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Hydrogels, renowned for their hydrophilic and viscoelastic properties, have emerged as key materials for flexible electronics, including electronic skins, wearable devices, and soft sensors. However, the application of pure double network hydrogel-based composites is limited by their poor chemical stability, low mechanical stretchability, and low sensitivity. Recent research has focused on overcoming these limitations by incorporating conductive fillers, such as liquid metals (LMs), into hydrogel matrices or creating continuous conductive paths through LMs within the polymer matrix. LMs, including eutectic gallium and indium (EGaIn) alloys, offer exceptional electromechanical, electrochemical, thermal conductivity, and self-repairing properties, making them ideal candidates for diverse soft electronic applications. The integration of LMs into hydrogels improves conductivity and mechanical performance while addressing the challenges posed by rigid fillers, such as mismatched compliance with the hydrogel matrix. This review explores the incorporation of LMs into hydrogel composites, the challenges faced in achieving optimal dispersion, and the unique functionalities introduced by these composites. We also discuss recent advances in the use of LM droplets for polymerization processes and their applications in various fields, including tissue engineering, wearable devices, biomedical applications, electromagnetic shielding, energy harvesting, and storage. Additionally, 3D-printable hydrogels are highlighted. Despite the promise of LM-based hydrogels, challenges such as macrophase separation, weak interfacial interactions between LMs and polymer networks, and the difficulty of printing LM inks onto hydrogel substrates limit their broader application. However, this review proposes solutions to these challenges.

Superparamagnetic iron oxide nanoparticles (SPMNPs) continue to emerge as one of the most potential candidates in biomedical applications. Their multiple functionalities arise from several advantages, such as their responsiveness to external magnetic stimuli, availability, biocompatibility, lack of toxicity, and easier to synthesize. Such MNPs can generate heat when they subjected to an alternating magnetic field, which can be used in tumor treatment if the released heat is as enough as to increase the tumor area temperature the tumor area from physiological temperature of 37 °C to 42–45 °C. In this regard, the size, distribution, magnetic properties of the magnetic nanoparticles play an important role. Thus, the Fe 3 O 4 NPs were synthesized via a simple and inexpensive coprecipitation route with the assistance of natural extracts of Peppermint (P) and Dracocephalum (D) as capping agents. The structural, morphological, and magnetic properties were characterized through the XRD, HRTEM, and vibrating sample magnetometer, respectively. Cytotoxic effect and IC50 values of the as-synthesized Fe 3 O 4 NPs on K562 were evaluated using MTT assay, being of 106.3 and 146.0 of the IC50 values for NPs synthesized with P and D-capping agents, respectively. The growth inhibition was dependent on treatment time, dose of NPs, and type of the employed capping agent. Furthermore, the synthesized NPs with dracocephalum had a more inhibitory effect than that of the other sample. The heating efficiency of the Fe 3 O 4  NPs was investigated via an induction heater generating alternating magnetic field at frequency of 92 kHz and amplitude of 10 kA/m. The temperature rise (Δ T ) of the as-prepared ferrofluids in the AC magnetic field was studied on different concentrations of magnetic nanoparticles. The specific absorption rate (SAR), as an indicative of heating efficiency, was obtained from Box-Lucas equation and linear fitting of Δ T -time curve. The results showed that the Δ T sharply increases with increasing the concentration of NPs from 3 to 9 mg/mL, but it was dependent on the size, distribution, and magnetic properties of the samples synthesized with two different capping agents. The SAR values of 33 W/g at 9 mg/mL obtained, for the P SPIONPs, suggests the use of those MNPs as the potential materials in tumor treatment via magnetic fluid hyperthermia.

In this study, Mg–Mn–Al ferrite with a chemical composition of Mg 0.8 Mn 0.2 Al 0.1 Fe 1.9 O 4 was synthesized via the sol–gel auto-combustion method. The effects of the sintering time and temperature on the magnetic properties and transmission behaviors were investigated in detail. X-ray diffraction (XRD) results revealed that the powders in the as auto-combusted state were in an amorphous state. Moreover, based on the differential thermal analysis (DTA) curve, the calcination temperature was calculated to be ~900 °C. According to the Archimedes equation, the highest density was obtained for the specimen sintered at 1250 °C for 5 h (94% of the theoretical density). In addition, permagraph results revealed the average magnetic properties of the mentioned samples are as follows: H c  = 7.0 Oe and M s  = 1400 G. According to vector network analyzer (VNA) results, the samples with qualified transmission behaviors showed low scattering parameters in a wide range of frequencies. Highlights Nanocrystalline Mg 0.8 Mn 0.2 Al 0.1 Fe 1.9 O 4 was formed via a sol–gel auto-combustion method. Microstructural, magnetic, and transmission behaviors (TB) were investigated. The maximum density was obtained for the sample sintered at 1250 °C for 5 h (~4.08 g/cm 3 ). The TB of the samples was improved by increasing Ms. The most favorable TB was obtained for the sample sintered at 1250 °C for 5 h.

