Hydrophilization of Magnetic Nanoparticles with Modified Alternating Copolymers. Part 2: Behavior in solution

Aqueous solutions of iron oxide nanoparticles (NPs) stabilized by poly(maleic acid-alt-1-octadecene) (PMAcOD) modified with the 5,000 Da poly(ethylene glycol) (PEG) or the short ethylene glycol (EG) tails were analyzed by small-angle X-ray scattering (SAXS). Advanced SAXS data analysis methods were employed to systematically characterize the structure and interactions between the NPs. Depending on the type of the grafted tail and the grafting density all NPs can be separated into three groups. All the samples contain mixtures of individual nanoparticles, their dynamic clusters and aggregates, and the fractions of these species are different in the different groups. The first group consists of NPs coated with PMAcOD modified with the long PEG tails with the maximal grafting density, and the content of dynamic clusters and aggregates in the samples of this group does not exceed 4%. The samples from the second group with less dense coatings demonstrate a larger amount (5-7%) of the aggregates and dynamic clusters. The samples from the third group consisting of the NPs protected by EG modified PMAcOD contain mostly individual NPs and some amount of dumbbell dimers without noticeable aggregation. Importantly, the solution behavior of the NPs is independent on the iron oxide core size. Our results therefore provide means of predicting stabilization and avoiding aggregation of NPs based on the type of a protective shell.     

双分布聚乙二醇接枝纳米二氧化硅的高效可控制备

在混合溶剂中通过"grafting to"的方法将2种分子量不同的聚乙二醇单甲醚(MPEG M_w=750,4000)接枝到氨基修饰的St?ber法二氧化硅(SiO_2-NH_2)表面,制备双分布纳米接枝复合物.采用二步法,先将带环氧端基的低分子量聚乙二醇单甲醚(MPEG-EO)与SiO_2-NH_2在甲苯溶剂中充分反应后,与高分子量的MPEG-EO在甲苯和正癸烷的混合溶剂中使用相同的反应条件和后处理方法,能便捷制备出具有双分布接枝的纳米复合物.在接枝反应体系中,分子链的链段尺寸和接枝密度之间存在着密切关系.一定的范围内,接枝密度随链段尺寸减小而增大.通过改变混合溶剂比例来调控接枝链段的尺寸,可以很好控制聚合物的接枝密度.在双分布接枝的纳米复合物中,低分子量的接枝密度为0.85 chains/nm~2,高分子量的接枝密度能达到0.40 chains/nm~2,体现出了简单、高效、可控的特点,与聚环氧乙烷(PEO)共混后分散良好,对于制备出均匀分散的纳米复合材料起到了一定的指导作用.     

Controlled Assembly of Block Copolymer Coated Nanoparticles in 2D Arrays

The defined assembly of nanoparticles (NPs) in polymer matrices is an important prerequisite for next‐generation functional materials. A promising approach to control NP positions in polymer matrices at the nanometer scale is the use of block copolymers. It allows the selective deposition of NPs in nanodomains, but the final defined and ordered positioning of the NPs within the domains has not been possible. This can now be achieved by coating NPs with block copolymers. The self‐assembly of block copolymer‐coated NPs directly leads to ordered microdomains containing ordered NP arrays with exactly one NP per unit cell. By variation of the grafting density, the inter‐nanoparticle distance can be controlled from direct NP surface contact to surface separations of several nanometers, determined by the thickness of the polymer shell. The method can be applied to a wide variety of block copolymers and NPs and is thus suitable for a broad range of applications.     

Comparative Studies on Hydrophilic and Hydrophobic Segments Grafted Poly(vinyl chloride)

Poly(vinyl chloride) (PVC) is one of the mostly produced plastics in the world and is widely used in single-use medical devices.However,the additives that are often necessary for PVC arouse concerns of its safety,thus quests the modifications of PVC itself.In this study,poly(ethylene glycol) (PEG) and polydimethylsiloxane (PDMS) segments were grafted onto PVC backbone in similar ways,and the chemical structures of the modified PVCs were characterized by Fourier transform infrared spectra,X-ray photoelectron spectra,thermogravimetric analysis and differential scanning calorimetry.Moreover,the water contact angle,protein adsorption,platelet adhesion,cell attachment and proliferation on different material surfaces were studied and compared.It was found that both PEG and PDMS grafting yielded improvement on biocompatibility compared with bare PVC,while hydrophobic PDMS grafted PVC showed more effective on cell attachment and proliferation than that of hydrophilic PEG grafted PVC.     

