RoboAICon2023: Hydrogel-based, magnetically controlled smart transformers

Researchers are creating clever soft transformers to drastically speed up research applications in the lab, much like the intelligent robots that appeared in the "Transformers" movie that could change shapes and function in many ways. Dachuan Zhang and a research team in materials science and chemical sciences in China have presented a remotely controlled soft transformer based on a shape memory hydrogel system. The paper has now been published in Advanced Intelligent Systems. By incorporating magnetite (Fe3O4) magnetic nanoparticles into a double network polymer structure of poly (N-(2-hydroxyethyl) acrylamide) containing gelatin, the research team was able to produce the hydrogel. 

While the magnetite nanoparticles provided photothermal heating and magnetic manipulation functions to distort the hydrogel for navigation in a magnetic field, the reversible coil-triple-helix transformation of the gelatin component gave the hydrogel shape memory and self-healing properties. The team then used shape recovery with laser irradiation to regain the distorted shape. Through magnetically powered actuation and light-assisted shape memory, Zhang et al. were able to remotely control the shape-memory processes. They developed a number of robots as proof of concept, including a hydrogel spacecraft that can dock in the air, hydrogel transformers, a lotus in full bloom, and a hydrogel athlete that could perform sit-ups. The project will serve as an inspiration for the creation of innovative smart polymer systems with coordinated multifunctionalities.

Hydrogels with shape memory 

Soft transformers are of higher interest in fundamental research and applications in the biological sciences, whereas the fictional Transformers permitted hard robots to morph into any form, including vehicles. A photothermally and magnetically controlled shape memory hydrogel was described by Zhang et al. in this work. They created a photothermal, flexible, self-healing construct that could be magnetically controlled by combining a chemically crosslinked polymer with a reversibly crosslinked gelatin network embedded with magnetite nanoparticles. Researchers are focusing more on shape memory hydrogels (SMHs) as intelligent polymeric materials with the goal of remotely controlling these materials to create a variety of actuation behaviours.

For instance, shape-memory polymers, which have gained interest in the fields of biomedicine, textiles, flexible electronics, and data encryption, may fix transient shapes and recover its architecture in response to external stimuli. To incorporate remotely controlled non-contact actuation, magnetic nanoparticles are useful additions. These magnetic nanoparticles will continually transform light into heat when near-infrared (NIR) light is shone upon hydrogels, heating the hydrogel. The hydrogel will undergo reversible deformation, making it suitable for use in soft robots that can move around freely. This tactic will support the creation of novel shape memory hydrogel systems for use in untethered robot applications.

Qualities of hydrogels with shape memory 

The scientists performed bending experiments with the material, which they referred to as HG for its constituent polymers because it can stably and briefly memorise its shape and regain the previous shape exactly under certain stimuli. They then withdrew the sample from the medium and retrieved the forms by re-immersing hydrogels in hot water (60 degrees Celsius) for 30 seconds to induce disaggregation and soften the hydrogel (60 degrees Celsius). A number of carefully monitored experiments were carried out by Zhang et al. to confirm the variables influencing the hydrogel's ability to retain its structure. The group created a hydrogel flower that flawlessly resembled a lotus bloom as a proof of concept.

The HG-Fe3O4 hydrogel was created by adding magnetite nanoparticles, and as a result of the constituents' ability to absorb and convert light to heat with light irradiation, the hydrogel's temperature rose. The material attained photo-activated self-healing during the light to heat conversion process. The researchers developed a space station made of HG-Fe3O4 hydrogel under a magnetic field to illustrate this phenomenon. They then used NIR to irradiate the connections and dock the spacecraft-like construct with the space station-like connector to achieve self-healing and reconnection in air.

Using photothermal effects to recover forms and remotely managing shape memory operations 

In the absence of magnetite nanoparticles, the scientists discovered that form recovery for the HG-hydrogel could only be accomplished by controlling the temperature to a particular value. The HG-Fe3O4 hydrogel now has magnetic characteristics thanks to the inclusion of magnetite, enabling remotely controlled shape memory recovery cycles. The researchers created a shape-transition robot in the shape of a hydrogel athlete to deform from 2-D to 3-D as a proof of concept. The hydrogel athlete could "push up" quickly in the absence of NIR and the presence of a magnet, then swiftly return to its flat conformation after the magnet was removed. In the second configuration, NIR was activated, and a magnet was used to elevate the hydrogel athlete.

In order to steer the construct for directional navigation, the scientists additionally made use of the interaction between permanent magnets and the component magnetite nanoparticles of the HG-Fe3O4 hydrogel. They demonstrated how magnet-induced directional navigation may lead a soft transformer around a maze using the hydrogel. Including experimental ideas have the potential to be used as soft carriers for a variety of biomedical purposes, such as drug administration and release.

The future of soft transformers in the biological sciences 

By doing this, Dachuan Zhang and colleagues created a fresh and efficient technique for creating soft hydrogel transformers with integrated magnetic and photothermal capabilities. The resulting HG-Fe3O4 hydrogels included noncontact shape deformation, magnetic actuation, photothermal performance, self-healing, and directional navigation in both water and air, among other very favourable characteristics. The researchers created a number of soft robot proof-of-concepts to illustrate the SMH system's dynamic capabilities, and they hope that this design concept can motivate the creation of new intelligent systems for use in bioengineering and biomedicine.

Journal information: Nature