We studied the features of hydrolytic degradation of polylactic acid (PLLA) implants depending on their structural filling with hydroxyapatite (HA). The resistance to
in vitro
hydrolysis was tested ...for the following samples: PLLA without HA (control; group 1), PLLA/HA 25 wt% (group 2), and PLLA/HA 50 wt% (group 3). Samples were incubated at 37°C. In the hydrolysate, lactate, calcium ions, and inorganic phosphate were determined. Additionally, the time of appearance of visual deformation and sample disintegration was recorded. PLLA degradation was higher in samples saturated with HA. The highest resistance to deformation was noted for samples without HA. Samples with a PLLA/HA 50 wt% demonstrated the maximum degradation of PLLA in combination with lower resistance to deformation and the highest bioavailability of calcium and phosphate. Group 2 samples are most promising for clinical use.
This study aims to investigate the comparative study of calcium phosphate coatings for flexible intramedullary nails (FINs) used to lengthen long tubular bones. The presence of a calcium phosphate ...coating deposited by micro-arc oxidation (MAO) or a composite coating based on a co-polymer of vinylidene fluoride with tetrafluoroethylene (VDF-TeFE) and hydroxyapatite (HA) on the surface of the FIN significantly enhanced the regeneration of bone in the area of osteotomy during limb lengthening by combined osteosynthesis. The investigation of the physico-chemical properties of the FIN coated with calcium phosphate via MAO demonstrated that the improved bone tissue formation resulted from favourable conditions for adhesion, proliferation and differentiation of multipotent stem cells into osteoblasts on the coating surface. The composite coatings only stimulated the formation of bone tissue in vivo, primarily because of the piezoelectric properties of the VDF-TeFE co-polymer.
•The M(H) magnetization curves of NiO nanoparticles (NPs) measured in pulsed fields of up to 250 kOe have been studied.•A model of NiO NP obtained from analysis of M(H) data have been ...proposed.•Surface and size effects as well as the origin and the magnitude of uncompensated magnetic moment have been revealed.
-The analysis of the M(H) magnetization curves of antiferromagnetic nanoparticles yields information about magnetic subsystems formed in these objects, which are characterized by a large fraction of surface atoms. However, in the conventionally investigated experimental magnetic field range of up to 60–90 kOe, this analysis often faces the ambiguity of distinguishing the Langevin function-simulated contribution of uncompensated magnetic moments μun of particles against the background of a linear-in-field dependence (the antiferromagnetic susceptibility and other contributions). Here, this problem has been solved using a pulsed technique, which makes it possible to significantly broaden the range of external fields in which the μun contribution approaches the saturation. Nanoparticles of a typical NiO antiferromagnet with an average size of ~ 4.5 nm have been investigated. Based on the thorough examination of the M(H) magnetization curves measured in pulsed fields of up to 250 kOe, a model of the magnetic state of NiO nanoparticles of such a small size has been proposed. The average moment is ~130 μB (μB is the Bohr magneton) per particle, which corresponds to 60–70 decompensated spins of nickel atoms localized, according to the Néel hypothesis (μun~ 3/2), both on the surface and in the bulk of a particle. A part of the surface spins unrelated to the antiferromagnetic core form another subsystem, which behaves as free paramagnetic atoms. Along with the antiferromagnetic core, an additional linear-in-field contribution has been detected, which is apparently related to superantiferromagnetism, i.e., the size effect inherent to small antiferromagnetic particles.
Purpose. Our research was aimed at studying the radiographic and histological outcomes of using flexible intramedullary nailing (FIN) combined with Ilizarov external fixation (IEF) versus Ilizarov ...external fixation alone on a canine model of an open tibial shaft fracture. Materials and Methods. Transverse diaphyseal tibial fractures were modelled in twenty dogs. Fractures in the dogs of group 1 (n=10) were stabilized with the Ilizarov apparatus while it was combined with FIN in group 2 (n=10). Results. On day 14, a bone tissue envelope started developing round the FIN wires. Histologically, we revealed only endosteal bone union in group 1 while in group 2 the radiographs revealed complete bone union on day 28. At the same time-point, the areas of cancellous and mature lamellar bone tissues were observed in the intermediary area in group 2. The periosteal layers were formed of the trabeculae net of lamellar structure and united the bone fragments. The frame was removed at 30 days after the fracture in group 2 and after 45 days in group 1 according to bone regeneration. Conclusion. The combination of the Ilizarov apparatus and FIN accelerates bone repair and augments stabilization of tibial shaft fractures as compared with the use of the Ilizarov fixation alone.
