Chemical composition and crystal structure are central to defining the functional properties of materials. But when a material is prepared in the form of nanoparticles, the structure and, as a ...consequence, the composition will also frequently change. Understanding these changes in the crystal structure at the nanoscale is therefore essential not only for expanding fundamental knowledge, but also for designing novel nanostructures for diverse technological and medical applications. The changes can originate from two thermodynamically driven phenomena: (i) a crystal structure will adapt to the restricted size of the nanoparticles, and (ii) metastable structural polymorphs that form during the synthesis due to a lower nucleation barrier (compared to the equilibrium phase) can be stabilized at the nanoscale. The changes to the crystal structure at the nanoscale are especially pronounced for inorganic materials with a complex structure and composition, such as mixed oxides with a structure built from alternating layers of several structural blocks. In this article the complex structure of nanoparticles will be presented based on two examples of well-known and technologically important materials with layered structures: magnetic hexaferrites (BaFe12O19 and SrFe12O19) and ferroelectric Aurivillius layered-perovskite bismuth titanate (Bi4Ti3O12).
Magnetically-assisted delivery of therapeutic agents to the site of interest, which is referred to as magnetic drug targeting, has proven to be a promising strategy in a number of studies. One of the ...key advantages over other targeting strategies is the possibility to control remotely the distribution and accumulation of the nanocarriers after parenteral administration. However, preparation of effective and robust magnetically responsive nanocarriers based on superparamagnetic iron oxide nanocrystals (SPIONs) still represents a great scientific challenge, since spatial guidance of individual SPIONs is ineffective despite the presence of high magnetic field gradient. A strategy to overcome this issue is the clustering of SPIONs to achieve sufficient magnetic responsiveness. In this mini-review, we address current and future strategies for the design and fabrication of magnetically responsive nanocarriers based on SPIONs for magnetically-targeted drug delivery, including the underlying physical requirements, the possibility of drug loading, and the control of drug release at the targeted site.
FLO-1 cell line represents an important tool in esophageal adenocarcinoma (EAC) research as a verified and authentic cell line to study the disease pathophysiology and antitumor drug screenings. ...Since in vitro characteristics of cells depend on the microenvironment and culturing conditions, we performed a thorough characterization of the FLO-1 cell line under different culturing conditions with the aim of (1) examining the effect of serum-free growth medium and air-liquid interface (A-L) culturing, which better reflect physiological conditions in vivo and (2) investigating the differentiation potential of FLO-1 cells to mimic the properties of the in vivo esophageal epithelium. Our study shows that the composition of the media influenced the morphological, ultrastructural and molecular characteristics of FLO-1 cells, such as the expression of junctional proteins. Importantly, FLO-1 cells formed spheres at the A-L interface, recapitulating key elements of tumors in the esophageal tube, i.e., direct contact with the gas phase and three-dimensional architecture. On the other hand, FLO-1 models exhibited high permeability to model drugs and zero permeability markers, and low transepithelial resistance, and therefore poorly mimicked normal esophageal epithelium. In conclusion, the identified effect of culture conditions on the characteristics of FLO-1 cells should be considered for standardization, data reproducibility and validity of the in vitro EAC model. Moreover, the sphere-forming ability of FLO-1 cells at the A-L interface should be considered in EAC tumor biology and anticancer drug studies as a reliable and straightforward model with the potential to increase the predictive efficiency of the current in vitro approaches.
Mechanical alloying of a mixture of copper and nickel powders has been applied for the preparation of copper–nickel alloy particles in the nanometer range. The particles were designed to be used for ...controlled magnetic hyperthermia applications. The milling conditions were optimized using the desired alloy composition. Utilizing a ball-to-powder mass ratio of 20, we could obtain a nanocrystalline Cu
27.5Ni
72.5 (at%) alloy with a crystallite size of around 10
nm and a Curie temperature of 45
°C.
Thermal demagnetization in the vicinity of the Curie temperature of the nanoparticles was determined by thermomagnetic measurements using an adapted TGA–SDTA apparatus. The size and morphology of the particles were determined by XRD measurements and TEM analyses. The magnetic properties were also examined with a VSM. The magnetic heating effects were measured for the powdered material.
► Cu
x
Ni
1−
x
nanoparticles were synthesized for magnetic hyperthermia applications. ► Generated heat can be controlled using nanoparticles with adaptable Curie temperature. ► Methodology for the synthesis and characterization of CuNi nanoparticles is reported. ► Structural properties, magnetic properties and temperature rises were investigated.
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•Controlled heteroaggregation of two different types of nanoparticles.•Heteroaggregates formed by electrostatic or chemical interaction.•Kinetics of heteroaggregates formation.