Optical method for predicting the composition of self-assembled monolayers of mixed thiols on surfaces coated with silver nanoparticles

With a simple optical method, based on UV-vis absorption spectra on glass slides, it is possible to predict the composition of self-assembled monolayers of mixed thiols, grafted on monolayers of silver nanoparticles. Glass slides are modified with the layer-by-layer technique, first forming a monolayer of mercaptopropyltrimethoxysilane, then grafting a monolayer of silver nanoparticles on it. These surfaces are further coated by single or mixed thiol monolayers, by dipping the slides in toluene solutions of the chosen thiols. Exchange constants are calculated for the competitive deposition between the colorless 1-dodecanethiol or PEG5000 thiol and BDP-SH, with the latter being a thiol-bearing molecule containing the strongly absorbing BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) moiety, synthesized on purpose. The constants are calculated by determining the fraction of BDP-SH deposited on the surface from a solution with a given molar fraction, directly measuring the absorption spectra of BDP-SH on the slides. Then, the exchange constant for the competitive deposition between 1-dodecanethiol and PEG5000 thiol is calculated by combining their exchange constants with BDP-SH. This allows to predict the fraction of the two colorless thiols coating the silver nanoparticles slides obtained from a toluene solution with a given molar fraction, for example, of PEG5000 thiol. The correctness of the calculated surface fraction is verified by studying the coating competition between 1-dodecanethiol and a PEG5000 thiol remotely modified with a strongly absorbing fluorescein fragment.     

Multilayers and poly(allylamine hydrochloride)-graft-poly(ethylene glycol) modified bovine serum albumin nanoparticles: Improved stability and pH-responsive drug delivery

To improve the colloidal stability of bovine serum albumin(BSA) nanoparticles(NPs) in diverse mediums, poly(allylamine hydrochloride)(PAH)/sodium poly(4-styrene sulfonate)(PSS) multilayers and poly(allylamine hydrochloride)-graft-poly(ethylene glycol)(PAH-g-PEG) coating were coated on the surface of BSA NPs.Stabilities of the BSA NPs in diverse mediums with different surfaces were detected by dynamic light scattering(DLS).Multilayers and PAH-g-PEG coated BSA NPs can be well dispersed in various mediums with a narrow polydispersity index(PDI).The BSA NPs with the highest surface density of PEG show the best stability.The multilayers and PAH-g-PEG coating do not deter the pH-dependent loading and release property of BSA NPs.At pH 9,the encapsulation efficiency of doxorubicin reaches almost 99%,and the release rate at pH 5.5 is significantly higher than that at pH 7.4.     

Using selenium-conjugated polyethylene glycol to enhance the stability of gold nanoparticles in biologically relevant samples

Using stabilizing agents to maintain the physicochemical properties of colloids in complex environments is crucial for their realworld applications. In this article, we describe how selenium-(Se-) terminated polyethylene glycol(PEG) can serve as a highaffinity stabilizing agent for gold nanoparticles(AuNPs). Compared to Au NPs modified with standard thiolated PEG(S-PEG),Se-PEG-coated Au NPs are much more stable under extreme conditions such as high/low pH, high salt content, and high temperatures. We demonstrate that the Se anchor can prevent the dissociation of PEG ligands from Au NP surfaces in living cells,where a higher concentration of biothiols is usually present. These results indicate that Se-PEG is an excellent stabilizing agent that may facilitate further studies on metal NPs for various complex and physiological systems.     

Effect of molecular weight on synthesis and surface morphology of high-density poly(ethylene glycol) grafted layers

This work describes studying the permanent grafting of carboxylic acid end-functionalized poly(ethylene glycol) methyl ether (PEG) chains of different molecular weights from the melt onto a surface employing poly(glycidyl methacrylate) ultrathin film as an anchoring layer. The grafting led to the synthesis of the complete PEG brushes possessing exceptionally high grafting density. The maximum thickness of the attached PEG films was strongly dependent on the length of the polymer chains being grafted. The maximum grafting efficiency was close to the critical entanglement molecular weight region for PEG. All grafted PEG layers were in the "brush regime", since the distance between grafting sites for the layers was lower than the end-to-end distance for the anchored macromolecules. Scanning probe microscopy revealed that the grafting process led to complete PEG layers with surface smoothness on a nanometric scale. Practically all samples were partly or fully covered with crystalline domains that disappeared when samples were scanned under water. Due to the PEG hydrophilic nature, the surface with the grafted layer exhibited a low (up to 21 degrees ) water contact angle.     

