respectively. We further found a linear increase in the α-helix content of BSA and β-sheet contents of FB and IgG proteins with the increasing side-on (%)-oriented protein molecules on the surfaces. This indicates that side-on orientations of adsorbed FB and IgG lead to the formation of β-sheets. Sodium dodecyl sulfate polyacrylamide gel electrophoresis was employed to quantify the protein types and their ratio in competitively adsorbed proteins on different surfaces. A theoretical analysis was also used to determine the % secondary structures of competitively adsorbed proteins from BSA/FB and BSA/IgG solutions, which very well agreed with experimental results. The competitive protein adsorption from both BSA/FB and BSA/IgG solutions was found to be entropy-driven, as revealed by thermodynamic studies performed using isothermal titration calorimetry.

Polyacrylamide-grafted calcium alginate microspheres as protein-imprinting materials

Protein-imprinted polyacrylamide (PAM)-grafted calcium alginate (CaA) microspheres were synthesized via free-radical grafting polymerization with potassium persulfate and sodium bisulfite as initiators. FTIR, 13C-NMR and SEM were used for characterization. Swelling behaviors were studied and it was found that modified calcium alginate (CaA) microspheres possessed larger swelling degree than calcium alginate, because grafted hydrophilic PAM side chains contributed to more water absorption. Moreover, the durability of the swollen samples was improved for the modified microspheres. Compared with calcium alginate microspheres, modified calcium alginate samples exhibited higher absorption capacity (approximately, 13.1 and 10.3 mg/g) for MIPs in single and binary protein solution. The rebinding selectivity of CaA-g-PAM microspheres (approximately, 2.7) was higher than that of calcium alginate (CaA) microspheres (approximately, 1.5) in binary protein solution. It was suggested that the introduction of PAM side chains was beneficial for the specific recognition of protein.

Changes in structure and performance during diafiltration of binary protein solutions due to repeated cycles of fouling/alkaline cleaning

The purpose of this work was to evaluate the effect of the temperature (50 and 60°C) of a NaOH cleaning solution during the diafiltration of a binary mixture of bovine serum albumin and β-lactoglobulin, through a 300kDa tubular ceramic membrane along repeated operational cycles. To this aim, final permeate volume, membrane and fouling resistances and individual protein concentration were analyzed. At the end of each individual study, the membranes were characterized by liquid–liquid displacement porosimetry. As a result, 50°C was found to be the most appropriated temperature due to its higher capability to restore the initial membrane resistance and the higher efficiency achieved in terms of protein separation. Both conditions fulfilled without altering the structural properties of the membrane as given by porosimetric analysis. In contrast, a great fouling resistance involving null protein transmission occurred when cleaning was performed at 60°C.

A generalized free-solvent model for the osmotic pressure of multi-component solutions containing protein–protein interactions

The free-solvent model has been shown to have excellent predictability of the osmotic pressure for single and binary non-interactive proteins in aqueous solutions. Here the free-solvent model is extended to be more generalized by including the contributions of intra- and inter-protein interactions to the osmotic pressure of a solution in the form of homo- and hetero-multimers. The solute–solvent interactions are considered to be unique for each homo- and hetero-multimer in solution. The effect of the various generalized free-solvent model parameters on the osmotic pressure are examined for a single protein solution with a homo-dimer, a binary protein solution with no protein–protein interactions, and a binary protein solution with a hetero-dimer. Finally, the limitations associated with the generalized free-solvent model are discussed.

Protein adsorption kinetics from single- and binary-solution

Comparison of protein mass-adsorption-rates to rates-of-change in interfacial tensions reveals that mass adsorption is decoupled from interfacial energetics. This implies that energy-barrier theories describing protein-adsorption kinetics do not accurately capture the physics of the process. An alternative paradigm in which protein molecules rapidly diffuse into an inflating interphase which subsequently slowly shrinks in volume, concentrating adsorbed protein and causing slow concomitant decrease in interfacial tensions, is shown to be consistent with adsorption kinetics measured by solution depletion and tensiometry. Mass adsorption kinetics observed from binary-protein solution is compared to adsorption kinetics from single-protein solution, revealing that organization of two different-sized proteins within the interphase can require significantly longer than that adsorbed from single-protein solution and may require expulsion of initially adsorbed protein which is not observed in the single-protein case.

