Poster printing

GelBot – A new 3D printing method to address sustainability in soft robots

3D printed vase deformed by human finger touch.

Future generations of robots will operate very differently from those that assemble entire vehicles or solder electronic components onto circuit boards at lightning speed in today’s factories. They will leave the factory halls and start working with people, handing them a tool at the right time or helping them assemble heavy components. They will appear in farming, helping to harvest fields or process fruit. And they will increasingly be found in living rooms, supporting and entertaining people or simply making them feel less alone.

Of course, these robots will also be different from the huge metal contraptions found in industrial factories today. Their appearance will change with their new functions. Whenever they come into contact with people, they will be soft and gentle so as not to hurt anyone – and “soft” here actually means that they are made of conformable materials; that their surface is elastic, flexible and extensible. Of course, they are at the same time equipped with comprehensive sensor technology that immediately registers every contact and every approach, so that they can react appropriately. Today, the development of these soft electronics and robotics relies mainly on synthetic materials such as silicone elastomers – a rubber with very good elastic properties but of fossil origin. It also means that if software bots become as ubiquitous in the future as smartphones are today, tech waste will increase dramatically again. This begs the question: Where are the biodegradable alternatives? And if they exist, how can we create truly autonomous robots that move, sense, and react to their environment?

Martin Kaltenbrunner, director of the Flexible Materials Laboratory at Johannes Kepler University in Linz, Austria, is investigating these sustainable alternatives for our future technologies. His team focuses on technologies that interface with the human body and, therefore, are equally soft and conformable. Wearable electronics, expandable power sources, and biomimetic robots are just a few examples. And by addressing sustainability, his team is adding a new twist to these soft technologies.

The scientific breakthrough was achieved in 2020, when Kaltenbrunner and his team discovered a frugal way to make biodegradable gels (biogels) that are extremely strong and long-lasting, but which disappear when they are disposed of. Based on the abundant biopolymer gelatin, their material had similar properties and performance to non-degradable silicone rubbers, paving the way for its use in soft robots.

Now, PhD students Andreas Heiden and David Preninger have built a system to 3D print this biogel into complex shapes. They printed finger-like robots that use complex sensor networks to detect their own deformation as well as objects in their environment. With Florian Hartmann, materials engineer at EPFL, they published their research in the famous journal Science Robotics.

Nature as a source of inspiration

Soft robotics takes great advantage of nature as a source of inspiration, introducing innate means of safe interaction between robotic devices and living organisms. Kaltenbrunner soon realized that although soft robotics was largely inspired by nature, one “characteristic” inherent in nature’s creations was missing: biodegradability. Once a soft robot has reached its end of life, there is often no easy way to recycle its components or deal with waste in an environmentally friendly way.

Introducing biodegradable materials into soft robotics seems like the logical solution, but existing materials were simply not durable enough or were difficult to process. Kaltenbrunner and his team were driven to design bioderived materials such as biopolymer gelatin-based gels, which can match the performance of conventional synthetic elastomers, but completely degrade after their intended use – leaving virtually no trace of their existence. About two years ago, published in the journal Nature Materials, they optimized these gels for use in electronics on the skin and for soft robots. Based on natural materials as degradable and durable building blocks, it is a widely applicable gelatin-based biogel that unites the challenging needs of resilient yet durable (soft) robots in a single platform. It is very stretchy and elastic – and its thermoplastic. An attribute that allows the material to melt when heated and makes it perfectly suited for 3D printing.

Complex shapes thanks to 3D printing

The deformable structure of soft robots poses challenges in manufacturing and assembly. Unlike conventional robots which are screwed together from individual parts, soft robots are made as monolithic blocks. To this end, 3D printing is a versatile manufacturing strategy that can also produce complex objects. Heiden and Preninger designed a custom system based on Fused Deposition Modeling (FDM) to print their biogel. FDM is one of the most common 3D printing methods today and relies on fusing molten polymers that return to solid when cooled. To imprint the biogel, the material is melted in a medical syringe and squeezed through the tip, leading to the deposition of a “thread” of biogel that quickly solidifies after extrusion. In this way several two-dimensional layers are then drawn, stacked on top of each other, to form the three-dimensional object.

XYZ calibration cube and gummybear model printed from gelatin-based biogel ink.

But what if a print fails? Usually you discard your print and restart. With a biodegradable solution, you don’t even have to worry about waste generation. Along with this green manufacturing approach using biodegradable materials, we have introduced an additional reuse cycle where the biogel is reprinted up to 5 times, maintaining over 70% of original performance metrics. Using such approaches for a circular economy will enable more sustainable solutions for less degradable materials.

Omnidirectional actuators with perception

By extending the fabrication of biodegradable gels to 3D printing, researchers have been able to produce versatile flexible actuators in various complex shapes and even include embedded sensor networks to let them interact with their surroundings. In their publication on scientific robotics, they demonstrated a finger-like actuator that is powered by pressurized air and can bend in any direction, similar to an elephant’s trunk or a tentacle of octopus. A combination of three inflatable chambers inside the actuator and the use of a cotton-textile reinforcement make this movement possible.

Fully actuated 3-chamber actuator with integrated sensor array detects human finger touch.

Additionally, the actuator features a distributed sensor array based on the transmission of light through transparent materials. These sensors acquire information about the flex state of the actuator, as well as the impact with objects in its environment. Without having eyes, this robot is able to detect an obstacle and remove it from its vicinity. The function of this unique robotic element demonstrates that motion and sensing can be achieved with durable materials and manufacturing solutions, without making big compromises in performance. And once they are no longer useful, they can simply be discarded. Its immersion in water causes the swelling and dissolution of the biogel and, in the presence of enzymes, its complete decomposition.

tags: c-Research-Innovation


Martin Kaltenbrunner is Full Professor at Johannes Kepler University Linz, Head of the Division of Soft Matter Physics and the Soft Materials Laboratory at LIT.

Martin Kaltenbrunner is Full Professor at Johannes Kepler University Linz, Head of the Division of Soft Matter Physics and the Soft Materials Laboratory at LIT.


Florian Hartmann is a post-doctoral researcher at EPFL’s Soft Transducer Laboratory.

Florian Hartmann is a post-doctoral researcher at EPFL’s Soft Transducer Laboratory.


Andreas Heiden holds a doctorate. student in the division of soft matter physics and the soft materials laboratory of the LIT of the Johannes Kepler University of Linz.

Andreas Heiden holds a doctorate. student in the division of soft matter physics and the soft materials laboratory of the LIT of the Johannes Kepler University of Linz.


David Preninger holds a Ph.D. student in the division of soft matter physics and the soft materials laboratory of the LIT of the Johannes Kepler University of Linz.

David Preninger holds a Ph.D. student in the division of soft matter physics and the soft materials laboratory of the LIT of the Johannes Kepler University of Linz.