BSA adsorption on differently charged polystyrene nanoparticles using isothermal titration calorimetry and the influence on cellular uptake

BSA adsorption onto negatively and positively charged polystyrene nanoparticles was investigated. The nanoparticles were characterized in terms of particle size, zeta potential, surface group density, and morphology. The adsorption behavior of BSA on the particle surface, as a function of pH and overall charge of the particle, was studied using ITC. Different thermodynamic data such as enthalpy changes upon binding and stoichiometry of the systems were determined and discussed. The degree of surface coverage with BSA was calculated using the thermodynamic data. The cellular uptake of particles before and after BSA adsorption was studied using HeLa cells in the presence and absence of supplemented FCS in the cell culture medium.     

刷状结构的阳离子性接枝微粒QPDMAEMA/SiO2对牛血清白蛋白的吸附特性

以微米级硅胶微粒为基质, 通过接枝聚合和大分子反应, 制备了具有刷状结构的阳离子性接枝微粒, 深入研究了其对牛血清白蛋白(BSA)的强吸附能力、吸附机理和吸附热力学. 首先使含叔胺基团的单体甲基丙烯酸二甲基氨基乙酯(DMAEMA)在硅胶微粒表面发生接枝聚合, 制得接枝微粒PDMAEMA/SiO₂, 然后以氯乙胺为试剂, 使接枝大分子PDMAEMA链中的叔胺基团发生季铵化反应, 获得了具有刷状结构的阳离子聚电解质的功能接枝微粒QPDMAEMA/SiO₂. 测定了微粒QPDMAEMA/SiO₂的zeta 电位, 实施了对BSA的等温吸附实验, 考察了介质pH值、离子强度及温度对吸附作用的影响, 研究了吸附热力学. 研究结果表明, 功能接枝微粒QPDMAEMA/SiO₂ 比接枝微粒PDMAEMA/SiO₂ 具有更高的zeta 电位, 在静电相互作用驱动下, 微粒QPDMAEMA/SiO₂对BSA具有很强的吸附能力. 吸附容量随介质pH值的增大呈现先增大后减小的变化趋势,当pH值等于BSA的等电点(pI=4.7)时, 具有最高的吸附容量(高达112 mg·g^-1). 以等电点为界, 离子强度对吸附容量会产生完全相反的影响作用: 当介质pH值小于BSA的等电点时, 电解质浓度增大, 吸附容量增高; 当介质pH值等于BSA的等电点时, 吸附容量几乎不随电解质的浓度发生变化. 吸附过程熵值减小而且放出热量,是一个焓驱动的吸附过程.     

刷状结构的阳离子性接枝微粒QPDMAEMA/SiO_2对牛血清白蛋白的吸附特性

以微米级硅胶微粒为基质,通过接枝聚合和大分子反应,制备了具有刷状结构的阳离子性接枝微粒,深入研究了其对牛血清白蛋白(BSA)的强吸附能力、吸附机理和吸附热力学.首先使含叔胺基团的单体甲基丙烯酸二甲基氨基乙酯(DMAEMA)在硅胶微粒表面发生接枝聚合,制得接枝微粒PDMAEMA/SiO2,然后以氯乙胺为试剂,使接枝大分子PDMAEMA链中的叔胺基团发生季铵化反应,获得了具有刷状结构的阳离子聚电解质的功能接枝微粒QPDMAEMA/SiO2.测定了微粒QPDMAEMA/SiO2的zeta电位,实施了对BSA的等温吸附实验,考察了介质pH值、离子强度及温度对吸附作用的影响,研究了吸附热力学.研究结果表明,功能接枝微粒QPDMAEMA/SiO2比接枝微粒PDMAEMA/SiO2具有更高的zeta电位,在静电相互作用驱动下,微粒QPDMAEMA/SiO2对BSA具有很强的吸附能力.吸附容量随介质pH值的增大呈现先增大后减小的变化趋势,当pH值等于BSA的等电点(pI=4.7)时,具有最高的吸附容量(高达112 mg?g-1).以等电点为界,离子强度对吸附容量会产生完全相反的影响作用:当介质pH值小于BSA的等电点时,电解质浓度增大,吸附容量增高;当介质pH值等于BSA的等电点时,吸附容量几乎不随电解质的浓度发生变化.吸附过程熵值减小而且放出热量,是一个焓驱动的吸附过程.     

