Acrylic acid copolymer nanoparticles for drug delivery: structural characterization of nanoparticles by small-angle x-ray scattering

Nanoparticles are possible carriers for drug delivery. Copolymer nanoparticles of acrylic acid, acrylic amide, acrylic butylester, and methacrylic methylester (CAA) dispersed in water and in 0.15 M NaCl-solution were investigated by small-angle x-ray scattering (SAXS) experiments. The particles were characterized in terms of parameters relevant for the in vivo distribution: particle shape and diameter, size distribution, surface structure, and their organization within tight systems.The CAA-nanoparticles exist in at least three populations of spheres with two minor subpopulations having radii of about 32 and 66 nm and the main moiety around 45 nm. The degree of polydispersity isR _w/R _N=1.05. The subpopulations possess different hydrophobic areas on their surfaces, leading to different recognition by opsonins in vivo and different organ distribution and clearance velocity. The particles are compact without channels and holes, which is proved by low internal hydrationw=0.22 g H₂O/g polymer. Drugs and coating surfactants will interact mainly with the outer surface and not tunnel into the carriers. The surface of the nanoparticles is fractal with a dimensionD=2.3. Probe-molecules with dimensions less than 11.4 nm in diameter will find a larger contact area than expected from the sphere radius. Adsorption rate and position of the arrival of surfactants, and possibly opsonins, may be affected thereby. The negative charges on the CAA-nanoparticle surface are nearly completely screened in physiological NaCl-solutions by counter-ions. Therefore, surface charges hamper carrier-cell interaction at short distances only and do not prevent specific recognition and clearance by the reticuloendothelial system (RES).     

Controlled clustering and enhanced stability of polymer-coated magnetic nanoparticles

The clustering and stability of magnetic nanoparticles coated with random copolymers of acrylic acid, styrenesulfonic acid, and vinylsulfonic acid has been studied. Clusters larger than 50 nm are formed when the coatings are made using too low or too high molecular weight polymers or using insufficient amounts of polymer. Low-molecular-weight polymers result in thin coatings that do not sufficiently screen van der Waals attractive forces, while high-molecular-weight polymers bridge between particles, and insufficient polymer results in bare patches on the magnetite surface. The stability of the resulting clusters is poor, but when an insufficient polymer is used as primary coating, and a secondary polymer is added to coat remaining bare magnetite, the clusters are stable in high salt concentrations (>5 M NaCl), while retaining the necessary cluster size for efficient magnetic recovery. The magnetite cores were characterized by TEM and vibrating sample magnetometry, while the clusters were characterized by dynamic light scattering. The clustering and stability are interpreted in terms of the particle-particle interaction forces, and the optimal polymer size can be predicted well on the basis of these forces and the solution structure and hydrophobicity of the polymer. The size of aggregates formed by limited polymer can be predicted with a diffusion-limited colloidal aggregation model modified with a sticking probability based on fractional coating of the magnetite cores.     

Preparation of Polymer Particles Coated with Hydroxyapatite

Polymer particles coated with hydroxyapatite were prepared by treating Pd0 immobilized polystyrene-co-acrylic acid particles in aqueous CaCl2 and NaH2PO2 solutions. Hydroxyapatite coating took place at neutral to alkaline pH conditions, and the homogeneous growth of the hydroxyapatite layer on the surface of polymer particles was observed at relatively low temperature (30-50 degrees C). The thickness of the hydroxyapatite layer increased with reaction time. Copyright 1999 Academic Press.     

SiO2/TiH2包覆粉体的制备及其释氢特性

熔体发泡法因可通过其简单的工艺制备高强度的泡沫铝而受到广泛的关注．TiH2颗粒可以作为泡沫铝的发泡剂，但其仍存在分解温度与铝熔点的温度失配问题．这种温度失配是导致泡沫铝制品孔洞结构难以控制的最大障碍，解决办法之一是延迟TiH2的分解过程．     

Colloid surface engineering via deposition of multilayered thin films from polyelectrolyte blend solutions

