Klebsiella oxytoca microorganisms. The distribution of nanoparticles in the body of laboratory animals and the physical properties of the nanoparticles were studied. The synthesized ferrihydrite nanoparticles are superparamagnetic at room temperature, and the characteristic blocking temperature is 23–25 K. The uncompensated moment of ferrihydrite particles was determined to be approximately 200 Bohr magnetons. In vitro testing of different concentrations of ferrihydrite nanoparticles for the functional activity of neutrophilic granulocytes by the chemiluminescence method showed an increase in the release of primary oxygen radicals by blood phagocytes when exposed to a minimum concentration and a decrease in secondary radicals when exposed to a maximum concentration. In vivo testing of ferrihydrite nanoparticles on Wister rats showed that a suspension of ferrihydrite nanoparticles has chronic toxicity, since it causes morphological changes in organs, mainly in the spleen, which are characterized by the accumulation of hemosiderin nanoparticles (stained blue according to Perls). Ferrihydrite can also directly or indirectly stimulate the proliferation and intracellular regeneration of hepatocytes. The partial detection of Perls-positive cells in the liver and kidneys can be explained by the rapid elimination from organs and the high dispersion of the nanomaterial. Thus, it is necessary to carry out studies of these processes at the systemic level, since the introduction of nanoparticles into the body is characterized by adaptive-proliferative processes, accompanied by the development of cell dystrophy and tension of the phagocytic system.Biogenic ferrihydrite nanoparticles were synthesized as a result of the cultivation of  Due to this, ferrihydrite plays a huge role in the metabolism of living organisms. It is formed in the core of the protein complex named ferritin, which is a capsule of the protein apoferritin. The size of the ferrihydrite nanoparticles is typically in a narrow range from 2 to 8 nm. With increasing particle size, the Fe2O3∙nH2O → hematite transformation occurs [Klebsiella oxytoca, isolated from pyrite deposits, to ferment iron citrate under anaerobic conditions and to form a trivalent metal hydrogel was first reported in [Klebsiella oxytoca can be a very promising drug for various applications and, therefore, they require comprehensive study. Of particular interest are the magnetic properties of nanoparticles of ferrihydrite. Although ferrihydrite is characterized by an antiferromagnetic ordering with a Néel temperature of ~350 K, the presence of defects caused by the nanoscale state leads to the appearance of the uncompensated magnetic moment in an antiferromagnetic particle of a magnitude reaching hundreds of Bohr magnetons [Klebsiella oxytoca is the presence of a polysaccharide capsule [Ferrihydrite Fen occurs . The abiorted in ,5. Ferriagnetons ,7,8,9. A capsule ,11,12,13 capsule ,14, in wHowever, when studying the effect of ferrihydrite nanoparticles on living organisms, it should be borne in mind that nanoparticles have the ability to adsorb proteins from biological fluids and form a protein layer called the protein corona ,16,17,18Thus, the prospect of the practical use of nanoparticles of ferrihydrite requires the study of the mechanisms of interaction of nanoparticles in different concentrations with cells of the body, the ways of their transformation and excretion, as well as possible toxic effects depending on the concentration of nanoparticles.Klebsiella oxytoca.This work aims to study the physical  and biological properties in vitro and in vivo of biogenic ferrihydrite nanoparticles prepared as a result of the cultivation of microorganisms Klebsiella oxytoca used were isolated from the sapropel of Lake Borovoye (Krasnoyarsk Territory). The sapropel selected in the lake was passed through a magnetic separator. Microorganisms grew on nutrient media containing various forms of iron . Microorganisms of the Klebsiella oxytoca culture were plated on Lovley medium [2+ oxalate, which was used as a chelator, with the following composition (g/l): NaHCO3—2.5; CaCl2∙H2O—0.1; KCl—0.1; NH4Cl—1.5; NaH2PO4∙H2O—0.6; Mohr’s salt (FeSO4∙(NH4)2SO4∙6H2O)—0.4; oxalic acid (H2C2O4)—0.22; yeast extract 0.05 g/L. Microorganisms of the Klebsiella oxytoca culture were also grown in Lovley medium on iron citrate with a concentration of 0.5 g/l with the following composition (g/L): NaHCO3—2.5; CaCl2∙H20—0.1; KCl—0.1; NH4Cl—1.5; NaH2PO4∙H2O—0.6; yeast extract 0.05 g/L. Sampling was carried out 3–28 days after the inoculation of microorganisms in a nutrient medium. The time dependences of the change in the dry weight of bacteria grown on Fe2+ oxalate and Fe3+ citrate were obtained , then the bacteria cells were destroyed by ultrasound ) 3 times for 3 min in distilled water at intervals of 10 min. Next, the resulting precipitate to remove fatty acids was sonicated and incubated in acetone for 30 min and washed with distilled water . Then, the precipitate was placed in a 2% NaOH solution, the incubation time was 1 h. The resulting precipitate was washed with distilled water with the addition of NaCl  until a pH of 8 supernatant was reached. Thus, a sol was obtained, which was subsequently dried at room temperature.−1.A qualitative analysis of the infrared spectra of ferrihydrite nanoparticles was carried out to determine the functional groups. The infrared spectra of ferrihydrite nanoparticles were measured on a VERTEX 80V  vacuum Fourier spectrometer in the mid-IR region of 400–4000 cm57(Cr) source with a line width at half maximum of 0.24 mm/s on an absorber made of sodium nitroprusside powder. The thickness of the samples was 5–10 mg/cm2 based on the natural iron content, at which the intensities of the spectrum lines are linearly dependent on the iron content in the phase. Isomer chemical shifts are indicated relative to α-Fe.Mössbauer measurements were carried out on an MS-1104Em spectrometer  with a CoMagnetic measurements were carried out on a vibration magnetometer . The tesThe objects of study were neutrophilic granulocytes of blood isolated from 29 apparently healthy blood donors and ferrihydrite nanoparticles, the concentrations of which were calculated based on the minimum and maximum amount of iron-containing substances in the human body. In this regard, the dose of nanoparticles in the minimum concentration was 25 mg, in the maximum—50 mg per 106 cells in 1 mL . The dong for 45 min. The purity of the yield of neutrophilic granulocytes was determined by monitoring the morphological composition of leukocyte suspensions, which was 97%. The suspension of neutrophilic granulocytes was washed twice to remove plasma proteins in Hanks’ Balanced Salt solution without phenol red for 10 min at 400 g. The supernatant was discarded, the remaining neutrophilic granulocytes were diluted in 1 mL of Hanks’ solution and a suspension was obtained. The number of neutrophilic granulocytes in the hemocytometer was counted.Neutrophilic granulocytes were isolated from whole blood by layering on ficoll-urographin (ρ = 1.119) and centrifuged at 400 The functional activity of blood neutrophilic granulocytes was determined using chemiluminescent analysis. The study of spontaneous and zymosan-induced luminol-dependent chemiluminescence was carried out using a CL3606M biochemiluminescence analyzer . The results of chemiluminescence analysis were characterized by the following parameters: the time to reach the maximum intensity (Tmax), the maximum value of the intensity (Imax), and the area (S) under the chemiluminescence curve. The enhancement of zymosan-induced chemiluminescence was assessed by the ratio of the induced area (Sind.) to the spontaneous area (Sspont.) and was defined as the activation index (AI).Ferrihydrite nanoparticles were added into experimental samples immediately before chemiluminescence analysis at concentrations of 25 mg/mL and 50 mg/mL. The effect of ferrihydrite nanoparticles on cells after joint incubation for 30 min at 37 °C was evaluated. A test sample for determining a spontaneous reaction contained 200 μL of a suspension of neutrophilic granulocytes (the cell concentration was 106 per 1 mL), 20 μL of donor serum, 240 μL of Hanks solution, 50 μL of luminol. The experimental sample for determining the zymosan-induced reaction contained 200 μL of a suspension of neutrophilic granulocytes, 20 μL of donor serum, 200 μL of Hanks solution, 50 μL of luminol, and 40 μL of zymosan. As a control, the chemiluminescent activity of the spontaneous and zymosan-induced response was measured in neutrophilic granulocytes without being exposed to ferrihydrite nanoparticles.Statistical analysis was carried out using the Statistica 6.1 software packages . The description of the sample was performed by calculating the median (Me) and the inter-quarter range in the form of 25 and 75 percentiles (C25 and C75). The significance of differences between the indices of independent samples was assessed using the nonparametric Mann–Whitney test. The significance of differences between the indices of dependent samples was assessed by the Wilcoxon U test.The studies were conducted on sexually mature male Wistar rats weighing 200–250 g. The maintenance and manipulations of animals were carried out following the basic ethical principles in the field of bioethics .Toxicological studies of the effect of ferrihydrite nanoparticles on tissues and organs of laboratory animals were carried out. The concentration of ferrihydrite nanoparticles in the preparation was 2.4 g/L. The dose of drug administration was 0.2 mL per animal every 8 days for 1 month. Ferrihydrite nanoparticles in the form of an aqueous suspension were injected intramuscularly into the thigh.n = 8 each): (1) animals without exposure; (2) animals that were injected with an aqueous sol of nanoparticles of ferrihydrite.Following the objectives of the study, laboratory animals were divided into 2 groups  compounds using Perls Prussian blue method ,33.Measurements of dynamic light scattering were performed on a Zetasizer Nano apparatus . The distribution of nanoparticles obtained by dynamic light scattering  has a poKlebsiella oxytoca bacteria is presented in The IR spectrum of dried sol of ferrihydrite nanoparticles produced by −1 that is assigned to Oh group within the crystal structure of ferrihydrite. The large width of this band is partially due to surface O–H bonds of adsorbed water molecules. Bending vibrations of H2O are pronounced at 1630 cm−1 [−1 is featured by two broad absorption bands peaking at 1498 and 1410 cm−1 assigned to carboxyl groups. The spectral range 900–1200 cm−1 is known as the “fingerprint” range. The spectrum of the sol under investigation contains the most intense bands in this range, that are the manifestations of stretching vibrations of C–C groups as well as symmetric and asymmetric vibrations of valence bonds C–O. In our sample, the vibrations of Fe-O bonds fall into this spectral range [−1 can be an indication of the presence of glucose. Vibrations at 564 and 604 cm−1 are assigned to TO–LO modes associated with α-Fe2O3 [IR spectrum of ferrihydrite nanoparticles is featured by the broad absorption band maximizing at 3420 cm α-Fe2O3 .2+ oxalate and Fe3+ citrate). 