Magnetic Fe3O4 nanoparticles coupled with a fluorescent Eu complex for dual imaging applications

Magnetic 8 nm Fe(3)O(4) nanoparticles (NPs) were synthesized and modified with dopamine (DPA) and polyethylene glycol (PEG) diacid. The water soluble Fe(3)O(4)-DPA-PEG NPs were then conjugated with the fluorescent Eu(iii) complex of tris(dibenzoylmethane)-5-amino-1,10-phenanthroline (BMAP), giving an Fe(3)O(4)-DPA-PEG-BMAP-Eu NP conjugate. The conjugate was both colloidally and chemically stable in phosphate buffered solutions and could be used as a probe for magnetic resonance and fluorescent imaging.     

Sol-gel immobilized short-chain poly(ethylene glycol) coating for capillary microextraction of underivatized polar analytes

Sol-gel coating with covalently bonded low-molecular-weight (MW<300 Da) poly(ethylene glycol) (PEG) chains was developed for capillary microextraction (CME). The sol-gel chemistry proved effective in the immobilization of low-molecular-weight PEGs thanks to the formation of chemical bonds between the organic-inorganic hybrid sol-gel PEG coating and the fused silica capillary inner surface. This chemical anchorage provided excellent thermal and solvent stability to the created sol-gel PEG coating as is evidenced by its high upper limit of allowable conditioning temperature (340 degrees C) and its practically identical performance before and after rinsing with various solvents. The prepared sol-gel PEG coating provided simultaneous extraction of moderately polar and highly polar analytes from aqueous samples without requiring derivatization, pH adjustment or salting-out procedures. Detection limits on the order of nanogram per liter (ng/L) were achieved in CME-GC-flame ionization detection experiments designed for the preconcentration and trace analysis of both highly polar and moderately polar compounds extracted directly from aqueous media using sol-gel short-chain PEG coated microextraction capillaries.     

Mechanical and frictional properties of nanoparticle monolayers grafted on functionalized mica substrates

Normal and lateral forces between two opposing monolayers of grafted polymer nanoparticles (NPs) were measured using the Surface Forces Apparatus in a humid atmosphere. The NPs made of N, N-diethylacrylamide and 2-hydroxyethyl methacrylate have a hydrodynamic diameter of ca. 660 nm at 25 degrees C. The effect of surface roughness was studied by creating surface asperities using different NP grafting densities ranging from 0.41 to 2.63 NPs/mum (2). An increase in the NPs grafting density gave rise to an increase in surface roughness and to a deformation of the nanoparticles caused by the lateral pressure between neighboring particles. An elastoplastic behavior of the nanoparticles was observed for large grafting densities, while a purely elastic behavior was observed for small grafting densities. The lateral forces measured between two opposing NP monolayers sliding past each other followed Amontons' law for all grafting densities. The friction coefficient between the surfaces appeared to increase significantly with an increase in surface roughness, which was inherent to an increase in the elastoplastic behavior of the NP monolayers.     

Forming biocompatible and nonaggregated nanocrystals in water using amphiphilic polymers

High-quality nanocrystals formed in organic solvents can be completely solubilized in water using amphiphilic copolymers containing poly(ethylene glycol) or PEG. These copolymers are generated using a maleic anhydride coupling scheme that permits the coupling of a wide variety of PEG polymers, both unfunctionalized and functionalized, to hydrophobic tails. Thermogravimetric analysis, size exclusion chromatography, cryogenic transmission electron microscopy, and infrared spectroscopy all indicate that the copolymers effectively coat the nanocrystals surfaces. The composite nanocrystal-polymer assemblies can be targeted to recognize cancer cells with Her2 receptor and are biocompatible if their surface coatings contain PEG. In the particular case of semiconductor nanocrystals (e.g., quantum dots), the materials in water have the same optical spectra as well as quantum yield as those formed initially in organic solutions.     

Functionalization of magnetic nanoparticles with amphiphilic block copolymers: self-assembled thermoresponsive submicrometer particles

