Soft Mechanical Properties Research Articles

The Si-doped BCC-based high-entropy alloy to overcome soft magnetic–mechanical properties trade-off via coherent B2 nanoprecipitates

The trade-off between magnetic property and mechanical property usually occurs in traditional soft magnetic materials (SMMs) because the strengthening strategy (e.g. precipitation hardening) can worsen soft magnetic properties through the hindrance of magnetic domain wall motion. This dilemma is overcome in current work by developing the FeCoNiAlSi0.01 (Fe24.94Co24.94Ni24.94Al24.94Si0.24 in at.%) high-entropy alloy (HEA) (termed as Si0.24 HEA) with excellent soft magnetic performance and attractive mechanical property through coherent B2 nanoprecipitates (6 nm) distributed in body-centered-cubic (BCC) matrix. The atom probe tomography (APT) result shows that the B2 nanoprecipitates have similar composition to the BCC matrix. The Si0.24 HEA shows small width of domain branching and low anisotropy constant leading to the optimum alternating current (AC) soft magnetic properties. The respective total loss (AC Ps), the coercivity (AC Hc), and the eddy current loss (Pe) at 950 Hz of the Si0.24 HEA are 21.20 W/kg, 230 A/m, and 16.25 W/kg, which is reduced by 45 %, 44 %, and 48 % compared with the FeCoNiAl (Si-free HEA). The Si0.24 HEA shows good mechanical property with the yield strength of 987 MPa and engineering strain of 30 %, which is 12 % and 1.3 times higher than that of the Si-free HEA. Moreover, the current studied HEAs exhibit high saturation magnetization (Ms = 108–115 Am2/kg) and Curie temperature (TC = 1053–1097 K, larger than TC of Fe (1043 K)), which indicates their perspective high-temperature applications as novel SMMs for the need of modern power electronics and electrical machines.

Additively manufactured FeCoNiSi0.2 alloy with excellent soft magnetic and mechanical properties through texture engineering

High-entropy alloys are widely used as structural materials and hold potential as functional materials. This study aims to develop a soft magnetic medium entropy alloy FeCoNiSi0.2 (Si0.2 MEA) with excellent soft magnetic properties and higher ductility using additive manufacturing technology. The microstructure of Si0.2 MEA is characterized by texture and large grains, with a single FCC phase structure. The texture strength of MEA initially increases and then decreases with the addition of Si, with Si0.1 MEA exhibiting the strongest fiber texture. Among the four FeCoNiSix MEAs, Si0.2 MEA demonstrates the best tensile properties (i.e. δ ∼39 %, σ0.2–287 MPA, σb∼551 MPa). The correlation generalized stacking fault energy calculation model indicates that Si0.2 MEA has the lowest generalized stacking fault energy (∼7 mJ/m2), suggesting superior ductility. The synergistic effect of texture and large grains promotes the formation of a magnetization “easy axis”, which makes Si0.2 MEA exhibit the best soft magnetic properties (Ms:150emu/g, Hc:1.04Oe). These results provide a new paradigm for developing laser additively manufactured soft magnetic medium entropy alloy.

Wireless and Opto-Stimulated Flexible Implants: Artificial Retina Constructed by Ferroelectric BiFeO3-BaTiO3/P(VDF-TrFE) Composites.

The degeneration of retinal photoreceptors is one of the primary causes of blindness, and the implantation of retinal prostheses offers hope for vision restoration in individuals who are completely blind. Flexible bioelectronic devices present a promising avenue for the next generation of retinal prostheses owing to their soft mechanical properties and tissue friendliness. In this study, we developed flexible composite films of ferroelectric BiFeO3-BaTiO3 (BFO-BTO) particles synthesized by the hydrothermal method and ferroelectric poly(vinyldene difluoride-trifluoroethylene) (P(VDF-TrFE)) polymer and investigated their applications in artificial retinas. Owing to the coupling of the photothermal effect of BFO-BTO particles and the pyroelectric effect of the P(VDF-TrFE) polymer, the composite films demonstrate a strong photoelectric response (a maximum peak-to-peak photovoltage > 80 V under blue light of 100 mW/cm2) in a wide wavelength range of light (from visible to infrared) with the inherent flexibility and ease of preparation, making it an attractive candidate for artificial retinal applications. Experimental results showed that blind rats implanted with artificial retinas of the composites display light-responsive behavior, showcasing the effectiveness of vision restoration. This study demonstrates a novel approach for employing ferroelectric materials in vision restoration and offers insights into future artificial retina design.