Adsorption of sterically stabilized latex particles at liquid surfaces: effects of steric stabilizer surface coverage, particle size, and chain length on particle wettability

A series of five near-monodisperse sterically stabilized polystyrene (PS) latexes were synthesized using three well-defined poly(glycerol monomethacrylate) (PGMA) macromonomers with mean degrees of polymerization (DP) of 30, 50, or 70. The surface coverage and grafting density of the PGMA chains on the particle surface were determined using XPS and (1)H NMR spectroscopy, respectively. The wettability of individual latex particles adsorbed at the air-water and n-dodecane-water interfaces was studied using both the gel trapping technique and the film calliper method. The particle equilibrium contact angle at both interfaces is relatively insensitive to the mean DP of the PGMA stabilizer chains. For a fixed stabilizer DP of 30, particle contact angles were only weakly dependent on the particle size. The results are consistent with a model of compact hydrated layers of PGMA stabilizer chains at the particle surface over a wide range of grafting densities. Our approach could be utilized for studying the adsorption behavior of a broader range of sterically stabilized inorganic and polymeric particles of practical importance.     

INCLUSION COMPLEX FORMATION BETWEEN α-CYCLODEXTRIN AND BIODEGRADABLE COMBLIKE COPOLYMERS WITH POLY(α,β-MALIC ACID) BACKBONES AND mPEG SIDE CHAINS

Inclusion complexes(ICs) composed ofα-cyclodextrins(α-CD) and biodegradable comblike copolymers with poly(α,β-malic acid)(PMA) backbones and methylated poly(ethylene glycol)(mPEG) side chains were prepared by the host-guest reaction.Two series of ICs with mPEG750 and mPEG2000 were prepared.The stoichiometry(EG/CD) of all the ICs in mPEG2000 series was 3.1,no matter what the graft degree was.While in mPEG750 series,the stoichiometry(EG/CD) was very different:it increased with the amount of mPEG decreasing...     

Disruptions in the crystallinity of poly(lauryl methacrylate) due to adsorption on silica

The effects of adsorption of poly(lauryl methacrylate) (PLMA), a side‐chain crystalline polymer, on silica were investigated. Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC) measurements were made on both bulk and adsorbed PLMA. The reversible heat flow rates were observed as a function of temperature and the degree of crystallinity of the samples determined based on the broad melting transitions of the side chains in the surface samples. It was found that adsorption caused a disruption of the side‐chain crystallinity primarily in the tightly bound layer of the polymer, but did not significantly affect its glass transition temperature. A change in the packing of the hydrophobic side chains, as a result of adsorption, was also observed for the tightly adsorbed polymer. These results indicated that PLMA side chains in proximity to the silica surface have different properties from those in bulk PLMA. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 89–96     

Adsorption of novel thermosensitive graft-copolymers: Core-shell particles prepared by polyelectrolyte multilayer self-assembly