This work reports an original approach to the synthesis of composite “core-shell” nanoparticles of o-EuFeO3@am-EuFeO3 via solution combustion synthesis (SCS) followed by heat treatment in the air. ...PXRD, 57Fe and 151Eu Mössbauer spectroscopy, FTIR, DSC-TGA, SEM-EDX, TEM-SAED and vibrating-sample magnetometry were used to analyze the as-prepared and heat-treated samples. It was shown that the formation of amorphous am-EuFeO3 “shell” on the surface of crystalline o-EuFeO3 “cores” arises from the partial carbonatization of europium oxide during the solution combustion. It was found that the average crystallite size of o-EuFeO3 “cores” (37–92 nm) and thickness of am-EuFeO3 “shell” (1–10 nm) can be easily varied through the simple temperature change of heat treatment in the range of 500–900 °C. Acquired composite nanoparticles o-EuFeO3@am-EuFeO3 demonstrate uniform isometric morphology with a well distinct core and shell. Magnetometry results indicate the paramagnetic behavior of composite nanoparticles in a wide range of temperatures and applied magnetic fields that contradict the Mössbauer spectroscopy results showing the magnetic ordering of Fe-sublattice of o-EuFeO3 “cores”. Thus, the results of this work confirm the possibility of obtaining a new class of rare earth orthoferrite nanomaterials with the core-shell structure that can have promising functional applications.
Display omitted
•New approach is proposed to the synthesis of EuFeO3-based core-shell nanoparticles.•Procedure is based on a solution combustion synthesis followed by heat treatment.•Core-shell structure forms due to partial carbonatization of nanoparticle surface.•Core and shell sizes can be controlled by simply varying the treatment temperature.•synthesized composite nanoparticles exhibit unusual magnetic behavior.
•A sample of NiO nanoparticles with an average size of 8 nm was synthesized.•The sample exhibits the superparamagnetic behavior with a blocking temperature of 185 K.•The magnetization curves in ...fields up to 250 kOe at temperatures of 80–300 K was measured.•The FM, AFM contributions and paramagnetism of the surface spins was extract.
It is well-known that the fraction of surface atoms and the number of defects in an antiferromagnetic particle increase with a decrease in the particle size to tens of nanometers, which qualitatively changes the properties of the particle. Specifically, in antiferromagnetic nanoparticles, spins in the ferromagnetically ordered planes can partially decompensate; as a result, an antiferromagnetic particle acquires a magnetic moment. As a rule, uncompensated chemical bonds of the surface atoms significantly weaken the exchange coupling with the antiferromagnetic particle core, which can lead to the formation of an additional magnetic subsystem paramagnetic at high temperatures and spin-glass-like in the low-temperature region. The existence of several magnetic subsystems makes it difficult to interpret the magnetic properties of antiferromagnetic nanoparticles. It is shown by the example of NiO nanoparticles with an average size of 8 nm that the correct determination of the contributions of the magnetic subsystems forming in antiferromagnetic nanoparticles requires magnetic measurements in much stronger external magnetic fields than those commonly used in standard experiments (up to 60–90 kOe). An analysis of the magnetization curves obtained in pulsed magnetic fields up to 250 kOe allows one to establish the contributions of the uncompensated particle magnetic moment μun, paramagnetic subsystem, and antiferromagnetic particle core. The μun value obtained for the investigated NiO particles is consistent with the Néel model, in which μun ∼ N1/2 (N is the number of magnetically active atoms in a particle), and thereby points out the existence of defects on the surface and in the bulk of a particle. It is demonstrated that the anomalous behavior of the high-field susceptibility dM/dH of antiferromagnetic NiO nanoparticles, which was observed by many authors, is caused by the existence of a paramagnetic subsystem, rather than by the superantiferromagnetism effect.