Needle-Like Multifunctional Biphasic Microfiber for Minimally Invasive Implantable Bioelectronics.

Implantable bioelectronics has attracted significant attention in electroceuticals and clinical medicine for precise diagnosis and efficient treatment of target diseases. However, conventional rigid implantable devices face challenges such as poor tissue-device interface and unavoidable tissue damage during surgical implantation. Despite continuous efforts to utilize various soft materials to address such issues, their practical applications remain limited. Here, a needle-like stretchable microfiber composed of a phase-convertible liquid metal (LM) core and a multifunctional nanocomposite shell for minimally invasive soft bioelectronics is reported. The sharp tapered microfiber can be stiffened by freezing akin to a conventional needle to penetrate soft tissue with minimal incision. Once implanted in vivo where the LM melts, unlike conventional stiff needles, it regains soft mechanical properties, which facilitate a seamless tissue-device interface. The nanocomposite incorporating with functional nanomaterials exhibits both low impedance and the ability to detect physiological pH, providing biosensing and stimulation capabilities. The fluidic LM embedded in the nanocomposite shell enables high stretchability and strain-insensitive electrical properties. This multifunctional biphasic microfiber conforms to the surfaces of the stomach, muscle, and heart, offering a promising approach for electrophysiological recording, pH sensing, electrical stimulation, and radiofrequency ablation in vivo.

Dynamic Transformation of High-Architectural Nanocrystal Superlattices upon Solvent Molecule Exposure.

The cluster-based body-centered-cubic superlattice (cBCC SL) represents one of the most complicated structures among reported nanocrystal assemblies, comprised of 72 truncated tetrahedral quantum dots per unit cell. Our previous report revealed that truncated tetrahedral quantum dots within cBCC SLs possessed highly controlled translational and orientational order owing to an unusual energetic landscape based on the balancing of entropic and enthalpic contributions during the assembly process. However, the cBCC SL's structural transformability and mechanical properties, uniquely originating from such complicated nanostructures, have yet to be investigated. Herein, we report that cBCC SLs can undergo dynamic transformation to face-centered-cubic SLs in response to post-assembly molecular exposure. We monitored the dynamic transformation process using in situ synchrotron-based small-angle X-ray scattering, revealing a dynamic transformation involving multiple steps underpinned by interactions between incoming molecules and TTQDs' surface ligands. Furthermore, our mechanistic study demonstrated that the precise configuration of TTQDs' ligand molecules in cBCC SLs was key to their high structural transformability and unique jelly-like soft mechanical properties. While ligand molecular configurations in nanocrystal SLs are often considered minor features, our findings emphasize their significance in controlling weak van der Waals interactions between nanocrystals within assembled SLs, leading to previously unremarked superstructural transformability and unique mechanical properties. Our findings promote a facile route toward further creation of soft materials, nanorobotics, and out-of-equilibrium assemblies based on nanocrystal building blocks.

A Smart Amorphous Wire Composite with Tunable Electromagnetic Shielding

Nowadays, in view of the increasingly serious problems of electromagnetic interference (EMI) and radiation pollution, smart EMI shielding materials with tunable shielding effectiveness (SE), especially “On/Off” switchable capability, are highly desirable. Herein, Co‐based amorphous wires (AWs) with excellent soft magnetic and mechanical properties are regularly arranged on a 3D‐printed mold as tunable EMI shielding composites. The EMI SE can be easily tuned in the range of ≈0.6–24.7 dB by way of rotation, which has been confirmed to be an effective way to achieve free tuning of EMI SE by simulation. In addition, by compositing AWs with reduced graphene oxide and constructing a double‐layer structure with a gap of 1/4 wavelength in the X‐band, a much wider SE tuning range of ≈1.0–57.7 dB is further realized. The representative “On/Off” switchable shielding capability that can switch between EM transmission and effective shielding, together with the wide SE tuning range larger than 50 dB, shows the great potential of Co‐based AW composites in smart EMI shielding applications.