The adsorption properties of thermosensitive graft-copolymers are investigated with the aim of developing self-assembled multilayers from these copolymers. The copolymers consist of a thermoreversible main chain of poly(N-isopropylacrylamid) and a weak polyelectrolyte, poly(2-vinylpyridine), as grafted side chains. Zeta-potential, single particle light scattering and adsorption isotherms monitor the adsorption of the thermoreversible copolymers to precoated colloidal particles. The results show a smaller surface coverage for a larger density of grafted chains. The surface coverage is discussed in terms of surface charge density in the adsorbed monolayer. Taking into account the monolayer adsorption properties, conditions are developed for the multilayer formation from these copolymers. A low pH provides a sufficient charge density of the grafted chains to achieve a surface charge reversal of the colloids upon adsorption. The charge reversal after each adsorbed layer is monitored by zeta-potential and the increase of the thickness is determined by light scattering. Stable and reproducible multilayers are obtained. The results imply that the conformation of the thermosensitive component in multilayers depends strongly on the grafting density, where the polymer with a higher grafting density adsorbs in a flat conformation while that with a lower grafting density adsorbs with more loops.     

Analysis of mass transport models for protein adsorption to cation exchanger by visualization with confocal laser scanning microscopy

The mass transfer of bovine serum albumin (BSA) to a cation exchanger, SP Sepharose FF, has been studied by finite batch adsorption experiments. The uptake curve was simulated with three mass transport models (i.e., effective pore diffusion model, surface diffusion model and Maxwell-Stefan model) incorporating the particle size distribution of the adsorbent particles. All the three models can simulate the uptake curves reasonably well. However, how well these models could simulate the real concentration profile within the adsorbent particle cannot be verified by the fitness of the models to the uptake curve. Thus, confocal laser scanning microscopy (CLSM) was used to visualize protein uptake to the porous adsorbent particles during the batch experiments. Using a fluorescent dye-labeled bovine serum albumin (BSA) for the dynamic adsorption experiments, the radial concentration profiles of the labeled BSA molecules into individual adsorbent particles at different times were obtained from the CLSM images. The protein distribution profiles within various particle diameters at different time were compared with the radial protein distributions predicted from the models. It reveals that surface diffusion model describes the intraparticle protein concentration profiles better than the other two models.     

Profiling protein-surface interactions of multicomponent suspensions via flow cytometry

This study presents the use of flow cytometry as a high-throughput quantifiable technique to study multicomponent adsorption interactions between proteins and surfaces. Flow cytometry offers the advantage of high-throughput analysis of multiple parameters on a very small sampling scale. This enables flow cytometry to distinguish between individual adsorbent particles and adsorbate components within a suspension. As a proof of concept study, the adsorption of three proteins--bovine serum albumin (BSA), bovine immunoglobulin gamma (IgG) and fibrinogen--onto five surface-modified organosilica microsphere surfaces was used as a model multicomponent system for analysis. By uniquely labeling each protein and solid support type with spectrally distinguishable fluorescent dyes, the adsorption process could be "multiplexed" allowing for simultaneous screening of multiple adsorbate (protein) and adsorbent (particle surface) interactions. Protein adsorption experiments quantified by flow cytometry were found to be comparable to single-component adsorption studies by solution depletion. Quantitative distribution of the simultaneous competitive adsorption of BSA and IgG indicated that, at concentrations below surface saturation, both proteins adsorbed onto the surface. However, at concentrations greater than surface saturation, BSA preferentially adsorbed. Multiplexed particle suspensions of optically encoded particles were modified to produce a positively and negatively charged surface, a grafted 3400 MW poly(ethylene glycol) layer, or a physisorbed BSA or IgG layer. It was observed that adsorption was rapid and irreversible on all of the surfaces, and preadsorbed protein layers were the most effective in preventing further protein adsorption.     

SURFACE MODIFICATION OF MICROPOROUS POLYPROPYLENE MEMBRANES BY GRAFT POLYMERIZATION OF N,N-DIMETHYLAMINOETHYL METHACRYLATE

