Researchers in Australia and the UK are bringing a sci-fi concept closer to reality as they work to overcome a major hurdle in the design of self-assembling nanobots.
Fans of the 2018 film Avengers: Infinity War will know the scene where Tony Stark taps a panel on his chest to release a billion tiny robots, which rapidly assemble into an Iron Man suit around him.
A bit of Hollywood, it’s true, but this kind of self-assembling nanotechnology is a very real and exciting field of research.
In the last couple of decades, scientists have developed nanoscale robots that can be programmed to undertake a range of microscopic tasks, from healing wounds to delivering drugs to cancer cells to positioning electrical components.
But Tony Stark did something real-world scientists are still struggling to achieve: getting these nanobots to combine into larger formations.
Now, a team including researchers from the University of NSW, the University of Oxford and Imperial College London has developed a design theory to control how accurately nanobots assemble in the absence of a mould or template.
“Traditionally we build structures by manually assembling components into the desired end product,” says Lawrence Lee from UNSW. “That works quite well and easily if the parts are large, but as you go smaller and smaller, it becomes harder to do this.”
Luckily, the natural world is full of tiny machines and so provides ample inspiration.
“Biology demonstrates how a near infinite array of complex systems and structures at many scales can originate from the self-assembly of component parts on the nanoscale,” Lee and colleagues write in their paper, published in ACS Nano.
Their research uses biological molecules – namely, DNA – as the component parts of nanobots. Each molecule can be encoded with instructions about how to assemble – but the most crucial challenge has been how to get the molecules to stop when the structure reaches the desired dimensions.
To tackle this, the team synthesised a new type of DNA-based building block called PolyBricks, which are so small that 2000 could fit across the thickness of a single human hair.
Each of these identical subunits is encoded with a “blueprint” of a pre-defined structure, including a set length. In order to control how many bricks join together – and therefore control the dimensions of the final product – the team used a design principle called strain accumulation.
“With each block we add, strain energy accumulates between the PolyBricks, until ultimately the energy is too great for any more blocks to bind,” Lee explains. “This is the point at which the subunits will stop assembling.”
Essentially, this was achieved by modifying the DNA sequence of each PolyBrick to regulate how much “strain” is added with each block.
This new mechanism provides a foundation for encoding nanobots to assemble into even more complex shapes.
Jonathan Berengut, co-author from UNSW, concludes: “It’s this type of fundamental research into how we organise matter at the nanoscale that’s going to lead us to the next generation of nanomaterials, nanomedicines, and nanoelectronics.”