Novel magnetic bovine serum albumin imprinted polymers with a matrix of carbon nanotubes, and their application to protein separation

Novel magnetic multi-walled carbon nanotubes@Fe(3)O(4) molecularly imprinted polymers (MWNTs@Fe(3)O(4)-MIPs) intended for bovine serum albumin (BSA) recognition were successfully developed. The MWNTs@Fe(3)O(4)-MIPs were characterized with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Scanning electron microscopy images showed that the Fe(3)O(4) nanoparticles (diameter: 50-60 nm) were coated with a layer of MIPs with an average thickness of 25-30 nm. The magnetic material was easily dispersed and retrieved through the application of an external magnetic field. Adsorption experiments showed that the estimated maximum amount of BSA that could be adsorbed onto the MWNTs@Fe(3)O(4)-MIPs was 52.8 mg/g, and the time taken to reach equilibrium was about 40 min. Meanwhile, the MWNTs@Fe(3)O(4)-MIPs exhibited excellent selectivity towards (i.e., recognition of) BSA. The feasibility of the use of the MWNTs@Fe(3)O(4)-MIPs as a solid-phase extraction (SPE) sorbent was evaluated, and the results showed that the MWNTs@Fe(3)O(4)-MIPs were able to separate the template protein BSA from a binary protein solution. The proposed sorbent based on MWNTs@Fe(3)O(4)-MIPs for BSA separation exhibited satisfactory recoveries ranging from 92.0% to 97.3% in real samples. It was also successfully used for the purification of BSA from bovine calf serum.

Covalent Heparin Modification of a Polysulfone Flat Sheet Membrane for Selective Removal of Low‐Density Lipoproteins: A Simple and Versatile Method

A simple, convenient and economical method for the heparinization of PSf membranes is described, with the aim of preparing an LDL adsorber for simultaneous LDL apheresis and hemodialysis. An atmospheric pressure glow discharge generator is used to activate the PSf membrane surface, with subsequent chemical binding of heparin in the presence of EDC and NHS. ATR-FTIR spectroscopy and XPS measurements confirm successful surface modification. The PSf-Hep membrane shows good blood compatibility, with a relatively low amount and normal morphology of adherent platelets. ELISA results indicate that the PSf-Hep membrane exhibits excellent selective affinity for LDL in single and binary protein solutions, suggesting potential applications in hemodialysis with simultaneous LDL removal.

Fibronectin Conformation Switch Induced by Coadsorption with Human Serum Albumin

The dynamic adsorption of human serum albumin (HSA) and plasma fibronectin (Fn) onto hydrophobic poly(hydroxymethylsiloxane) (PHMS) and the structures of adsorbed protein layers from single and binary protein solutions were studied. Spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation monitoring (QCM-D) together with atomic force microscopy (AFM) were used to measure the effective mass, thickness, viscoelastic properties, and morphology of the adsorbed protein films. Adsorbed HSA formed a rigid, tightly bound monolayer of deformed protein, and Fn adsorption yielded a thick, very viscoelastic layer that was firmly bound to the substrate. The mixed protein layers obtained from the coadsorption of binary equimolecular HSA-Fn solutions were found to be almost exclusively dominated by Fn molecules. Further sequential adsorption experiments showed little evidence of HSA adsorbed onto the predeposited Fn layer (denoted as Fn ≫ HSA), and Fn was not adsorbed onto predeposited HSA (HSA ≫ Fn). The conformational arrangement of the adsorbed Fn was analyzed in terms of the relative availability of two Fn domains. In particular, (4)F(1)·(5)F(1) binding domains in the Hep I fragment, close to the amino terminal of Fn, were targeted using a polyclonal antifibronectin antibody (anti-Fn), and the RGD sequence in the 10th segment, in the central region of the molecule, was tested by cell culture experiments. The results suggested that coadsorption with HSA induced the Fn switch from an open conformation, with the amino terminal subunit oriented toward the solution, to a close conformation, with the Fn central region oriented toward the solution.

