Living robots, made of frogs' stem cells, can reproduce by a form of replication unseen in plants or animals.
Scientists at the University of Vermont, Tufts University in Massachusetts, and the Wyss Institute for Biologically Inspired Engineering at Harvard University, have discovered a completely new method of biological reproduction, and applied the finding to produce self-replicating living robots. These 'xenobots' are not yet usable but they have promise in the future for the development of regenerative medicine or delivering a drug to a specific spot in a person's body.
'There's nothing theoretical that would stop us from making these out of human cells,' commented Dr Sam Kriegman, first author of the study, published in Proceedings of the National Academy of Sciences. 'They could perform useful work inside of human bodies in places where traditional robots can't go because our bodies detest even the smallest amount of metal.'
Last year the same research team developed the first living robots, taking stem cells from frog embryos to form structures capable of self-assembly, movement and sensing of their environment (see BioNews 1031). By altering the cell anatomy using minuscule surgical tools and electrodes, and adding cardiac cells for movement, they produced multicellular robots less than 1mm long, with limb-like structures for propulsion, or holes for carrying objects.
In the most recent development, scientists noticed individual clumps of cells appearing to work as a swarm, pushing loose cells into piles which developed into new xenobots. This is the first time multicellular organisms have been found to self-replicate based on movement, rather than involving the growth of offspring on the organism's own body. The team used an algorithm modelled on evolution to evaluate which xenobot shape would produce the most offspring. The algorithm predicted a C-shape configuration, so they carved the naturally spherical xenobots into this shape to maximise reproduction rate. In a controlled environment, the engineered C-shape cell clumps could sustain themselves for at least five generations using this new form of replication.
The authors highlight this as an advancement towards regenerative medicine and the use of self-replicating xenobots as a model system. 'If we knew how to tell collections of cells to do what we wanted them to do, ultimately, that's regenerative medicine – that's the solution to traumatic injury, birth defects, cancer, and ageing,' said Professor Michael Levin, co-leader of the new research and director of the Allen Discovery Centre at Tufts University, 'all of these different problems are here because we don't know how to predict and control what groups of cells are going to build. Xenobots are a new platform for teaching us.'
The next step in the research is developing similar living robots out of mammal cells, eventually creating robots that can act without human oversight.