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Soft Composites - Multifunctional Magnetic Soft Composites

Soft composites with magnetic fillers that respond to magnetic fields are magnetically responsive soft materials.

Magnetically responsive soft materials are made of soft composites with magnetic fillers that are mixed into soft polymeric matrices.

Researchers and businesses are interested in these active materials because magnetic fields can make them change shape quickly and in a predictable way.

Stimulus-responsive soft materials with static and dynamic shape programming and reconfiguration capabilities have gotten a lot of attention as carriers for easy integration of functions like actuation and sensing. These materials have a lot of potential for use in soft robotics, reconfigurable structures, biomedical devices, morphable electronics, and other fields.

The soft and flexible matrix allows for big and fast changes in shape, letting the body adapt both actively and passively to external forces, stimuli, and constraints.

Soft materials that respond to light, temperature, humidity, an electric field, or a magnetic field have active fillers or microstructures in soft matrices.

Under a remote magnetic field, soft materials that respond to magnetism can be moved and acted on quickly and without being attached.

The better performance of soft materials that respond to magnetic fields in high power density actuators opens up new possibilities in soft robotics and biomedicine.

Micro/nanoscale particles, fibers, wires, polymer chains, or chemical groups that respond to stimuli and cause mechanical and multiphysics matrix responses for different physical behaviors and properties that can be changed can be the active components.

Material Composition

Magnetically responsive material systems rely on mechanical, electrical, and magnetic qualities. Both the system's materials and structures must be carefully designed to permit massive shape-morphing, programmable deformation, substantial actuation force, and customizable physical attributes.

Functional magnetic soft materials combine magnetic fillers with soft matrices. Magnetic composites can be made to do different things by choosing the right filler (ferromagnetic particles, superparamagnetic particles, permanent magnets, etc.) and polymer matrix (hydrogels, soft elastomers, shape memory polymers (SMPs), etc.).

Functional Magnetic Fillers

Magnetic fillers transform electromagnetic energy into mechanical deformation, work, and thermal energy through inductive heating. In a magnetic field, different things happen to systems made of ferromagnetic (hard and soft-magnetic) particles, superparamagnetic particles, or permanent magnets.

Soft-Magnetic Fillers

Soft iron, soft ferrite, iron-silicon alloys, iron-nickel alloys, etc. are soft-magnetic fillers. Compared to hard-magnetic materials, they have high permeability and low coercivity. Soft-magnetic particles like carbonyl iron are embedded in hydrogels and elastomers to make ferrogels and magnetorheological elastomers (MREs).

By using magnetostrictive behavior, these materials may alter form and sense stress and magnetic fields.

In recent decades, researchers have worked to define and predict the magnetostrictive behavior of MREs based on dipole interactions, microstructures, particle distributions, and particle morphologies. Studies of the mechanics of magnetic soft composites help us understand how materials behave and give us a tool for designing.

Hard-Magnetic Fillers

Soft-magnetic composites can't sustain magnetization in an external magnetic field, limiting its programming flexibility. Magnetically responsive materials implanted with hard-magnetic fillers such as neodymium-iron-boron (NdFeB), hard ferrite, alnico alloys, and samarium-cobalt are being investigated to produce excellent material programmability and intricate shape transformations.

Hard-magnetic materials have poor permeability when magnetized to saturation (∼1.6 T for NdFeB and ∼0.35 T for hard ferrite) in a strong magnetic field. When the applied magnetic field is not in line with the direction of magnetization in a hard-magnetic material, a magnetic torque is made to get it in line.

Functional Soft Polymeric Matrices

Soft robotics and changeable buildings use soft materials. Matrix characteristics vary by function. In addition to magnetic fillers, the magnetic composite matrix must be carefully designed for specific purposes. Hydrogels, soft elastomers, SMPs, and fluids are frequent matrices.

Hydrogels

Hydrogels are hydrophilic, elastic polymers. Polymer networks may hold 90 wt% of water. Biomedically useful hydrogels are due to their low rigidity, high carrier loading, and superior biocompatibility. Incorporating magnetic particles into hydrogels boosts their application potential in soft actuators, medication delivery, and cell manipulation.

Magnetic hydrogels are soft with rigidity equivalent to tissues and organs, allowing substantial matrix compression or elongation by external magnetic fields.

Activated by a permanent magnet, a porous magnetic hydrogel embedded with Fe3O4 nanoparticles causes a significant deformation with a compressive strain of up to 80%, resulting in regulated drug and cell agent release from the porous scaffold. Biocompatibility makes hydrogels ideal for biomedical uses.

Soft Elastomers

Elastomers are soft polymeric materials having elastic properties, meaning their deformation under mechanical stresses is reversible. Soft elastomers are utilized as the matrix of magnetically sensitive materials to enable massive deformations.