3+. Here, the anionic octahedra are connected by edges, both in the layer and between the layers, providing a relatively weak distortion of the octahedra associated with the Fe1 position. When a fragment with hexagonal packing is formed, single layers of iron-occupied octahedra are formed [The maxima and features on the P(QS) distributions indicate possible nonequivalent positions of iron. Based on the P(QS) shape, the sum of three doublets with different quadrupole splittings is taken as the model spectrum. The model spectrum was fitted to the experimental spectrum by varying the entire set of hyperfine parameters. As a result of such decoding of the spectra, three types of ferric iron positions are identified: Fe1 with QS ~0.55 mm/s, Fe2 with QS ~1 mm/s, and Fe3 with QS ~1.5–1.8 mm/s. The origin of these positions is explained as follows. The crystal–chemical model of ferrihydrite is a trigonal layered structure with dense packing of anions  with a le formed , which aZFC dependence, and bifurcation of the dependences M(T)ZFC and M(T)FC which begins in the vicinity of Tmax. For ferritin, the Tmax value is ≈13 K, for the ferrihydrite nanoparticles, ≈23 K. The temperature Tmax can be logically considered as the temperature of the SPM blocking. At this temperature, the system of magnetic moments of nanoparticles passes from a blocked (at T < Tmax) to an unblocked (at T > Tmax) state. According to our data, for the nanoparticles of ferrihydrite, the temperature Tmax for samples of different batches (prepared at different times) varied by no more than 3 K [than 3 K ,38,39.max, the dependences M(H) exhibit hysteresis. The coercive force HC at T = 4.2 K for ferrihydrite nanoparticles is ≈2.1 kOe, which exceeds HC for ferritin  are completely reversible. Their shape is described by the Langevin function corresponding to SPM behavior, and the contribution is linear on the field, corresponding to the antiferromagnetically ordered “core” of particles [articles ,38,39,402O2, OH, O2, HClO) was studied. The study of the lucigenin-dependent reaction determined the activity of the superoxide anion radical [Luminol-dependent chemiluminescence was used to determine the basic activity of cells and the reserve capacity of neutrophilic granulocytes when exposed to a nonspecific inductor in the form of zymosan. The ability of neutrophilic granulocytes to form a general pool of secondary oxygen radicals  was revealed. Thus, the functional activity of neutrophilic granulocytes changes only concerning the superoxide anion radical when exposed to ferrihydrite nanoparticles at a minimum concentration .Assessment of the activity of neutrophilic granulocytes on the effect of the maximum concentration of ferrihydrite nanoparticles revealed a statistically significant decrease (½ times) in the indicators of maximum intensity in the zymosan-induced process. The area under the curve of the chemiluminescent response stimulated by zymosan also decreased by two times relative to the control. In the case of zymosan-induced chemiluminescence, the index of activation (IA) was decreased twice when exposed to nanoparticles .The study of the reaction of neutrophilic granulocytes to the effect of ferrihydrite nanoparticles in the minimum concentration after joint incubation for 30 min also revealed an increase in the intensity and area under the curve of the lucigenin-dependent chemiluminescent process relative to the control (by three and five times). In the case of exposure to the maximum concentration of nanoparticles, a decrease in the indicator characterizing the time to peak (10 times) in the spontaneous chemiluminescence reaction and in the indicator of the maximum intensity of the chemiluminescence process (six times) was found. The chemiluminescence index, which characterizes the maximum area under the curve of the zymosan-induced reaction, decreased by five times after the incubation of neutrophilic granulocytes with nanoparticles. Long-term exposure to ferrihydrite nanoparticles resulted in a three-fold decrease in IA.The intramuscular injection of aqueous sol of ferrihydrite did not cause clinically pronounced negative changes. Microscopic examination showed that in all samples of organs and tissues of the experimental group, similar changes are observed, which are a consequence of the deposition of iron upon its excessive intake.The study of liver samples of the control group corresponds to the normal structural organization of the organ. The liver is of a typical structure: the beam structure is preserved, the central veins, sinusoidal capillaries are unchanged. Most hepatocytes are mononuclear, a small number of hepatocytes are also found. The portal tracts are not thickened. During the Perls reaction in the liver, the formation of Prussian blue was not observed.In animals treated with a sol of ferrihydrite nanoparticles, histological changes in liver tissue were detected. Despite a slight expansion of the central veins and sinusoidal capillaries filled with protein light eosinophilic mass, hepatocytes were in a state of moderate protein dystrophy  and an iThe study of histological sections of the spleen from rats of the control group shows a typical structure. The organ parenchyma is represented by clearly distinguishable red and white pulp. White pulp is characterized by the presence of formed lymphatic follicles with pronounced germinal centers, periarterial, mantle and marginal zones. Histological examination of tissues of intact animals showed that in the spleen during the Perls reaction formation of Prussian blue was not observed.In the spleen of rats receiving a sol of ferrihydrite nanoparticles, the distribution of nanoparticles was noted both in the parenchyma and in the organ stroma . The depIn the animals of the control group, a normal histological picture of the structure of the renal cortex and medulla was observed. The vascular glomeruli are not enlarged, the basement membrane is thin, the space between the capsule and glomerulus is preserved. The openings of the straight and convoluted tubules are not enlarged, the epithelial cells of the proximal convoluted tubules are cubic, pink cytoplasm, spherical cell nuclei. Histological examination of tissues of intact animals showed that during the Perls reaction the formation of Prussian blue in the kidney was not observed.In the kidneys of the rats endured the introduction of an aqueous sol of ferrihydrite nanoparticles , moderatIn the control group of animals at the end of the experiment, the histological examination did not reveal significant violations in the structural organization of the lung. The histological structure of the organ of animals treated with a suspension of ferrihydrite nanoparticles was unchanged. The cavities of most of the alveoli are straightened, optically empty. The interalveolar walls are not thickened, their capillaries are moderately congested, and paretic congestion of larger vessels is noted. There are scattered small areas in which the alveolar cavities are widened and optically empty, the interalveolar walls are thinned and partially torn. These are foci of acute emphysema. The lumens of the small bronchi are dilated, free, with a moderately pronounced focal peribronchial lymphoid infiltration around .Alveolar macrophages are detected partially perivascular and peribronchial and are also noted in interalveolar septa. They are represented by a few cells containing a small number of ferrihydrite nanoparticles, which give a positive Perls reaction.2+ oxalate and Fe3+ citrate) presented in The dependences of the dry weight of bacteria cultured under anaerobic conditions on media containing various forms of iron  reach the parameters of IS precipitation during cultivation on Fe3+ citrate after 3–6 days. With a further increase in the cultivation duration, the values of isomeric shifts monotonously decrease. Thus, it is seen from the analysis of IS dependences that the process of production of nanoparticles of ferrihydrite by microorganisms during cultivation on Fe2+ oxalate is delayed by 14–15 days compared to cultivation on Fe3+ citrate. The dependences of the quadrupole splitting QS and the occupancies of the detected positions of Fe(1), Fe(2), Fe (3) for the discussed cultivation modes correlate with each other.The results of Mössbauer spectroscopy correlate with the results of the dry weight production of bacterial sediments. At the initial stages of cultivation (3–14 days), the values of isomeric shifts (IS) and the nature of the changes in Mössbauer spectra of precipitates formed during the cultivation of microorganisms on FeKlebsiella oxytoca deserves particular attention for practical