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Flexible materials embedded with hard magnetic particles have recently gained widespread recognition as small-scale actuators due to their capacity to be a rapid and precise shape-shifting material. Strontium ferrite (SrFe 12 O 19 ) particles have been shown as a great candidate for such applications, since it is an inert hard magnetic material tha...
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... An Ultem TM cup containing the un-cured suspension was attached to an 8 mm transverse sample rod using wax as glue and Teflon tape for additional support and loaded in the VSM ( Fig. 1(a)) parallel and perpendicular to the field direction. 18 All samples were initially in the liquid state and contained in a 6 mm Ultem TM cylindrical cup ( Fig. 1(c)) for molding purposes. The magnetic characterization was done in a biaxial EZ-9 Vibrating Sample Magnetometer (VSM). ...
... (a) Schematic of sample loading in VSM using transverse rod.18 Sample molding in (b) 50 mm long cylinder, (c) Ultem TM cup used for in situ measurement, (d) plastic cup.ARTICLE pubs.aip.org/aip/adv ...
Magnetic composite polymers combine the properties of both magnet and polymers which enable them to produce complex shape magnetic components. These materials have potential applications ranging microfluidics, vibration dampers, actuators, and minimally invasive medical devices, because when magnetic fields are applied to them, they can change shape precisely, quickly, and consistently. Our study investigates the behavior of strontium ferrite particles [SrO(Fe2O3)6] suspended in polydimethylsiloxane (PDMS) under the influence of gravity, applied magnetic fields, and time dependent behavior at different temperatures. We found that curing the PDMS and strontium ferrite suspension without a magnetic field result in a well-distributed particle arrangement with no coagulation. However, the particles align along the magnetic field lines while curing in the presence of a magnetic field (Hallback Cylinder), leaving a clear PDMS layer on top, while there is very little sedimentation due to gravity. To check this, we fabricated a 40 mm long sample and conducted hysteresis measurements in vibrating sample magnetometer (VSM) at various positions, showing minimal variation in magnetic saturation (Ms) values. Furthermore, we found a time-dependent curve of the transient angle as a function of temperature change, where the angle decreased over time as the particle’s magnetic moments aligned with the direction of the magnetic field. At lower temperatures, the transient angle decreased sharply due to lower dynamic viscosity in the uncured specimen. Hysteresis analysis and time-dependent studies at varying temperatures showed a notable change in curing that occurs at ∼55 °C, indicating the transition from a magneto-rheological fluid to a magnetorheological elastomer. The packing fraction of strontium ferrite particles and saturation magnetization were correlated, while coercivity was field-angle independent and remanence was field angle dependent.
... We use elastomer polymer polydimethylsiloxane (PDMS) material to fabricate the swimmer due to its desirable properties [38]: biocompatibility, good elasticity, chemical and thermal stability. Exploiting the good blending property of PDMS, the fabrication of the head of the swimmer was done by mixing PDMS with Fe 3 O 4 nanopowder to replicate magnetic properties [39]. PDMS [SYLGARD 184 elastomer kit] is used as the base material for the swimmer and Fe 3 O 4 is used to incorporate magnetic properties on the head of the swimmer. ...
The motion of comoving magnetic microswimmers is modeled by considering the inter-hydrodynamic interactions (HI) under low Reynolds number conditions. The microswimmer is a two-link design consisting of a magnetic head attached to a slender tail via a torsional spring, and it is driven by an external planar oscillatory magnetic field. The inter-HI considered are the head-head and tail-tail interactions. The propulsion velocity for the comoving mode is calculated and compared with that of an isolated mode. The comparative results show that the comoving mode velocity can be either similar or greater than the isolated mode, depending on the actuation frequency. The parametric dependency results show that the velocity generated in comoving mode depends on the average separation distance and length-to-width ratio of the tail. For proof of concept, a low-cost fabrication protocol is implemented to design a millimeter-sized magnetic flagellated swimmer. The experimental result shows that the comoving swimming mode generates larger velocity in comparison to isolated swimming.
... Among the many potential types of devices and actuation modes, magnetically responsive actuators are particularly exciting since they are rapid, contactless, and driven by magnetic fields that may be used safely near humans [26][27][28]. Several sophisticated engineered materials and structures have been designed to shape and actuate soft magnetic actuators [29][30][31][32]. A soft magnetic actuator was created using ionic polymer metal composites to replicate the deformation of the doubly curved leaves [33]. ...
Many biological systems are made to operate more quickly, efficiently, and with more power by storing elastic energy. This work introduces a straightforward bioinspired design for the quick manufacture of pre-stressed soft magnetic actuators. The actuator requires a lower magnetic field strength to be activated and can regain its original shape without the need for external stimuli. These characteristics are demonstrated in this work through the creation of actuators with round and helical shape structures inspired by the tendril plant and chameleon's tongue. Both the final form of the actuator and its actuation sequence may be programmed by controlling the direction and strength of the force utilised to pre-stress the elastomeric layer. Analytical models are presented to trace the actuators' energy storage, radius, and pitch. High-speed shape recovery after releasing the magnetic force and a strong grasping force are achieved due to the stored mechanical elastic energy. Experiments are conducted to analyse the shape changes, grasping action, and determine the actuation force. The manufacture of the grippers with zero-magnetic field strength holding capacities of up to 20 times their weight is made possible by the elastic energy that actuators store in their pre-stressed elastomeric layer. The outcomes of our research show that a unique magnetic field-controlled soft actuator can be created in different shapes and designs based on requirements.