Multilayer thin films were constructed on polystyrene colloidal particles by depositing alternating layers of poly(allylamine hydrochloride) (PAH) at pH 7.5 and varying composition blends of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS) at pH 3.5. Following the deposition of each layer, microelectrophoresis experiments showed alternating zeta-potentials, suggesting the formation of multilayered films on the particles. Scanning and transmission electron microscopy were used to examine the surface morphology of the colloidal particles, with homogeneous surface coatings apparent for films deposited from PAA/PSS blend solutions containing up to 90 wt % PAA. The colloidal stability of these particles is greater than those coated with individual PAH and PAA layers. In the case of the blend PAA/PSS = 25:75 wt %, up to 20 layers were assembled without compromising the colloidal stability of the dispersion. The results demonstrate that the deposition of layers from PE blend solutions containing a strong and weak PE can be used as a facile method for controlling the surface properties and hence the colloidal stability of core-shell particles, as well as the thickness and morphology of the coatings. Control of these parameters is important for subsequent processing and application of these particles in controlled delivery, photonics, catalytic, and separation applications.     

Preparation of dually, pH- and thermo-responsive nanocapsules in inverse miniemulsion

pH- and thermo-sensitive nanocapsules were successfully synthesized via inverse miniemulsion copolymerization of N-isopropyl acrylamide (NIPAM), N,N'-methylene bisacrylamide (MBA), and a functional monomer, 4-vinyl pyridine (4-VP). The size and size distribution of nanocapsules were measured by dynamic light scattering (DLS). The particle morphology was observed by transmission electron microscopy (TEM). The final morphology of particles was strongly influenced by the hydrophobicity of functional monomers. The use of a hydrophilic functional monomer, acrylic acid, led to the formation of solid particles, while the use of the more hydrophobic functional monomer, 4-VP, resulted in the formation of nanocapsules. The particle morphology, size, and size distribution were investigated in terms of the content of 4-VP, MBA, and the type and content of surfactant. The pH- and thermo-sensitivities were characterized by measuring the size variation with the change of temperature and pH. The organic-inorganic nanocapsules were prepared by coating a layer of silica particles on the surface of the sensitive nanocapsules.     

Structural Characterization by SIMS of Alumina Coatings on Stainless Steel

Al₂O₃ coatings were obtained by the alkoxide route and deposited on stainless steel using the dip coating technique. The starting precursor was aluminum sec-butoxide modified by acrylic acid in order to prevent its precipitation in the presence of water.Useful information for the structural organization of alumina coatings on stainless steel is deduced from SIMS analysis. SIMS data reveal that the coating structure brings into play two different layers: an outer alumina layer that is more or less doped, mainly by iron, and an internal layer corresponding to the alumina/steel interphase. Beneath the interphase, the presence of an oxidized steel layer on the substrate surface is detected.Whatever the coating, the alumina/steel interphase exhibits a nearly constant thickness. On the other hand, a thickness variation of the oxidized steel layer is observed between samples under study: this thickness increases with the curing time of the coating.     

Deposition of aerosol nanoparticles on filters coated with layer of carbon nanotubes

Problems concerning intensification of fine gas purification from suspended particles by coating filter fibers with permeable layers of carbon nanotubes, as well as problems relevant to the rebound of Brownian nanoparticles from nanofibers, are discussed. When passing nanoaerosols of sodium chloride through different filtering partitions, the internal surface of which is coated with a thin layer of carbon nanotubes, no peculiarities are observed for deposition of nanoparticles with diameters of larger than 3.5 nm.     

Dispersant adsorption and viscoelasticity of alumina suspensions measured by quartz crystal microbalance with dissipation monitoring and in situ dynamic rheology

