Evaporation from carbon nanotube buckypapers with different functionalization : analytical possibilities of the mass measurements

The evaporation of liquids from porous films is a very complex phenomenon, which can be followed by simultaneous weight monitoring, electric resistance measurement, infrared imaging and contact angel measurement. The appropriate evaluation of these measurement results can carry both quantitative and qualitative analytical information. The aim of our recent work is to demonstrate this opportunity through the example of the evaporation of simple solvents from porous buckypapers prepared from carbon nanotubes with different functionalization. In this work the focus will be on the analytical possibilities of the mass measurements

Evaporation from carbon nanotube forest : analytical possibilities of the mass measurements

The evaporation of liquids from porous materials is a very complex phenomenon, which can be followed by simultaneous weight monitoring, electric resistance measurement, infrared imaging and contact angel measurement. The appropriate evaluation of these measurement results can carry both quantitative and qualitative analytical information. The aim of our recent work is to demonstrate this opportunity through the example of the evaporation of simple solvents from a carbon nanotube forest. In this work the focus will be on the analytical possibilities of the mass measurements

PEGylation of surfacted magnetite core–shell nanoparticles for biomedical application

The surface of oleate double layer coated (surfacted) magnetite nanoparticles (OA@MNPs) was coated by PEG (poly(ethylene glycol) of Mw=1000, 4000 or 20,000Da, respectively, to get core-shell structured nanomagnets. The oleate bilayers were prepared in two different ways; (i) oleic acid was added directly into the magnetite co-precipitation mixture containing the MNPs to obtain OA@s-MNP samples - s-MNP standing for "as-synthesized MNP" and (ii) sodium oleate (oleate anion, OA) was added to the purified MNPs to obtain OA@p-MNP samples - p-MNP standing for "purified MNP". The effect of the surfactant addition method on the pH- and ionic strength-dependent stability (dynamic laser light scattering and laser-Doppler electrophoresis experiments), the biomedical applicability (MRI measurements) and the biocompatibility (blood sedimentation and blood smear tests) of the core-shell MNPs was studied. Different mechanisms of oleate adsorption were found in ATR FT-IR experiments (inner sphere surface complexation via ligand exchange for the s-MNPs and additional H-bonding for the p-MNPs), suggesting different behaviour. The colloidal stability and salt tolerance of the two kinds of OA@MNPs were similar, but the hydrodynamic diameter of the OA@s-MNP was considerably larger than that of OA@p-MNP. In accordance with this, the r2 relaxation was also higher for the s-MNP samples (~400 and ~200mM-1s-1, respectively). The physico-chemical tests indicate that the OA-coated MNPs form clusters and the degree of clustering of OA@s-MNPs is significantly greater than that of OA@p-MPNs. PEGylation does not appear to affect colloidal stability and salt tolerance meaningfully. The adsorption of PEG was proved experimentally. We have found that the PEG top layer decreases the electrostatic contribution, nevertheless increases the steric contribution of the original electrosteric stabilization caused by the OA double layer. However, an increase in the molecular weight above 1000Da and the amount of added PEG above 5mmol/g gradually reduces the salt tolerance of the samples. The results indicate strong potential for biomedical application and biocompatibility of the PEGylated MNPs

Mechanism of in situ surface polymerization of gallic acid in an environmental-inspired preparation of carboxylated core-shell magnetite nanoparticles.

Magnetite nanoparticles (MNPs) with biocompatible coatings are good candidates for MRI (magnetic resonance imaging) contrasting, magnetic hyperthermia treatments, and drug delivery systems. The spontaneous surface induced polymerization of dissolved organic matter on environmental mineral particles inspired us to prepare carboxylated core-shell MNPs by using a ubiquitous polyphenolic precursor. Through the adsorption and in situ surface polymerization of gallic acid (GA), a polygallate (PGA) coating is formed on the nanoparticles (PGA@MNP) with possible antioxidant capacity. The present work explores the mechanism of polymerization with the help of potentiometric acid-base titration, dynamic light scattering (for particle size and zeta potential determination), UV-vis (UV-visible light spectroscopy), FTIR-ATR (Fourier-transformed infrared spectroscopy by attenuated total reflection), and XPS (X-ray photoelectron spectroscopy) techniques. We observed the formation of ester and ether linkages between gallate monomers both in solution and in the adsorbed state. Higher polymers were formed in the course of several weeks both on the surface of nanoparticles and in the dispersion medium. The ratio of the absorbances of PGA supernatants at 400 and 600 nm (i.e., the E4/E6 ratio commonly used to characterize the degree of polymerization of humic materials) was determined to be 4.3, similar to that of humic acids. Combined XPS, dynamic light scattering, and FTIR-ATR results revealed that, prior to polymerization, the GA monomers became oxidized to poly(carboxylic acid)s due to ring opening while Fe(3+) ions reduced to Fe(2+). Our published results on the colloidal and chemical stability of PGA@MNPs are referenced thoroughly in the present work. Detailed studies on biocompatibility, antioxidant property, and biomedical applicability of the particles will be published

Striking analogies and dissimilarities between graphene oxides and humic acids: pH-dependent charging and colloidal stability