Surface modification of microporous polypropylene hollow fiber membranes was performed by radical-induced graft polymerization of N,N-dimethylaminoethyl methacrylate (DMAEMA). The influences of temperature, monomer concentration and pre-adsorbed amount of benzoyl peroxide on grafting degree were studied respectively. It was found that the appropriate graft temperature was 75℃, at which the grafting degree was the highest and the hydrolytic decomposition of DMAEMA the lowest. Scanning electron photomicrography and the average pore diameters of the modified membranes demonstrated that part of the micropores on the membrane surface was plugged by the grafted polyDMAEMA chains, especially at high grafting degree. Contact angle and water swelling experiments showed that a moderate grafting degree could improve the hydrophilicity of the membranes. In the range of I 1.3%o-12.0% grafting degree, the water swelling percentage reached its maximum (51.1%) and the contact angle reached its minimum (74 degrees). The bovine serum albumin (BSA) adsorption experiment indicated that the grafted polyDMAEMA had a dual effect on protein adsorption. At the first stage, the BSA adsorption decreased with increasing of DMAEMA grafting degree. As the interaction between BSA and polyDMAEMA on membrane surface increased, the BSA adsorption increased with increasing of DMAEMA grafting degree.     

Electrostatic interaction between chitosan-modified latex particles and bovine serum albumin

Electrostatic interaction between poly(methyl methacrylate) latex particles with different levels of chitosan modification and bovine serum albumin (BSA) was investigated. The critical flocculation concentration is in the range 5–15 nmol dm⁻³ for these latex products toward added BSA. A series of isothermal equilibrium adsorption experiments shows that the adsorption process is divided into two distinct intervals. Adsorption of BSA on latex particles in intervals I and II is primarily controlled by charge neutralization and hydrophobic interaction, respectively. Intervals I and II can be reasonably described by an empirical parabola equation and the Langmuir isotherm model, respectively. The maximum amount of BSA adsorbed per unit weight of polymer particles was observed at pH ≅ 5. A maximum elution yield of about 80% can be achieved using NaSCN as the elution electrolyte, and NaSCN is more effective in inducing desorption of BSA from the particle surface than NaCl. The chitosan content has very little effect on the interaction between latex particles and BSA. By contrast, the influence of the content of 2,2′-azobis(2-amidinopropane) dihydrochloride, a cationic initiator used in preparing the chitosan-modified latex products, on the BSA adsorption process is significant. Received: 26 March 1999 Accepted in revised form: 3 June 1999     

Polystyrene‐graft‐poly(ethylene oxide) copolymers prepared by macromonomer technique in dispersion. I. Liquid chromatographic separation of product mixtures

Products of the radical dispersion copolymerization of methacryloyl‐terminated poly(ethylene oxide) (PEO) macromonomer and styrene were separated and characterized by size exclusion chromatography (SEC), full adsorption‐desorption (FAD)/SEC coupling and eluent gradient liquid adsorption chromatography (LAC). In dimethylformamide, which is a good solvent for PEO side chains but a poor solvent for polystyrene (PS), amphiphilic PS‐graft‐PEO copolymers formed aggregates, which were very stable at room temperature even upon substantial dilution. The aggregates disappeared at high temperature or in tetrahydrofuran (THF), which is a good solvent for both homopolymers and for PS‐graft‐PEO. FAD/SEC procedure allowed separation of homo‐PS from graft‐copolymer and determination of both its amount and molar mass. Effective molar mass of graft‐copolymer was estimated directly from the SEC calibration curve determined with PS standards. Presence of larger amount of the homo‐PS in the final graft‐copolymer products was also confirmed with LAC measurements. The results indicate that there are at least two or maybe three polymerization loci; namely the continuous phase, the particle surface layer and the particle core. The graft copolymers are produced mainly in the continuous phase while PS or copolymer rich in styrene units is formed mostly in the core of monomer‐swollen particles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2284–2291, 2000     

Conformational Changes of Bovine Serum Albumin Induced by Adsorption on Different Clay Surfaces: FTIR Analysis