Adsorption behavior and water content of adsorbed layers of four dispersants for aqueous ceramic processing were studied by quartz crystal microbalance with dissipation monitoring (QCM-D) on alumina surfaces. The dispersants were a poly(acrylic acid), a lignosulfonate, and two hydrophilic comb copolymers with nonionic polyoxyethylene chains of different molecular weights. A Voigt model was applied to analyze the viscoelastic behavior of the adsorbed dispersant layers. The results from QCM-D were compared with viscoelastic properties determined by in situ dynamic rheology measurements of highly concentrated alumina suspensions during slip casting. The QCM-D results showed that both the poly(acrylic acid) and the lignosulfonate adsorbed in low amounts and in a flat conformation, which generated thin, highly rigid layers less than 1 nm thick. The water content of these layers was found to be around 30% for the lignosulfonate and 35% for the poly(acrylic acid). High casting rate and strength in terms of storage modulus were observed in the final consolidate of the suspensions with the two polyelectrolytes. In contrast, the high molecular weight comb copolymer adsorbed in a less elastic layer with a thickness of about 6 nm, which is enough to provide steric stabilization. The viscous behavior of this layer was attributed to high water content, which was calculated to be around 90%. Such a water-rich layer gives a lubrication effect, which allows for reorientation of particles during the consolidation process, resulting in a high final strength of the ceramic material. During consolidation, the suspension showed a slow casting rate, most likely due to rearrangement facilitated by the lubricating layer. The short-chain comb copolymer adsorbed in a 1.5 nm thick, rigid layer and gave low final strength to the consolidated suspension. It is likely that the poor consolidation behavior is caused by flocculation due to insufficient stabilization of the dispersion.     

Effect of the Solvent on the Water Properties of Water/Oil Microemulsions

Porous poly(styrene-divinylbenzene) (PS-DVB) particles were modified by adsorption of hydrophobically-modified dextrans, to provide chromatographic matrices for biomolecule chromatography. The dextran distribution and the pore characteristics of various coated PS-DVB beads were examined using nitrogen adsorption–desorption, mercury intrusion, and size exclusion chromatography. It was found that the adsorption of dextran does not result in homogeneous layers but rather in inhomogeneous ones. At high dextran loading and high content of hydrophobic groups in the adsorbed polymer, most of the pores of the macroporous rigid material are filled with a soft and porous dextran network being stabilized by hydrophobic interactions. According to chromatographic experiments, most of the surface was nevertheless expected to be covered at least by a thin and dense protecting layer since proteins—even those that are small enough to penetrate the dextran network—cannot interact nonspecifically with the internal pore surface. At low content of hydrophobic groups, dextran deposits preferentially as a thicker and more diffuse layer. However, the thickness of the coating is expected to be irregular and probably contributes to an increase in the roughness of the polystyrene surface.     

Single step hybrid coating process to enhance the electrosteric stabilization of inorganic particles

We report on a single-step coating process and the resulting colloidal stability of silica-coated spindle-type hematite nanoparticles (NPs) decorated with a layer of poly(acrylic acid) (PAA) polyelectrolyte chains that are partially incorporated into the silica shell. The stability of PAA coated NPs as a function of pH and salt concentration in water was compared to bare hematite particles and simple silica-coated hematite NPs, studying their electrophoretic mobility and the hydrodynamic radius by dynamic light scattering. Particles coated with this method were found to be more stable upon the addition of salt at pH 7, and their aggregation at the pH of the isoelectric point is reversible. The hybrid coating appears to increase the colloidal stability in aqueous media due to the combination of the decrease of the isoelectric point and the electrosteric stabilization. This coating method is not limited to hematite particles but can easily be adapted to any silica-coatable particle.     

Effect of SiO2 coating layer morphology on TiH2 gas release characteristic

In this study, a uniform and compact SiO2 film-coating layer was prepared on the surface of TiH2 particles by sol-gel method using inexpensive raw materials. The preparation process of SiO2-coated TiH2 particles and the effect of the coating layer morphology on the gas release characteristic were investigated in detail. When the pH value of TiH2 suspending solution is about 4.0 and the concentration of silicic acid is more than 0.5 mol/L, the coating layer shows a SiO2 particle-coating morphology. While a homogeneous and dense film-coating layer can be obtained when the solution pH value and concentration of silicic acid are about 4.0 and 0.5 mol/L. The results of gas release at 700 degrees C show that TiH2 particles coated with silicon dioxide layers can efficiently delay the starting time of gas release of TiH2 powders to 60-100 s. Comparing the particle-coating layer, the SiO2 film-coating layer has a better delaying effect on gas release of TiH2 particles.     