applications. In [Klebsiella oxytoca bacteria was studied by IR spectroscopy, it was suggested that there were glucose, polysaccharides, and amines in the sample. The IR spectra of proteins and their decay products (peptides) feature by the presence of two main absorption bands, namely amide I at 1650 cm−1 and amide II at 1550 cm−1, due to stretching vibrations of the C = O bond (amide I) and planar bending vibrations of the NH bond (amide II) [−1 and 1550 cm−1 makes it possible to detect the presence of amides in the analyzed sample. In the spectrum of the sol studied by us, modes characteristic of amides are not observed, but absorption bands characteristic of polysaccharide structures are present.The organic matrix of the studied sol of biogenic nanoparticles ions. In , where tmide II) . Thus, tP of ferrihydrite and ferritin particles [P) f(μP) + C-H (TrueType), in which NP is the number of particles per unit mass of the sample, L(μ) is the Langevin function, f(μP) is the distribution function of magnetic moments , and the term C-H is responsible for the antiferromagnetic canting of the sub lattices and other contributions [P value varies in the range 160–230 μB (μB is the Bohr magneton) for samples of different batches [P values are explained in the framework of the Néel hypothesis [P~μat⋅Nb, where μat is the magnetic moment of the atom, N is the number of magnetically active atoms in the particle, and the exponent b is 1/3, 1/2, and 2/3 in the case of defects on the surface, in the volume of the particle, and an odd number of ferromagnetic ordered planes, respectively. For the obtained ferrihydrite, N ~ (1.5–2) × 103, μFe ≈ 5 μB. From these data, we obtain agreement between the obtained μP (160–230 μB) and the Néel model hypothesis for b ≈ 1/2, which corresponds to the presence of defects in the particle volume. A similar conclusion was obtained in the analysis of data on ferritin [Taking into account the distribution of magnetic moments in magnitude allows one to rather accurately estimate the value of the average uncompensated moment μarticles ,39,43,44ibutions ,46,47,48 batches ,39. The pothesis  for smalferritin .An in vitro study of the effect of ferrihydrite nanoparticles on the functional activity of neutrophilic granulocytes has shown that at the first stage of cell response, the antioxidant potential of cells is activated, which contributes to their protection from reactive oxygen species. Consequently, the first reaction to nanoparticles in cells is the activation of a defense mechanism aimed at reducing the concentration of free radicals. This is indicated by the low response of zymosan-induced chemiluminescence of cells after incubation with nanoparticles at the maximum concentration, and this reflects the low activity of oxygen radicals and thus a decrease in the level of cell metabolism upon prolonged exposure to nanoparticles. It is also interesting that the minimum concentrations of ferrihydrite nanoparticles increase the activity of primary oxygen radicals, while the maximum concentrations decrease the production of secondary radicals.Thus, the effect of nanoparticles on phagocytes significantly reduces the level of free radical oxidation. The short-term effect of nanoparticles can be modulating and depend on the initial level of cell reactivity. A unique feature is that the reduction in oxidative stress due to nanoparticle exposure occurs exclusively in a stimulated response. Thus, the effect of nanoparticles is realized mainly on activated cells.The results of testing the biogenic water sol of ferrihydrite on laboratory animals indicate that the toxicokinetics  of nanoparticles are controlled by both physiological and physicochemical mechanisms, namely active endocytosis carried out by various cells and gradual excretion from the body.Thus, the effect of biogenic ferrihydrite nanoparticles can be explained, on the one hand, by the ability to penetrate through biological barriers (dispersion of nanoparticles), the ability of nanoparticles to directly penetrate from the sites of primary deposition into the bloodstream with subsequent retention in internal organs, especially in organs rich in cells of the reticuloendothelial system, particularly in the spleen and partly in the liver. On the other hand, the effect of nanoparticles is explained by the ability of iron nanoparticles to release toxic ions near ultrastructural and molecular targets for their impact . Perhaps these processes are the result of a free radical oxidation due to the presence of an increased amount of iron, which has an influence on the formation of free radicals. As a consequence, increased oxidation can stimulate inflammatory processes in the organs and tissues of the body as a result of the release of iron ions.Along with the negative effect of the sol nanoparticles on organs and tissues, one should note their positive effect, associated with the activation of compensatory–adaptive processes in the studied organs and tissues, characterized by an increase in the number of binuclear hepatocytes, Kupffer cells, as well as increased hematopoiesis, which is manifested by an increase in extramedullary foci of hematopoiesis in the liver and spleen.Elimination of biogenic ferrihydrite nanoparticles consists of three main mechanisms: renal, hepatobiliary, and through the mononuclear phagocytic system. In the liver, the elimination of nanoparticles is carried out by endocytosis, followed by their enzymatic cleavage and excretion into bile through the biliary system. The accumulation of Kupffer cells in the liver is periportal, i.e., migration occurs from the sinusoids to the biliary tract of the portal tracts, followed by penetration into their lumen. These observations are consistent with the literature data on the existence of a mechanism for the elimination of nanoparticles from the body in bile .The spleen has the largest accumulation of ferrihydrite nanoparticles compared to other organs. This indicates the active participation of the spleen in the processes of elimination of nanoparticles from the blood and their accumulation in the cells of the mononuclear phagocyte system (monocytic–macrophage system). No significant morphological changes were found in the spleen. This indicates the broad compensatory capabilities of this organ. The spleen protects other organs from the effects of nanoparticles by decreasing their concentration in the blood.In the kidneys, discirculatory changes are weakly expressed, which indicates the implementation of adaptive mechanisms. The relatively small number of Perls-positive cells indicates that the kidneys do not accumulate ferrihydrite nanoparticles.In the rat lung, macrophages that give a positive Perls reaction lie perivascular, which indicates the interaction of these cells with ferrihydrite nanoparticles immediately after their penetration into the tissue from the lumen of the vessel. Single accumulations of Perls-positive macrophages are found in the interalveolar septa and peribronchial, which indicates the interaction of alveolar macrophages with ferrihydrite nanoparticles, namely migration into the lumen of the bronchial tree. A small number of Perls-positive macrophages indicates the elimination of nanoparticles by phagocytosis and their removal from the lung by the transport system.Klebsiella oxytoca bacteria were studied. Using the method of Mössbauer spectroscopy, the optimal conditions and duration of the synthesis were determined. The study of the organic shell covering the surface of the nanoparticles by IR spectroscopy showed that it consists of polysaccharides. According to the static magnetic properties, ferrihydrite nanoparticles are close to a commercial product—horse spleen ferritin. The uncompensated magnetic moment of the ferrihydrite particles amounts to about 200 Bohr magnetons, which corresponds to ~ 40 uncompensated spins in a particle with N ~ 1.5–2 × 103 iron atoms. This is consistent with the Néel hypothesis, in which the presence of defects in the volume of a small antiferromagnetic particle leads to the appearance of its magnetic moment proportional to N1/2 [In this work, nanoparticles of biogenic ferrihydrite synthesized as a result of the cultivation of  to N1/2 . At roomIn vitro testing has shown a decrease in the functional activity of blood phagocytes when exposed to ferrihydrite nanoparticles that did not contact plasma proteins. In vivo testing of ferrihydrite nanoparticles was shown that the water sol has chronic toxicity since it leads to morphological changes in the organs, mainly the spleen, which is characterized by the accumulation of iron nanoparticles in the form of hemosiderin, which gives a positive Perls reaction .The positive effect of nanoparticles of ferrihydrite is reflected in the activation of phagocytosis in the liver. According to our data, iron nanoparticles have another important property, directly or indirectly, to stimulate the proliferation and intracellular regeneration of hepatocytes. The partial detection of Perls-positive cells in the liver and kidneys can be explained by the rapid excretion from organs and the high dispersion of the nanomaterial.Thus, the introduction of nanoparticles into the body is characterized by adaptive-proliferative processes, accompanied by the development of cell dystrophy and tension of the phagocytic system. The biological effects we observed may be associated with the formation of a protein corona on the surface of nanoparticles; however, further studies are required for a more complete and deeper understanding.Nanoparticles can accumulate and remain in the body for a fairly long time, and their interaction with biological objects is largely determined by the properties of nanoparticles. Therefore, it is necessary to investigate these processes at the systemic level and involve methods for predicting the properties of nanoparticles and modeling the mechanisms of interaction of nanoparticles with biological molecules and systems.


