Poised on the threshold of the robotic age, machines performing tasks ranging from home care to critical medical procedures are visible all around us. At the same time, scientists are actively researching tiny devices that can transform therapeutics. For example, one could design nanoscale-robots that could delve into our body, reach a diseased site, and smartly deliver the correct drugs.

In one such attempt, Dipankar Bandyopadhyay and his team of researchers from the Indian Institute of Technology, Guwahati, have fabricated biocompatible, vitamin C‑fortified robotic antioxidant molecules from tea extracts. The novelty of the research lies in the environment-friendly fabrication method of these Teabots and their fuel-free navigation. 

Free radicals or reactive oxygen species (ROS) are reactive by-products produced in cells during metabolic activity. ROS can damage proteins and other cellular components, a phenomenon known as oxidative stress. The researchers demonstrated that the Teabots, propelled by sound waves, can swim towards free radicals in cells and neutralise them. 

Any mechanical device designed for drug delivery has to pass through the rigours of the body’s defence mechanism, which can easily reject it as a foreign element. Even if made from biocompatible materials, the device faces hurdles from biological barriers such as the intestinal layers or blood-brain barrier. Hence there is an increasing demand for nanobots synthesised from non-toxic sources such as plants, which are often readily accepted by the body.

Bandyopadhyay’s team zeroed in on white tea buds (Camellia sinensis) for their high antioxidant content and biocompatibility. Using green chemistry principles (methods that avoid the use of toxic chemicals for synthesising the product), they distilled 100 – 200 nanometre-sized purified pellets from the tea extract, to derive the Teabots. These nanobots have a mesh-like surface with a negative charge on them. 

Now, the researchers were faced with the task of piloting the particles. For this, the researchers took advantage of existing studies which have shown that nanoscale particles can be steered by ultrasound waves. By using 3 – 10MHz waves (a safe range often used in medical diagnosis), the team found that they could control the movement of the Teabots. 

“The nanomotors absorbed the sound energy converting it to mechanical energy. By altering the direction of the waves falling on the Teabots, the direction of motion could be changed. This way, the Teabots moved about without any fuel,” says Tamanna Bhuyan, first author of the study.

The researchers first subjected cells grown in culture to oxidative stress and then added the Teabots to the system. When exposed to optimised sound waves, the Teabots moved towards the diseased cells. Upon reaching the target cells, the Teabots neutralised 65% of the free radicals. 

To enhance efficacy, the team decided to load the Teabots with Ascorbic Acid (AA) or Vitamin C, another potent antioxidant. However, Vitamin C is an unstable molecule and to overcome this hurdle and deliver stable molecules inside the cells, they made use of the electrostatic interaction between them. The charged mesh-like surface of the Teabots readily encapsulated the positively charged Vitamin C molecules along with preventing them from degrading. 

At the stressed cells, the acidic conditions of the cell fluids gradually broke down the Vitamin C loaded Teabots to release the antioxidant molecules. The AA-Teabots could now scavenge up to 90% of the free radicals. In another experiment, the team found that the AA-Teabot combination was also effective in breaking down toxic amyloid fibres (which form in neurodegenerative disorders like Alzheimer’s disease). 

Aynur Unal, former Dean of engineering and technology at Ansal University and Founder of Digital Monozukuri, who was not involved in the study comments: ​“This proof-of-concept study indicates potential in creating Nano motors for smart drug delivery systems which can play a critical role in Precision Medicine.” 

“Our study offers a scope for on-site acoustic control of Teabots for drug delivery using safe hand-held ultrasonic probes, which is an attractive alternative to regular oral or injected drug formulations,” says Bhuyan.