Ecoflex and Poly(dimethylsiloxane) are commercially available. Hard-magnetic elastomers may be magnetized to change form.

Programmable magnetization allows an artificial cilium with biomimetic recovery and power strokes. MREs experience strain and modulus shift due to significant particle-particle and particle-matrix interactions. Because of their controlled stiffness variations and field-dependent features, MREs are utilized to create active vibration absorbers and isolators.

Shape Memory Polymers

Soft matrices allow simple shape change under magnetic actuation, but they can't lock the deformed shape without a constant magnetic field. Deformed structures demand constant power for applications. In these circumstances, SMPs lock the distorted shape. SMPs may memorize temporary forms and regain their original shapes under external stimuli like temperature, light, etc.

When the temperature is above a thermally activated SMP's Tg, the material becomes rubbery and deformable.

After cooling below Tg, the material gets glassy and remains distorted. When heated above Tg, the SMP returns to its original shape. The modulus varies by orders of magnitude during the thermally-activated transition of SMPs.

Induction heating of magnetically sensitive particles in SMP matrices under a high-frequency alternating magnetic field may cause the phase transition and shape memory effect of SMPs.

Magnetorheological Fluids And Particle-Filled Fluids

Magnetorheological fluid (MRF) comprises magnetic particles in silicone oil, fluorocarbon, and water. Magnetostrictive MRFs alter form in magnetic fields. Distributed particles may move freely in a fluid to create chain-like structures under a magnetic field, indicating a significant magnetorheological effect. MRF-filled 3D-printed structures may actively modify system stiffness and damping.

Infiltrating ferrofluid in a porous matrix with microchannels creates a magnetically responsive composite surface with controlled magnetic nanoparticle mobility. Under a gradient magnetic field, droplets of ferrofluid can change into different shapes and configurations that can do different things. They can act as cooperative and autonomous liquid robots.

Fabrication Methods

The magnetic soft composites' functionality is determined by the system's material and geometric designs. Advanced manufacturing technologies provide more complex structures and application options.

While molding may produce 2D or rather basic 3D geometries, additive manufacturing methods, often known as 3D printing, can produce complicated structures using magnetically sensitive soft materials quickly. The general manufacturing techniques of magnetically sensitive soft materials will be covered in this part.

Molding

Molding is a common method of fabricating hard and soft-magnetic composites by combining magnetic fillers and polymeric precursors and curing them to generate particular forms or structures. Magnetic fields during curing may create anisotropic composites with chain-like microstructures.

After solidification, a high magnetic field may disperse magnetization in hard-magnetic materials. This programming approach needs a well-designed fixture or fixing strategy to distort the material before magnetizing it.

An inactive (elastomer with aluminum particles) and active (elastomer with NdFeB particles) beam is sandwiched between two fixtures with a predefined profile. This helps vary the composite beam's magnetization.

Additive Manufacturing

3D printing, or additive manufacturing, builds an item layer by layer. Various printing technologies have recently been developed for making magnetically sensitive soft materials with micrometer to centimeter-scale structures and programmable magnetization distributions.

A recent study studied two-photon polymerization to make magnetic composites tiny. Spatial and temporal laser pulses induce microstructure polymerization in photo-curable materials.

Biocompatible and biodegradable composite precursors polymerize at the laser focal point, producing magnetic hydrogel robots of different sizes. This technology permits the submicron-resolution production of miniature 3D structures. This method boosts magnetic composites' biological applications.

Other Methods Of Fabrication

Conventional microfabrication can make submicron-resolution magnetic soft devices. Single-domain nanomagnet arrays are fabricated by e-beam lithography on hinged panels. Multiple 2D modules transform into 3D designs using the reprogrammable magnetization of nanomagnets. The standard micro/nanofabrication method gives the suggested method nanometer-scale resolution.

Recent attempts have also created microscale magnetic soft machines from supplied building blocks made of diverse functional units and materials. Non-magnetic bodies and magnetic wheels self-assemble via dielectrophoretic forces caused by an electric gradient. Chemical-aid assembly can make smaller magnetic soft machines.

In prior work, DNA was used to link magnetic particles. This structure can swim under an oscillating magnetic field. There is still room to develop magnetic soft machine manufacturing at the micrometer and nanoscale scales, achieving arbitrary 3D structures with improved multifunctionalities.

Magnetic Soft Materials - Their Function And Operation

By combining magnetic fillers with polymeric matrices and using sophisticated production processes, design freedom may be attained. Magnetic fillers may transform electromagnetic energy from permanent magnets or electromagnetic coils into elastic, kinetic, and/or thermal energy. Programmable magnetic features, including particle alignment and magnetization distribution, enable form morphing in a magnetic field.

Magnetically responsive soft materials navigate by crawling, rolling, leaping, and climbing using complicated dynamic movements controlled by the amount and direction of the magnetic field. Magnetic composites are useful for sensitive item handling due to their shape-configuration and navigation under magnetic fields.