The aims of this study were to compare the initial implant stability obtained using four different osteotomy techniques in low-density synthetic bone, to evaluate the instrument design in comparison to the implant design, and to determinate a possible correlation between the insertion torque and initial stability quotient (ISQ).Four groups were identified in accordance with the osteotomy technique used (n = 10 implants per group): group G1, osteotomy using the recommended drilling sequence; group G2, osteotomy using an undersized compactor drill; group G3, osteotomy using an undersized drill; and group G4, osteotomy using universal osseodensification drills. Two polyurethane blocks were used: block 1, with a medullary portion of 10 pounds per cubic foot (PCF 10) and with a 1 mm cortical portion of PCF 40, and block 2, with a medullary of PCF 15 and with a 2 mm cortical portion of PCF 40. Tapered implants of 4 mm in diameter and 11 mm in length were used. The insertion torque (IT) and ISQ were measured. The dimensions of the final instrument used in each group and the dimensions of the implant were used to calculate the total area of each part, and these data were compared.Differences between the four groups were found for IT and ISQ values depending on the technique used for the osteotomy in the two synthetic bone models (p < 0.0001). All groups showed lower values of initial stability in block 1 than in block 2.Undersized osteotomies with instruments designed according to the implant body significantly increased the initial stability values compared to beds prepared with universal drills and using the drilling sequence standardized by the manufacturer. Referred to as one of the greatest advances in dentistry, dental implants have revolutionized oral rehabilitation since their inception. However, the installation of implants in areas of low bone density has been a major challenge for predictability in treatments. Thus, the search for new alternatives for these situations has been a hot topic in implant dentistry, with new micro- and macrogeometric designs of implants being presented –5. In adInitially reported by Huwais and Meyer , osseodeThe main objective of this study was to compare the level of initial stability, measured by the insertion torque and frequency analysis by resonance (RFA), established by different instruments and/or techniques proposed to increase the initial stability for osteotomy. Implants were inserted in low-density polyurethane synthetic blocks, simulating bone with two different densities. In addition, the area of the implant body, with and without threads, in relation to the body of the last instrument used for the conformation of the osteotomy in each group, was measured and analyzed. A possible correlation between insertion torque and ISQ was analyzed.In the present study, four different groups were identified based on the received osteotomy procedures:Group G1: the standard osteotomy sequence recommended by the implant manufacturer for the 4.0 mm conical implant—a pilot drill, followed by a 2.0 mm drill and a 3.5 mm conical drill, and ending with a 4.0 mm conical drill ;Group G2: an osteotomy sequence using a compactor instrument—a pilot drill, then a 2.0 mm drill, and then a compactor drill with counterclockwise rotation ;Group G3: an undersized osteotomy sequence—a pilot drill, then a 2.0 mm drill, and then a 3.0 mm conical drill ;Group G4: an osteotomy sequence with burs for the osseodensification of the Densah Burs system : a pilot drill, followed by tapered universal drills with incremental diameters of 2.3 mm (ref. VT1828) and 3.3 mm (ref. VT2838) with counterclockwise rotation.Fig 1 shows a representative image of the last instrument used in the osteotomy for each group.All the osteotomies were performed using an implant surgical motor  with a 20:1 contra-angle at a speed of 1100 rpm.Synthetic foam blocks of two different densities made of polyurethane foam, which is approved and recognized as a standard material for testing instruments and bone implants by the American Society for Testing and Materials , were usFig 2.After the osteotomies, 80 implants were inserted into the 2 blocks, with 20 samples per group, for a total of 10 samples from each group per block. All the implants used presented the same macrogeometric characteristics: Maestro implants  with a Morse taper connection and dimensions of 4 mm in diameter and 11 mm in length. These implants have a conical shape with trapezoidal threads and healing chambers, as shown in The following measurements were performed: 1) the measurement of insertion torque (IT), using a digital torquemeter model TQ-680 , with the maximum torque measured during the insertion of the implants in the synthetic blocks until the moment when the implant platform was at the bone level; 2) measurement of the initial stability by RFA using the Osstell Mentor Device , wherein immediately after the insertion of each implant, a Smart-pegs device number 16 was manually screwed to the implant. Two measurements were taken in different directions for each sample.A of a cylinder of diameter d and height h, the following formula was used:The total area of the implant body without the threads and the size of the total external area of the implant including the threads were calculated and compared with the size of the total area calculated for the bodies of the instruments used for the osteotomies in each group. To calculate the total area of each part, two mathematical formulas were used, with the cylindrical and conical parts of each design being considered separately. To calculate the total surface area A of a conical form with diameters  and height h, the following formula was used:For the calculation of the total surface area Fig 3 shows the values considered for the calculation according to the geometry of each part.Both formulas were used according to Spivak . Fig 3 sThe D’Agostino and Pearson omnibus normality test was applied to verify the normality of the data. One-way ANOVA was applied to detect statistical differences in the data for different groups in the same bone block. Then, Bonferroni’s multiple comparison test was used to statistically compare the data between the groups in the same bone block model. Pearson’s correlation test was used to evaluate the correlation between insertion torque and initial stability quotient in all proposed groups. The GraphPad Prism program version 5.01 for Windows  was used to perform all statistical analyses. Results were considered statistically significant when the p-value <0.05.In both blocks, normality was detected in the distribution of data measured for the insertion torque and initial stability quotient (ISQ).Fig 4 shows the data values (mean and standard deviation) for each group in the two blocks.For all four groups within the same synthetic bone model, block 2 presented a 134.3% higher average insertion torque and a 39.2% higher average ISQ compared with block 1. Furthermore, in both blocks, the four groups presented statistically significant (p < 0.0001) differences in insertion torque. The bar graph in Table 1 shows a comparative statistical analysis of the insertion torque between the four groups in both block models tested.Fig 5 shows the data values (mean and standard deviation) for each group in the two blocks.The ISQ values measured of the implants presented different values for the proposed groups in both blocks, with statistically significant differences (p < 0.0001). The bar graph in Table 2 shows a comparative statistical analysis of the ISQ values between the four groups in both block models tested.Table 3 shows the analysis results for each group in both synthetic bone blocks.No correlation was detected between the insertion torque and ISQ values in the proposed groups. 2, and the total area calculated with the threads was 175 mm2. The calculations of the areas of the osteotomy instruments corresponding to each group and the difference between the two area values calculated for the implant are presented in Table 4.The area of the implant body (without the threads) was calculated as 159.9 mmIn this pilot in vitro study, we compared four osteotomy techniques (one using the recommended drill sequence for the implant design and three undersized sequences) used for implant bed preparation in low-density synthetic polyurethane bone blocks. Moreover, the areas of the implant body, the implant body plus the external threads, and the relevant instruments were calculated to evaluate the relation of the area to the initial implant stability . The results showed that in block 1 , which simulated type 4 bone, even when using undersized osteotomy, the initial implant stability  was quite low for all groups in comparison with that in block 2 , which simulated type 3 bone. Additionally, by analyzing the calculated areas of each part used (implant and instruments) in relation to the initial stability data obtained, we verified that the design relationship between the parts had a significant influence on the results.The installation of implants in low-bone-density areas can cause problems for good initial stability, which is considered an important condition to obtain adequate osseointegration –29. InitThe insertion torque is the first clinical information obtained during implant installation in relation to initial stability. In bone types 1 and 2, which present high density, an adequate initial implant stability with a high insertion torque is easily obtained by using the drilling sequence recommended for osteotomy for the implant design used . HoweverComparing the results obtained in each block used, block 2 showed greater values of initial stability compared to those found for block 1. The insertion torque was 134.3% greater, and ISQ was 39.2% greater. These results are in agreement with other studies that showed that the bone density , 45, andIn terms of the initial stability measured using the RFA method , the results showed different values depending on the density of the blocks, which corroborated the results of other similar studies –51. In bLages and collaborators reported that IT and RFA were independent and incomparable methods for measuring primary stability and alerted clinicians to the importance of defining only one method for assessing implant stability . As repoOur results showed that the implant design compared to the instrument design used for the osteotomy is an important factor to consider. In both synthetic bone densities tested, the best results for initial stability were obtained in groups G2 and G3, in which the instrument design considered the design of the implant body. Although the relation of the calculated area of the instrument within the bone bed and the implant body with and without the threads presented similar values for groups G3 and G4, the IT and RFA results were much higher for group G3, which led us to conclude that the difference lay in the design of the dimensions of each part used.As a limitation of the present study, we can cite the homogeneity of the blocks used, which rarely occurs under clinical conditions. The used blocks were selected with two thicknesses of cortical lamina, which is variable in clinical situations. Still, all maneuvers were performed without clinical conditions. The lack of an organic portion, present in bone but not in the synthetic polyurethane blocks used here, is another important factor that must be considered in regard to the obtained results. Future studies with other implant models, especially those with designs similar to the instrument used in the G4 group, would help to corroborate our results.From the results obtained, and within the limitations of the present in vitro study, we observed that to increase the initial stability values of the implants, undersized osteotomy should be performed with an instrument designed according to the dimensions of the implant body. The preparation of the implant bed with universal osseodensification instruments led to a low initial stability of the implants, especially in lower-density bone (PCF 10), in comparison to the stability achieved through preparation with undersized instruments that were designed for the implant model used.


