Fri. Jun 9th, 2023

A new microscopic robot based on an algae shows promise for medical applications according to a study published in Science Robotics on Nov. 22.

A team of researchers led by Materials Scientist Li Zhang of the Chinese University of Hong Kong in Shatin developed the microrobot. Each microrobot consists of a spirulina algae, a miniscule, spring-shaped species of algae commonly used as a dietary supplement coated in iron oxide nanoparticles so its movement can be controlled by a magnetic field.

The thickness of the coating can be controlled by the amount of time the algae is dipped in the container of nanoparticles which then determines the amount of time the microrobot takes to biodegrade in the body. With the thinnest coating tested, the microrobot degrades in a few hours and with the thickest coating tested it degrades in a few days.

Magnetism is an ideal method of powering and controlling microrobots because a magnetic field can pass through the human body without harm. Other scientsts’ attempts to build microrobots often struggle to find a safe power source because most compounds which could serve as fuels are toxic to humans.

The use of spirulina also conveys an advantage to the microrobot in terms of movement. Because of the algae’s spiral shape, the microrobot can easily be made to move forward or backward like a rotating corkscrew, depending on how the magnetic field is manipulated.

One method of tracking the microrobot within the body is made possible by another one of spirulina’s natural properties: fluorescence. Researchers injected samples of microrobots under the skin of mice and found when the microrobots were relatively close to the surface of the body their fluorescence could be observed to reveal their location. However, this method of tracking would not work if the microrobot was deep inside the body. To address this challenge, researchers tried using a common medical technology called magnetic resonance (MR) imaging.

They tested MR detection of the microrobots using two groups of rats, a group which had samples of microrobots injected under their skin and a group which ingested a solution containing the microrobots. They found that MR imaging enabled them to see the location of the microrobots both under the rats’ skins and in their stomachs because it picked up on the microrobots’ iron oxide nanoparticle coating. The thicker the coating, the stronger the image of the microrobots appeared. Higher concentrations of microrobots also led to stronger images. However, increasing the thickness of the nanoparticle coating reduced fluorescence visibility.

The researchers also observed a fascinating, unexpected effect when testing the spirulina microrobot. Though it was shown to be safe for use with normal cells, when it was placed in two lab dishes each containing a different type of cancerous tumor cell, 90 percent of cancerous cells in one dish and 50 percent in the other died within 48 hours.

Tests suggested that spirulina algae produced one or more compounds toxic only to cancerous cells. Of the compounds spirulina produces, the researchers believe one called C-phycocyanin is the most likely to have played a significant role in the death of the cancerous cells, based on previous studies showing C-phycocyanin’s toxicity to such cells. However, further testing is necessary to establish C-phycocyanin’s role, determine if other compounds are involved in the cancer-killing effect and ascertain how effective it is under various conditions.

Overall, the results of this initial research are promising, and the researchers intend to move forward with development of the microrobot. However, they believe it will be about ten years before the microrobot is ready for real-world use. The researchers must first test its ability to carry cargo, such as medications, and demonstrate why and when using a microrobot as a delivery method would be preferable to traditional methods such as pills and injections.

Abbey Bigler is a fourth-year student majoring in English with minors in business and technical writing, communication studies and biology. She can be reached at

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