Researchers successfully constructed robots that are small enough to "swim" through bodily fluids (or even cells) and can navigate complex biological materials.
These tiny "submarines" could be used to perform functions such as delivering drugs to precise locations, such as a spot on the retina. They could also make it possible to perform gene therapy in a specific cell, the Max Planck Institute for Intelligent Systems reported.
There are two challenges standing in the way of the success of these vehicles. The first is that they must be small enough to be injected into the eyeball with a syringe, and the second is that it must be able to move through body fluid. To get around these issues the researchers described an "artificial scallop" that is only a few hundred micrometers in diameter. The device travels through liquid by opening and closing its shells.
"The shell is only a few times larger than the thickness of a human hair," says study leader Peer Fischer. "A liquid like water is about as viscous for these devices as honey or even tar is for us." And with so much friction in fluids, symmetrical movements, such as the reciprocal opening and closing of a scallop shell, would not result in any forward propulsion. The back-and-forth movements caused by the opposing movements would simply cancel each other out.
The researchers tested their robot directly in model fluids, which have characteristics that distinguish them from water. The substance was similar to synovial fluid, which is found in the joints and contains hyaluronic acid molecules which arrange themselves into network-like structures resulting in high viscosity.
In order to tailor the robots to this fluid quality, the researchers controlled the scallop so it opened much faster than it closed.
"This temporally asymmetric pattern of movement causes the fluid to be less viscous during opening than during the subsequent closing stroke," said doctoral student Tian Qiu, a member of the team in Stuttgart.
To control the robots the researchers integrated tiny rare-earth magnets into the scallop shells and applying an external magnetic field.
"We're interested in the next step, for example whether we can also guide this robot through the extracellular matrix of a tissue," Fischer said.
The findings were published in a recent issue of Nature Communications.