...Composite particles combining nanoparticles of different functional materials, as well as nanoclusters of nanoparticles of controlled size, can be synthesized by the assembly of nanoparticles in an aqueous suspension. Different interactions between the nanoparticles in the suspension can be applied for their heteroaggregation and controlled by engineering the surface properties of the nanoparticles. The heteroaggregation of nanoparticles in a suspension was studied on a model system composed of superparamagnetic carboxyl-functionalized silica-coated maghemite nanoparticles (cMNPs) (24nm in size) and larger, amino-functionalized, silica nanoparticles (aSNPs) (92nm). The heteroaggregates formed with electrostatic attractions between the nanoparticles displaying an opposite electrical surface charge, or with chemical interactions originating from covalent bonding between the molecules at their surfaces. The suspensions were characterized with measurements of the zeta-potential and dynamic light scattering (DLS). The heteroaggregates were analyzed by transmission (TEM) and scanning (SEM) electron microscopy. The kinetics of the heteroaggregation was followed by continuous monitoring of the changes in the average hydrodynamic size by DLS. The results show that covalent bonding is much more effective than attractive electrostatic interactions in terms of a much greater and more homogeneous coverage of the larger central aSNP by the smaller cMNPs in the outer layer.
Overall energy of interaction between two oleic- and ricinoleic-acid-coated nanoparticles in different organic solvents. The additional repulsion between the ricinoleic-acid-coated nanoparticles ...exist, because of the polar interactions, in contrast to the oleic-acid-coated nanoparticles.
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► Colloidal stability of suspensions is correlated to dielectric constant of solvent. ► OA-nanoparticles cannot be dispersed in solvents that have
ε > 5. ► RA-nanoparticles can be dispersed in solvents that have
ε > 5. ► RA-nanoparticles are electron-acceptors; OA- nanoparticles are electron-donors. ► Solvation forces improved colloidal stability of RA-nanoparticles.
The colloidal stability of oleic- and ricinoleic-acid-coated nanoparticles in organic solvents with dielectric constants
ε
r ranging from 2.0 to 9.8 was studied. Although the acids are structurally similar, there is an
OH group in the ricinoleic acid’s tail, a marked improvement in the colloidal stability of the ricinoleic-acid-coated magnetic nanoparticles in moderately polar organic solvents and monomer methyl methacrylate was observed as a result. The bonding of both acids provokes a significant change in the surface properties of the iron-oxide nanoparticles. A clear shift from a strong electron-donor to a weak electron-donor was confirmed with the bonding of the oleic acid. The effect of ricinoleic acid bonding is even more dramatic: a clear shift toward a weak electron-acceptor is evident. A detailed analysis of the total energy of interaction, including the vOCG theory, between two particles was used to describe the different behaviors of the coated nanoparticles. In the case of the oleic acid nanoparticles in an apolar medium, such as decane, a small net attraction of ∼0.84
k
B
T, which is insufficient to cause nanoparticles agglomeration, exists. In polar media the net attraction is larger than 1.5
k
B
T, resulting in precipitation of the oleic-acid-coated nanoparticles. The same findings apply to the ricinoleic-acid-coated nanoparticles, but only when dispersed in the apolar medium. In the polar medium an additional repulsion due to polar solvation forces exists, resulting in a decrease of the net attraction to as low as ∼0.14
k
B
T.
Barium hexaferrite nanoplatelets (BHF NPLs) are permanent nanomagnets with the magnetic easy axis aligned perpendicular to their basal plane. By combining this specific property with optimised ...surface chemistry, novel functional materials were developed, e.g., ferromagnetic ferrofluids and porous nanomagnets. We compared the interaction of chemically different phosphonic acids, hydrophobic and hydrophilic with 1-4 phosphonic groups, with BHF NPLs. A decrease in the saturation magnetisation after functionalising the BHF NPLs was correlated with the mass fraction of the nonmagnetic coating, whereas the saturation magnetisation of the NPLs coated with a tetraphosphonic acid at 80 °C was significantly lower than expected. We showed that such a substantial decrease in the saturation magnetisation originates from the disintegration of BHF NPLs, which was observed with atomic-resolution scanning transmission electron microscopy and confirmed by a computational study based on state-of-the-art first-principles calculations. Fe K-edge XANES (X-ray absorption near-edge structure) and EXAFS (Extended X-ray absorption fine structure) combined with Fourier-transformed infrared (FTIR) spectroscopy confirmed the formation of an Fe-phosphonate complex on the partly decomposed NPLs. Comparing our results with other functionalised magnetic nanoparticles confirmed that saturation magnetisation can be exploited to identify the disintegration of magnetic nanoparticles when insoluble disintegration products are formed.
Fructose-6-phosphate aldolase (FSA) is an important enzyme for the C-C bond-forming reactions in organic synthesis. The present work is focused on the synthesis of a precursor of D-fagomine catalyzed ...by a mutant FSA. The biocatalyst has been immobilized onto several supports: magnetic nanoparticle clusters (mNC), cobalt-chelated agarose (Co-IDA), amino-functionalized agarose (MANA-agarose) and glyoxal-agarose, obtaining a 29.0%, 93.8%, 89.7% and 53.9% of retained activity, respectively. Glyoxal-agarose FSA derivative stood up as the best option for the synthesis of the precursor of D-fagomine due to the high reaction rate, conversion, yield and operational stability achieved. FSA immobilized in glyoxal-agarose could be reused up to 6 reaction cycles reaching a 4-fold improvement in biocatalyst yield compared to the non-immobilized enzyme.
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