NaBH4 is an efficient reducer; the precipitation yields for Pt, Pd, Ru, Rh are 75, 90, 65 and 85%, respectively. By precipitation with ascorbic acid, it is possible to efficiently separate Pt, Rh, and Ru from Pd from the two-component mixtures. The obtained Pt, Pd, and Rh precipitates have the catalytic ability of the catalytic reaction of p-nitrophenol to p-aminophenol. The morphological characteristic of the PGM precipitates was analyzed by AFM, SEM-EDS, and TEM.The paper presents basic studies on the precipitation of platinum, palladium, rhodium, and ruthenium nanoparticles from model acidic solutions using sodium borohydride, ascorbic acid, and sodium formate as reducing agents and polyvinylpyrrolidone as a stabilizing agent. The size of the obtained PGM particles after precipitation with NaBH The main advantages of PGMs include the ability to catalyze various chemical reactions, chemical and mechanical resistance, and resistance to high temperatures [PGMs  is likely to have an important role in the future for catalytic reactions because nanoparticles are more active than catalysts of a large size , the autDue to the use of significant amounts of PGM in industry and thus the high demand for these metals, new and efficient methods of recovering these metals are investigated. For this purpose, hydrometallurgical methods can be applied to recover PGMs from converters to leach solutions and to recycle PGMs by synthesis of catalytically active nanomaterials. This approach, i.e., metal recovery and reuse, is a key concept in converting waste into resources (WTR) in a circular economy.NPs  are of great interest to scientists because they have unique properties compared to their bulk counterparts. Depending on the synthesis, the materials may differ in morphology, structure and size . NPs canThe scientific goal of the research is to form NPs of PGM  from one- and two-component model solutions as a base for the recycling of spent automotive converters. The influence of the precipitation parameters on the size, structure, morphology and catalytic properties of the obtained particles/nanoparticles is determined. The effects of the type and concentration of a reducer, addition of a stabilizing agent, and pH on the size and morphology of the particles are also investigated. The development of an effective reduction method from leach solutions may have a significant impact on the recycling of precious metals from spent automotive converters and reuse of PGM, leading to limitation of metal mining from natural resources. Thus, the proposed fundamental research from various model solutions is vital to establish conditions that could be applied for the real leach solutions  to produce catalytically active materials that may have a high application potential in the future, e.g., obtaining energy in the form of hydrogen through photoreforming from biomass or wastewater treatment from organic substances.4 (96%), PdCl2 (99.9%), RhCl3 (99.9%) and RuCl3 (99.9%) supplied by Sigma Aldrich . Polyvinylpyrrolidone PVP  was used as the stabilizing agent. Sodium borohydride NaBH4 , ascorbic acid C6H8O6 , sodium formate HCOONa, and formic acid HCOOH  were used as reducing agents in the study.One-component model solutions were prepared by dissolving in 0.1 M HCl the required amounts of PtClTo obtain NPs, scientists proposed the use of PVP as a stabilizing agent. Depending on the synthesis, it can be used as a surface stabilizer, growth modifier, and dispersant for NPs. As a stabilizer, PVP prevents particle aggregation caused by repulsive forces. This is because the polymer contains hydrophobic carbon chains that extend into the solvents and interact with each other as a steric hindrance effect ,41.2CO3. The molar ratio of the metal precursor to the reducing agent and to the stabilizing agent was 1:(1 or 2):(1 or 5) depending on the experiment. The precipitation yield (P) was calculated according to the formula:0 is the initial mass of the metal ions in the solution before precipitation and mp is the mass of the metal ions in the solution after precipitation. The mass change of the metal ions in the solution before and after precipitation was calculated on the basis of the AAS technique (Atomic Absorption Spectrometry) determination of the metal ion concentrations. The samples after precipitation were centrifuged before AAS analysis .The stabilizing agent PVP was added to the appropriate amount of the PGM precursor and mixed for 10 min. After proper mixing, the reducer was added drop by drop, at the mixing speed of 500 rpm. The pH of the solution was then adjusted to neutral/basic (pH 7–8) with 1 M Na4 as a hydrogen ion donor source following the reduction reaction:The prepared precipitates were subjected to the catalytic reaction of p-nitrophenol (NPh) to p-aminophenol (APh) in the presence of NaBH0 for 4-nitrophenol/4-aminophenol −0.76 V) [4− ions) on the surface of PGM-NPs before NPh reduction, followed by the production of hydrogen radicals by electron transfer. Hydrogen species are added to adsorbed NPhs to form APh through the formation of the 4-hydroxylaminophenol intermediate and the removal of two water molecules from the nitro group. Finally, the product–APh–is detached from the surface of PGM-NP to provide a place for another catalytic cycle [The reduction of NPh to APh by sodium borohydride is a thermodynamically favorable reaction (E−0.76 V) . The mecic cycle ,44.NPh) was calculated from Equation (3):0,NPh is the concentration of NPh before the reaction and Cp,NPh is the concentration of NPh after the reaction.NaOH was added to the resulting solution to raise pH to 11.5 and keep NPh in anionic form. The UV-Vis spectrum of the basic form of NPh has a maximum at a wavelength of 400 nm. The spectra were recorded 25 min after the initiation of the reaction to monitor changes in NPh concentration, i.e., the addition of the reducing agent and the appropriate amount of PGM-NP catalyst. The conversion degree  was used for the measurement of metal ion concentrations in aqueous samples at the following wavelengths: 266.0, 244.8, 343.5, 349.9, nm for Pt(IV), Pd(II), Rh(III), Ru(III) respectively. SEM-EDS (SEM FEI Quanta 250 FEG), digital microscope of the VHX-7000 series , Hitachi HT7700 transmission electron microscope  working in high contrast and high-resolution mode, and AFM  were applied to analyze the structure and morphology of nanoparticles obtained of precipitation stages from model solutions. The solutions after reduction were analyzed by UV-Vis  to confirm the presence of nanoparticles.The results of the production of palladium particles without a stabilizing agent from a one-component solution (2 mM Pd(II) in 0.1 M HCl) confirmed a positive impact of formic acid (4 mM HCOOH) as a palladium reducing agent. The volume ratio of the precursor and the precipitant was 1:1. The tests were carried out without the addition of a stabilizing agent at two different temperatures, 23 and 50 °C. The images taken under the optical microscope showed that the precipitated particles are metallic a. AdditiThe effect of solution pH on the precipitation yields of PGM without stabilizing agent is shown in The studies on Pd precipitation with HCOOH show that the metallic particles, larger than the nanosize, are obtained. Therefore, to obtain Pd-NP, the addition of a PVP stabilizing agent was proposed, as also suggested by other researchers ,47,48. TRegardless of the reducer used, in all cases the efficiency of Pd precipitationndecreases with the increasing concentration of PVP. In the case of Pt and Ru, the type of the reducer and the PVP concentration do not significantly affect the precipitation efficiency.Pt > 80%), on the other hand, AA is an inefficient reducer for palladium (PPd < 10%) (4 and the precipitation efficiency of Rh is greater than 80%. The most pronounced change in the precipitation efficiency can be seen for Pd reduced with HCOONa. The reduction efficiency decreases as the molar ratio of PVP increases from 100 (for molar ratio of PGM:PVP:reducer was 1:1:2) to 20% (PGM:PVP:reducer was 1:5:2).On the one hand, AA is an efficient reducer for platinum (Pd < 10%) a. This pThe influence of the type and concentration of a reducer on the formation of PGM-NP was investigated and the results for the precipitation of PGM from acidic solutions are presented in 4 followed by HCOONa. However, due to the fact that AA shows low efficiency in the precipitation of Pd and Rh and has the potential to separate PGM by precipitation from their mixtures, it was chosen as a weak reducing agent for further research. For two selected reducers (AA and NaBH4) AFM analysis was used to determine the size of the obtained PGM particles. The results are presented in The concentration of the reducer has no significant influence on the precipitation yield for all PGMs. The most effective reducing agent for all metals is NaBH4 are smaller than Pt-NPs after precipitation with AA. Of all samples, the smallest particles of 3 nm are obtained for Pd-NPs using AA or NaBH4 as reducing agent (molar ratio PGM:PVP:reducer 1:1:2). The largest particles for Ru are obtained after reduction with AA and are around 90 nm (molar ratio of PGM:PVP:reducer 1:1:2). Thus, the type of the reducer used affects in a significant way the size of the particles obtained. The reduction with NaBH4 and the PGM:PVP:reducer 1:1:2 molar ratio, 7–8 pH, ambient temperature are the best conditions for the formation of Pt, Pd, and Rh-NPs up to 5 nm. The change in the molar ratio of PVP to PGM from 2 to 5 does not result in a significant difference in the size of Rh NPs, while an increase in the NP size of Pt and Pd is observed. On the other hand, the conditions for the effective formation of the smallest Ru-NPs with a size of up to 4 nm cover the reduction with NaBH4 and the molar ratio of PGM:PVP:reducer 1:1:1, 7–8 pH, ambient temperature. Moreover, in this case, no significant influence of PVP ratio on the size of the obtained particles is observed. AFM images, confirming the particle size, are presented in the All obtained PGM-particles are nanoparticles; their size is below 90 nm. Pt-NPs after precipitation with NaBHTEM images are taken for some selected samples to check the structure and compare the particle size estimated with AFM technique .4 , due to the high thermodynamic instability and excess surface energy, the synthesized particles can undergo nucleation and Ostwald ripening [4 than with AA. The trend of PGM particles to agglomerate has been observed by various researchers under various conditions [TEM images of Pt or Pd-NP are used to determine the structure and size of the obtained particles. Particles precipitated with AA a,c are s4 b,d have 4 , the TEM4 . It can ripening . These pnditions ,51,52,53Values of the particle size estimated from TEM images indicate that the NPs are much smaller than these estimated on the basis of AFM images. It is possible that the size obtained by AFM corresponded to aggregates in which single nanoparticles could not be observed. Due to a higher resolution of the TEM images than of the AFM ones, it is possible to distinguish between much smaller particles .SEM-EDS analysis was used to confirm the presence of Pt in the metallic form of nanoparticles .When the SEM-EDS images are compared with each other, it can be seen that oxygen and Pt do not overlap in the images. This indicates that the particles obtained do not form oxides but only metallic forms. In addition, the images show brighter points that can be attributed to the clusters of metals. Both TEM and SEM confirmed that the metal agglomerates formed during precipitation. A similar situation can be seen for Pd, Rh, and Ru-NPs, the presented images confirm that the obtained NPs are not metal oxides .The influence of the presence of two different PGMs in the stock solutions was investigated, and the results of the precipitation of both PGMs from acidic solutions are presented in 4 is high for both PGMs in two-component mixture, therefore their separation is impossible. TEM images were taken for selected two-component samples  which shifted to 313 nm during the first minutes of reaction corresponding to an acidic form of NPh ,44,55. AA hypsochromic shift of the NPh maximum to lower wavelengths during the reaction was observed. The maximum at 260 nm corresponds to the basic (ionized) form of APh at 11.5 pH; it is clearly visible that, at the beginning of the reduction  proves that Pd-NPs provide the highest conversion degree of NPh conversion (about 90% after 5 min of reduction) compared to the NPs of other PGMs . The lowResearch related to the separation of PGM nanoparticles from aqueous solutions by precipitation of PGM precipitation may be used in the future to develop a method to obtain PGM from solutions after leaching spent automotive catalysts. The perspective of recovering metals  from secondary resources is beneficial not only for the environment (less waste), but also for the economy (PGM recycling). It should be emphasized that the content of these valuable metals in waste (spent automotive converters) is several times higher than the content of PGM content in the richest available natural ores available in the world.4 is an efficient reducer for all PGMs; the precipitation yields of Pt, Pd, Ru, Rh are 75, 90, 65, and 85%, respectively. The size of the PGM particles after precipitation with NaBH4 solution did not exceed 55 nm and the sizes of the PGM particles of PGM after precipitation with AA were below 90 nm. Precipitation of PGM with AA can be used for the separation of platinum from palladium from aqueous acidic solutions.NaBHThe development of the PGM nanoparticle precipitation method is very important for the development of knowledge in the field of separation processes, as it makes it possible to use aqueous solutions containing PGM  to produce catalytically active materials. The obtained Pt-NP, Pd-NP, and Rh-NP have the catalytic ability to catalyze the reaction of NPh to APh.


