Structural and mechanical properties of Laponite-PEG hybrid films

Inorganic/organic hybrids were obtained by the sol-gel type organic modification reaction of Laponite sidewalls with poly(ethylene glycol) (PEG) bearing alkoxysiloxy terminal functionality. By casting an aqueous dispersion of the hybrid, the flexible and transparent hybrid films were obtained. Regardless of the inorganic/organic component ratio, the hybrid film had the ordered structure of Laponite in-plane flat arrays. The mechanical strength of hybrid films was drastically improved by the presence of cross-linking among alkoxysilyl functionalities of PEG terminals and the absence of PEG crystallines. Hybrid films, especially those that consisted of PEG with short chain, showed good mechanical properties that originate from quasi-homogeneous dispersion of components due to anchoring of PEG terminal to Laponite sidewall and interaction of PEG to Laponite surface.     

Size-selective protein adsorption to polystyrene surfaces by self-assembled grafted poly(ethylene glycols) with varied chain lengths

We report about the surface modification of polystyrene (PSt) with photoreactive alpha-4-azidobenzoyl-omega-methoxy poly(ethylene glycol)s (ABMPEG) of three different molecular weights (MWs of approximately 2, approximately 5, and approximately 10 kg/mol) and with two poly(ethylene glycol)/poly(propylene glycol) triblock copolymers (PEG-PPG-PEG) of about identical PEG/PPG ratio (80/20, w/w) and MW(PEG) of approximately 3 and approximately 6 kg/mol, all via adsorption from aqueous solutions. For ABMPEGs, an additional UV irradiation was used for photografting to the PSt. Contact angle (CA) and atomic force microscopy data revealed pronounced differences of the hydrophilicity/hydrophobicity and topography of the surfaces as a function of PEG type and concentration used for the modification. In all cases, an incomplete coverage of the PSt was observed even after modification at the highest solution concentrations (10 g/L). However, clear differences were seen between PEG-PPG-PEGs and ABMPEGs; only for the latter was a nanoscale-ordered interphase structure with an influence of MW(PEG) on the PEG density observed; after modification at the same solution concentrations, the density was significantly higher for lower MW(PEG). The adsorption of three proteins, myoglobin (Mgb), bovine serum albumin (BSA), and fibrinogen to the various surfaces was analyzed by surface plasmon resonance. Pronounced differences between the two PEG types with respect to the reduction of protein adsorption were found. At high, but still incomplete, surface coverage and similar CA, the shielding of ABMPEG layers toward the adsorption of Mgb and BSA was much more efficient; e.g., the adsorbed Mgb mass relative to that of unmodified PSt was reduced to 10% for ABMPEG 2 kg/mol while for both PEG-PPG-PEGs the Mgb mass was still around 100%. In addition, for the ABMPEG layers an effect of MW(PEG) on adsorbed protein mass-decrease with decreasing MW-could be confirmed; and the highest Mgb/BSA selectivities were also observed. A "two-dimensional molecular sieving", based on PEG molecules having a nanoscale order at the hydrophobic substrate polymer surface has been proposed, and the main prerequisites were the use of PEG conjugates which are suitable for an "end-on" grafting (e.g., ABMPEGs), the use of suitable (not too high) concentrations for the surface modification via adsorption/self-assembly, optionally the photografting on the substrate (possible only for ABMPEG), and presumably, a washing step to remove the excess of unbound PEGs. The results of this study also strongly support the hypothesis that the biocompatibility of hydrophobic materials can be very much improved by PEG modifications at surface coverages that are incomplete but have an ordered layer structure controlled by the size and steric interactions of surface-bound PEGs.     

Physicochemical analysis of ion beam-induced surface modifications on polyethylene glycol films for liquid crystal alignment

ABSTRACT

We investigated the surface modification induced by the ion-beam (IB) irradiation of a polyethylene glycol (PEG) film and its liquid crystal (LC) alignment characteristics. The X-ray photoelectron spectroscopy analysis revealed the chemical modification; as the IB incidence angle increased, the number of surface C–O bonds decreased, inducing an anisotropic dipole moment on the PEG film surface. In addition, the physical modification was demonstrated via atomic force microscopy analysis using three-dimensional images as a function of the IB incidence angle. The surface roughness was analyzed; the modification with the smoothest surface was observed for an IB incidence angle of 45°. This modification affected the LC alignment state of the PEG film, as demonstrated by the polarized optical microscopy analysis with pre-tilt angle measurements. Furthermore, for the same IB incidence angle, the residual DC measured using the capacitance–voltage curves was extremely low. Hence, a PEG film irradiated with an IB incidence angle of 45° could be a suitable LC alignment layer.     

