Artificial muscle fibres grown in a lab may allow robots of the future to be more supple in their movements, making them better able to access and navigate awkward spaces.
The human body moves thanks to the coordination of many skeletal muscle fibres that twitch and pull in sync. While some muscles align in one direction, others form intricate patterns that help parts of the body move in intricate ways.
In recent years, scientists and engineers have looked to muscles as potential actuators for ‘biohybrid’ robots – machines powered by soft, artificially grown muscle fibres. Such bio-bots could squirm and wiggle through spaces where traditional machines cannot.
For the most part, however, researchers have only been able to fabricate artificial muscle that pulls in one direction, limiting any robot’s range of motion.
Now, however, engineers at the Massachusetts Institute of Technology (MIT) say they have developed a method to grow artificial muscle tissue that twitches and flexes in multiple coordinated directions.
As a demonstration, they grew an artificial, muscle-powered structure that pulls both concentrically and radially, much like how the iris in the human eye acts to dilate and constrict the pupil.
The researchers fabricated the artificial iris using a new ‘stamping’ approach they developed. First, they 3D-printed a small, handheld stamp patterned with microscopic grooves, each as small as a single cell. Then they pressed the stamp into a soft hydrogel and seeded the resulting grooves with real muscle cells. The cells grew along these grooves within the hydrogel, forming fibres. When the researchers stimulated the fibres, the muscle contracted in multiple directions, following the fibres’ orientation.
Ritu Raman, the Eugene Bell career development professor of tissue engineering in MIT’s Department of Mechanical Engineering, said: “With the iris design, we believe we have demonstrated the first skeletal muscle-powered robot that generates force in more than one direction. That was uniquely enabled by this stamp approach.”
The team says the stamp can be printed using tabletop 3D printers and fitted with different patterns of microscopic grooves. The stamp can be used to grow complex patterns of muscle – and potentially other types of biological tissues, such as neurons and heart cells – that look and act like their natural counterparts.
Raman added: “We want to make tissues that replicate the architectural complexity of real tissues. To do that, you really need this kind of precision in your fabrication.”
Machines made flesh
Raman’s lab at MIT aims to engineer biological materials that mimic the sensing, activity, and responsiveness of real tissues in the body. Broadly, her group seeks to apply these bioengineered materials in areas from medicine to machines. For instance, she is looking to fabricate artificial tissue that can restore function to people with neuromuscular injury. She is also exploring artificial muscles for use in soft robotics, such as muscle-powered swimmers that move through the water with fish-like flexibility.
When the team stimulated their artificial iris with pulses of light, the muscle contracted in multiple directions, similar to the iris in the human eye. Raman notes that the team’s artificial iris is fabricated with skeletal muscle cells, which are involved in voluntary motion, whereas the muscle tissue in the real human iris is made up of smooth muscle cells, which are a type of involuntary muscle tissue. They chose to pattern skeletal muscle cells in an iris-like pattern to demonstrate the ability to fabricate complex, multidirectional muscle tissue.
“In this work, we wanted to show we can use this stamp approach to make a ‘robot’ that can do things that previous muscle-powered robots can’t do,” Raman says. “We chose to work with skeletal muscle cells. But there’s nothing stopping you from doing this with any other cell type.”
She notes that while the team used precision-printing techniques, the stamp design can also be made using conventional tabletop 3D printers. Going forward, she and her colleagues plan to apply the stamping method to other cell types, as well as explore different muscle architectures and ways to activate artificial, multidirectional muscle to do useful work.
“Instead of using rigid actuators that are typical in underwater robots, if we can use soft biological robots, we can navigate and be much more energy-efficient, while also being completely biodegradable and sustainable,” Raman says. “That’s what we hope to build toward.”
She and her colleagues published their results in the journal Biomaterials Science.
Credit: Untitled Title/Shutterstock
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