Protein‐resistant polyurethane by sequential grafting of poly(2‐hydroxyethyl methacrylate) and poly(oligo(ethylene glycol) methacrylate) via surface‐initiated ATRP

Protein-resistant polyurethane (PU) surfaces were prepared by sequentially grafting poly(2-hydroxyethyl methacrylate) (poly(HEMA)) and poly(oligo(ethylene glycol) methacrylate) (poly(OEGMA)) via surface-initiated atom transfer radical polymerization (s-ATRP). The chain lengths of poly(HEMA) and poly(OEGMA) were regulated via the ratio of monomer to sacrificial initiator in solution. The surfaces were characterized by water contact angle and X-ray photoelectron spectroscopy (XPS). The protein resistant properties of the surfaces were assessed by single and binary adsorption experiments with fibrinogen (Fg), lysozyme (Lys), and lactalbumin (Lac). The adsorption of all three proteins on the sequentially grafted poly(HEMA)-poly(OEGMA) surfaces (PU/PH/PO) was greatly reduced compared with the unmodified PU. Adsorption decreased with increasing poly(OEGMA) chain length. On the PU/PH/PO surface with longest poly(OEGMA) chain length (∼100), the decrease in Lys adsorption was in the range of 95-98% and the decrease in Fg and Lac adsorption was >99% compared with the unmodified PU. Adsorption from binary protein solutions showed that the PU/PH/PO surfaces resisted these proteins more or less equally, that is, independent of protein size.

Volumetric interpretation of protein adsorption: Kinetics of protein-adsorption competition from binary solution

The standard solution-depletion method is implemented with SDS-gel electrophoresis as a multiplexing, separation-and-quantification tool to measure competition between two proteins ( i and j) for adsorption to the same hydrophobic adsorbent particles (either octyl sepharose or silanized glass) immersed in binary-protein solutions. Adsorption kinetics reveals an unanticipated slow protein-size-dependent competition that controls steady-state adsorption selectivity. Two sequential pseudo-steady-state adsorption regimes (State 1 and State 2) are frequently observed depending on i, j solution concentrations. State 1 and State 2 are connected by a smooth transition, giving rise to sigmoidally-shaped adsorption-kinetic profiles with a downward inflection near 60 min of solution/adsorbent contact. Mass ratio of adsorbed i, j proteins ( m i / m j ) remains nearly constant between States 1 and 2, even though both m i and m j decrease in the transition between states. State 2 is shown to be stable for 24 h of continuous-adsorbent contact with stagnant solution whereas State 2 is eliminated by continuous mixing of adsorbent with solution. In sharp contrast to binary-competition results, adsorption to hydrophobic adsorbent particles from single-protein solutions (pure i or j) exhibits no detectable kinetics within the timeframe of experiment from either stagnant or continuously mixed solution, quickly achieving a single steady-state value in proportion to solution concentration. Comparison of binary competition between dissimilarly-sized protein pairs chosen to span a broad molecular-weight (MW) range demonstrates that selectivity between i and j scales with MW ratio that is proportional to protein-volume ratio (ubiquitin, Ub, MW = 10.7 kDa; human serum albumin, HSA, MW = 66.3 kDa; prothrombin, FII, 72 kDa; immunoglobulin G, IgG, MW = 160 kDa; fibrinogen, Fib, MW = 341 kDa). Results are interpreted in terms of a kinetic model of adsorption that has protein molecules rapidly diffusing into an inflating interphase that is spontaneously formed by bringing a protein solution into contact with a physical surface (State 1). State 2 follows by rearrangement of proteins within this interphase to achieve the maximum interphase concentration (dictated by energetics of interphase dehydration) within the thinnest (lowest volume) interphase possible by ejection of interphase water and initially-adsorbed proteins. Implications for understanding biocompatibility are discussed using a computational example relevant to the problem of blood–plasma coagulation.