Blood compatibility of particulate carriers investigated by cell electrophoresis and particle electrophoresis: a preliminary report

Polyethylene glycol (PEG) and dextran were covalently coupled, or only adsorbed, to the surface of three kinds of inorganic particles in order to shield their surface and reduce their nonspecific binding to red blood cells. Surface modification as well as interaction of particles with red blood cells was followed up by particle electrophoresis. This allowed a quick evaluation of the efficiency of polymer coupling. Moreover, the nonspecific binding of particles to red blood cells was easily investigated with cell electrophoresis, showing the inhibitory effect of immobilized PEG-5000 or dextran. The electrophoretic mobility analysis presented here may be used for screening blood compatibility of particulate drug carriers and could be helpful in formulating long-living circulating particles.     

核壳结构金属-有机骨架及其衍生物在锂离子电池负极材料中的应用

金属–有机框架(MOFs)材料具有比表面积较大、孔径可调、制备容易、结构与功能多样性等优势,被广泛应用于电化学能源转化与储存领域。其中独特的核壳结构材料由于表面修饰的作用往往更能表现出核内与壳层的协同作用。本文介绍了具有核壳结构MOFs作为锂离子电池负极材料的发展现状,并重点综述其衍生物(多孔碳材料、金属氧化物、金属硫/硒化物以及金属/金属氧化物)的制备方法以及在锂离子电池负极中的应用。MOFs通过高温煅烧或改变化学反应条件的方法,可制备出结构可调的传统无机电极材料并表现出更优异的电化学性能。最后总结了核壳结构MOFs材料作为锂电负极材料存在的问题和挑战,并提出可能的解决途径和未来的应用前景。     

Preparation of the TiO2 Thin Film Photocatalyst by the Dip-Coating Process

Titanium dioxide (TiO2) coated glass-plate thin film photocatalysts for elimination of air pollutants, were prepared by the dip-coating process with titanium alkoxide including polyethylene glycol (PEG). The surface structure of these thin films changed drastically with the size of the PEG. They were either transparent or opaque. Nitrogen oxides (NOx), one of the most hazardous of air pollutants, were found to be efficiently eliminated by the thin film photocatalyst. The photocatalytic activities of the transparent and opaque thin films were found to be almost equal. This may be due to the two films having the same surface area. The highest activity was obtained for thin films around 1 m.     

Role of electronegativity in the qualitative inference of the TOF-SIMS fragment pattern of inorganic compounds

The role of the electronegativity of atoms in inorganic compounds in TOF-SIMS fragmentation is discussed. From a study of approximately 30 inorganic compounds--chlorides, oxides, nitrates, and sulfates--a simple rule has been proposed for the dependence of fragment pattern appearance on the electronegativity (electron affinity), which can be easily obtained from handbooks, and the valence of positive and negative ions in these compounds. TOF-SIMS measurements of metal and alloy surfaces, should be corrected for the ionization potentials and/or electronegativities of atoms present in surface contaminants.     

Mesoporous hybrid and nanocomposite thin films. A sol–gel toolbox to create nanoconfined systems with localized chemical properties

Mesoporous Thin Films (MTF) can be created by combining sol–gel synthesis, template self-assembly and chemical surface modification. A wide palette of inorganic (oxides, phosphates, carbon-based, etc.) and hybrid organic–inorganic frameworks with a variety of composition, pore sizes, and nanoscale, organic or biological functions located in the inorganic skeleton, pore surface or pore interior can be obtained. The properties of the functional pore systems are tuned by the pore size and geometry, wall composition and surface features. These MTF with interesting electronic and optical controlled features are indeed a “nanofacility”. Well-defined monodisperse sized pores also act as nanoreactors, or nanocavities with controlled environment and behaviour. In the last years, the production of accessible MTF, in which either the pore surface or pore volume can be modified by organic functional groups or nanoparticles has been thoroughly explored. Each highly controlled MTF originated from a reproducible and modular synthesis is in itself a building block for more complex structures, presenting order at different length scales (molecular, mesoscopic, macroscopic), and novel properties derived thereof. Selected examples of optical and chemical behaviour of these multiscale materials are presented to illustrate these points.     

