3D Printing Solved a Tissue Issue

If nothing else, building a robot is a humbling experience that will give a person an appreciation for the design of the human body. The nervous system, brain, and muscles far surpass the capabilities and efficiency of even the most advanced artificial sensing, control, and actuation systems ever built. Take actuation systems, for instance. While recent advances have made them quite fluid in their movements, they are still big, bulky energy hogs when compared with biological muscle tissue.

If you can't beat them, borrow them. Many researchers in the field have adopted this mantra because biological systems are so advanced that our only realistic hope of mimicking them appears to be far off in the future. This has resulted in some interesting — yet highly experimental — research efforts in which natural muscle tissue has been integrated into robots for actuation.

But these efforts are still fraught with problems because the human body is such a tightly integrated machine. Growing cells outside of the body, then expecting them to act as they do in vivo does not pan out in the real world. For one thing, these tissues tend to be restricted in their movements, which means the robots that leverage them will have a limited range of motion.

Engineers at MIT have moved the state of the art forward in this area by developing a technique that gives lab-grown muscle tissues a much more natural range of motion. Their method involves a novel “stamping” approach that enables artificial muscles to contract in multiple directions, just like natural muscle fibers.

The key to this work is a 3D-printed stamp with microscopic grooves, each as small as a single cell. By pressing this stamp into a soft hydrogel and seeding it with muscle cells, researchers create a structured environment that guides the muscle fibers to grow in specific patterns. Unlike previous artificial muscle tissues, which primarily contracted in a single direction, these new structures can flex and move in complex ways.

The researchers designed the stamp so it can be fabricated using standard 3D printing techniques, meaning labs around the world can replicate and build upon this work without needing expensive, specialized equipment. The reusable nature of the stamp further enhances its practicality, reducing costs and making it easier to scale up production.

In one demonstration of this technology, the team created a biohybrid structure modeled after the human iris. In nature, the iris controls the size of the pupil using concentric and radial muscle fibers that work together to dilate and constrict the opening. The MIT team replicated this design by using their stamping method to create an artificial iris embedded with genetically engineered muscle cells. These engineered cells respond to light, allowing researchers to control their contractions and mimic the natural movement of the eye’s pupil.

Looking ahead, the team aims to refine their technique by exploring different muscle architectures and integrating other cell types, such as neurons and heart cells. By combining these elements, they hope to develop even more sophisticated biohybrid robots capable of performing complex tasks with the efficiency and adaptability of living organisms.