Effect of Mo addition on AC soft magnetic property, hardness and microstructure of FeCoNiMox (0 ≤ x ≤ 0.25) medium entropy alloys

The FeCoNi medium entropy alloy (MEA) has good alternating current (AC) magnetic properties but poor mechanical properties. This limits its application in soft magnetic materials. In this work, the effects of adding a small amount of Mo on the soft magnetic properties, hardness, and microstructure of FeCoNiMox (0 ≤ x ≤ 0.25) MEAs were investigated. The results indicate that a suitable addition of Mo can simultaneously improve the AC soft magnetic properties and hardness of the alloys. When x = 0.15, the total loss (Ps), AC coercivity (AC Hc), and maximum AC applied magnetic field (AC Hm) of the alloy were improved by 41%, 37%, and 38% over those of the x = 0 alloy, respectively. When x = 0.25, the nano-hardness of the alloy is 91% higher than that of the x = 0 alloy. The results of the microstructure analysis show that the appropriate addition of Mo homogenized the microstructure and refined the grains of the alloys. Meanwhile, the addition of Mo also led to the appearance of two FCC phases with alternating distribution and inhibited the formation of dislocation in the alloys. The mechanisms of adding elemental Mo to improve the soft magnetic properties and hardness of the alloys are discussed. Our work provides an effective way to enhance the soft magnetic and mechanical properties of MEA simultaneously.

Multifunctional Nanofibrous Scaffolds Capable of Localized Delivery of Theranostic Nanoparticles for Postoperative Cancer Management.

Postoperative recovery of cancer patients can be affected by complications, such as tissue dysfunction or disability caused by tissue resection, and also cancer recurrence resulting from residual cancer cells. Despite impressive progress made for tissue engineering scaffolds that assist tissue regeneration for postoperative cancer patients, the majority of existing tissue engineering scaffolds still lack functions for monitoring and killing residual cancer cells, if there are any, upon their detection. In this study, multifunctional scaffolds that comprise biodegradable nanofibers and core-shell structured microspheres encapsulated with theranostic nanoparticles (NPs) are developed. The multifunctional scaffolds possess an extracellular matrix-like nanofibrous architecture and soft tissue-like mechanical properties, making them excellent tissue engineering patch candidates for assisting in the repair and regeneration of tissues at the cancerous sites after surgery. Furthermore, they are capable of localized delivery of theranostic NPs upon quick degradation of core-shell structured microspheres that contain theranostic NPs. Leveraging on folic acid-mediated ligand-receptor binding, surface-enhanced Raman scattering activity, and near-infrared-responsive photothermal effect of the theranostic gold NPs (AuNPs) delivered locally, the multifunctional scaffolds display excellent active targeting, diagnosis, and photothermal therapy functions for cancer cells, showing great promise for adaptive postoperative cancer management.

Microstructure, mechanical and soft magnetic properties of in-situ TiC reinforced Fe27.5Ni27.5Co45-based medium entropy composites

The insufficient mechanical properties of conventional soft magnetic materials (SMMs) hinder their widespread applications, and unfortunately, traditional strengthening mechanisms could dramatically deteriorate their soft magnetic properties without adjusting the alloy composition. Here, we developed TiC/Fe27.5Ni27.5Co45 medium-entropy composites (MECs) possessing multi-scale microstructure consisting of ultrafine and micron-sized grains by introducing in-situ formed TiC nano particles during the spark plasma sintering (SPS) process. Compared with the precipitate-free Fe27.5Ni27.5Co45 medium-entropy alloy, TiC/Fe27.5Ni27.5Co45 MEC with ∼ 8.7 vol% TiC (noted as Ti5-MEC) demonstrated a significant improvement in compressive yield strength (from 459 MPa to 1114 MPa), attributing to the grain-boundary strengthening and dispersive precipitation strengthening, as well as hetero-deformation induced (HDI) strengthening. Meanwhile, the Ti5-MEC exhibits a high saturation magnetization (Ms) of 153.1 emu/g and a low coercivity (Hc) of ∼ 8.2 Oe, indicating excellent soft magnetic properties, primarily due to the multi-scale microstructure. Our work has demonstrated that engineering multi-scale microstructures in MECs is an effective strategy to achieve desirable combinations of soft magnetic and mechanical properties.