Characterisation of hydroxyapatite surface modified by poly(ethylene glycol) and poly(hydroxyethyl methacrylate) grafting

Hydroxyapatite (HA) has many applications in medicine as a biocompatible and bioactive biomaterial. Numerous studies have shown that modification of the HA surface can improve its biological and chemical properties. However, little is known about the surface properties of modified materials. In this paper the influence of organic polymers: polyethylene glycol (PEG) and polyhydroxyethyl methacrylate (pHEMA) on the surface properties and surface chemistry of hydroxyapatite (HA) is presented. The surface properties of modified HA were characterised by the FT-IR, XPS, BET, and zeta potential measurements. Specific surface area was determined by BET. Infrared and XPS spectra confirmed the presence of PEG and pHEMA on the surface of HA. The BET N₂ adsorption revealed slight changes in the HA surface chemistry after grafting modification. The surface chemical properties of the HA were considered to be based on the zeta potential. The decrease in zeta potential results in the increasing stability of the modified material and also in the reduction of bacterial adhesion. The reaction for surface modification of HA is proposed and described.     

Effects of ionic strength and surface charge on protein adsorption at PEGylated surfaces

PEGylated Nb2O5 surfaces were obtained by the adsorption of poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) copolymers, allowing control of the PEG surface density, as well as the surface charge. PEG (MW 2 kDa) surface densities between 0 and 0.5 nm(-2) were obtained by changing the PEG to lysine-mer ratio in the PLL-g-PEG polymer, resulting in net positive, negative and neutral surfaces. Colloid probe atomic force microscopy (AFM) was used to characterize the interfacial forces associated with the different surfaces. The AFM force analysis revealed interplay between electrical double layer and steric interactions, thus providing information on the surface charge and on the PEG layer thickness as a function of copolymer architecture. Adsorption of the model proteins lysozyme, alpha-lactalbumin, and myoglobin onto the various PEGylated surfaces was performed to investigate the effect of protein charge. In addition, adsorption experiments were performed over a range of ionic strengths, to study the role of electrostatic forces between surface charges and proteins acting through the PEG layer. The adsorbed mass of protein, measured by optical waveguide lightmode spectroscopy (OWLS), was shown to depend on a combination of surface charge, protein charge, PEG thickness, and grafting density. At high grafting density and high ionic strength, the steric barrier properties of PEG determine the net interfacial force. At low ionic strength, however, the electrical double layer thickness exceeds the thickness of the PEG layer, and surface charges "shining through" the PEG layer contribute to protein interactions with PLL-g-PEG coated surfaces. The combination of AFM surface force measurements and protein adsorption experiments provides insights into the interfacial forces associated with various PEGylated surfaces and the mechanisms of protein resistance.     

Metal oxide surface charge mediated hemostasis

Blood coagulates faster upon contact with polar glasslike surfaces than on nonpolar plastic surfaces; this phenomenon is commonly termed the glass effect. However, the variable hemostatic response that we report here for contact-activated coagulation by different metal oxides, all of which are polar substrates, requires a refinement of this simple polarity model of how inorganic metal oxides activate the intrinsic pathway of blood coagulation. To our knowledge, the role of metal oxide surface charge as determined at the physiological pH and Ca2+ concentration of blood has not been previously investigated. We find that basic oxides with an isoelectric point above the pH of blood are anticoagulant while acidic oxides with an isoelectric point below the pH of blood are procoagulant. Using a thromboelastograph, we find that the onset time for coagulation and rate of coagulation post-initiation depend on both the sign and the magnitude of the initial surface charge density of the metal oxide. This work presents a useful strategy based on a quantifiable material parameter to select metal oxides to elicit a predictable and tunable biological response when they are in contact with blood.     

Zeta potentials of PDMS surfaces modified with poly(ethylene glycol) by physisorption

Controlling zeta potential of PDMS surface coated with a layer of PEG is important for electroosmosis and electrophoresis in PDMS made microfluidic chips. Here, zeta potentials of PDMS surfaces modified by simple physisorption of PEG of different concentrations in phosphate buffer solutions, pure water, and PEG solution were reported. Coating PEG on PDMS surfaces was achieved by immersing a PDMS layer into the PEG solution for 10 min and then taking it out and placing it in an oven at 80℃ for 10 h. To avoid damaging the PEG layer on the PDMS surface, an induction current method was employed for zeta potential measurement. Zeta potentials of PEG modified PDMS in electrolyte solutions were measured. The results show that 2.5% PEG can effectively modify PDMS surface with positive zeta potential value in phosphate buffer solutions, pure water and 10% PEG solution. Further increase in PEG solution beyond 5% for surface modification has no obvious effect on zeta potential change.     

