No abstract

No abstract

No abstract

No abstract

For the first time, zirconia nanofibers with an average diameter of about 75 nm have been fabricated by calcination of electrospun zirconium acetylacetonate/polyacrylonitrile fibers in the range of 500–1100 °C. Composite and ceramic filaments have been characterized by scanning electron microscopy, thermogravimetric analysis, nitrogen adsorption analysis, energy-dispersive X-ray spectroscopy, and X-ray diffractometry. The stages of the transition of zirconium acetylacetonate to zirconia have been revealed. It has been found out that a rise in calcination temperature from 500 to 1100 °C induces transformation of mesoporous tetragonal zirconia nanofibers with a high specific surface area (102.3 m2/g) to non-porous monoclinic zirconia nanofibers of almost the same diameter with a low value of specific surface area (8.3 m2/g). The tetragonal zirconia nanofibers with high specific surface area prepared at 500 °C can be considered, for instance, as promising supports for heterogeneous catalysts, enhancing their activity.

Remote nano-magneto-mechanical actuation of magnetic nanoparticles (Mnps) by non-heating extremely low frequency magnetic field (ELF MF) is explored as a tool for non-invasive modificationof bionanomaterials in pharmaceutical and medical applications. Here we study the effects of ELF MF (30-160 Hz, 8-120 kA/m) on the activity and release of a model enzyme, superoxide dismutase 1 (SOD1) immobilized by polyion coupling on dispersed Mnps aggregates coated with poly(L-lysine)-blockpoly(ethylene glycol) block copolymer (s-MNPs). Such fields do not cause any considerable heating of Mnps but promote their rotating-oscillating mechanical motion that produces mechanical forces and deformations in adjacent materials. We observed the changes in the catalytic activity of immobilized SOD1 as well as its release from the s-MNPs/SOD1 polyion complex upon application of the ELF MF for 5 to 15 min. At longer exposures (25 min) the s-MNPs/SOD1 dispersion destabilizes. The bell-shaped effect of the field frequency with maximum at f = 50 Hz and saturation effect of field strength (between 30 kA/m and 120 kA/m at f = 50 Hz) are reported and explained. The findings are significant as one early indication of the nano-magneto-mechanical disruption by eLf Mf of cooperative polyion complexes that are widely used for design of current functional healthcare bionanomaterials.Non-invasive functional control of bionanomaterials in inaccessible areas of a human body (e.g., biochemical reactions, drug release, gene expression, etc.) could greatly advance development of diagnostics and therapeutic modalities 1 . This control can be accomplished by remote actuation of nanoparticles by external fields 2-6 . In recent years magnetic nanoparticles (MNPs) have been investigated for cell separation, targeted drug delivery, and magnetic resonance imaging (MRI) 7-9 . Remote actuation of MNPs by radio frequency (200-800 kHz) magnetic fields has been used in hyperthermia for cancer therapy 10-12 . However, this approach has a risk of tissue overheating and damage. Recently an alternative nano-magneto-mechanical actuation of MNPs by non-heating extremely low frequency magnetic field (ELF MF) has attracted increasing attention in drug delivery and nanomedicine [13][14][15][16][17] .The phenomenon of nano-magneto-mechanical actuation is linked to the ability of MNPs to undergo mechanical motion in ELF MF and as a consequence produce mechanical forces and deformations in adjacent materials. It is well known, that a single-domain MNPs can relax in an external magnetic field, reducing an angle between the MNPs magnetic moment μ and the field vector H [18][19][20] . Two basic types of relaxation phenomena are dependent on the size of the magnetic core. MNPs with D m less than some critical value d* experience rotation of magnetic moments μ towards the vector H, which proceeds mainly by overcoming the crystallographic anisotropy of the lattice, without causing significant mechanical motion of the particle (Néel relaxation). MNPs with a diameter D m greater than d*...

No abstract

No abstract