The damage process and failure mechanisms were analyzed by a series of quasi-static compressive experiments of seven materials including pure epoxy (EP), three different PPI (pores per linear inch) foam nickel-iron, and three different PPI foam nickel/iron-epoxy interpenetrating phase composites (IPC). Plotting the stress–strain curves of different materials, their change rules are discussed, then the effective elastic modulus and yield limit of the materials are provided, and the energy absorption properties of different materials are analyzed by the stress–strain curves. It was found that the effective elastic modulus and specific stiffness of the three IPC materials were higher than pure foam nickel-iron. The brittleness of epoxy can be obviously changed by selecting a suitable PPI foam nickel-iron composited with it. The unit volume energy absorption rate of foam nickel/iron-epoxy was significantly higher than pure epoxy and pure foam nickel-iron. It was also found that the energy absorption rate decreased with the increase in PPI. The stress relaxation rate decreased first and then increased with the increase in PPI. The creep behavior of the three composites was obvious in the creep elastic stage, and the creep rate increased with the increase in PPI. The creep rate decreased with the increase in PPI in the creep transition stage. The porous metal foam material has the advantages of sound absorption, shock absorption, light weight, heat resistance, and high strength, etc., and has been widely used in machinery, chemistry, construction, aerospace, biomedicine, and other fields . This miA composite foam material filled with epoxy resin in the foam nickel-iron is a new type of IPC material. It has been found that IPC obtained by interpenetrating foam metal and epoxy resin can effectively improve the mechanical properties of the material. Yu Wei et al.  studied 3, 0.21 g/cm3, and 0.26 g/cm3, respectively. SEM  images and the figures of the pore diameter distribution for PPI30 and PPI40 are shown in The foam nickel-iron used in the experiment was an open-cell foam nickel-iron. The pore sizes of the three foam nickel-iron were PPI20, PPI30, and PPI40 , and their apparent densities are 0.18 g/cmFirst, the foam nickel-iron was processed into a rectangular specimen of 20 mm × 20 mm × 30 mm, and the processed foam nickel-iron specimen was cleaned with industrial alcohol and dried to remove all impurities in the holes of the foam nickel-iron specimen during the preparation process. Then, two plastic beakers were respectively used to fill a certain amount of epoxy resin and curing agent with a 1:1 volume ratio, and put into a constant temperature water bath to heat for a period of time to increase their fluidity. In order to enhance the wetting property of the epoxy resin, a 2% volume defoamer was added to the epoxy resin. The defoaming agent was poured into the epoxy resin and stirred for about 15 min to ensure that the bubbles in the epoxy resin were fully discharged. Then, the heated curing agent was poured into the epoxy resin and stirred quickly. The mixed liquid was put into the vacuum pump to remove bubbles, again to ensure that the bubbles in the mixed liquid were completely discharged. Then, the mixture was poured into the mold to be fully soaked with the foam nickel-iron, while a single piece of pure epoxy resin of the same size was poured. After curing at 25 °C for a week, the mold was removed, the specimen was taken out, the excess epoxy resin on the surface of the specimen was removed, and the two ends of the specimen were polished and leveled with sandpaper to meet the experimental requirements. In addition, for stress relaxation and creep specimens, plasticizer with a volume ratio of 2% was added in the preparation process of epoxy resin. The PPI used in the experiment in this paper were 20/30/40, respectively. According to the purpose of the experiment, six composite material specimens under each PPI were made, three pure foam nickel-iron specimens under each PPI were made, and three pure epoxy resin specimens were made. The specimens were grouped and numbered for reserve. The prepared specimens were subjected to compression experiments at 25 °C with the experimental instrument of an INSTRON testing machine , and the loading rate was 1 mm/min. All experimental data were automatically collected by computer. The calculation of mechanical properties followed these standards. For the compressive test of pure epoxy (EP) and foam nickel/iron-epoxy interpenetrating phase composites (IPC), we referred to the GB/T 2569 (China). For the compressive test of foam nickel-iron, we referred to ISO 13314. For the compressive test of pure Ni/Fe alloy, we referred to ASTM E9-09. For the creep test, we referred to ISO 7850. The experimental equipment and a close-up of the specimen are shown in As can be seen from s and ρs represent the elastic modulus and density of the matrix material, respectively; E* and ρ* represent the elastic modulus and density of the foam material, respectively; and C1 is the proportionality constant. According to the calculation of the experimental results, C1 of the foam nickel-iron material in the formula can be 0.14, as shown in * of the foam material also increased.In Equation (1), EThe force–displacement curve was obtained by the experimental equipment, and the displacement was divided by the initial specimen height to obtain the strain, as shown in Equation (2). The stress was obtained by dividing the force by the initial specimen section area, as shown in Equation (3).ε is strain and ∆l and l0 represent the compressive displacement of the specimen and the initial height of the specimen, respectively. In Equation (3), σ is stress, and F and A0 represent force and initial section area of specimen, respectively.In Equation (2), As shown in C can be obtained from the following formula:The energy absorption of the material under compression can be calculated from the experimental stress–strain curve. The calculation formula of the energy absorption capacity εm is the maximum strain at the stage of compression to compaction; σ and ε represent compressive stress and strain, respectively; C is equivalent to the area enclosed by the compressive stress–strain curve when the strain is mε. The energy absorption of seven materials can be analyzed by using this formula. Among them, the end point of the platform was used as the calculation node of the energy absorption for three kinds of pure foam Ni-Fe with different PPI and IPC with PPI30 and 40, while the maximum stress point before failure was used as the calculation node for the other two materials without the platform stage. As shown in In Equation (4), It can be seen from the experiment that the stress relaxation phenomenon appeared in the specimen of foam Ni-Fe/EP IPC material with different PPI. This experiment gives a test force within 530 s after the displacement is kept constant when the amount of compression is 2.5 mm, and the stress relaxation is obtained as shown in It can be seen from The creep curves of deformation and time of IPC specimens with different PPI were measured by creep experiments, as shown in (1)The three-stage deformation characteristics of typical foam materials appeared in the compression process of pure foam Ni-Fe. Foam Ni-Fe/EP interpenetrating phase composites (IPC) have four stages of deformation. The plastic platform stage was very short when PPI was 20, similar to that of pure epoxy resin.(2)The effective elastic modulus of the three kinds of foam Ni-Fe/EP interpenetrating phase composites (IPC) was smaller than that of the pure epoxy resin, but all were greatly improved than that of the pure foam Ni-Fe. Compared with the pure epoxy resin, the foam Ni-Fe/EP composites with PPI30 and 40 had a plastic platform in the compression process, which was higher than that of the pure foam Ni-Fe. The mechanical properties of the three IPC materials first increased and then decreased with the increase in PPI.(3)Through the comparison and analysis of the mechanical properties of the three materials such as strength, stiffness, specific strength, and specific stiffness, the foam Ni-Fe/EP interpenetrating phase composites with PPI30 and 40 were better than those of pure foam Ni-Fe and pure epoxy and the energy absorption performance was higher than that of pure epoxy resin and pure foam Ni-Fe. As the PPI increased, the energy absorption rate per unit volume of IPC materials decreased.(4)The three kinds of foam Ni-Fe/EP IPC materials had obvious stress relaxation phenomenon, and the stress relaxation rate decreased first and then increased with the increase in PPI, indicating that the material had obvious viscoelastic and plastic unloading capacity, which is similar to epoxy resin.(5)The creep behavior of the three kinds of foam Ni-Fe/EP IPC materials was obvious, and the creep rate increased with the increase in PPI in the creep elastic stage. The creep rate decreased with the increase in PPI in the creep transition stage.