Piezoresistivity modeling of soft tissue electrical-mechanical properties: A validation study.

In general, the electrical property of soft tissues is sensitive to the force applied to their surface. To further study the relationship between the force and the electrical property of soft tissues, this paper attempts to investigate the effect of static and higher-order stresses on electrical properties. Overall, a practical experimental platform is designed to acquire the force information and the electrical property of soft tissues during a contact procedure, which is featured different compression stimuli, such as constant pressing force, constant pressing speed, and step-force compression, etc. Furthermore, the piezoresistive characteristic is innovatively introduced to model the mechanical-electrical properties of soft tissue. Finite Element Modeling (FEM) is adopted to fit the static piezoresistivity of the soft tissue. Finally, experimental studies were performed to demonstrate the effect of stress on the electrical properties and the feasibility of the proposed piezoresistive model to describe soft tissues' mechanical and electrical properties.

Fabrication and excellent performance of amorphous FeSiBCCr/organic-inorganic hybrid powder core

Soft magnetic composites (SMCs) are widely used in relevant inductance components in power and electronic fields. The development of high frequency devices requires SMCs to exhibit good insulation and excellent soft magnetic properties. The insulation coating for SMCs is crucial, and it is necessary to ensure that the coating thickness is uniform and maintains excellent adhesion to the powder. In the present work, a novel and efficient solution for the formation of insulating coatings, i.e. phytic acid/silane (denoted as PAS) organic-inorganic hybrid solution, was prepared by the condensation reaction between PA and γ-(2,3-epoxypropoxy) propyl trimethoxy silane. The FeSiBCCr@PAS powder with a core-shell structure has been successfully prepared through chemical reaction in a modified PAS solution. The effects of insulating coating content on the magnetic and mechanical properties of FeSiBCCr@PAS powder cores were systematically investigated. The PAS hybrid insulating coating can significantly improve the DC-bias performance and reduce the core loss. The optiomal powder core, which was prepared by using the powder coated with 3 g/L phytic acid, exhibits a minimum core loss (P50mT/1MHz) of 2979.2 mW/cm3, high effective permeability μe(0.1A/m) of 33.8, and superior DC-bias(100Oe) performance of 80.8%. Present work developed an effective method to prepare high performance powder cores with good soft magnetic and mechanical properties.

One-pot ternary sequential reactions for photopatterned gradient multimaterials

One-pot ternary sequential reactions for photopatterned gradient multimaterials

Insight of electro-chemo-mechanical process inside integrated configuration of composite cathode for solid-state batteries

The complicated electro-chemo-mechanical process that occurs inside the composite cathode for solid-state batteries (SSBs), is of first importance to be insighted for the development of SSBs to seek higher energy density. Herein, exampled with layered transition-metal oxide of LiNixCoyMn1-x-yO2 (NCM), an electro-chemo-mechanical model containing electrochemical kinetics, finite-strain constitutive model and cohesive zone model was built to uncover the impact of ionic conductivity and Young's modulus (E) of solid-state electrolyte (SE) on the electro-chemo-mechanical process inside composite cathode and the intergranular failure of single cathode particle. The intergranular failure of NCM particles is powerfully determined by the Young's modulus of SE and the primary particle size, which is postponed by the coarse-primary NCM with soft SE of E=∼2 GPa. Compared with Young's modulus, increasing the ionic conductivity can uniform the distribution of both Li-ion and stress in the whole composite NCM cathode, realizing improved electrochemical performance with larger normalized capacity and lower the interfacial impendence. Hence, high-adequate ionic conductivity of 5 × 10−4 S cm−1 and soft mechanical property of E=∼2 GPa can be proposed as the guideline of SE for great electrochemical performance with prolongated lifespan of composite NCM cathode, paving an avenue to foster the application of SSBs.

