A team of researchers from the University of Maryland has 3D-printed a soft robotic hand agile enough to play Nintendo’s Super Mario Bros.—and win.

The feat, highlighted on the cover of the latest issue of Science Advances, demonstrates a promising innovation in the field of “soft robotics,” which creates new types of flexible, inflatable robots powered by water or air rather than electricity. Soft robots’ inherent safety and adaptability have sparked interest in their use for applications like prosthetics and biomedical devices. Unfortunately, controlling the fluids that make these soft robots bend and move has been especially difficult.

But in a key breakthrough, the team led by Ryan D. Sochol, assistant professor of mechanical engineering, developed the ability to 3D-print fully assembled soft robots with “integrated fluidic circuits” in a single step.  

“Previously, each finger of a soft robotic hand would typically need its own control line, which can limit portability and usefulness,” said the publication’s co-first author, Joshua Hubbard ’19. Now pursuing a Ph.D. in chemical and biomolecular engineering at the University of California, Berkeley, he performed the research while an undergraduate researcher in Sochol’s Bioinspired Advanced Manufacturing (BAM) Laboratory at UMD. “But by 3D-printing the soft robotic hand with our integrated ‘fluidic transistors,’ it can play Nintendo based on just one pressure input.”

As a demonstration, the team designed an integrated fluidic circuit that allowed the hand to operate in response to the strength of a single control input. For example, applying  low pressure caused only the first finger to press the Nintendo controller to make Mario walk, while a high pressure led to the character jumping. Guided by a set program that autonomously switched between off, low, medium and high pressures, the robotic hand was able to complete the first level of Super Mario Bros. in fewer than 90 seconds.

“Recently, several groups have tried to harness fluidic circuits to enhance the autonomy of soft robots,” said co-first author of the study, Ruben Acevedo Ph.D. ’21. “But the methods for building and integrating those fluidic circuits with the robots can take days to weeks, with a high degree of manual labor and technical skill.”

To overcome these barriers, the team turned to “PolyJet 3D Printing,” which is like using a color printer, but with many layers of multimaterial “inks” stacked on top of one another.  

“Within the span of one day and with minor labor, researchers can now go from pressing ‘start’ on a 3D printer to having complete soft robots—including all of the soft actuators, fluidic circuit elements and body features—ready to use,” said study co-author Kristen Edwards ’20, now studying for a Ph.D. in mechanical engineering and machine learning at the Massachusetts Institute of Technology.

The choice to validate their strategy by beating the first level of Super Mario Bros. in real time was motivated by science just as much as it was by fun. Because the video game’s timing and level make-up are established, and just a single mistake can lead to an immediate game over, playing Mario provided a new means for evaluating soft robot performance that is uniquely challenging in a manner not typically tackled in the field.

In addition to the Nintendo-playing robotic hand, Sochol’s team also reported turtle-inspired soft robots in their paper, and all of the team’s soft robots were printed at UMD’s Terrapin Works 3D-printing hub.

The team’s strategy is “open source,” with the paper available for anyone to read, and it includes a link in the supplementary materials to a GitHub with all of the electronic design files from their work.

“(A)nyone can readily download, modify on demand and 3D-print—whether with their own printer or through a printing service like us—all of the soft robots and fluidic circuit elements from our work,” said Sochol. “It is our hope that this open-source 3D-printing strategy will broaden accessibility, dissemination, reproducibility and adoption of soft robots with integrated fluidic circuits and, in turn, accelerate advancement in the field.” 

The team is exploring the use of its technique for biomedical applications including rehabilitation devices, surgical tools and customizable prosthetics. Sochol is a faculty affiliate of the Fischell Department of Bioengineering and well as a member of both the Maryland Robotics Center and the Robert E. Fischell Institute for Biomedical Devices, providing a fertile environment to continue advancing the team’s strategy to address pressing biomedical challenges.