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Scientists Discover Way to Send Information into Black Holes Without Using Energy

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Tiny Robots That Can Swim Inside Your Body And Scientists Can Control Them With Magnets!

Micro- and nanorobots—machines so small that thousands of them could fit on the tip of a needle—are rapidly transforming the way scientists think about medicine, engineering, and environmental science. Though invisible to the naked eye, these tiny devices carry enormous potential. From delivering drugs directly inside the human body to cleaning polluted water at a microscopic level, they could redefine how we solve some of the world’s biggest challenges.

One of the most promising ways to control these robots is through magnetic fields. Unlike chemical fuels or electrical connections, magnetic fields can act from a distance, pass through biological tissues, and precisely guide movement without direct contact. This makes them especially useful for operating in liquid environments such as blood, water, or other fluids.

Why Magnetic Fields Matter

To understand how magnetic fields move these tiny robots, imagine trying to push a small object floating in water using a force from far away. One method is to use magnetic field gradients—variations in magnetic strength that pull objects toward a source. While effective at short distances, these forces weaken very quickly as distance increases. In fact, they decrease extremely fast, making them less practical when the magnetic source is not close to the robot.

A more efficient approach is to use uniform magnetic fields that create torques, or rotational forces, on magnetic materials. These torques do not weaken as quickly over distance, making them better suited for controlling microscopic robots remotely. However, rotation alone does not automatically result in forward movement. The real challenge lies in converting this spinning motion into actual movement through a fluid.

Turning Rotation into Motion

Scientists have developed clever strategies to convert rotational motion into forward movement. These strategies fall into three main categories: propelling, rolling, and swimming.

1. Propelling: Like Tiny Helicopters in Liquid

Propellers are microscopic structures that spin when exposed to rotating magnetic fields. Due to the interaction between the rotating structure and the surrounding fluid, this spinning motion pushes the robot forward—similar to how a boat’s propeller works.

Interestingly, many of these propellers can also behave like rollers if they come close to a surface. This overlap shows that these categories are not strictly separate, and a single structure can perform multiple types of motion depending on its environment.

2. Rolling: Moving Along Surfaces

Rollers are robots that move by rolling along a surface when exposed to magnetic fields. The surface provides the necessary asymmetry and resistance, allowing rotation to translate into forward motion. This is similar to how a wheel rolls along the ground instead of spinning in place.

3. Swimming: Inspired by Nature

Swimming robots are perhaps the most fascinating. These devices change their shape in a repeating cycle, creating motion similar to how bacteria or sperm cells move. Unlike propellers or rollers, swimmers rely on flexible structures that bend and twist in response to magnetic fields.

The Physics Behind the Movement

At such tiny scales, the rules of motion are very different from what we experience in everyday life. Micro- and nanorobots operate in what scientists call a low Reynolds number environment. In simple terms, this means that fluid resistance (like viscosity) dominates over inertia.

In this regime, motion is governed by the Stokes equations, which describe how fluids behave under these conditions. One important consequence of this is the Scallop Theorem, a principle stating that simple back-and-forth (reciprocal) motion cannot produce net movement at these scales.

To visualize this, imagine opening and closing a scallop shell in water. If the motion is perfectly symmetrical, the scallop ends up in the same place after each cycle. The same applies to tiny robots—if they move in a purely reciprocal way, they won’t go anywhere.

To overcome this limitation, robots must perform non-reciprocal motion, such as continuous rotation or asymmetric shape changes. This breaks the symmetry and allows them to move forward.

Another important factor is symmetry breaking. For a robot to move, it must have some form of asymmetry—either in its shape, motion, or environment. For example:

  • Rollers rely on the presence of a nearby surface

  • Propellers require asymmetrical shapes

  • Swimmers often use a head-and-tail design

Without such asymmetry, motion would cancel out, leaving the robot stationary.

A Surprising Discovery: One Structure, Multiple Motions

Traditionally, scientists designed micro-robots for a single type of movement—either propelling, rolling, or swimming. However, recent research by Thomas Vach and Damien Faivre has challenged this idea.

Their work shows that randomly shaped magnetic nanostructures, created through chemical synthesis, can perform all three types of motion. This is a significant shift from earlier approaches that relied on carefully engineered designs.

Even more surprising is their observation of swimming behavior. Individual rigid nanostructures cannot swim on their own due to the constraints of the Scallop Theorem. However, when multiple particles come together and form chain-like structures under a magnetic field, they can collectively behave like swimmers.

This phenomenon is known as magnetically guided self-assembly, where particles spontaneously organize into functional structures. Once assembled, these chains can move through fluids in ways that were previously thought impossible for such simple components.

Unexpected Directions of Motion

Another intriguing finding from this research is that the direction of movement is not always aligned with the shape of the structure. In some cases, chain-like assemblies swim in directions that are not parallel to their length.

While this behavior had been predicted theoretically, it had not been observed experimentally until now. This discovery highlights the complex interactions between magnetic forces, fluid dynamics, and structural geometry at the nanoscale.

Why This Matters

These findings expand our understanding of what is possible with magnetic actuation. Instead of designing highly specialized robots for each task, scientists may be able to use simpler, more versatile structures that can adapt to different modes of movement.

This flexibility could lead to major advancements in several fields:

  • Medicine: Targeted drug delivery, minimally invasive surgery, and precision diagnostics

  • Environmental Science: Removal of pollutants from water or soil at microscopic levels

  • Manufacturing: Assembly of tiny components for advanced electronics

Looking Ahead

The ability to control tiny robots using magnetic fields is still an evolving field, but the progress so far is remarkable. By combining physics, materials science, and engineering, researchers are unlocking new ways to move and control matter at the smallest scales.

The discovery that simple, randomly shaped nanostructures can perform multiple types of motion challenges long-held assumptions and opens the door to more adaptable and efficient designs.

In the future, these microscopic machines could work together in large numbers, forming swarms that perform complex tasks—much like colonies of bacteria or flocks of birds, but guided by human design.

What once seemed like science fiction is quickly becoming reality. And as researchers continue to explore the hidden world of micro- and nanorobots, one thing is clear: even the smallest machines can have a massive impact.

Reference: Vach, P., Faivre, D. The triathlon of magnetic actuation: Rolling, propelling, swimming with a single magnetic material. Sci Rep 5, 9364 (2015). https://doi.org/10.1038/srep09364

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