Highly conductive tissue-like hydrogel interface through template-directed assembly

Over the past decade, conductive hydrogels have received great attention as tissue-interfacing electrodes due to their soft and tissue-like mechanical properties. However, a trade-off between robust tissue-like mechanical properties and good electrical properties has prevented the fabrication of a tough, highly conductive hydrogel and limited its use in bioelectronics. Here, we report a synthetic method for the realization of highly conductive and mechanically tough hydrogels with tissue-like modulus. We employed a template-directed assembly method, enabling the arrangement of a disorder-free, highly-conductive nanofibrous conductive network inside a highly stretchable, hydrated network. The resultant hydrogel exhibits ideal electrical and mechanical properties as a tissue-interfacing material. Furthermore, it can provide tough adhesion (800 J/m2) with diverse dynamic wet tissue after chemical activation. This hydrogel enables suture-free and adhesive-free, high-performance hydrogel bioelectronics. We successfully demonstrated ultra-low voltage neuromodulation and high-quality epicardial electrocardiogram (ECG) signal recording based on in vivo animal models. This template-directed assembly method provides a platform for hydrogel interfaces for various bioelectronic applications.

Design Parameters and Human Biocompatibility Assessment Protocols for Organic Semiconducting Neural Interfaces: Toward a Printed Artificial Retina with Color Vision

AbstractOrganic semiconductors have emerged as promising neural interfacing materials due to their innate biocompatibility, soft mechanical properties, and mixed electron/ion conduction. One exciting application is their use as artificial photosensors for retinal prostheses via optically induced neuromodulation. In this study, the optoelectronic and neural interfacing properties of six organic semiconductor polymers and small molecules, split into donor/acceptor pairs that form promising candidates for a trichromatic artificial retina that closely mimics the native response of the human eye are presented. The biocompatibility of these materials using primary human retinal cell cultures by systematic measurement of both cell viability and morphological analysis of retinal ganglion cell neurite elongation over time is investigated. Comparable cell viability between human retinal cell cultures established on all the organic semiconductors and a glass control, which is a standard measurement for biocompatibility in materials science is observed. In contrast, differences in the morphological biocompatibility between the organic semiconductor materials and glass control are detected by analyzing neurite elongation with specific immunomarkers. The difference in the two results has implications for the future assessment of material biocompatibility for bioelectronics, and optimal methodology for assessing morphological biocompatibility in neural interface devices is discussed.

Advances in Ultrathin Soft Sensors, Integrated Materials, and Manufacturing Technologies for Enhanced Monitoring of Human Physiological Signals

AbstractRecent advances in soft sensors and flexible electronics offer various applications in detecting physical, electrical, and chemical signals. However, there are still technical barriers in current mechanical, electrical, and material properties for enhanced signal sensing. When measuring signals from the human skin, minimizing the skin‐sensor contact impedance is still challenging while maximizing sensitivity through optimized materials and soft electronics. Here, this review summarizes recent advances in materials, manufacturing, and integration technologies to develop ultrathin soft sensors for monitoring various human physiological signals. The enhancements in soft and compliant structures and mechanical properties are critical to making reliable wearable electronic systems. This article shares the details of soft sensors, integration processes, manufacturing methods, and their applications to target physical, electrical, and chemical signals. In addition, the limitations and current trends in developing multifunctional sensors, self‐powered devices, and integration with external stimuli systems are discussed.