Interactions between proteins and clays perturb biological activity in ecosystems, particularly soil extracellular enzyme activity. The pH dependence of hydrophobic, hydrophilic, and electrostatic interactions on the adsorption of bovine serum albumin (BSA) is studied. BSA secondary structures and hydration are revealed from computation of the Amide I and II FTIR absorption profiles. The influence of ionization of Asp, Glu, and His side chains on the adsorption processes is deduced from correlation between p(2)H dependent carboxylic/carboxylate ratio and Amide band profiles. We quantify p(2)H dependent internal and external structural unfolding for BSA adsorbed on montmorillonite, which is an electronegative phyllosilicate. Adsorption on talc, a hydrophobic surface, is less denaturing. The results emphasize the importance of electrostatic interactions in both adsorption processes. In the first case, charged side chains directly influence BSA adsorption that generate the structural transition. In the second case, the forces that attract hydrophobic side chains toward the protein-clay interface are large enough to distort peripheral amphiphilic helical domains. The resulting local unfolding displaces enough internal ionized side chains to prevent them from establishing salt bridges as for BSA native structure in solution. On montmorillonite, a particular feature is a higher protonation of the Asp and Glu side chains of the adsorbed BSA than in solution, which decreases coulombic repulsion. Copyright 2000 Academic Press.     

α-Al2O3与Co-Ni合金电化学共沉积动力学模型

在经典复合电沉积机理基础上,考虑到粒子与电极表面之间的多种作用力,以吸附强度来表征粒子与电极表面的作用力大小,根据粒子在电极表面的临界吸附强度,把粒子的吸附分为有效吸附和非有效吸附.当吸附强度大于临界吸附强度时,粒子能被有效吸附嵌入到沉积层中,粒子被有效吸附的概率和平均吸附强度有关.建立了相应的复合电沉积动力学模型.该模型在α-Al2O3与Co-Ni合金的复合共沉积体系中,在电流密度为1～20 A•dm2范围内得到了验证.通过数学模型和实验结果研究了电流密度对粒子沉积量φc、吸脱附常数K、有效吸附概率P和平均吸附强度的影响规律.     

Synthesis of a “molecular rope curtain”: Preparation and characterization of a sliding graft copolymer with grafted poly(ethylene glycol) side chains by the “grafting onto” strategy

A sliding graft copolymer (SGC) with poly(ethylene glycol) (PEG) side chains was prepared by ester formation between terminal carboxyl groups of oxidized PEG methyl ether with molecular weight of 2000 (mPEG2000‐COOH) and hydroxyl groups of a polyrotaxane consisting of PEG and cyclodextrins (CDs). Formation of the SGC structure was confirmed by ¹H NMR, attenuated total reflectance Fourier‐transformed infrared, and gel permeation chromatography. The SGC was soluble in good solvents of PEG and insoluble in poor solvents of PEG. Estimation of the number of grafted mPEG chains suggested a “rope‐curtain” like structure, in which an mPEG chain is connected to each CD ring. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Surface-grafted poly(acrylic acid) brushes as a precursor layer for biosensing applications: effect of graft density and swellability on the detection efficiency

Carboxyl groups along poly(acrylic acid) (PAA) brushes attached to the surface of a gold-coated substrate served as the precursor moieties for the covalent immobilization of amino-functionalized biotin or bovine serum albumin (BSA) to form a sensing probe for streptavidin (SA) or anti-BSA detection, respectively. Surface-grafted PAA brushes were obtained by acid hydrolysis of poly(tert-butyl acrylate) brushes, formerly prepared by surface-initiated atom transfer radical polymerization of tert-butyl acrylate. As determined by surface plasmon resonance, the PAA brushes immobilized with functionalized biotin or BSA probes not only showed good binding with the designated target analytes but also maintained a high resistance to nonspecific protein adsorption, especially those PAA brushes with a high surface graft density. Although the probe binding capacity can be raised as a function of the graft density of the PAA brushes or the amount of carboxyl groups along the PAA chains, the accessibility of the target analyte to the immobilized probe was limited at the high graft density of the PAA brushes. The effect was far more apparent for the BSA-anti-BSA probe-analyte pair than for the much smaller biotin-SA probe-analyte pair. The impact of the swellability of the PAA brushes, as tailored by the degree of carboxyl group activation, on both the sensing probe immobilization and analyte detection was also addressed. This investigation demonstrated that PAA brushes having a defined graft density have a promising potential as a precursor layer for biosensing applications.     