Composite poly-L-lactide acid-based scaffolds with hydroxyapatite (HAp) content up to 75 wt.% were fabricated via solution blow spinning. The influence of HAp concentration on structure, wettability, ...mechanical properties and chemical and phase composition of the produced materials was examined. It was found that with an increase of HAp content the average fiber diameter was increased, the uniaxial strength and relative elongation were reduced, while the phase composition and surface wettability did not change. The performance of the scaffolds during implantation in the parietal bone of a rat skull for a period from 15 to 90 days was studied. The materials have shown high ability to integrate with both soft and hard tissues. It was found that scaffolds with 25 wt.% HAp content significantly enhance osteogenesis during scarification (damage) of the periosteum. Overall, the fabricated scaffolds proved to be highly efficient for replacing bone defects in long tubular bones.
•Nickel oxide nanoparticles with an average size of ~8 nm were synthesized by thermal decomposition of nickel oxalate.•New magnetic subsystems are formed in these nanoscale antiferromagnetic ...particles.•Magnetic hysteresis in NiO nanoparticles was studied using both standard quasi-static (VSM) measurements and strong pulsed magnetic fields of up to 130 kOe.•Interaction between magnetic subsystems causes complex character of magnetization switching.
We report on the investigations of a system of 8-nm NiO particles representing antiferromagnetic (AFM) materials, which are weak magnetic in the form of submicron particles, but can be considered to be magnetoactive in the form of nanoparticles due to the formation of the uncompensated magnetic moment in them. The regularities of the behavior of magnetization switching in AFM nanoparticles are established by studying the magnetic hysteresis loops under standard quasi-static conditions and in a quasi-sinusoidal pulsed field of up to 130 kOe with pulse lengths of 4–16 ms. The magnetic hysteresis loops are characterized by the strong fields of the irreversible magnetization behavior, which is especially pronounced upon pulsed field-induced magnetization switching. Under the pulsed field-induced magnetization switching conditions, which are analogous to the dynamic magnetic hysteresis, the coercivity increases with an increase in the maximum applied field H0 and a decrease in the pulse length. This behavior is explained by considering the flipping of magnetic moments of particles in an external ac magnetic field; however, in contrast to the case of single-domain ferro- and ferrimagnetic particles, the external field variation rate dH/dt is not a universal parameter uniquely determining the coercivity. At the dynamic magnetization switching in AFM nanoparticles, the H0 value plays a much more important role. The results obtained are indicative of the complex dynamics of the interaction between magnetic subsystems formed in AFM nanoparticles.
•Three-dimensional periodic superconducting structures demonstrate diverse pinning mechanisms.•For carcasses consisted of octahedral and tetrahedral tin nanoparticles with the diameter of 128 and 70 ...are found to be a type-I superconductor.•The tin sample formed by 80 and 42 nm particles demonstrates an analog of intertype superconductivity: features of both type-I and II superconductors are observed on the magnetization isothermal curves.
Magnetization hysteresis loops of tin samples with an inverted opal structure are presented. The sample formed by tin particles with the size of 70 and 128 nm is found to be a type-I superconductor. The tin sample formed by 80 and 42 nm particles demonstrates an analog of intertype superconductivity: features of both type-I and II superconductors are observed on the magnetization isothermal curves. A behavior of the irreversible and reversible magnetizations supports coexistence of type-I and II superconducting nanoparticles in this sample.
Anisotropic Magnetization of an NbN Film Gokhfeld, D. M.; Savitskaya, N. E.; Popkov, S. I. ...
Journal of experimental and theoretical physics,
06/2022, Letnik:
134, Številka:
6
Journal Article
Recenzirano
The structural and magnetic properties of a niobium nitride (NbN) film prepared by reactive sputtering onto a quartz substrate are investigated. It is shown using scanning electron microscopy that ...the film has a columnar structure with a diameter of crystallite columns of about 50 nm. The film magnetization loops are measured for the field orientation parallel and perpendicular to its surface. Based on the experimental data, the critical current densities of the film are estimated in both cases. For the field parallel to the film surface, the estimate is 6.5 × 10
4
A/cm
2
at the liquid helium temperature. For the field perpendicular to the surface, the critical current density is close to the depairing current density (10
7
A/cm
2
). Analysis of the results based on different models of magnetic vortex pinning in superconductors shows that in the former case, pinning occurs at the boundaries of columns in the bulk of the sample, while in the latter case, it is determined by the influence of the surface barrier.
PDF