Flexible Electrodes as a Measuring System of Electrical Impedance Imaging

Electrical Impedance Tomography (EIT) is a detection imaging technology developed 30 years ago. When the conventional EIT measurement system is used, the electrode and the excitation measurement terminal are connected with a long wire, which is easily affected by external interference, and the measurement result is unstable. In this paper, we developed a flexible electrode device based on flexible electronics technology, which can be softly attached to the skin surface for real-time physiological monitoring. The flexible equipment includes an excitation measuring circuit and electrode, which eliminates the adverse effects of connecting long wires and improves the effectiveness of measuring signals. At the same time, the design also uses flexible electronic technology to make the system structure achieve ultra-low modulus and high tensile strength so that the electronic equipment has soft mechanical properties. Experiments have shown that when the flexible electrode is deformed, its function is completely unaffected, the measurement results remain stable, and the static and fatigue performances are satisfactory. The flexible electrode has high system accuracy and good anti-interference.

Soft, strong, tough, and durable protein-based fiber hydrogels

Load-bearing soft tissues normally show J-shaped stress-strain behaviors with high compliance at low strains yet high strength at high strains. They have high water content but are still tough and durable. By contrast, naturally derived hydrogels are weak and brittle. Although hydrogels prepared from synthetic polymers can be strong and tough, they do not have the desired bioactivity for emerging biomedical applications. Here, we present a thermomechanical approach to replicate the combinational properties of soft tissues in protein-based photocrosslinkable hydrogels. As a demonstration, we create a gelatin methacryloyl fiber hydrogel with soft tissue-like mechanical properties, such as low Young's modulus (0.1 to 0.3 MPa), high strength (1.1 ± 0.2 MPa), high toughness (9,100 ± 2,200 J/m3), and high fatigue resistance (2,300 ± 500 J/m2). This hydrogel also resembles the biochemical and architectural properties of native extracellular matrix, which enables a fast formation of 3D interconnected cell meshwork inside hydrogels. The fiber architecture also regulates cellular mechanoresponse and supports cell remodeling inside hydrogels. The integration of tissue-like mechanical properties and bioactivity is highly desirable for the next-generation biomaterials and could advance emerging fields such as tissue engineering and regenerative medicine.

Physical properties and cellular responses of gelatin methacryloyl bulk hydrogels and highly ordered porous hydrogels

Protein-based hydrogels hold a high content of water in their three-dimensional (3D) network structure and exhibit innate biological activities as well as soft tissue-like mechanical properties, resulting in being highly applicable to various tissue engineering fields. However, precisely controlling the 3D porous structure of protein-based hydrogels remains a challenging task, and understanding the influence of their porous structure on physical properties and cellular responses is crucial for tissue engineering applications. In this study, we prepared highly ordered gelatin methacryloyl hydrogels with regular interconnected pores and traditional bulk hydrogels with irregular pores to evaluate their differences in physiochemical properties and cellular behaviors. Highly ordered gelatin methacryloyl hydrogels exhibited a high degree of compliance owing to their sponge-like structure whereas gelatin methacryloyl bulk hydrogels exhibited relatively higher moduli but were brittle due to a densely packed structure. The highly ordered gelatin methacryloyl hydrogels with interconnected pores supported higher cell viability (about 100%) due to an efficient flux of oxygen and nutrients compared to the dense bulk hydrogels showing cell viability (around 80%). Also, cells in the highly ordered gelatin methacryloyl hydrogels displayed a more stretched morphology compared to those in the gelatin methacryloyl bulk hydrogels that exhibited a more round morphology during the cell culture period.

Effect of stress relaxation on soft magnetic properties of Fe76Si9B10P5 metallic glass

Stress relief can improve the soft magnetic properties of Fe-based metallic glasses (MGs) and is vital for industrial applications. In this work, we investigated the evolution of soft magnetic properties, relaxation dynamics, and mechanical properties of Fe-based MGs under different applied tensile strains and stress relaxation times. We found that stress relaxation can significantly reduce coercivity Hc by 95% compared with as-quenched state. Furthermore, the coercivity Hc, apparent activation volume Vact and time constant tr all show analogous two-stage variation with annealing time, accompanied by approximate crossovers. This suggests that the microstructure change emerges, further verified by the domain wall motion and the transition from elastic to plastic. These results are helpful in preparing Fe-based MGs with excellent soft magnetic and mechanical properties by controlling the stress relaxation condition.