Certain kinds of magnetic particles may create a considerable quantity of heat through inductive heating in a high-frequency alternating magnetic field, which can be used to treat malignancies using hyperthermia.

Heat may be used with magnetic composite physics to activate form memory remotely. Magnetic materials and magnetic fields, as well as soft materials that are sensitive to magnetic fields, make it possible to find new ways to program electronics and find signals.

Programmable Shape Morphing And Tunable Properties

Well-designed magnetic soft materials respond to an external magnetic field with programmable deformation. The magnetic soft composites' programmable magnetization distribution is a benefit.

Regionally polymerizing photo-curable resin aligns Fe3O4 nanoparticles, giving the actuator spatially dispersed magnetic anisotropy. By altering magnetic field directions, alternate particle chain directions enable the actuator to create two wavy forms.

Magnetization distribution of hard-magnetic materials may be programmed for intricate form morphing. By assigning a non-uniform and continually changing magnetization distribution, a beam exhibits time-varying undulatory deformation in a rotating magnetic field. Magnetic soft composite reprogrammability increases shape morphing for reconfigurable deformations.

A new attempt displays magnetization reprogramming by heating magnetic soft composites over the CrO2 magnetic microparticles' Curie temperature and cooling them with a reprogramming field on. This method lets you erase and rewrite magnetization on demand using targeted heating, which makes active metamaterials more flexible and easy to set up in different ways.

A brown wooden plastic brick
A brown wooden plastic brick

Dynamic Deformation-Based Motion And Navigation

Unlike light, heat, or pH, electromagnetic coils can alter the magnetic field's amplitude, direction, and distribution. With well-designed time-dependent uniform, gradient, oscillating, or rotating magnetic fields, magnetic soft composites may achieve dynamic motion and navigation. Magnetically-driven hydrogel microswimmers inspired by bacterial motions may move under a rotating magnetic field.

By programming magnetic particle alignments, various microrobot morphologies may swim differently. The microswimmer reorients magnets around a hinge using a periodic magnetic field to simulate scallop swimming. Programming particle alignment and discrete magnetization facilitates dynamic deformation-based motion. A jellyfish-inspired robot has intricate architecture and magnetism.

Object Manipulation And Assembly

Modern industry and product design employ modular assembly to incorporate separate, functioning parts into customized systems. Modularity allows design freedom but requires well-designed modules with dependable inter-module connections. Magnetically sensitive materials may be constructed via dipole-dipole interactions, for example. By interacting with built-in magnets, pneumatic actuators of different shapes and functions can be quickly put together into prototypes of robots or used to replace broken parts.

Due to their well-controlled transformation and transportation, magnetic soft composites can gather, operate, and assemble things. A millimeter gripper, guided by a magnetic field and regulated heat and pH conditions, can grab and remove a cluster of cells. An immobile sperm is captured, transported, and released into an egg by a magnetically driven robot.

Heat Generation And Energy Output

Magnetic particles lose thermal energy owing to magnetic hysteresis in a high-frequency alternating magnetic field. Various applications use magnetically sensitive materials to generate effective heat.

Directly using generated heat is one use. Magnetic hyperthermia heats tumor-introduced nanoparticles inductively. Magnetic particle imaging has been used to generate localized hyperthermia.

Applying a gradient magnetic field to ferrofluid reduces collateral harm to healthy organs. Biocompatible composites containing magnetic particles contained in soft matrices also overcome the off-target delivery issue. Magnetic double network hydrogels have excellent mechanical characteristics and magnetic hyperthermia.

Inductive heating may assist in modifying the temperature-dependent features of magnetically sensitive soft materials in addition to directly using the generated thermal energy. The thermal energy that is made can also work with the multiphysics responses of different types of soft matrices to change shape, deliver medicine, and heal themselves.

Magnetic Soft Composites For Electronics

Flexible electronics are becoming more important in wearable gadgets, flexible sensors, and self-sensing soft robots.

By actively morphing the form under a magnetic field or passively by mechanical loading, magnetically responsive soft materials' electromagnetic and electrical characteristics may be altered.

Recent research shows that magnetically sensitive soft materials may be used for flexible electronics, including antennas, filters, capacitors, inductors, and sensors. An antenna built of magnetic SMP covered with silver paste allows continuous height variation with form locking.

Changing the antenna's height under a magnetic field changes its resonance frequency. Recent work creates a magneto-mechano-electric origami system.

By putting programmed magnetic soft materials in a bifold origami assembly in a uniform way, magnetic actuation gives each unit cell independent control over folding and unfolding, with instant shape locking. This makes it possible to change the physical properties and set up electronics for digital computing.

