Machines that can fix themselves are such staples in fantastic fiction that the concept has its own name at TV Tropes (the 'net's ultimate guide to fiction cliches): Self Healing Phlebotinum.
In reality, chemists and engineers have devised materials and coatings that "self-heal” minute holes or thin cracks, often by melting and reforming under some sort of applied heat. But the size of the gap that can be repaired has been extremely limited.
This new self-healing technique is both chemical and mechanical. The researchers were inspired by the human circulatory system to create a plastic, or polymer, laced with extremely narrow "veins," then filled them with one of two different liquids, or monomers.
When the plastic ruptures and cracks, the veins break open and the liquids mix, setting off two sequential chemical reactions: First the mixture turns into a gel. Then, it hardens up.
As long as the liquids continue to pump out of their channels and mix together, the plastic continues to grow, effectively "scarring over" and sealing off the hole or gap.
Sentient space ship fans take note: We're not quite in TARDIS territory yet. This new plastic has been tested only in the laboratory. If it can be made to work in real-world conditions, however, it's likely to have diverse applications in both inner and outer space.