Magnetite nanoparticles were synthesized by the co-precipitation method with and without the assistance of an additive, namely, gelatin, agar-agar or pectin, using eco-friendly conditions and materials embodying a green synthesis process. X-ray diffraction and transmission electron microscopy were used to analyze the structure and morphology of the nanoparticles. Magnetic properties were investigated by SQUID magnetometry and 57Fe Mössbauer spectroscopy. The results show that the presence of the additives implies a higher reproducibility of the morphological magnetic nanoparticle characteristics compared with synthesis without any additive, with small differences associated with different additives. To assess their potential for magnetic hyperthermia, water-based suspensions of these nanoparticles were prepared with and without citric acid. The stable solutions obtained were studied for their structural, magnetic and heating efficiency properties. The results indicate that the best additive for the stabilization of a water-based emulsion and better heating efficiency is pectin or a combination of pectin and agar-agar, attaining an intrinsic loss power of 3.6 nWg−1.

The synthesis of silver nanoparticles (Ag-NPs) was achieved by a simple green chemistry procedure using sodium alginate (Na-Alg) under ultrasonic radiation as a stabilizer and physical reducing agent. The effect of radiation time on the synthesis of Ag-NPs was carried out at room temperature until 720 min. The successful formation of Ag-NPs has been confirmed by UV-Vis, XRD, TEM, FESEM-EDX, zeta potential, and FT-IR analyses. The surface plasmon resonance band appeared at the range of 452–465 nm that is an evidence of formation of Ag-NPs. The XRD study showed that the particles are crystalline structure in nature, with a face-centered cubic (fcc) structure. The TEM study showed the Ag-NPs have average diameters of around 20.16–22.38 nm with spherical shape. The FESEM-EDX analysis confirmed the spherical shape of Ag-NPs on the surface of Alg and the element of Ag with the high purity. The zeta potential showed high stability of Alg/Ag-NPs especially after 720 min irradiation with value of −67.56 mV. The FT-IR spectrum confirmed that the Ag-NPs have been capped by the Alg with van der Waals interaction. The Alg/Ag-NPs showed the antibacterial activity against Gram-positive and Gram-negative bacteria. These suggest that Ag-NPs can be employed as an effective bacteria inhibitor and can be applied in medical field.

Soft magnetic materials are widely used in electrical and electronic industries due to their desirable electromagnetic features, i.e. relatively high electrical resistivity and low eddy current loss at high frequencies. From industrial point of view, once the size of grains is reduced to micron scale regimes, their performance is only narrowed to a few megahertz frequencies, due to their higher conductivity and domain wall resonance. Thus, one way to resolve this issue and utilize these materials at high frequency applications, is to reduce the size of grains from micron to sub or nanoscale before they are being compacted for sintering. In this aspect, however, several methods are employed to synthesize these nanoparticles, a mechanical alloying is found to be a proven route to produce a vast variety of materials with both non-equilibrium and equilibrium phases in a controlled size and shape of powder particles at desired tonnages. Mechanical alloying (MA) is a solid-state powder metallurgy route which involves a repeated action of fracturing and re-welding of powder particles in a high-energy ball mill. The final products characteristics are strongly dependent on the variable parameters of the process, i.e. milling time, ball-to-powder weight ratio, rotation speed, grinding media and milling atmosphere. Thus, this work reviews the key role of these parameters on the structure and magnetic behaviors of soft magnetic materials. Eventually, the mechanism of mechanical alloying and effect of diffusivity are also highlighted.

