For decades, science fiction writers have toyed with the prospect of a future where miniaturised vessels transport crews inside the human body. From the 1966 classic Fantastic Voyage to the 1980s comedy Innerspace, shrinking stuff (otherwise known as nanotechnology) has been one of those human fascinations that won't go away.
We are yet to perfect any sort of Wonkavision that might shrink a human, but chemists have demonstrated the first complete movement regulation of a motorised “nanovehicle” inside the human body. These tiny machines could prove to be effective treatment for drug delivery in the human body.
They are also calling them nanorockets, which is a pretty cool name. And before you try to call it, the NanoRockets has already been claimed as my new band name.
Their potential function lives up to the hip nomenclature. Nanorockets can serve as mini-medicine cargo transporters for the human body. Self-propelled catalytic micro- and nanomotors have been the subject of intense study for some years, but chemists struggled to figure out how to provide a few key crucial functionalities. Knowing how to hit the brakes was the biggest dilemma.
However, chemists at Radboud University in the Netherlands have figured out how to build in effective speed-regulation mechanisms so that a nanorocket can be controlled remotely.
By providing temperature-responsive brakes, the nanorocket’s temperature sensitivity enables it to stop in diseased tissues where body temperatures tend to be higher or lower depending on the condition.
Potential solution
"I have always been fascinated by designing not just complex structures at the nanoscale, but also with functionality for supramolecular assemblies and motility [or muscular contraction] of biological systems," says Daniela Wilson, head of Radboud University's bio-organic chemistry department and nanomedicine theme leader.
In 2012, Wilson and her research group developed an innovative approach to the design of nanomotors using a process of self-assembly as their own driving force for movement. Amphiphilic polymers, which contain molecules with simultaneous water-soluble and water-insoluble properties, were developed allowing for the catalytic movement of the nanomotors.
However, a nanorocket lacking key control functions – for direction, acceleration, deceleration, etc – might appeal to someone planning the tiniest nano firework display ever, but are not much use to medics searching for new ways to precisely deliver drugs inside the human body.
“We began searching for ways to effectively control movement at the nanoscale three years ago and found body temperature to be a potential solution,” says Wilson. “So we incorporated temperature-responsive valves into the nanomotor system to regulate access to its own fuel.”
In other words, the molecularly built nanorockets can adapt to their environment and accordingly adjust speed and behaviour.
How, you ask. This one just gets weirder and weirder. The brakes use brushes made from polymers that literally grow on the surface of the nanorockets and then swell or collapse in response to the environmental temperature they sense.
Precious cargo
Using soft nanosystems, the Dutch bio-organic chemists developed nanorockets that self-assemble, giving them the ability to change shape. This is what makes them ideal candidates for transporting precious cargo, such as medicine, within the human body.
“Thermosensitive molecular brushes were grown in order to switch the motors on and off in a controllable fashion,” says Wilson. “The long brushes function as a reversible brake system for the nanomotors by locally sensing the environment (in this case the temperature) and regulating access to the fuel inside their catalytic structures.
“After the inclusion of a temperature-responsive brake system, the motion of the nanorocket becomes far more controllable, so it can be stopped more precisely at a disease site.”
The question of steering the nanorocket while inside the human body was solved with a little help from magnetic fields. “We found low magnetic fields could serve as a kind of steering wheel,” she says.
The incorporation of magnetic, metallic nickel into the core of the rockets meant magnetic fields could be used to guide and steer the rockets in whichever direction was required.
This development in nanotechnology shows great potential for modern medicine, particularly in the treatment of diseased tissues where temperatures are higher. However, they still have one more obstacle to overcome. While not toxic to living cells, the heat-responsive nanorockets are not completely biodegradable, a regulatory prerequisite for medicine delivery in the human body.
“Our nanorocket system is not biodegradable or biocompatible but we’re working on it,” says Wilson.
In fact, Wilson and her team are already two moves ahead. “What would be even more interesting than temperature-responsive brakes would be a system that responds to light,” she says. “This would allow us to start or stop a nanorocket by shining a laser light on it.”