Immobilization of heparin on polysulfone surface for selective adsorption of low-density lipoprotein (LDL)

A versatile method was developed to immobilize heparin covalently on polysulfone sheets (PSu) to achieve selective adsorption of low-density lipoprotein (LDL). This was achieved by activation of PSu with successive treatments of chlorodimethyl ether and ethylenediamine, and subsequent chemical binding of heparin with bifunctional linker molecules. A heparin density up to 0.86 microg cm(-2) on a dense PSu film was achieved. The modified PSu films were characterized by attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The hydrophilicity of the PSu film was improved greatly by covalent immobilization of heparin. The water contact angle of PSu film was decreased from 86.6 + or - 3.7 degrees to 50.5 + or - 3.2 degrees after binding of 0.36 microg cm(-2) heparin. An enzyme-linked immunosorbent assay was used to measure the binding of LDL on plain and modified PSu films. It was found that the heparin-modified PSu film could selectively recognize LDL from binary protein solutions. Furthermore, it was possible to desorb LDL from heparinized PSu, but not from plain PSu, with heparin, sodium chloride or urea solution, which indicates a selective but reversible binding of LDL to heparin. The results suggest that heparin-modified PSu membranes are promising for application in simultaneous hemodialysis and LDL apheresis therapy.

Protein attachment onto silica surfaces – a survey of molecular fundamentals, resulting effects and novel preventive strategies in CE

This review addresses the fundamentals governing the adsorption of individual protein molecules onto the surface of fused-silica capillaries, the protein aggregation to adsorbate clusters and their final accretion to monolayers with subsequent stratification to protein multilayers. The attention in CE protein separation has primarily been focused on (i) tuning the BGE including the buffer type, ionic strength, pH and additives, (ii) tailored post-rinse procedures to detach adhered protein residues and (iii) the optimization of capillary wall shielding in order to reduce protein attachment. Improvements in protein separation as well as related adverse effects are mainly discussed on the basis of parameters known to become deteriorated in case of protein adhesion, e.g. repeatability of the EOF and of migration times, peak width, theoretical plate numbers, resolution and asymmetry factor. However, knowledge of the molecular principles controlling protein adsorption onto silica surfaces is indispensable for separation optimization. Furthermore, it facilitates troubleshooting and the interpretation of undesired concomitant phenomena. This review comprehensively discusses protein adsorption models derived from surface chemistry primarily in terms of their relevance for CE, clearly showing that the adsorption process in its complexity is only partially revealed by models, which address single or binary protein solutions. In a further section theoretical concepts and surface models are related to surface phenomena encountered in CE. The final part of the review surveys recent concepts for prevention of protein adhesion, thereby addressing capillary treatment, favorable buffer types, dynamic and adhesive semi-permanent coating strategies covering the literature from 2000-2008.

Protein‐resistant polyurethane via surface‐initiated atom transfer radical polymerization of oligo(ethylene glycol) methacrylate

Protein-resistant polyurethane (PU) surfaces were prepared by surface-initiated simultaneous normal and reverse atom transfer radical polymerization (s-ATRP) of poly(oligo(ethylene glycol) methacrylate) (poly (OEGMA)). Oxygen plasma treatment was employed for initial activation of the PU surface. The grafted polymer chain length was adjusted by varying the molar ratio of monomer to sacrificial initiator in solution from 5:1 to 200:1. The modified PU surfaces were characterized by water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Protein adsorption experiments from tris-buffered saline (TBS) and plasma were carried out to evaluate the protein-resistance of the surfaces. Adsorption from single and binary protein solutions as well as from plasma was significantly reduced after modification. Adsorption decreased with increasing poly(OEGMA) chain length. Fibrinogen (Fg) adsorption on the 200:1 monomer/initiator surface was in the range of 3-33 ng/cm(2) representing 96-99% reduction compared with the unmodified PU. Fg adsorption from 0.01-10% plasma was as low as 1-5 ng/cm(2). Moreover, binary protein adsorption experiments using Fg and lysozyme (Lys) showed that protein size is a factor in the protein resistance of these surfaces.