State of dispersion of magnetic nanoparticles in an aqueous medium: experiments and Monte Carlo simulation

Monte Carlo simulation results predicting the state of dispersion (single, dimer, trimer, and so on) of coated superparamagnetic iron oxide (Fe(3)O(4)) nanoparticles in an aqueous medium are compared with our experimental data for the same. Measured values of the volume percentage of particles in the dispersion, core particle diameter, coating-shell thickness, grafting density of the coating agent, saturation magnetization, and zeta potential for the citric acid-coated and poly(acrylic acid) [PAA]-coated particles have been used in our simulation. The simulation was performed by calculating the total interaction potential between two nanoparticles as a function of their interparticle distance and applying a criterion for the two particles to aggregate, with the criterion being that the minimum depth of the secondary minima in the total interaction potential must be at least equal to k(B)T. Simulation results successfully predicted both experimental trends-aggregates for citric acid-coated particles and an individual isolated state for PAA-coated particles. We have also investigated how this state changes for both kind of coating agents by varying the particle volume percentage from 0.01 to 25%, the particle diameter from 2 to 19 nm, the shell thickness from 1 to 14 nm, and grafting density from 10(15) to 10(22) molecules/m(2). We find that the use of a lower shell thickness and a higher particle volume percentage leads to the formation of larger aggregates. The possible range of values of these four variables, which can be used experimentally to prepare a stable aqueous dispersion of isolated particles, is recommended on the basis of predictions from our simulation.     

Organic pigment particles coated with titania via sol-gel process

This paper presented a novel method for the organic pigment coated with titania to improve the weatherability and dispersion ability in waterborne system. The organic pigment was first orderly adsorbed by two kinds of electrolyte: poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC), then coated by titania via sol-gel process from titanium n-butoxide (TBOT). The effects of the numbers of polyelectrolyte layer, water content, and TBOT content on the morphology, particle size, surface element composition, porosity and pore size, thermal stability, and UV shielding property of the organic pigment were systematically investigated. It was found that only two layers of electrolyte adsorption and one-step coating of titania could obviously enhance the UV shielding property even thermal stability of the organic pigment. The thickness of the titania layer could be easily tailored by TBOT content.     

Hybrid ZnO/polymer thin films prepared by RF magnetron sputtering

Zinc oxide/poly(acrylic acid) (ZnO/PAA) multilayered hybrid films with different layer thicknesses were prepared by radio frequency magnetron sputtering. Zinc peroxide was used as precursor materials for the preparation of ZnO layers, since the zinc peroxide decomposes to ZnO during the film deposition. The films have a high transmittance in the visible region and exhibit visible photoluminescence emission. The band gap energy of the films—determined by the Tauc relationship—decreases with increasing layer thickness (3.40–3.36 eV) due to the increasing crystalline size of the ZnO particles. The morphological investigations showed that a real layered hybrid film structure formed.     

Size, charge, and interactions with giant lipid vesicles of quantum dots coated with an amphiphilic macromolecule

Semiconductor colloidal quantum dots (QDs) are promising fluorescent probes for biology. Initially synthesized in organic solvents, they can be dispersed in aqueous solution by noncovalent coating with amphiphilic macromolecules, which renders the particles hydrophilic and modifies their interactions with other biological compounds. Here, after coating QDs with an alkyl-modified polyacrilic acid, we investigated their colloidal properties in aqueous buffers by electrophoresis, electron microscopy, light scattering, and rate zonal centrifugation. Despite polymer dispersity and variation of the size of the inorganic nanoparticles, the polymer-dot complexes appeared relatively well-defined in terms of hydrodynamic radius and surface charge. Our data show that these complexes contain isolated QD surrounded by a polymer layer with thickness 8-10 nm. We then analyzed their interaction with giant unilamellar vesicles, either neutral or cationic, by optical microscopy. At neutral pH, we found the absence of binding of the coated particles to lipid membrane, irrespective of their lipid composition. An abrupt surface aggregation of the nanoparticles on the lipid membrane was observed in a narrow pH range (6.0-6.2), indicative of critical binding triggered by polymer properties. The overall features of QDs coated with amphiphilic polymers open the route to using these nanoparticles in vivo as optically stable probes with switchable properties.     