BSA adsorption on bimodal PEO brushes

BSA adsorption onto bimodal PEO brushes at a solid surface was measured using optical reflectometry. Bimodal brushes consist of long (N=770) and short (N=48) PEO chains and were prepared on PS surfaces, applying mixtures of PS(29)-PEO(48) and PS(37)-PEO(770) block copolymers and using the Langmuir-Blodgett technique. Pi-A isotherms of (mixtures of) the block copolymers were measured to establish the brush regime. The isotherms of PS(29)-PEO(48) show hysteresis between compression and expansion cycles, indicating aggregation of the PS(29)-PEO(48) upon compression. Mixtures of PS(29)-PEO(48) and PS(37)-PEO(770) demonstrate a similar hysteresis effect, which eventually vanishes when the ratio of PS(37)-PEO(770) to PS(29)-PEO(48) is increased. The adsorption of BSA was determined at brushes for which the grafting density of the long PEO chains was varied, while the total grafting density was kept constant. BSA adsorption onto monomodal PEO(48) and PEO(770) brushes was determined for comparison. The BSA adsorption behavior of the bimodal brushes is similar to the adsorption of BSA at PEO(770) monomodal brushes. The maximum of BSA adsorption at low grafting density of PEO(770) can be explained by ternary adsorption, implying an attraction between BSA and PEO. The contribution of primary adsorption to the total adsorbed amount is negligible.     

'Stealth' corona-core nanoparticles surface modified by polyethylene glycol (PEG): influences of the corona (PEG chain length and surface density) and of the core composition on phagocytic uptake and plasma protein adsorption

Nanoparticles possessing poly(ethylene glycol) (PEG) chains on their surface have been described as blood persistent drug delivery system with potential applications for intravenous drug administration. Considering the importance of protein interactions with injected colloidal dug carriers with regard to their in vivo fate, we analysed plasma protein adsorption onto biodegradable PEG-coated poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA) and poly(-caprolactone) (PCL) nanoparticles employing two-dimensional gel electrophoresis (2-D PAGE). A series of corona/core nanoparticles of sizes 160–270 nm were prepared from diblock PEG-PLA, PEG-PLGA and PEG-PCL and from PEG-PLA:PLA blends. The PEG Mw was varied from 2000–20 000 g/mole and the particles were prepared using different PEG contents. It was thus possible to study the influence of the PEG corona thickness and density, as well as the influence of the nature of the core (PLA, PLGA or PCL), on the competitive plasma protein adsorption, zeta potential and particle uptake by polymorphonuclear (PMN) cells. 2-D PAGE studies showed that plasma protein adsorption on PEG-coated PLA nanospheres strongly depends on the PEG molecular weight (Mw) (i.e. PEG chain length at the particle surface) as well as on the PEG content in the particles (i.e. PEG chain density at the surface of the particles). Whatever the thickness or the density of the corona, the qualitative composition of the plasma protein adsorption patterns was very similar, showing that adsorption was governed by interaction with a PLA surface protected more or less by PEG chains. The main spots on the gels were albumin, fibrinogen, IgG, Ig light chains, and the apolipoproteins apoA-I and apoE. For particles made of PEG-PLA45K with different PEG Mw, a maximal reduction in protein adsorption was found for a PEG Mw of 5000 g/mole. For nanospheres differing in their PEG content from 0.5 to 20 wt %, a PEG content between 2 and 5 wt % was determined as a threshold value for optimal protein resistance. When increasing the PEG content in the nanoparticles above 5 wt % no further reduction in protein adsorption was achieved. Phagocytosis by PMN studied using chemiluminescence and zeta potential data agreed well with these findings: the same PEG surface density threshold was found to ensure simultaneously efficient steric stabilization and to avoid the uptake by PMN cells. Supposing all the PEG chains migrate to the surface, this would correspond to a distance of about 1.5 nm between two terminally attached PEG chains in the covering ‘brush’. Particles from PEG5K-PLA45K, PEG5K-PLGA45K and PEG5K-PCL45K copolymers enabled to study the influence of the core on plasma protein adsorption, all other parameters (corona thickness and density) being kept constant. Adsorption patterns were in good qualitative agreement with each other. Only a few protein species were exclusively present just on one type of nanoparticle. However, the extent of proteins adsorbed differed in a large extent from one particle to another. In vivo studies could help elucidating the role of the type and amount of proteins adsorbed on the fate of the nanoparticles after intraveinous administration, as a function of the nature of their core. These results could be useful in the design of long circulating intravenously injectable biodegradable drug carriers endowed with protein resistant properties and low phagocytic uptake.     

