The capability that living creatures have to repair themselves is astounding.  Imagine you accidentally cut yourself with a knife while you’re making dinner.  It’s not a huge deal, a little inconvientent perhaps, but nothing your body can’t handle.  Now imagine cutting a sheet of plastic with that same knife.  The plastic does not have the same capability to re-heal itself like we do.  Once it’s cut, it can’t spontaneously heal itself back into it’s original conformation.

However, this is a phenomenon scientists have been trying achieve for nearly a decade.  By experimenting with plastics, metals and carbon composites, researchers are attempting to create self-healing materials.

Mediocre Microcapsules

Self-healing fluid and hardening agent in a cracked material. Source: The University of Illinois

For the past decade, self-healing technology involves microcapsules filled with a self-healing fluid embedded into the material that is to be repaired, say a plastic. The fluid in the capsules is a monomer of the polymer plastic.  Accompanying the microcapsules are catalyst hardening agents that react with the healing fluid to solidify it.

When the crack in the plastic punctures the microcapsules, the healing fluid within is released into the crack.  The fluid polymerizes when it comes into contact with the catalyst, and the mixture seals the crack.

This method is effective, but not very efficient.  It can repair cracks between fifty and one hundred micrometers wide, but the fluids have to move through the material by diffusion, which can take a long time.  Also, there is a limit to the number of capsules that can be put in the material without weakening it’s structural integrity.

Circulatory Channels

Pressurized self-healing channels. Source: The Journal of the Royal Society Interface. Hamilton et al. September 2011.

New research being conducted by scientists at the University of Illinois attempts to mimic an animal circulatory system by copying the blood vessels and heart.  Instead of having the self-healing fluids in capsules, they have put it in channels in the material.  Similar to the microcapsules, when the channels are punctured, the fluid within them is released into the crack.

In addition to this change, pressure is also applied at the inlets and outlets of the channel to force the fluid into the crack in the material. This added pressure acts like a heart does in a circulatory system.  The heart forces blood to move all throughout an animal’s body.  The pressure applied to the self-healing fluid has the same effect.  This technique ensures that the entire crack can be effectively repaired.  With the applied pressure method cracks up to one millimetre wide can be repaired.

Current Applications

This technology has innumerable applications in infrastructure and engineering.  NASA is looking into self-healing materials particularly for their space stations.  Cracks and damages on these structures could risk the safety of the entire mission.  With self-healing materials, the lives of astronauts are more secure, and they can focus on exploration, rather than restoration.

For more information on NASA’s work on self-healing materials, check out this video.

References

Nature article on microcapsule method:

http://www.nature.com.ezproxy.library.ubc.ca/nature/journal/v409/n6822/full/409794a0.html

BBC article on current self-healing research:

Journal of the Royal Society Interface article on channel method:

NASA video:

Posted: 10|10|11 at 3:52 pm. Filed under: New and innovative science, Science in the News, Uncategorized.
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