For the first time the four block copolymers derived from 1-alkyl[2-(acryloyloxy)ethyl]dimethylammonium bromides with hexyl (ADA) or cetyl (ADHA) groups and 2-hydroxyethylacrylate (HEA) or N-isopropylacrylamide (NIPAM) were synthesized and employed for functionalization of monodisperse iron oxide nanoparticles (NPs). The polyADA (pADA) or polyADHA (pADHA) block consists of long hydrophobic tails (C(6) or C(16)) connected to a positively charged quaternary ammonium group, making this block amphiphilic. The second block was either fully hydrophilic (pHEA) or thermoresponsive (pNIPAM). The dependence of the NP coating on the length of the hydrophobic tail in the amphiphilic block, the composition of the hydrophilic block, and the NP sizes have been studied. Unusual self-assembling of iron oxide NPs into well-defined composite submicrometer particles was observed for pADHA-b-pNIPAM in the wide range of concentrations (at the pADHA repeating unit concentrations of 0.065 × 10(-2)-2.91 × 10(-2) mmol/mL per 1 mg/mL NPs) but only two concentrations, 1.62 × 10(-2) and 1.94 × 10(-2) mmol/mL, led to regular spherical particles. The thermoresponsive behavior of these composite particles was tested using ζ-potential and dynamic light scattering measurements, while the morphology of particles was characterized by transmission electron microscopy. Coating of NPs with pADHA-b-pHEA results in the formation of individually coated NPs. The different composite particle morphologies are explained by different properties of pHEA and pNIPAM. It is demonstrated that the composite particles based on pADHA-b-pNIPAM are responsive to a magnetic field and can be recommended as magnetic stoppers in biorelated membrane separations. The incorporation of Pd species in submicrometer particles makes them promising candidates for catalytic applications as magnetically recoverable catalysts with a high magnetic response.     

Colloidal stability of magnetic iron oxide nanoparticles: influence of natural organic matter and synthetic polyelectrolytes

The colloidal behavior of natural organic matter (NOM) and synthetic poly(acrylic acid) (PAA)-coated ferrimagnetic (γFe(2)O(3)) nanoparticles (NPs) was investigated. Humic acid (HA), an important component of NOM, was extracted from a peat soil. Two different molecular weight PAAs were also used for coating. The colloidal stability of the coated magnetic NPs was evaluated as a resultant of the attractive magnetic dipolar and van der Waals forces and the repulsive electrostatic and steric-electrosteric interactions. The conformational alterations of the polyelectrolytes adsorbed on magnetic γFe(2)O(3) NPs and their role in colloidal stability were determined. Pure γFe(2)O(3) NPs were extremely unstable because of aggregation in aqueous solution, but a significant stability enhancement was observed after coating with polyelectrolytes. The steric stabilization factor induced by the polyelectrolyte coating strongly dictated the colloidal stability. The pH-induced conformational change of the adsorbed, weakly charged polyelectrolytes had a significant effect on the colloidal stability. Atomic force microscopy (AFM) revealed the stretched conformation of the HA molecular chains adsorbed on the γFe(2)O(3) NP surface at pH 9, which enhanced the colloidal stability through long-range electrosteric stabilization. The depletion of the polyelectrolyte during the dilution of the NP suspension decreased the colloidal stability under acidic solution conditions. The conformation of the polyelectrolytes adsorbed on the NP surface was altered as a function of the substrate surface charge as viewed from AFM imaging. The polyelectrolyte coating also led to a reduction in magnetic moments and decreased the coercivity of the coated γFe(2)O(3) NPs. Thus, the enhanced stabilization of the coated maghematite NPs may facilitate their delivery in the groundwater for the effective removal of contaminants.     

Gold nanoparticles coated with semi-fluorinated oligo(ethylene glycol) produce sub-100 nm nanoparticle vesicles without templates

Gold nanoparticles (NPs) with diameters of 5, 10, and 20 nm coated with semifluorinated oligo(ethylene glycol) ligands were formed into sub-100 nm hollow NP assemblies (NP vesicles) in THF without the use of a template. The NP vesicles maintained their structure even after the solvent was changed from THF to other solvents such as butanol or CH(2)Cl(2). NMR analyses indicated that the fluorinated ligands are bundled on the NPs and that the solvophobic feature of the fluorinated bundles is the driving force for NP assembly. The formed NP vesicles were surface-enhanced Raman scattering-active capsules.     

Correct Identification of the Core-Shell Structure of Cell Membrane-Coated Polymeric Nanoparticles

Transmission electron microscopy (TEM) observations of negatively stained cell membrane (CM)-coated polymeric nanoparticles (NPs) reveal a characteristic core-shell structure. However, negative staining agents can create artifacts that complicate the determination of the actual NP structure. Herein, it is demonstrated with various bare polymeric core NPs, such as poly(lactic-co-glycolic acid) (PLGA), poly(ethylene glycol) methyl ether-block-PLGA, and poly(caprolactone), that certain observed core-shell structures are actually artifacts caused by the staining process. To address this issue, fluorescence quenching was applied to quantify the proportion of fully coated NPs and statistical TEM analysis was used to identify and differentiate whether the observed core-shell structures of CM-coated PLGA (CM−PLGA) NPs are due to artifacts or to the CM coating. Integrated shells in TEM images of negatively stained CM−PLGA NPs are identified as artifacts. The present results challenge current understanding of the structure of CM-coated polymeric NPs and encourage researchers to use the proposed characterization approach to avoid misinterpretations.     

