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The variability in the shapes and sizes of objects presents a significant challenge for two-finger robotic grippers when it comes to manipulating them. Based on the chemistry of vitrimers (a new class of polymer materials that have dynamic covalent bonds, which allow them to reversibly change their mechanical properties under specific conditions), we present two designs as 3D-printed shape memory polymer-based shape-adaptive fingertips (SMP-SAF). The fingertips have two main properties needed for an effective grasping. First, the ability to adapt their shape to different objects. Second, exhibiting variable rigidity, to lock and retain this new shape without the need for any continuous external triggering system. Our two design strategies are: 1) A curved part, which is suitable for grasping delicate and fragile objects. In this mode and prior to gripping, the SMP-SAFs are straightened by the force of the parallel gripper and are adapted to the object by shape memory activation. 2) A straight part that takes on the form of the objects by contact force with them. This mode is better suited for gripping hard bodies and provides a more straightforward shape programming process. The SMP-SAFs can be programmed by heating them up above glass transition temperature (54°C) via Joule-effect of the integrated electrically conductive wire or by using a heat gun, followed by reshaping by the external forces (without human intervention), and subsequently fixing the new shape upon cooling. As the shape programming process is time-consuming, this technique suits adaptive sorting lines where the variety of objects is not changed from grasp to grasp, but from batch to batch.

Although the integration of healing mechanisms in soft robots is still quite novel, some impressive self-healing soft robotic prototypes have been presented in academics in the last five years. These advances on the application level, reveal limitation of SH polymers and push the material development towards increasing mechanical and healing performance and including additional functionalities. To achieve the final goal of a soft robot that detects and heals macroscopic damage autonomously, multiple technologies like SH polymers, SH sensors, smart motion controllers, health monitors and integrated stimulus providing devices, must be combined in an intelligent system. The authors believe that the fast advances in the subfields, show that this ambitious objective will be achieved in the coming five years. It is however important to involve material scientists at every stage, such that they get clear insights in the requirements and needed improvements for the materials. A synergetic relation between all fields will result in mutual benefits.

Self-healing polymers can address the damage susceptibility in soft robotics. However, in most cases, their healing requires a heat stimulus, provided by an external device. This paper presents a self-healing soft actuator with an integrated healable flexible heater, functioning as the stimuli-providing system. The actuator is constructed out of thermoreversible elastomers that are crosslinked by the Diels-Alder (DA) reaction, which provides the healing ability. The heater is manufactured from a DA-based composite network filled with 20 wt% carbon black to provide electrically conductive properties for resistive Joule heating. The flexibility of the heater does not compromise the actuator performance upon integration and the self-healing properties of both heater and actuator allow for damage repair. This includes very large damages, as both heater and actuator can recover (near 100%) from being cut completely in two pieces, using Joule heating at 90 °C with a bias voltage of about 30 V. The embedded heater, avoids the need for external intervention in the healing process, and provides healing quality assessment and a healing on-demand mechanism, paving the way for an optimum healing solution of damage resilient soft robots that require heat as a healing stimulus.

Self-healing materials can prolong the lifetime of structures and products by enabling the repairing of damage. However, detecting the damage and the progress of the healing process remains an important issue. In this study, self-healing, piezoresistive strain sensor fibers (ShSFs) are used for detecting strain deformation and damage in a self-healing elastomeric matrix. The ShSFs were embedded in the self-healing matrix for the development of self-healing sensor fiber composites (ShSFC) with elongation at break values of up to 100%. A quadruple hydrogen-bonded supramolecular elastomer was used as a matrix material. The ShSFCs exhibited a reproducible and monotonic response. The ShSFCs were investigated for use as sensorized electronic skin on 3D-printed soft robotic modules, such as bending actuators. Depending on the bending actuator module, the electronic skin was loaded under either compression (pneumatic-based module) or tension (tendon-based module). In both configurations, the ShSFs could be successfully used as deformation sensors, and in addition, detect the presence of damage based on the sensor signal drift. The sensor under tension showed better recovery of the signal after healing, and smaller signal relaxation. Even with the complete severing of the fiber, the piezoresistive properties returned after the healing, but in that case, thermal heat treatment was required. With their resilient response and self-healing properties, the supramolecular fiber composites can be used for the next generation of soft robotic modules.

Intrinsic self-healing polymer networks were developed based on dynamic covalent bonding by means of thermoreversible Diels-Alder (DA) cycloadditions. The DA bonds are preferentially broken in case of damage, but also reversibly reform, leading to a repeatable healing cycle and an increased lifetime for many applications, such as sustainable coatings [1], [2]. However, thermo-mechanical robustness is requiring a network in the (partially) vitrified state, with a sufficient-ly high Tg. This work focuses on the effect of vitrification on DA reaction kinetics, using fully reversible model systems of furan and maleimide compounds. In bulk, using (MT)DSC, vitrification is followed through (non-)isothermal heat capacity meas-urements, while non-isothermal microcalorimetry provides heat flow information. These results are used to optimize the parameters of a kinetic model, consid-ering the DA endo−exo stereochemistry. In addition, dynamic rheometry allows the construction of time-temperature-transformation (TTT) and continuous-heating-transformation (CHT) diagrams for both reversible elastomers and thermo-sets [3]. A double asymptotic behavior of the isoconversion lines is revealed, and also two subsequent gelation/degelation events can occur during non-isothermal curing. This bulk study was extended towards thin films through AC chip calorime-try, yielding preliminary results to compare vitrification in bulk and thin layers. This work is the first systematic study of diffusion-controlled reversible DA network formation. The DA reaction was proven to proceed in diffusion-controlled conditions, allowing self-healing in mobility-restricted applications [2], [4].