A Small Victory in Robotics

Coming in at less than a centimeter in length, microrobots can go where no robot has gone before. In theory, these tiny machines could even roam about the human body to diagnose and treat diseases. But in practice, we are still a long way away from that goal. There are many technical hurdles arising from the tiny scale of these robots that must first be cleared before these dreams become a reality.

Today’s tiniest robots are very limited in their capabilities because it is extremely difficult to pack much useful hardware into a robot the size of a small ant. They are also, out of necessity, very much purpose-built. There is no extra room to be found, so microrobots are generally designed to do one thing and one thing only. Both of these factors significantly limit the adoption of these robots for any real-world applications.

A group led by researchers at Seoul National University is working to change everything we know about microrobots. They are building a modular robotics toolkit that makes it possible to design a small army of microrobots with diverse capabilities in a jiffy. These sub-centimeter robots can walk, navigate, and sense the environment around them, and they are almost entirely 3D-printed.

Instead of creating a single-purpose microrobot, the team developed a base body that can be outfitted with a variety of interchangeable modules. Each module provides a distinct function, and together they allow the microrobot to adapt to new environments or missions. The main body acts as the central control unit and houses the actuators that make the robot move. From there, specialized modules — such as feet for walking, heads for sensing or communication, and connectors for linking multiple robots — can be attached as needed.

To bring these modular microrobots to life, the researchers built a custom multi-material digital light processing 3D printer. Unlike ordinary 3D printers, this one can print multiple types of resins simultaneously, including soft, stiff, conductive, and dielectric materials, with a resolution as fine as 10 micrometers. This capability makes it possible to print all the mechanical, structural, and electrical parts of the robot in one go. It also allows the mass production of components: up to eight identical microrobot units can be printed in a single run.

An important contribution made by the team is a new type of dielectric elastomer actuator (DEA). Actuators are what make the robots move, and at this scale, they need to be both powerful and lightweight. So, the team developed a soft-stiff hybrid actuator that bends and flexes when an electric field is applied. The soft parts provide flexibility and displacement, while the stiff layers guide and amplify motion. This design gives the microrobots enough strength and range of motion to stride across sand, climb over obstacles, and even swim through water.

Different foot modules allow the robot to adapt to different environments. On flat ground, it can rely on electrostatic adhesion to grip and slide forward; on rough or granular surfaces, asymmetrical feet provide directional traction; and on water, a webbed, buoyant module lets the robot float and paddle.

The head modules expand their functionality even further. One version emits light signals to communicate with other robots, another detects approaching objects to avoid collisions, and a third senses ambient light levels. The team demonstrated real-time communication between microrobots, where a leader equipped with a light-emitting head directed a follower to move using optical signals.

These robots are neither small enough nor capable enough to swim through our bloodstream to provide medical therapies, but even so, this modular toolkit is a meaningful step forward for the field.