About this Research Topic
Active structures display the key features of smart behaviour, i.e. the possibility to sense external stimuli and respond with a specific action, as well as adaptability, i.e. the ability to change shape or properties to cope with environmental changes. In addition, no need for continuous external power/mechanical stimulus is required for such a response and a large set of possible stimuli (heat, solvent absorption, pH changes, light, electrical and magnetic fields) may be employed. Actively moving structures are able to convert a stimuli-responsive behaviour into a macroscopic movement and this can be achieved either thanks to the material’s intrinsic shape memory behaviour or to a specific microstructural arrangement, or even to a combination of both features. As a consequence, the active structure response relies on a finely engineered choice of materials, shapes and microstructures.
The interest towards the realization of polymer-based active structures was driven in an early stage by the aim of obtaining shape memory polymers with tailored properties and to employ them in innovative applications: this large scientific effort contributed to a great understanding of this peculiar response and highlighted a variety of possible shape memory effects for specific polymer families. The second rise of interest stemmed from the emerging 3D-printing technologies: in fact, the so-called “4D-printing” assessed the possibility to obtain active structures based on inherently shape-changing materials and/or on properly structuring the material in multi-material assembly or in combination with specific printing strategies, such as layering materials with built-in programmed stress to later be exploited for self-assembly or soft actuation.
However, in spite of a large amount of research in these fields, some aspects may be still considered frontier topics within the progress of active structures, and this regards in particular, the ability to obtain a fully reversible response and to fully exploit it in softly actuated systems.
This Research Topic focuses on various aspects related to actively moving polymers, and in particular on synthesis/preparation, characterization and modelling of polymer-based systems capable of reversible motion, providing also some examples, proof of concepts and applications cases. Areas of interest could include but are not limited to:
• Polymer systems inherently capable of reversible motion: two-way shape memory polymers; reversible (or stress-free) two-way shape memory polymers; 3D-printing of reversible shape memory polymers
• Polymer-based systems capable of structurally-driven reversible motion: multi-material printing, composite materials or functionally graded materials; polymer-based bi-stable and multi-stable structures
• Polymer-based actively moving structure: exploitation of reversible motions in structures; processing and assembly of actively moving structures; application of active structures in soft robotics
Keywords: shape memory, polymers, reversible actuation, actuation, 4D printing, 4D printed actuators, 4D printed metamaterials, metamaterials, soft robotics, shape changing polymers
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