Swedish researchers successfully 4D print micron-scale soft robots

China3D printingA team of researchers from Linköping University in Sweden used a custom extrusion-based3D printingMachine developed a set of micro-actuators for micro-robots. The actuator contains an electroactive polymer that, after printing, changes shape when charged, giving it 4D functionality.

While 4D printed soft robots are usually limited to the centimeter or millimeter scale, specially developed techniques allow researchers to shrink their actuation mechanisms down to the micrometer range, with a thickness of about 20 micrometers. They claim their custom machine is versatile and scalable, and hope to “expand the range of soft robotics” with previously unseen complex microrobots.




The smallest 4D printed microrobot. Image via Linköping University.

Electroactive Polymer Technology

Electroactive polymer (EAP) technology is the driving force behind many soft robotic devices. It describes a material that activates or activates when subjected to an electric charge. In soft robotics, this is equivalent to a muscle contraction (and often looks like one).
According to the researchers, trying to reduce the size of EAP actuators often presents many challenges. Microfabrication techniques such as photolithography enable lower drive potentials and higher power-to-weight ratios, but tend to involve complex processes. This makes it difficult to integrate them with current markets and technologies.

Here, additive manufacturing offers many benefits, as products can be modified on the fly, significantly reducing energy costs and reducing waste generation by a factor of ten. Ultimately, the team believes, this could make EAP devices cheaper and more feasible for a wider range of applications.


4D printed microactuators

The first phase of the research involved building the printer. The basis of the machine is a three-axis programmable CNC table, equipped with a high-precision fluid distribution system. Attached to the dispensing system is a 5mL locking syringe, allowing for lateral movement of the platform to control the extrusion rate. The team used commercially available glass slides as templates.
They first placed a thin layer of gold just 40nm thick on a glass slide to create a conductive layer. The researchers then used a syringe to dispense a layer of UV-curable urethane acrylate gel onto the conductive layer. The gel will go on to form the “body and arms” of the microactuator. After the gel was fully cured under UV light, the team deposited a layer of polypyrrole (EAP) on the other side of the gold sheet.


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Customized3D printingmachine. Image courtesy of Linköping University.

The team managed to repeat the process multiple times, printing microactuators with lengths ranging from 5,000 microns all the way up to 1,000 microns. The thinnest microactuator they developed was only 20 microns thick.The researchers found that with other3D printingThey can start devices at potentials as low as 1V compared to the typical 1kV+ method.Scientists believe that their work shows that through3D printingTechnology has huge potential to miniaturize low-cost microrobots.



Drive down to 1V. Image via Linköping University.

There are many different actuation methods for 4D printed soft robots – electrical actuation is one of them. Rice University researchers recently 4D printed their own soft robots that activate in response to changes in temperature. They intend to develop the technology to the point where it can be used in biomedical implants that reconfigure themselves on demand.

Elsewhere, Nanyang Technological University researchers have gone a step further, printing soft robots that do not require any real-time human input at all. The process involves swelling the elastomer with ethanol to induce stress in the structure of the actuator. As the ethanol evaporates on its own and the elastomer dries, the material deforms due to the elastic energy inherently stored in it.

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