Magnetic Control

Magnetic fields program and regulate magnetic soft composites' behavior. Permanent magnets are the most common and easy-to-handle magnetic field generators, with tailorable direction and amplitude by modifying the relative orientation and distance to the item.

Most applications need dependable and accurate programming of the robotic arm to move the magnets. Commonly used are electromagnetic coils and array magnets. With these solutions, the direction, size, gradient, and frequency of a magnetic field can be controlled in magnetic composites without the need for mechanical parts that move.

Magnetic Fields That Are Uniform

Uniform magnetic fields are used to predictably deform magnetic composites without magnetic tugging. A Halbach array, made of permanent magnets arranged in a ring, provides a consistent static magnetic field.

The Helmholtz coils use a pair of circular coils to create homogenous magnetic fields; the applied current dictates the field's direction and size. Changing the external magnetic field may create complex movements. When Helmholtz coils are placed on three orthogonal axes, they create magnetic fields that can be used to change the shape of things in three dimensions.

Non-Uniform Magnetic Fields

Non-uniform B fields may yield more DOFs than uniform ones. We may suppose that three B field components (Bx, By, Bz) are not uniform, whereas their five independent first-order derivatives, or gradient terms, are uniform. Bzz isn't independent since Bxx+Byy+Bzz = 0.

With this premise, these five gradient terms can regulate magnetic soft composites. In Lum et al.'s work, all eight independent B field parameters (Bx, By, Bz, Bxx, Bxy, Bxz, Byy, Byz) and the magnetization profile of the magnetic soft materials (Mx, My, Mz) are given as design inputs, and an automatic computational optimization approach is formulated to generate a set of desired values for these design inputs, which can realize targeted kinematics for a fixed-free beam structure made of magnetic Eight electromagnetic coils are needed to regulate the eight B field characteristics individually.

Previous work tuned these eight coils to provide adequate magnetic gradient force in all spatial directions. Using a similar formulation and optimization function, various coil configurations may be made.

People Also Ask

What Is A Soft Composite?

Soft magnetic composites (SMCs) are made of ferromagnetic powder particles wrapped in an electrically insulating membrane and used in electromagnetic applications.

What Is An Example Of A Composite Material?

Composite materials are those made up of two or more separate elements or substances, the combination of which provides the final matter with the joint properties of its components, that is, the qualities of the two original substances at the same time. For instance, adobe, concrete, and bone.

What Are The Four Types Of Composites?

Composites are typically categorized based on the material used for the matrix. Polymer matrix composites (PMCs), metal matrix composites (MMCs), ceramic matrix composites (CMCs), and carbon matrix composites are the four primary composite types (CAMCs).

What Are The Three Three Classifications Of Composite Materials?

Composite materials are divided into three types: polymer-matrix composites, metal-matrix composites, and ceramic-matrix composites. They are widely used in a wide range of technical applications.

Conclusion

This article focuses on magnetically sensitive soft materials and their multifunctionality, including form morphing with adjustable qualities, dynamic motion and navigation, object manipulation and assembly, heat production and energy output, and soft and programmable electronics.

Magnetic soft composites have advanced soft robotics, biomedical devices, active metamaterials, and electronics. Magnetic soft composites are remote-controlled, quick, and programmable, yet they have limits.

Magnetic soft composites are currently best for microscale to centimeter-scale applications. Larger magnetic soft composites may lose benefits owing to bulky actuation systems.

All magnetically sensitive materials in the external magnetic field are affected. Specially engineered material characteristics, complicated magnetic actuations, and multi-physics control techniques are needed for on-demand localized and global controls. Thus, smarter promotion of soft magnetic composites for genuine applications is needed.

About The Authors

Suleman Shah

Suleman Shah - Suleman Shah is a researcher and freelance writer. As a researcher, he has worked with MNS University of Agriculture, Multan (Pakistan) and Texas A & M University (USA). He regularly writes science articles and blogs for science news website immersse.com and open access publishers OA Publishing London and Scientific Times. He loves to keep himself updated on scientific developments and convert these developments into everyday language to update the readers about the developments in the scientific era. His primary research focus is Plant sciences, and he contributed to this field by publishing his research in scientific journals and presenting his work at many Conferences. Shah graduated from the University of Agriculture Faisalabad (Pakistan) and started his professional carrier with Jaffer Agro Services and later with the Agriculture Department of the Government of Pakistan. His research interest compelled and attracted him to proceed with his carrier in Plant sciences research. So, he started his Ph.D. in Soil Science at MNS University of Agriculture Multan (Pakistan). Later, he started working as a visiting scholar with Texas A&M University (USA). Shah’s experience with big Open Excess publishers like Springers, Frontiers, MDPI, etc., testified to his belief in Open Access as a barrier-removing mechanism between researchers and the readers of their research. Shah believes that Open Access is revolutionizing the publication process and benefitting research in all fields.

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