This work aims to investigate the relationship between the microstructure of Ni-Zn ferrite and its electrical and magnetic properties in the presence and absence of as small amounts as 0.12% of 0.4CaO + 0.8SiO2 over different sintering times. The X-ray diffraction pattern showed a single spinel phase formation in all the samples. The results indicate that grain growth occurred by increasing sintering time from 15 to 270 min in the two types of samples prepared in this study although it was greatly impeded by the additive oxides. Moreover, the oxides increase the resistivity of the ferrite and decrease its zinc loss. Magnetic properties such as induction magnetization (BS) and saturation magnetization (MS) decreased in the presence of the additives while its coercivity (HC) increased. Finally, the density of the samples was observed to increase with increasing sintering time in both types of the samples but with a higher value in the samples with no additives.

Sr–Ca hexaferrite nanopowders with a nominal chemical composition of Sr 1−x Ca x Fe 12 O 19 , Sr 1−x Ca x Fe 11.5 Cr 0.5 O 19 and Sr 0.85−x Ca x La 0.15 Fe 11.5 Cr 0.5 O 19, with x = 0, 0.1, 0.3, and 0.5, were synthesized via sol–gel auto combustion method. Structural and phase formation of the samples were evaluated through X-ray diffraction (XRD). The XRD results indicated the Sr–Ca hexaferrites formation with the presence of α-Fe 2 O 3 as second phase, after subsequent heat treatment of the synthesized samples at 1030 °C for 2.5 h. By increasing the amount of Ca from x = 0 to x = 0.5, the intensity of second phase (α-Fe 2 O 3 ) increased. Furthermore, the hexaferrite lattice constant “c” decreased while the “a” remained almost constant. Field emission scanning electron microscopy results indicated that the grains shape becomes more needle and spherical like with increasing the X content. By doping Cr 3+ at x = 0.5, the grains would vary from needle-like shape to platelet hexagonal. The magnetic behavior of the Sr–Ca hexaferrite samples with and without adding La 3+ and Cr 3+ ions were studied. The best result was achieved for the nanopowders with a chemical composition of Sr 0.35 Ca 0.5 La 0.15 Fe 11.5 Cr 0.5 O 19 with coercivity (H cJ ) = 5474.28 Oe, saturation magnetization (M s ) = 61.16 emu/g and remnant magnetization (M r ) = 42.57 emu/g.

A facile and eco-friendly synthetic approach was employed to synthesize superparamagnetic magnetite (Fe 3 O 4 ) nanoparticles with cubic lattice structure. Zucchini and pomegranate peel-extracts were used as natural stabilizer and surfactant. The X-ray diffraction patterns revealed that the green synthetic technique was successful in formation of highly distributed Fe 3 O 4 nanoparticles using both of the above extracts. The infrared (IR) analysis further confirmed the phase formation and the binding of extracts with Fe 3 O 4 nanoparticles. Based on UV–Vis analysis, the samples showed the characteristic of surface plasmon resonance in the presence of Fe 3 O 4 nanoparticles. The as-synthesized samples were heated at 550 °C for 2 h. It was found that the particles however grew, their sizes remained in nanoscale regime, indicating their thermal stability. The VSM analysis indicated that the as-synthesized samples have a saturation magnetization of 21.4 emu/g (using zucchini peel extract) and 13.3 emu/g (using pomegranate peel extract), which increased respectively to 45.8 emu/g and 38.1 emu/g after the heating process. A negligible coercivity in the samples with the particle sizes of less than 10 nm suggests superparamagnetic behavior of the samples.

Fe 3 O 4 and Ni 0.5 Zn 0.5 Fe 2 O 4 nanoparticles were synthesized via precipitation and mechanical alloying, respectively, and assessed as a potential magnetorheogical (MR) additive. X-ray diffraction and transmission electron microscopy were employed to evaluate the phase formation and structural and morphological changes. Vibrating sample magnetometer (VSM) was used to measure magnetic characteristics of the samples. The MR characteristics of carbonyl iron (CI)-based and 1 wt.% (Ni 0.5 Zn 0.5 Fe 2 O 4 + Fe 3 O 4 ) CI-based suspensions were measured from a steady and rotational rheometry by applying magnetic field strengths ranging from 0 to 558.39 kA/m with 79.77-kA/m increments. The results indicated that the MR effect of the micron-sized, CI-based MR fluid significantly improved in the presence of nanoparticle additives, e.g., having higher-yield characteristics. Chain-like structure formed in the presence of nanoscale additives improved the MR performance and sedimentation stability of the CI particles.