Designer tissue to heal our hearts

“And how can you mend a broken heart? How can you stop the rain from falling down?”  If soul legend Al Green’s song tugged at your heartstrings, you might want to reach out for some tissues now.  Tissues can wipe your tears, but if you talk to an engineer, you’ll learn that they can also mend your broken heart.

Engineers have invented a new material that behaves like the tissues of the human heart.  Though it cannot bring back your lost love, it can help surgeons patch up their patients’ damaged hearts.

Artificial tissues for repairing damaged skins and organs base their structure on a ‘scaffold’ – an engineered, three-dimensional layer of porous organic polymer.  Tissue engineers have been tinkering with scaffold designs so that they mimic the mechanical movements of different types of human tissue.  Yet coming up with one that is compatible with our heart and blood vessels has caused much heartache.

The trouble is that unlike skin tissue, which wrinkles as you pull on two opposite ends, heart and blood vessel tissues actually expand as they are pulled.  This very feature allows our heart and blood vessels to pump and push our blood along to where it needs to go.

Two years ago, a team of engineers at the University of California, San Diego took this problem to heart.  They have now invented a new biomaterial and have described their finding in a recent issue of Advanced Functional Materials (DOI: 10.1002/adfm.201002022)

The team has come up with a scaffold that mimics the movement of heart and blood vessel tissues. “[Our new material] behaves just like a blood vessel,” says Professor Shaochen Chen, of the Jacobs School of Engineering, University of California, San Diego, and co-author of the study.

The engineers developed a scaffold pattern based on two new shapes.  Unlike most scaffolds which consist of circular or square holes, the new shapes – dubbed “reentrant honeycomb” and “cut missing rib” – were engineered to exhibit a negative Poisson’s ratio, a property that enables the scaffold to expand as it is stretched.  The material maintains this property regardless of the number of scaffold layers.

The researchers then created the scaffold using a fabrication technique which Chen developed five years ago.  The technique shines light on a solution of polymers with a computer projection system and precisely controlled mirrors.  “The patterns of scaffolds are normally very random.  [With this technique] we can make a very uniform pattern throughout the whole material, or different shapes in different areas,” says Chen.  “We can now make a designer material.”

Optical image of scaffold expanding in response to stretching. Image credit: UC San Diego / Professor Shaochen Chen

For the new biomaterial the researchers used polyethylene glycol, a polymer commonly used in medical procedures. “The polymer is a very soft material just like a blood vessel, so you can ‘tune’ it to make it harder or softer.  ”

Chen says that the biomaterial can be used in heart bypass surgeries to repair damaged tissues on heart walls, arteries, and veins.  Heart cells don’t grow back naturally, so tissue engineers would have to ‘seed’ the scaffold with cells which can be developed from stem cells.

But surgery is just one of the material’s many potential uses.  Other applications include defense, energy, and communications.  For example, engineers could tune the scaffold to change its optical properties.  In defense applications this could alter radio signals and help aircrafts evade detection.

The researchers have applied for a patent for their invention.  They will approach the development of its potential applications step by step, one application at a time.  As a starting point, they want to study the use of the material for blood vessel repair.  “We want to see how this material attaches to a tissue surface, how cells grow in it, and when you put it into an animal model, how it is compatible with natural tissue,” Chen says.

The rain may keep falling, but at least there’s an answer for our broken hearts.

 

by Monique Tsang

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