The mechanical properties and strength formation mechanism of cement–fly-ash-stabilized slag–coal gangue mixture were examined using an unconfined compressive strength test, splitting strength test, triaxial test, and scanning electron microscopy to solve the limitations of land occupation and environmental pollution that is caused by fly ash from the Xixia District thermal power plant in Yinchuan, slag from the Ningdong slag yard, and washed coal gangue. Its performance as a pavement base mixture on the road was investigated. The results demonstrated that as the slag replacement rate increased, the maximum water content increased while the maximum dry density decreased. The addition of slag reduced the unconfined compressive strength and splitting strength of the specimens; furthermore, the higher the slag substitution rate, the lower the unconfined compressive strength and splitting strength of the specimens. As the cement content increased, the specimen’s unconfined compressive strength increased. Based on the principle of considering the mechanical properties and economic concerns, the slag replacement rate in the actual construction should be ~50% and should not exceed 75%. Based on the relationship between the compressive strength and splitting strength of ordinary concrete, the relationship model between the unconfined compressive strength and splitting strength of cement–fly-ash-stabilized slag–coal gangue was established. The failure mode, stress–strain curve, peak stress, and failure criterion of these specimens were analyzed based on the triaxial test results, and the relationship formulas between the slag substitution rate, cement content, peak stress, and confining pressure were fitted. As per the SEM results, the mixture’s hydration products primarily included amorphous colloidal C-S-H, needle rod ettringite AFt, unhydrated cement clinker particles, and fly ash particles. The analysis of the mixture’s strength formation mechanism showed that the mixture’s strength was the comprehensive embodiment of all factors, such as the microaggregate effect, secondary hydration reaction, and material characteristics. Consequently, using coal gangue as a road base filling material can not only prevent pollution but also reduce natural resource exploitation, thus paving the approach for high-value and large-scale resource utilization [Coal gangue is a rock type with lower carbon content and higher hardness compared with coal. Coal gangue comprises multiple rocks and forms one of the primary wastes in coal production. Although >300 million tons of coal gangue are discarded each year, China’s utilization rate of coal gangue has reduced ,2,3,4. Alization ,6,7,8.The preparation of a coal-gangue-reinforced base mixture has been extensively investigated. Zhu et al.  examinedBased on the abovementioned problems, this study used cement, fly ash, slag, and coal gangue to prepare a road base mixture; performed unconfined compressive strength tests, splitting strength tests, triaxial tests, and scanning electron microscopy tests of eight types of mixtures with different proportions; and examined the variation law of mechanical properties and the strength formation mechanism of mixtures with different admixtures. Note that five types of mixtures with different slag substitution rates were tested to obtain the optimal slag substitution rate. The mechanical properties of the cement–fly-ash-stabilized slag–coal gangue mixture were comprehensively evaluated, which provided a theoretical basis for practical engineering.Fly ash and furnace slag were obtained from the Xixia Thermal Power Plant in Yinchuan, Ningxia. The cement was Jockey Grade 42.5 ordinary Portland cement. Coal gangue was obtained from the local Helan Mountain in Yinchuan.XRD and XRF were used to examine the mineralogical and chemical compositions of the slag, fly ash, and coal gangue. 2. Mullite, also known as monalite, is a series of minerals that are composed of aluminosilicate, and its primary component is 3Al2O3·2SiO2. Gypsum primarily comprises sulfate minerals and its main component is CaSO4·nH2O. The primary components of the fly ash and furnace slag, as shown in 2, Al2O3, Fe2O3, and trace amounts of CaO and K2O. The SiO2 and Al2O3 mass fractions in the fly ash were large, accounting for ~78% of the total mass, and the burning loss was <10%, thus meeting the performance control standard of a highway coalgangue-filled sub-grade [2 and Al2O3 in the furnace slag accounted for ~70% of the total mass; however, the proportion of basic oxides accounted for ~14% of the total mass. Consequently, the furnace slag was highly active and weakly alkaline. The phase composition of furnace slag is primarily a glass matrix that is made of nCaO·SiO2 in which basic oxides react with SiO2, Al2O3, and Fe2O3 after the hydration reaction, thus showing the hard cementing property of the effluent [As per ub-grade . The maseffluent ,20,21,22The natural particle size distribution of the slag was uneven and very different, which needed to be broken and screened. This study followed the following three principles when determining the range of the slag content. The first aim was to ensure that the gradation of the mixture after adding the slag met the requirements of cement–fly-ash-stabilized materials in the specification such that the gradation of the mixture was relatively excellent. The second aim was to keep the unconfined compressive strength of the mixture from being affected by too much fine material after adding slag. The third aim was to maximize the utilization rate of slag solid waste. Based on the foregoing considerations and the characteristics of slag and coal gangue, the 0–4.75 mm content in the slag was higher; however, the 0–4.75 mm content in the coal gangue was lower. The crushing treatment of the slag and coal gangue was minimized to the greatest extent possible. Finally, it was decided that the 0–4.75 mm coal gangue should be replaced with 0–4.75 mm slag.2 holes and replaced with 0–4.75 mm coal gangue. As shown in The compaction test is a method of overcoming the friction resistance between particles, reducing the gap between particles, and improving the compactness of the mixture. To some extent, the compaction test can show the actual construction’s compaction process, and the maximum dry density and best water content of the mixture can be obtained via the compaction test, laying the groundwork for the specimen formed using the static pressure method.The unconfined compressive strength tests and splitting tests were performed following JTGE51-2009 . The teTo show the failure mechanism of the cement–fly-ash-stabilized furnace slag and coal gangue mixtures under triaxial compression, triaxial shear strength tests were performed. A YY-RBSZ-1000 rock triaxial (creep) tester developed by Rugao Yuanye Survey Machinery Factory was adopted .The unit features a triaxial pressure unit, two hydraulic pumps, displacement sensors, and pressure sensors, with one hydraulic pump to provide vertical load and one hydraulic pump to provide a stable confining pressure. The maximum axial pressure is 1000 kN, the maximum confining pressure is 30 MPa, the static accuracy of axial and confining pressure loading is 0.5%, and the temperature stability of the axial and confining pressure loading is 0.5%/°C.Scanning electron microscopy was undertaken using an EVO 18 tungsten filament scanning electron microscope produced by ZEISS  which has a resolution of 3 nm and acceleration voltage of 0.2–30 kV. Regarding the working principle, when the sample surface is bombarded by the high energy electrons, >99% of the interaction between the incident electron energy will be converted into thermal energy, while the remaining 1% of the incoming electron energy will stimulate a secondary electron, the backscattering electron, and a characteristic X-ray.As per the test procedures, 5-LZ-0 to 5-LZ-100 in Rc is the unconfined compressive strength (MPa) of the specimen, P is the maximum pressure of the specimen under failure (N), A is the cross-sectional area (mm2) of the specimen, and D is the diameter of the specimen (mm).The unconfined compressive strength was calculated using Equation (1):The unconfined compressive strengths of mixtures listed in 2 and Al2O3, in the fly ash and furnace slag gradually underwent a secondary hydration reaction under the excitation of the cement hydration product, namely, Ca(OH)2, generating a large number of crystal substances, such as C-S-H and C-A-H. The chemical reaction formula is shown in Equation (2):As can be seen from 2 and other active substances involved in the reaction gradually decreased as the degree of the number of secondary hydration reactions increased, the rate of the secondary hydration reaction decreased. Furthermore, the specimen’s water glue was relatively low, and the water required for the late hydration reaction was insufficient, resulting in the specimen’s strength growing slowly in the later stages. Because of the high concentrations of SiO2, Al2O3, and basic oxides in the furnace slag, the chemical activity of the furnace slag was higher than that of the coal gangue, and the slow secondary hydration reaction continued, even after an extended curing period [The formation of these crystals made the interface between the furnace slag, coal gangue, and cement mortar closer and considerably improved the internal compactness and bonding strength, and, in turn, the overall strength of the specimen. At 56 and 90 days, the strength growth rate of the specimen significantly decreased, and its average value was 10.5. Moreover, with the increase in the furnace slag substitution rate, the strength growth of the specimen became more obvious. Because the amount of Ca(OH)g period ,32. WithMATLAB was used to fit the unconfined compressive strengths of the specimens with different furnace slag substitution rates at curing periods of 7, 28, 56, and 90 days, as shown in As can be seen from 2 increased, which accelerated the hydration rate of the specimen in the early stage. When the cement ratio increased to 6%, the 7-day unconfined compressive strength growth of the specimen decreased to 0.4 MPa. This was because, as the cement ratio increased, the content of Ca(OH)2 in the specimen increased; however, the content of active substances such as SiO2 and Al2O3, which can participate in the secondary hydration reaction early in curing, decreased, and the secondary hydration reaction rate did not significantly increase, indicating that the specimen’s strength growth range slowed down. The specimen’s unconfined compressive strength significantly improved after 28 days compared to the age of 7 days. The average growth rate of the specimen’s compressive strengths at various cement ratios was 68.7%, which was primarily determined by the secondary hydration reaction and the microaggregate effect. The specimen’s strength growth rate noticeably decreased between 56 and 90 days, with an average value of 10.8%. The strength growth of the specimen became more visible as the cement ratio increased. This was because as the degree of secondary hydration reaction increased, the amount of Ca(OH)2 and other active substances that were involved in the reaction gradually decreased, lowering the rate of the reaction. However, with the increase in the cement ratio, the Ca(OH)2 content in specimens increased, and a relatively large amount of Ca(OH)2 in the specimens still had secondary hydration reactions with the fly ash, furnace slag, and coal gangue at a later curing period. Consequently, even after increasing the cement ratio, the specimens maintained a relatively high strength growth rate in the later stages of curing. The results of the tests demonstrated that the appropriate dosage of cement had a clear effect on the specimen’s early strength. When the cement dosage was >5%, the effect of increasing the cement dosage on the early strength improvement of the specimen was not obvious; however, it showed a relatively obvious strength growth at the later stage of curing. Consequently, when the early strength requirements of the cement and fly ash materials are high, measures such as improving raw material technical indexes and optimizing grading design should be implemented. Only increasing the cement ratio could improve the early unconfined compressive strength of the specimens. MATLAB was used to fit the unconfined compressive strength of the specimens with different cement ratios at 7, 28, 56, and 90 days, as shown in As can be seen from Ri is the splitting strength (MPa) of the specimen, p is the maximum pressure of specimen failure (N), and h is the height (mm) of the specimen after immersion.Equation (3) shows the calculation method for the