A study in Nature Materials describes the development of a self-healing polymer that uses a network of 3-dimensional channels, analogous to blood capilaries in the skin, to deliver "healing agents" to cracks in the surface.
This technology, to my mind, falls into the category of ideas that challenge the boundary between the definition of living and non-living:
A living organism is defined as something that metabolizes, reproduces, and responds.
The self-healing polymer doesn't metabolize or reproduce, but it definitely responds.
The way it works, apparently, is that when a crack occurs in the surface of the polymer, "healing agent" is delivered to the scene of the crack via a "three-dimensional microvascular network" inside the material. Exactly what mechanism causes the healing agent to respond to the presence of a rupture is unclear. What differentiates this from previous successes with self-healing materials is that the embedded network of vessels can deliver more of the healing material whenever necessary, making it possible for the same spot to be healed numerous times. In the study, the same spot was cracked and repaired seven times.
The authors of the study write: "This approach opens new avenues for continuous delivery of healing agents for self-repair as well as other active species for additional functionality."
What sort of "additional functionality" do they have in mind? It doesn't seem a far stretch that, with the implementation of microvascular networks like the one described, a variety of other applications could blossom, beyond merely self-healing materials. Similar ideas for internal, self-regulated delivery of medicine without IVs, for example, are already under development, using nanotechnology.
Interestingly, the use of the word "species" suggests a self-conscious recognition of the proximity of the technology to artificial intelligence. If the networks could be engineered to rebuild and extend themselves, either in response to external stimuli or to an internal "clock," they would move a step closer to fulfilling the criteria for being "alive." Viruses avoid being categorized as organisms by using the machinery of the cells they invade to reproduce, instead of their own. Microvascular networks such as these would similarly be reliant on the host organism - for example, on the surrounding tissue to provide physical support.
But, like viruses, they might carry out the majority of lifelike functions independently - moving a step closer to the creation of a synthetic organism.