Enhancement of surface wettability via the modification of microtextured titanium implant surfaces with polyelectrolytes

Micrometer- and submicrometer-scale surface roughness enhances osteoblast differentiation on titanium (Ti) substrates and increases bone-to-implant contact in vivo. However, the low surface wettability induced by surface roughness can retard initial interactions with the physiological environment. We examined chemical modifications of Ti surfaces [pretreated (PT), R(a) ≤ 0.3 μm; sand blasted/acid etched (SLA), R(a) ≥ 3.0 μm] in order to modify surface hydrophilicity. We designed coating layers of polyelectrolytes that did not alter the surface microstructure but increased surface ionic character, including chitosan (CHI), poly(L-glutamic acid) (PGA), and poly(L-lysine) (PLL). Ti disks were cleaned and sterilized. Surface chemical composition, roughness, wettability, and morphology of surfaces before and after polyelectrolyte coating were examined by X-ray photoelectron spectroscopy (XPS), contact mode profilometry, contact angle measurement, and scanning electron microscopy (SEM). High-resolution XPS spectra data validated the formation of polyelectrolyte layers on top of the Ti surface. The surface coverage of the polyelectrolyte adsorbed on Ti surfaces was evaluated with the pertinent SEM images and XPS peak intensity as a function of polyelectrolyte adsorption time on the Ti surface. PLL was coated in a uniform thin layer on the PT surface. CHI and PGA were coated evenly on PT, albeit in an incomplete monolayer. CHI, PGA, and PLL were coated on the SLA surface with complete coverage. The selected polyelectrolytes enhanced surface wettability without modifying surface roughness. These chemically modified surfaces on implant devices can contribute to the enhancement of osteoblast differentiation.     

Silica coating of nanoparticles by the sonogel process

A modified aqueous sol-gel route was developed using ultrasonic power for the silica coating of indium tin oxide (ITO) nanoparticles. In this approach, organosilane with an amino functional group was first used to cover the surface of as-received nanoparticles. Subsequent silica coating was initiated and sustained under power ultrasound irradiation in an aqueous mixture of surface-treated particles and epoxy silane. This process resulted in a thin but homogeneous coverage of silica on the particle surface. Particles coated with a layer of silica show better dispersability in aqueous and organic media compared with the untreated powder. Samples were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and the zeta potential.     

Ion chromatography on reversed-phase materials coated with mixed cationic and nonionic surfactants

Columns suitable for use in anion chromatography can be prepared by coating a packed reversed-phase HPLC column (C18 silica or polystyrene particles) with a cationic surfactant. The efficiency is improved dramatically by first coating the column with a nonionic surfactant and then subsequently with the cationic surfactant. The thickness of the first coated layer as well as the chemical structure of the surfactant have a major effect on the column performance. Actual separations are included to demonstrate the convenience and practical use of the coated columns. Using this approach, columns with 12,900 theoretical plates for the 15-cm column (or 86,000 plates/m) were produced, giving well shaped peaks with an average asymmetry factor of 1.09. The coated layers were found to be stable, giving retention times with an average relative standard deviation of 1.6% for 12 consecutive runs.     

Electrophoretic characterization of insulin growth factor (IGF-1) functionalized magnetic nanoparticles

The synthesis of composite nanoparticles consisting of a magnetite core coated with a layer of the hormone insulin growth factor 1 (IGF-1) is described. The adsorption of the hormone in the different formulations is first studied by electrophoretic mobility measurements as a function of pH, ionic strength, and time. Because of the permeable character expected for both citrate and IGF-1 coatings surrounding the magnetite cores, an appropriate analysis of their electrophoretic mobility must be addressed. Recent developments of electrokinetic theories for particles covered by soft surface layers have rendered possible the evaluation of the softness degree from raw electrophoretic mobility data. In the present contribution, the data are quantitatively analyzed based on the theoretical model of the electrokinetics of soft particles. As a result, information is obtained on both the thickness and the charge density of the surrounding layer. It is shown that IGF-1 adsorbs onto the surface of citrate-coated magnetite nanoparticles, and adsorption is confirmed by dot-blot analysis. In addition, it is also demonstrated that the external layer of IGF-1 exerts a shielding effect on the surface charge of citrate-magnetite particles, as suggested by the mobility reduction upon contacting the particles with the hormone. Aging effects are demonstrated, providing an electrokinetic fingerprint of changes in adsorbed protein configuration with time.