Grafting of polyethylene glycols onto nanometer silica surface by 1,4‐phenylene diisocyanate

In this paper, polyethylene glycol (PEG) molecules have been grafted onto the surface of nanometer silica in toluene by using 1,4‐phenylene diisocyanate (PPDI) as a coupling agent, and dibutyltion dilaurate (DBTDL) as a catalyst. This process was executed by using a one‐step procedure involving a first reaction of PPDI with silica and a subsequent reaction of isocyanate‐bound silica with PEG. The PEG‐grafted silica has been characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and SEM analyses. The effects of reaction time, temperature and molar ratio of reactant on the effectiveness of the surface grafting were also investigated. Optimum grafting conditions of PEG were obtained at the temperature of 80 °C for 8 h. Maximum grafting of PEG molecules ratio was 22.6%, and maximum overall grafting ratio was 35%, as determined by TGA. Copyright © 2010 John Wiley & Sons, Ltd.     

Polyethylene glycol grafted cotton as phase change polymer

Thermal storage cotton possessing solid–solid phase change properties was prepared by direct grafting of polyethylene glycol (PEG) on cotton fiber/cloth. Attempt has been made to characterize intermediates so that desired grafting could be obtained. The grafting was done by using urethane linkage and the grafted cotton was found to undergo solid–solid phase transition. The modified cotton was characterized by using Fourier transform infrared spectroscopy (FT-IR), ¹³C CPMAS, polarizing optical microscopy, differential scanning calorimetry (DSC) and thermogravimetry respectively. The DSC study revealed quite good storage effect of grafted cotton and the enthalpy of melting was found to be 55–59 J/g with a peak appearing at around 60 °C. During cooling scan, the crystallization peak appeared at around 38 °C. Further, thermogravimetric analysis confirmed good thermal stability up to 300 °C. Appreciable improvement of mechanical properties of cotton has been observed after grafting. The polarizing optical micrograph clearly showed change of morphology after grafting, i.e., the grafted PEG adhering to fiber surface.     

Bimodal polymer mushrooms: compressive forces and specificity toward receptor surfaces

End-grafted poly(ethylene glycol) (or PEG) polymer chains are used to extend the in vivo circulation time of targeted liposomes and nanoparticles; however, the most efficacious structure for also imparting high target specificity remains unknown. Using the surface force apparatus, we have measured the specific and nonspecific forces between bimodal mixtures of grafted polymer mushrooms and model receptor surfaces. Specifically, supported lipid membranes anchoring 2000 or 5000 Da PEG with a controlled fraction of PEG(2000) bearing biotin ligands were compressed against opposing streptavidin surfaces. The presence of the longer 5000 Da chain increased the steric repulsion of the bimodal mushroom layer and thus decreased the net adhesive force when shorter chains were ligated. However, the 5000 Da chain did not detectably alter the distance where ligand-receptor binding occurs and adhesion begins. This latter result is in good agreement with theoretical predictions based on summing the repulsive steric and attractive bridging forces. Further, all ligated structures adhered to receptors under both static and dynamic fluid flow conditions. The dynamic movement of the flexible PEG tethers permitted ligand-receptor bonds to form far beyond the equilibrium edge of the bimodal mushroom layer. This work demonstrates that liposome targeting should be enhanced by grafting ligands to liposomes with a tether that has a contour length longer than the equilibrium height of the bimodal mushroom layer.     

反应性梳状聚乙二醇改性聚酯薄膜表面及其内皮细胞相容性的研究

以高密度梳状PEG(CPEG)作为表面改性材料, 将PEG末端羟基转化为醛基, 将梳状PEG和线形PEG固定在氨基化的PET膜表面, 并利用表面的反应性醛基进一步固定了氨基酸和整合素配体多肽片段RGD多肽. 红外光谱、 接触角和X射线光电子能谱(XPS)测定结果表明, 该法可有效地固定氨基酸和多肽, 获得模拟细胞膜中多糖-蛋白质复合物结构的特异性功能表面. 对两种不同结构的PEG细胞培养实验结果表明, CPEG比线形PEG(LPEG)具有更好的抗非特异粘附性. 此外, CPEG比LPEG具有更多的活性反应基团, 用PEG末端活性的醛基固定整合素配体多肽片段RGD, 可有效地诱导材料表面的内皮细胞化, 改善材料的细胞相容性.