... It has a compacted density of 3.58 g/cm 3 and an average particle diameter of 1.3 µm. Due to its biocompatibility and ability to be magnetised using composites containing UF-S2 particles at relatively low magnetic fields, this powder is intriguing for the manufacturing of soft actuators [51,52]. ...
Magnetorheological elastomer (MRE) composite actuators are extraordinary since they can be controlled remotely, move swiftly, adapt to rough surfaces, and engage with humans in a secure manner. Despite all these advantages, pure MREs are not stable enough because of their high degree of softness and a magnetic field is always required to actuate and hold them in the required position accordingly. This paper offers a new conceptual design for bi-stable MRE-based electroactive composite actuators with high performance. The idea is a combination of MRE composites and 4D printing (4DP) of conductive shape memory polymers. The silicone resins are loaded with strontium ferrite magnetic particles and a thin conductive carbon black polylactic acid (CPLA) is 4D printed and embedded as a core inside the composite. A set of parametric studies is carried out to examine the material properties, 4DP characteristics, and magnetization conditions required for the process. As an outcome, a functional, lightweight, bi-stable, composite actuator with programmable magnetic patterns is developed. This actuator can be positioned in the actuated situation without any stimuli as long as required. The shape memory behaviour, bi-directionality, and remote controlling of the composite actuator are driven by Joule heating and magnetic fields. The actuator with a weight of 1.47 g can hold and lift weights up to 200 g. Finally, some experiments are conducted to demonstrate the immense potential of the developed composite actuators as mechanical and biomedical devices. Due to the absence of similar concepts and results in the specialized literature, this paper is likely to advance the state-of-the-art smart composite actuators with remotely controlled shape-memory features.
The growing field of applications where magnetic actuation is required relies on significant developments in materials science, particularly using polymer matrices to enhance the design and multifunctionality of small‐sized devices through additive manufacturing techniques. Thermoplastic polyurethane (TPU) is widely used for fused deposition modeling 3D printing technology and, as an elastomer, confers the degrees of freedom necessary to develop soft actuators capable of complex shape deformations. Such actuators can be triggered through different stimuli, with magnetic actuation standing out for its capacity to induce fast deformations of remotely actuated systems. Magnetic TPU composites with strontium hexaferrite (SrFe12O19) were produced through a solvent‐free melt‐mixing technique. These composites display a magnetomechanical actuation mechanism, being able to deform (bend and twist) through DC and AC magnetic fields, showcasing their potential as a promising material for the fabrication of future magnetic actuators.
Hard-magnetic soft materials (hMSMs) are smart composites that consist of a mechanically soft polymer matrix impregnated with mechanically hard magnetic filler particles. This dual-phase composition renders them with exceptional magneto-mechanical properties that allow them to undergo large reversible deformations under the influence of external magnetic fields. Over the last decade, hMSMs have found extensive applications in soft robotics, adaptive structures, and biomedical devices. However, despite their widespread utility, they pose considerable challenges in fabrication and magneto-mechanical characterization owing to their multi-phase nature, miniature length scales, and nonlinear material behavior. Although noteworthy attempts have been made to understand their coupled nature, the rudimentary concepts of inter-phase interactions that give rise to their mechanical nonlinearity remain insufficiently understood, and this impedes their further advancements. This holistic review addresses these standalone concepts and bridges the gaps by providing a thorough examination of their myriad fabrication techniques, applications, and experimental, and modeling approaches. Specifically, the review presents a wide spectrum of fabrication techniques, ranging from traditional molding to cutting-edge four-dimensional printing, and their unbounded prospects in diverse fields of research. The review covers various modeling approaches, including continuum mechanical frameworks encompassing phenomenological and homogenization models, as well as microstructural models. Additionally, it addresses emerging techniques like machine learning-based modeling in the context of hMSMs. Finally, the expansive landscape of these promising material systems is provided for a better understanding and prospective research.
The ability to precisely maneuver miniature objects in flow through a well‐controlled manner is envisaged to have an extensive impact in micro manipulation for profound medical and biological applications. In this work, the magnetic microrobots are fabricated by employing a distinct block‐to‐block approach in which the microrobotic structures are developed using several magnetic and nonmagnetic blocks. To demonstrate the on‐board control strategies of the microrobots, two distinct modes of motion are introduced and actuated with the aid of the developed in‐house electromagnetic system. To delve into the physics of microrobot locomotion, theoretical and numerical investigations are performed that further provide practical relevance for extensive applications with profound reliability. A mixing task is conducted to elucidate the enriched controllability of the microrobot in furnishing an on‐demand flow agitation function with high efficiency. Furthermore, the directions of such mixing are engineered using the proposed modes of motion which can unlock the possibilities to precisely control the directional inhomogeneities of the fluids encountered in diversely microfluidic systems. Aside from it, the multidimensional controllability of the microrobot motions exhibiting distinct flow behaviors is further demonstrated to precisely disperse the particles suspended in the fluid medium. Subsequently, such behaviors combined with the adaptive modes of microrobot motion can be potentially employed as one of the strategies to prevent the fouling problems encountered in several microfluidic applications. The presented work provides the feasible functions of the microrobots where they can play a pivotal role in dampening their functional limitations inherent in dynamic environment, and pave to emerge as fully autonomous microrobots for future engineering applications.