splitting strength of the specimen with a diameter of 150 mm:The splitting test was performed for the eight mixing ratios listed in As can be seen from 2 in the specimen, restrained the growth of Ca(OH)2 grains, and reduced the thickness of the interface transition zone. With the continuous consumption of Ca(OH)2, the amount of gel material generated increases, further improving the splitting strength of the specimen. At 56 and 90 days, the splitting strengths of the specimen with a furnace slag replacement rate of 50% were slightly better than those of the specimens with furnace slag replacement rates of 25, 75, and 100%. The strength growth law from 5-LZ-25 to 5-LZ-100 showed that, with the increase in furnace slag substitution rate, the splitting strength of the specimen first increased and then decreased, and the change in this trend was determined by the failure mode of the splitting test specimen. The fracture and compressive strength variations and the strength formation mechanism of the specimens were similar; however, their failure modes were different. When the furnace slag substitution rate increased from 25 to 50%, the interface transition zone of the microscopic pore structure increased, the continuous deflection of microcracks consumed more fracture energy, and the splitting tensile strength improved. However, as the substitution rate of the furnace slag increased, the amount of 0–4.75 mm coal gangue decreased, and the pores of furnace slag could not be filled with cement, fly ash, and coal gangue fine particles, resulting in specimen compaction. Furthermore, as the substitution rate of the furnace slag increased, the density of the specimen decreased and the proportion of cement clinker in the specimen decreased, reducing the number of secondary hydration reactions. Furthermore, the proportion of unreacted furnace slag and fly ash increased, reducing the splitting strength of the specimen.At the age of 7 days, with the increase in the cement ratio and decrease in the furnace slag substitution rate, the splitting strength of the specimen demonstrated an increasing trend. The primary causes were the same as in the unconfined compressive strength test. When compared to 7 days, the splitting strength of the specimen at 28 days had significantly improved, where the average growth rate of the splitting strength of the specimen was 81.0%. On the one hand, the average particle size of the fly ash particles was considerably smaller than that of the coal gangue and furnace slag, allowing for a more evenly filled accumulation system among the aggregates and a more sufficient secondary hydration reaction. On the other hand, with the extension of the curing age, active substances in the fly ash and furnace slag gradually underwent secondary hydration reactions, which consumed Ca(OH)Thus, the splitting strength of coal gangue that was stabilized by cement, fly ash, and furnace slag was a comprehensive reflection of the coal gangue strength, hydration reaction degree of the cementing material, and the internal cohesion of the mixture. Because the strength of the furnace slag aggregate was lower than that of the coal gangue, the splitting strengths of the specimens mixed with furnace slag were generally lower than those of 5-LZ-0. Furthermore, the porosity of furnace slag promoted the infiltration of the cement–fly ash slurry into the aggregate and improved the specimen’s compactness and stability. Moreover, the active substances in the furnace slag and fly ash underwent a secondary hydration reaction in the middle and late stages of curing, thus producing many C-A-H and C-S-H cementing products that improved the internal structure of the interface area of each aggregate and increased the specimen’s strength. When the cement ratio was 4% and the furnace slag replacement rate was 50%, the 90-day splitting strength of the specimen was >0.4 MPa, which met the technical indexes of highway pavement base materials in China.ft is the concrete splitting tensile strength (MPa), fc is the compressive strength of the concrete cylinder (MPa), and the values of k and n were obtained using nonlinear regression analysis.From the abovementioned test results, the unconfined compressive strength of the test specimen was positively correlated with the splitting strength, which is important since the relationship between them is a hot topic for researchers. However, few studies exist on the relationship between the unconfined compressive strength of the pavement base material and its splitting strength. Therefore, using Equation (4), the relationship between the unconfined compressive strength and the splitting strength of the pavement base material was obtained:The regression was analyzed in the form of the power function. The regression equation showing the relationship between the unconfined compressive strength and splitting strength was given byAs can be seen from The following are shown in σ–ε curve was obtained, as shown in σ is the axial stress (MPa), F is the axial load (N), A1 is the effective cross-sectional area of the specimen (mm2), ε is the axial strain, Δl is the axial displacement (mm), h is the initial height of the specimen (mm), and A is the initial cross-sectional area of the specimen (mm2).After the load–displacement curve was collected by the tester and calculated using Equations (4) and (5), it was converted into stress and strain values, and the σ–ε curves of the specimens could be roughly divided into three stages: (1) The elastic stage—At the beginning of loading, with the increase in load, the σ–ε curves of the specimens were almost linear, showing obvious elastomer properties. (2) Elastic–plastic stage—With the increase in load, the strain increase rates of the specimens were significantly higher than that of the elastic stage, and the slopes of the σ–ε curves of the specimens gradually decreased. (3) The stage of destruction—The curves of the specimens began to decrease after reaching the peak stress as the load was increased further; however, there was no obvious peak, demonstrating the ductility of the semi-rigid base failure. The peak stress of the specimens was lower with furnace slag than without, but the corresponding peak strain was higher with furnace slag. The incorporation of furnace slag reduced the strength of the specimens while increasing their ductility to a certain extent. When the confining pressure was 0, the specimens’ peak stress was less than when the confining pressure was present, and the slope of the failure stage curve was steeper. When the confining pressure was 0.5 MPa, both the peak stress and peak strain of the specimens tended to increase; furthermore, the descending slope of the failure stage curve slightly decreased. When the confining pressure was 1 MPa, the peak stress and peak strain of the specimens increased further, and the descending slope of the curve in the failure stage became more gentle. When the confining pressure was 1.5 MPa, the downward trend of the specimens in the failure stage was gentler than that when the confining pressure was 0, showing better ductility.σ–ε curve of the specimens in As per the full σ1 is the peak stress of the specimen under three-direction stress (MPa), σ0 is the peak stress of the specimen under uniaxial stress (MPa), σ2 is the confining pressure (MPa), and A is a coefficient that is related to the furnace slag substitution rate α and cement ratio β.By fitting the relationship between the peak stress and confining pressure of the specimen, the unified strength calculation formula of the specimen was obtained :(7)σ1σ0=β.From Substituting Equation (8) into Equation (7) to obtain the relationship between the peak stress and confining pressure of specimens at different furnace slag substitution rates gaveFrom By substituting Equation (10) into Equation (7), we obtained the relationship between the peak stress and confining pressure of specimens with different cement ratios:The strength formation mechanism of the cement–fly-ash-stabilized furnace slag–coal gangue mixture was similar to that of concrete mixed with fly ash. Under the action of water, complex chemical reactions occur within the mixture to generate various substances, such as C-S-H, C-A-H, and ettringite (AFt), which improves the compactness and strength of the mixture. We selected 5-LZ-50 as a representative sample and dried it. Then, the samples at 7, 28, and 90 days of age were tested using XRD and scanning electron microscopy (SEM), where the changes of hydration products at different ages were analyzed and their micromorphologies were observed, as shown in 2 in the mixture were low, but the contents of C2S and C3S were high. With the increase in age, the amount of Ca(OH)2 in the mixture increased. Due to the secondary hydration of fly ash, the contents of AFt, C-S-H, and Ca(OH)2 in the mixture continued to increase, the strength of the mixture was further increased in the later stage due to the mutual interleaving, and part of C2S and C3S in the mixture was consumed under the secondary hydration in the later stage. Therefore, it can be seen from 2 in the later stages of the mixture were increasing, and the contents of C2S and C3S were decreasing.From From the microscopic point of view, the strength formation mechanism of the coal gangue mixture that was stabilized by cement and fly ash could be explained as the physical filling of each admixture and the development of hydration products from an amorphous gel to highly crystalline material. As shown in 2 generated by cement hydration to generate many C-S-H and C-A-H gels, which gradually grew and developed into the micropore space inside the specimen and gradually increased the specimen’s compactness and internal cohesion [cohesion , indireccohesion . TherefoAccording to the test and microscopic detection results, the strength formation mechanism of the specimen mainly included the following three aspects. The first one was that when the furnace slag, cement, fly ash, and coal gangue were fully mixed, the phase composition in the pore of furnace slag involved the solid phase , liquid phase (water molecules), and the gas phase (the unfilled area in the furnace slag pores). With the increase in the treatment time, cement and fly ash in the furnace slag hole gradually formed the C-S-H gel, which filled the furnace slag pores and improved the bearing capacity of the furnace slag. Second, cement, fly ash, and coal gangue with fine particles could fill in between the furnace slag particles and coal gangue, forming a microfilling effect and improving the compactness and stability of the cement–slurry interface. The third aspect was the low strength of the slag aggregate itself, but under the comprehensive filling effect of cement, fly ash, and coal gangue powder and its own certain activity, the slag substitution rate had a positive impact on the compressive strength of the test part in the later period of the curing.(1)With the increase in the furnace slag substitution rate, the optimal water content of the specimen increased and the maximum dry density decreased. The addition of the furnace slag reduced the unconfined compressive strength of the specimen, where the greater the substitution rate of the furnace slag, the lower the unconfined compressive strength of the specimen. However, with an extended curing period, the effect of the furnace slag on the unconfined compressive strength of the specimen gradually weakened. With the increase in cement ratio, the unconfined compressive strength of the specimen increased. Considering the principle of mechanical properties and economic concerns, it is suggested that the replacement rate of furnace slag in actual construction should be about 50% and should not exceed 75%.(2)The results showed that the power function agreed well with the experimental results and can be used in practical engineering applications.(3)The triaxial test results were analyzed in terms of the failure mode, stress–strain relationship curve, peak stress, and failure criterion of the specimens. The results showed that (i) under the triaxial stress, the failure mode of the specimens was greatly affected by confining pressure and they showed typical shear failure, and (ii) according to the test results, the formulas for the relationship between the furnace slag substitution rate, cement ratio, peak stress, and confining pressure were obtained.(4)The SEM results showed that the hydration products of the mixture included colloidal C-S-H, needle-like ettringite (AFt), unhydrated cement clinker particles, and fly ash particles. The strength of the mixture was a comprehensive embodiment of the microaggregate effect, secondary hydration reaction, and the characteristics of the materials.