Our bodies move because many muscle fibers work together. These fibers twitch and pull at the same time. Some muscles line up in one direction. Others form complex patterns. This teamwork lets us move in different ways.

Scientists and engineers study muscles to power biohybrid robots. Biohybrid means mixing living parts with machines. These robots use soft, lab-grown muscle fibers as actuators. Actuators are parts that make machines move. Bio-bots could wiggle through tight spaces. Regular robots with hard parts struggle there. Until now, artificial muscle only pulled one way. This limited how robots could move.

MIT engineers found a new way to grow artificial muscle. This muscle twitches and bends in many directions. They made a demo with a muscle-powered structure. It pulls inward and outward at once. This mimics the iris in our eyes. The iris controls the pupil’s size by shrinking or stretching.

The engineers created this artificial iris with a “stamping” method. They 3D-printed a small stamp with tiny grooves. Each groove is as small as one cell. They pressed the stamp into a soft hydrogel. Then they added real muscle cells to the grooves. The cells grew into fibers along the paths. When the team triggered the fibers, the muscle moved in many directions.

In an MIT press release, the engineers say their iris design shows a robot muscle moving more than one way. The stamp made this possible. The stamp can have different groove patterns. It’s printable with regular 3D printers. This could grow complex muscle or even other tissues like nerves.

Training space

The engineers want to build materials that act like real body tissues, and sense and respond like natural ones. They aim to use them in medicine and robotics. For example, they could repair damaged muscles. Or they could power soft robots that swim like fish. The engineers have made gel mats to grow muscle cells. They also engineered cells to twitch with light. Now, they can grow muscle that moves in multiple directions. This matches how real muscles work, like the iris or arm muscles. This work is published in Biomaterials Science.

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