This study provides a comparative framework on the elucidation of analogies and differences in the interfacial protolytic processes and the associated colloidal behaviour of a typical humic acid (HA) and a set of singlelayer graphene oxide (SLGO) and (multi-layered) graphite oxide samples in aqueous electrolyte media. The pH dependence of the surface charge densities of HA and SLGO was explored at three different salt concentrations by potentiometric acid-base titration, along with simultaneous determination of zeta potential and hydrodynamic sizes. Charging curves obtained in the pH range of 3 to 10 by cyclic titrations reveal the presence of a small hysteresis, proving the chemical stability of SLGO and graphite oxides in weakly acidic and alkaline solutions. HAand SLGOdisplay a parallel shift of the pH-dependencies of their negative charge densities with increasing ionic strength, demonstrating a unique combination of particle and polyelectrolyte-like behaviour, which is absent formulti-layered graphite oxide exhibiting charging curves that resemble to “classical” colloidal particles. An accurate purification of SLGO results in inherent change in its surface properties; however, the salt tolerance of aqueous HA solutions is still superior to that of SLGO dispersions

Magnetic hyaluronate hydrogels: preparation and characterization

a b s t r a c t A novel soft way of hyaluronate (HyA) based magnetic hydrogel preparation was revealed. Magnetite nanoparticles (MNPs) were prepared by co-precipitation. Since the naked MNPs cannot be dispersed homogenously in HyA-gel, their surface was modified with natural and biocompatible chondroitin-sulfate-A (CSA) to obtain CSA-coated MNPs (CSA@MNPs). The aggregation state of MNPs and that loaded with increasing amount of CSA up to 1 mmol/g was measured by dynamic light scattering at pH $ 6. Only CSA@MNP with Z 0.2 mmol/g CSA content was suitable for magnetic HyA-gel preparation. Rheological studies showed that the presence of CSA@MNP with up to 2 g/L did not affect the hydrogel's rheological behavior significantly. The results suggest that the HyA-based magnetic hydrogels may be promising formulations for future biomedical applications, e.g. as intra-articular injections in the treatment of osteoarthritis

Novel carboxylated PEG-coating on magnetite nanoparticles designed for biomedical applications

Fabrication of PEG coating on magnetite nanoparticles (MNPs) is one of the most favoured ways to ensure biocompatibility. Surface modification of magnetite by an own-prepared comb-like PEG-copolymer (PEGA-AA) was compared with two commercially available ones (carboxy-PEG (PEG-C) and phosphate-PEG (PEG-P)). ATR FT-IR data revealed that all polymers form complexes on the surface of MNPs. Electrophoresis and dynamic light scattering (DLS) experiments showed that both the type and quantity of the polymers' anchoring groups influence the aggregation of coated nanomagnets. PEG-C shell does not provide excess negative charges, so magnetite particles became aggregated. However PEG-P and PEGA-AA gradually modify the surface: neutralizing the originally positively charged MNPs below loading 0.5 mmol/g, while above it a polyanionic layer forms on nanomagnets dispersing them in salty media at pH ~6.5. The PEGA-AA comb-like copolymer is more efficient for MNPs PEGylation due to the uniform distribution of carboxylates and PEG chains along the carbon skeleton

Hemocompatibility and Biomedical Potential of Poly(Gallic Acid) Coated Iron Oxide Nanoparticles for Theranostic Use

Polyacid covered core-shell iron oxide nanoparticles were designed for potential use in biomedicine with special attention to theranostics - magnetic resonance imaging (MRI), magnetic hyperthermia and magnetic drug targeting. The magnetite nanoparticles coated with a gallic acid shell polymerized in situ on the nanoparticle surface (PGA@MNPs) were tested for hemocompatibility in blood, sedimentation rate, blood smear and blood cell viability experiments and for antioxidant capacity in Jurkat cells in the presence of H2O2 as reactive oxygen species. No signs of interaction of the nanoparticles with whole blood cells were found. In addition, the PGA@MNPs reduced significantly the oxidative stress mediated by H2O2 supporting earlier findings of MTT tests, namely, the improvement of cell viability in their presence. The in vitro tests revealed that PGA@MNPs are not only biocompatible but also bioactive. Preliminary experiments revealed that the nanoparticles are especially efficient MRI and magnetic hyperthermia agents. The r2 relaxivity was found to be one of the highest among published values (387 mM-1s-1) and they possess a relatively significant specific absorption rate (SAR) value of 11 W/g magnetite

Chondroitin-Sulfate-A-Coated Magnetite Nanoparticles: Synthesis, Characterization and Testing to Predict Their Colloidal Behavior in Biological Milieu

Biopolymer coated magnetite nanoparticles (MNPs) are suitable to fabricate biocompatible magnetic fluid (MF). Their comprehensive characterization, however, is a necessary step to assess whether bioapplications are feasible before expensive in vitro and in vivo tests. The MNPs were prepared by co-precipitation, and after careful purification, they were coated by chondroitin-sulfate-A (CSA). CSA exhibits high affinity adsorption to MNPs (H-type isotherm). We could only make stable MF of CSA coated MNPs (CSA@MNPs) under accurate conditions. The CSA@MNP was characterized by TEM (size ~10 nm) and VSM (saturation magnetization ~57 emu/g). Inner-sphere metal–carboxylate complex formation between CSA and MNP was proved by FTIR-ATR and XPS. Electrophoresis and DLS measurements show that the CSA@MNPs at CSA-loading > 0.2 mmol/g were stable at pH > 4. The salt tolerance of the product improved up to ~0.5 M NaCl at pH~6.3. Under favorable redox conditions, no iron leaching from the magnetic core was detected by ICP measurements. Thus, the characterization predicts both chemical and colloidal stability of CSA@MNPs in biological milieu regarding its pH and salt concentration. MTT assays showed no significant impact of CSA@MNP on the proliferation of A431 cells. According to these facts, the CSA@MNPs have a great potential in biocompatible MF preparation for medical applications