The shape – morphing performance of magnetoactive soft materials

Magnetoactive soft materials (MSMs) are soft polymeric composites filled with magnetic particles that are an emerging class of smart and multifunctional materials with immense potentials to be used in various applications including but not limited to artificial muscles, soft robotics, controlled drug delivery, minimally invasive surgery, and metamaterials. Advantages of MSMs include remote contactless actuation with multiple actuation modes, high actuation strain and strain rate, self-sensing, and fast response etc. Having broad functional behaviours offered by the magnetic fillers embedded within non-magnetic matrices, MSMs are undoubtedly one of the most promising materials in applications where shape-morphing, dynamic locomotion, and reconfigurable structures are highly required. This review article provides a comprehensive picture of the MSMs focusing on the materials, manufacturing processes, programming and actuation techniques, behaviours, experimental characterisations, and device-related achievements with the current state-of-the-art and discusses future perspectives. Overall, this article not only provides a comprehensive overview of MSMs’ research and development but also functions as a systematic guideline towards the development of multifunctional, shape-morphing, and sophisticated magnetoactive devices

Smart material based on magnetorheological elastomer and its 3D printing

Intelligent or smart materials have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as temperature, pH, electric or magnetic fields, etc. Magnetorheological (MR) materials are a class of smart materials whose properties can be varied by applying an external magnetic field. Two major branches of the magnetorheological materials are MR fluids and MR elastomers. The MR fluids largely suffer from the sedimentation problem. Whereas, MR elastomers conquer the sedimentation problem, the price is to be paid for lower MR effect. For current MR elastomers, a need of magnetic field is mandatory during the fabrication process for the anisotropic configuration of the magnetic particles within the matrix material. However, the applied magnetic field does not promise a unique particle alignment. Similarly, main concerns of current MR elastomer-based applications such as vibration isolators and absorbers are a high-power requirement and bulky configuration. To this end, the focus of this study is to explore the development of hybrid MR elastomer that potentially bridges the gap between MR fluid and MR elastomer. Two different types of fabrication methods have been adopted, first is conventional molding and second is additive manufacturing also known as 3D printing. This is the first time to implement 3D printing method to develop MR elastomers, thus, feasibility and implementation of a new fabrication method, 3D printing has been studied in detail. Lastly, this study explores the techniques to lower the range of the magnetic field needed for the current MRE-based systems. In the conventional fabrication method, a cavity of an elastomer matrix was formed by molding and MR materials were deposited into the cavity to form an MR core within the elastomer matrix. Three different types of MR cores, namely, low viscosity fluid MR core, high viscosity fluid MR core, and solid MR core were considered. On the other hand, in a 3D printing method, extrusion-based multi-material printing was implemented, where MR fluid filaments were printed within an elastomer matrix in the layer-by-layer fashion. The choice of printing materials determines the final structure of the 3D printed hybrid MR elastomer. Printing with a vulcanizing MR suspension produces the solid MR structure inside the elastomer matrix while printing with a non-vulcanizing MR suspension (MR fluid) results in the structures that the MR fluid is encapsulated inside the elastomer matrix. The 3D printability of different materials has been studied by measuring their rheological properties and it was found that the highly shear thinning, and thixotropic properties are important for 3D printability. The quality of the printed filaments strongly depends on the key printing parameters such as extrusion pressure, initial height, feed rate and time. Two different patterned were considered in this study, namely, line-patterned and dot-patterned 3D printed MR elastomers (3DP-MREs), line-patterned samples were formed by continuous printing while dot-patterned samples were formed by discontinuous printing. The cyclic compression and forced vibration experimental testing show that both conventionally developed, and the 3D printed MR elastomers could change their elastic and damping properties when exposed to an external magnetic field. Furthermore, both core-shelled and 3D printed MR elastomers also exhibit an anisotropic behavior when the direction of the magnetic field is changed with respect to the orientation of the printed filaments or printed layers. Core-shell hybrid MR elastomer with high viscosity fluid core avoids the sedimentation issue of the current MR fluid and show a higher MR effect than that of current MR elastomers and also exhibits anisotropic MR effect. Similarly, the sedimentation and settling of magnetic particles are highly unlikely within the small MR fluid filaments in 3DP-MREs. The 3D printing method can develop different configurations of MR fluid or magnetic particles without applying a magnetic field. Putting together, 3DP-MREs or core-shell hybrid MREs with high viscosity fluid MR core are bridge materials between MR fluid and MR elastomers. Moreover, core-shell hybrid MR elastomer and 3DP-MREs also offer the low working range of magnetic field, the increase in the stiffness is much gentler after 300 mT magnetic field. Lastly, a new method was introduced for the development of MRE based vibration isolator by the simultaneous application of preloading and magnetic field. The vibration isolator can work in the low magnetic field range. The preloading effect was noteworthy for significant enhancing the performance of vibration isolator even in lower magnetic field strength.Doctor of Philosoph

Structural performance of a climbing cactus: making the most of softness

International audienceClimbing plants must reach supports and navigate gaps to colonize trees. This requires a structural organization ensuring the rigidity of so-called ‘searcher’ stems. Cacti have succulent stems adapted for water storage in dry habitats. We investigate how a climbing cactus Selenicereus setaceus develops its stem structure and succulent tissues for climbing. We applied a ‘wide scale’ approach combining field-based bending, tensile and swellability tests with fine-scale rheological, compression and anatomical analyses in laboratory conditions. Gap-spanning ‘searcher’ stems rely significantly on the soft cortex and outer skin of the stem for rigidity in bending (60–94%). A woody core contributes significantly to axial and radial compressive strength (80%). Rheological tests indicated that storage moduli were consistently higher than loss moduli indicating that the mucilaginous cortical tissue behaved like a viscoelastic solid with properties similar to physical or chemical hydrogels. Rheological and compression properties of the soft tissue changed from young to old stages. The hydrogel–skin composite is a multi-functional structure contributing to rigidity in searcher stems but also imparting compliance and benign failure in environmental situations when stems must fail. Soft tissue composites changing in function via changes in development and turgescence have a great potential for exploring candidate materials for technical applications

Approaches of combining a 3D-printed elastic structure and a hydrogel to create models for plant-inspired actuators

International audienceInspired by the interesting functional traits of a climbing cactus, Selenicereus setaceus, found in the forest formations of Southeastern Brazil, we formulated a hypothesis that we can directly learn from the plants to develop multi-functional artificial systems by means of a multi-disciplinary approach. In this context, our approach is to take advantage of 3D-printing techniques and shape-memory hydrogels synergistically to mimic the functional traits of the cactus. This work reports on the preliminary investigation of cactus-inspired artificial systems. First, we 3D-printed soft polymeric materials and characterized them, which defines the structure and is a passive component of a multi-material system. Second, different hydrogels were synthesized and characterized, which is an active component of a multi-material system. Finally, we investigated how the hydrogel can be integrated into the 3D-printed constructs to develop artificial functional systems. Graphic abstrac