Stealth MePEG-PCL micelles: effects of polymer composition on micelle physicochemical characteristics,in vitro drug release,in vivo pharmacokinetics in rats and biodistribution in S<Subscript>180</Subscript> tumor bearing mice

The amphiphilic copolymer of poly(methoxy-polyethyleneglycol polycaprolactone) (MePEG-PCL) was synthesized. Micelles loading hydroxycamptothecin (HCPT) as a model drug were prepared by solid-dispersion and dialysis–hydration method. The MePEG-PCL micelles were further characterized in terms of critical association concentrations (CAC), PEG surface density, fixed aqueous layer thickness, in vitro drug release and in vivo pharmacokinetics and biodistribution. The results showed that longer polycaprolactone (PCL) chain length would lead to the reduction of CAC value, stabilized HCPT, increasing drug-loading coefficient, sparser PEG surface density and slower drug release patterns. On the other hand, longer PEG chain length would give rise to less negative zeta potential and larger fixed aqueous layer thickness, as well as sparser PEG surface density and quicker drug release. MePEG-PCL micelles with PEG molecular weight of 2,000, 5,000, 10,000 could extend the AUC of HCPT in blood compartment by 9.13, 13.82, 21.25 times and increase the AUC of ¹²⁵I-HCPT in the tumor of S₁₈₀ mice by 7.94, 11.32, 26.08-fold, respectively. It was suggested that the PEG and PCL chain length may play a very important role in the micelles in vitro properties and in vivo behavior.This revised version was published online in January 2005 with corrections to the authors. Two authors - Yan Zhang and Shoukuan Fu - have been added.     

LLDPE/SMA共混膜表面接枝PEG的研究

聚乙烯综合性能优良且价格低廉,但由于较低的表面能和惰性化学结构,其着色性、生物相容性及制品表面涂饰性能差,与各种涂饰剂的粘结强度很低,限制了其用途的拓展,须进行表面改性.聚乙烯制品的表面改性方法已有不少研究报道[1~4],相对而言,采用添加表面改性剂的方法在工艺上仍最     

Cross-Linked Polymers as Scaffolds for the Low-Temperature Preparation of Nanostructured Metal Oxides

The current state of the art of the use of cross-linked organic polymers, both insoluble (resins or gels) and soluble (micro- and nanogels), as aids for the low-temperature preparation of stable metal oxide nanoparticles or nanostructured metal oxides is reviewed herein. Synthetic strategies for inorganic oxide nanomaterials of this kind can greatly benefit from the use of cross-linked polymers, which may act as scaffolds/exotemplates during inorganic nanoparticle synthesis, or as stabilizers following post-synthetic modification of the nanoparticles. Furthermore, the peculiar properties of the organic cross-linked polymers add to those of the inorganic oxide nanoparticles, producing materials with combined properties. The potential applications of such highly promising composite nanomaterials will be also briefly sketched.     

Novel nylon-supported organic-inorganic hybrid membrane with hierarchical pores as a potential immobilized metal affinity adsorbent

Chitosan-based porous organic-inorganic hybrid membranes supported by microfiltration nylon membranes were prepared, in which gamma-glycidoxypropyltrimethoxysilane (GPTMS) was used as an inorganic source as well as crosslinking reagent. Polyethylene glycol (PEG) with different molecular weight and content was used as imprinting molecule for morphology control. In situ crosslinking of chitosan and simultaneous polymerization of GPTMS in PEG template environment endowed the hybrid membrane with specific characteristics. Distinct hybrid effect between chitosan (CS) and GPTMS was revealed by shifting in X-ray diffraction (XRD) pattern, decomposition in simultaneous thermogravimetry and differential scanning calorimetry (TG/DSC) testing. As manifested by scanning electron microscopy (SEM), the molecular weight and content of PEG had remarkable effect on the resulting surface morphology of the hybrid membrane and a given surface morphology could be obtained by extracting of the imprinted PEG molecular. Among three types of porogen used: PEG 400, PEG 4000 and PEG 20000, only PEG 20000 could result in a porous surface. Moreover, a special porous surface with three-dimensional (3D) hierarchical structure-in-structure pore fashion was obtained when content of PEG 20000 was controlled at 15%. Experimental results also showed that the hybrid membrane had low swelling ratio and high stability in acidic solution. After conveniently coordinated with copper ions, the porous metal chelating hybrid membrane could effectively adsorb the model protein, bovine serum albumin (BSA). As expected, the hybrid membrane imprinted with 15% PEG 20000 had remarkably high copper ion binding and BSA adsorption capacity, which might result from the large surface area, high ligand density and suitable interconnected 3D hierarchical porous surface.     