Adsorption of immunogamma globulin onto various synthetic calcium hydroxyapatite particles

This paper presents data on adsorption of immunogamma globulin (IgG) onto synthetic rodlike calcium hydroxyapatite particles (CaHaps) with various particle lengths and calcium/phosphate (Ca/P) atomic ratios ranging from 1.54 to 1.65 and compares the obtained results to those of acidic (bovine serum albumin, BSA), neutral (myoglobin, MGB), and basic (lysozyme, LSZ) proteins reported before. The effect of electrolyte concentration on IgG adsorption was also examined. The initial rate of IgG adsorption was similar to that of BSA and was slower than that of MGB and LSZ. This fact was interpreted by the difference in the structural stability and molecular weight of these proteins. The isotherms of IgG adsorption onto the CaHap particles were of pseudo-Langmuir type. The saturated amount of adsorbed IgG values (nsIgG) for the particles with mean particle length less than 70 nm decreased with increasing Ca/P ratio. The adsorption behavior of IgG molecules was very similar to that of basic LSZ, though IgG has zero net charge. The nsIgG value was increased with increased mean particle length of CaHaps; the relationship was less significant than that for BSA but similar to those for MGB and LSZ. The similar adsorption behavior of IgG and LSZ suggested that the Fab parts of IgG molecules preferentially adsorb onto CaHap to provide the reversed Y-shaped conformation of IgG. The change of the adsorption mode of IgG molecules from the reversed Y-shaped conformation to side-on by "spreading" the Fc part of IgG molecules onto the particle surface over a longer adsorption time was suggested. The nsIgG value was increased with increasing electrolyte concentration by screening the intra- and intermolecular electrostatic interactions of proteins.     

Synthesis of membrane adsorbers via surface initiated ATRP of 2-dimethylaminoethyl methacrylate from microporous PVDF membranes

Surface-initiated atom transfer radical polymerization(SI-ATRP) was used to tether poly(2-dimethylaminoethyl methacrylate)(PDMAEMA) onto microporous PVDF membranes in order to synthesize membrane adsorbers for protein adsorption. The alkaline treatment and bromine addition reaction were used to anchor ATRP initiators on membrane surface. Then PDMAEMA was grafted from the membrane surface via SI-ATRP. Fourier transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy(SEM) revealed the chemical composition and surface topography of the PVDF-g-PDMAEMA membrane surfaces. These results showed that PDMAEMA was grafted from the membrane surface successfully and a grafting yield as high as 1500 μg/cm2 was achieved. The effects of the grafting time and the density of initiators on the static and dynamic binding capacity of bovine serum albumin(BSA) were systematically investigated. Both the static and dynamic binding capacities increase with the bromination and polymerization time. However, the benefits of the initiator density on binding capacities are limited by the graft density of PDMAEMA chains.