Nanorockets are tiny machines that are ideal candidates for drug delivery in the human body. Chemists at Radboud University have provided temperature responsive brakes to enable the first complete movement regulation of a nanorocket. This feature has interesting practical applications, as temperature sensitivity allows the rocket to stop in diseased tissues where temperatures are normally higher.

The bioorganic chemists at Radboud University use soft nanosystems that self-assemble and form functional units spontaneously. The nanorockets can therefore change shape, making them perfect candidates for containing loads like medicine.

Daniela Wilson, head of Radboud University’s bioorganic chemistry department and Nanomedicine theme leader, notes that their biggest challenge is to provide their nanorockets with several functionalities. She adds that they have now demonstrated the first molecularly built brake system that enables the rockets to start and stop at preferred locations.

The brakes are temperature responsive and consist of brushes made of polymers. These long chains of responsive units are grown onto the surface of the nanorockets. The brushes collapse or swell depending on the environmental temperature. This behavior is used to regulate fuel access to the rocket. Hydrogen peroxide (H 2 O 2 ) is used as fuel in this specific case. The brushes have a high sensitivity and they immediately collapse at a temperature of more than 35 degrees Celsius, making the machine stop. Wilson notes that the shape of the nanorocket or the catalytic activity is not affected when this happens. Nanorockets furnished with this valve system are therefore able to move with great efficiency in water, even when the concentration of fuel is low.

Wilson and colleagues have conducted another study in which they show that low magnetic fields can be used as a steering wheel for the nanorockets. The rockets are steered and guided into desired directions with magnetic fields created by growing magnetic metallic nickel into the core of the rockets.

Wilson admits that there is always room for improvement. It would be interesting to have light responsive brakes instead of a system that responds to temperature, as this would allow a nanorocket to be started or stopped by shining a laser light on it. The nanorockets are not completely biodegradable yet, even though they are not toxic to living cells. Being completely biodegradable is one of the prerequisites for their use as medicine carriers in the body. Wilson cites these as only some examples of the next challenges for her group.

The full study was published in the journal Nature Chemistry.