Tuning the Surface of Nanoparticles: Impact of Poly(2‐ethyl‐2‐oxazoline) on Protein Adsorption in Serum and Cellular Uptake

Due to the adsorption of biomolecules, the control of the biodistribution of nanoparticles is still one of the major challenges of nanomedicine. Poly(2‐ethyl‐2‐oxazoline) (PEtOx) for surface modification of nanoparticles is applied and both protein adsorption and cellular uptake of PEtOxylated nanoparticles versus nanoparticles coated with poly(ethylene glycol) (PEG) and non‐coated positively and negatively charged nanoparticles are compared. Therefore, fluorescent poly(organosiloxane) nanoparticles of 15 nm radius are synthesized, which are used as a scaffold for surface modification in a grafting onto approach. With multi‐angle dynamic light scattering, asymmetrical flow field‐flow fractionation, gel electrophoresis, and liquid chromatography‐mass spectrometry, it is demonstrated that protein adsorption on PEtOxylated nanoparticles is extremely low, similar as on PEGylated nanoparticles. Moreover, quantitative microscopy reveals that PEtOxylation significantly reduces the non‐specific cellular uptake, particularly by macrophage‐like cells. Collectively, studies demonstrate that PEtOx is a very effective alternative to PEG for stealth modification of the surface of nanoparticles.

     

Novel mesoporous mixed Nb-M (M = V, Mo, and Sb) oxides for oxidative dehydrogenation of propane

Novel thermally stable mesoporous mixed metal Nb-M (M = V, Mo and Sb) oxides were synthesized in the presence of a nonionic Pluronic P123 surfactant. These oxides displayed promising pore structures and chemical compositions for selective oxidative functionalization of propane: high surface areas (up to 200 m2/g), large pore sizes (5-14 nm), and high pore volumes (up to 0.46 cm3/g). The oxidative dehydrogenation of propane to propylene over mesoporous mixed metal Nb-M oxides employed as a probe reaction suggested that the M component was dispersed as the molecular surface species and also formed a solid solution with NbOx in the inorganic walls of these mesoporous mixed metal oxides.     

Metabolic delivery of methacryloyl groups on living cells and cell surface modification via thiol-ene "click" reaction

Methacryloyl groups are delivered on a living cell surface via a glycosylation pathway. The mannosamine derivative ManMA is synthesized as a precursor of cell-surface sialic-acid residues. HeLa cells are cultivated in a culture medium containing ManMA, after which a sufficient amount of PEG(4)10K-SH is in contact with the cells in the presence of a photoinitiator. The cells are then exposed to UV-light for 10 min. The immobilization of PEG(4)10K-SH, termed PEGylation, on the cell surface is confirmed by fluorescence microscopy. The surface modification does not influence cell viability. Biotinylation of cell surface can also be achieved by the addition of a vinyl compound during PEGylation. By using this process, the functionalities of a cell surface can be freely controlled.     

An aqueous-based surface modification of poly(dimethylsiloxane) with poly(ethylene glycol) to prevent biofouling

We report a simple modification of poly(dimethylsiloxane) (PDMS) surfaces with poly(ethylene glycol) (PEG) through the adsorption of a graft copolymer, poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) from aqueous solution. In this approach, the PDMS surface was treated with oxygen plasma, followed by immersion into aqueous solution containing PLL-g-PEG copolymers. Due to the hydroxyl/carboxylic groups generated on the PDMS surface after oxygen plasma, the polycationic PLL backbone is attracted to the negatively charged surface and PEG side chains exhibit an extended structure. The PEG/aqueous interface generated in this way revealed a near-perfect resistance to nonspecific protein adsorption as monitored by means of optical waveguide lightmode spectroscopy (OWLS) and fluorescence microscopy.