CONCERTINAS may be more commonly associated with 19th-century reed music than modern heart surgery, but it turns out their shape is ideal as a scaffold on which to grow cardiac tissue.
Tissue scaffolds are already used to aid the growth of cartilage tissue in the lab. Heart tissue is more difficult to grow in this way, however. In order for the heart to beat properly, the new cells must be aligned in the same direction as existing muscle fibres. Previous attempts to build cardiac tissue scaffolds have failed as they allowed the cells to grow haphazardly.
Now a team from the Harvard-MIT Division of Health Sciences and Technology and the Draper Laboratory in Cambridge, Massachusetts, have built a scaffold that mimics the structure of heart tissue, allowing cells to grow in the same direction.
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The scaffold is made from a biodegradable polymer sheet that has been zapped with a laser to create a honeycomb structure. Each of the individual pores is shaped like a concertina and is roughly 500 micrometres across (see image). The team seeded the inner walls of the honeycomb with cells from the hearts of 2-day-old rats before incubating the scaffold in an oxygen and nutrient-rich solution for a week. During this time the cells multiplied, orienting themselves along the long axis, says team leader Lisa Freed.
The team believe this is because the cells build up in layers, starting from the walls and growing in towards the centre. With the concertina shape, this eventually leads to an oval ring of aligned cells within the pore. A scaffold made from square pores resulted in a circle of cells with no preferred orientation (Nature Materials, ).
The cells formed electrical connections with one another, allowing them to contract in a coordinated manner. What’s more, when an electric current was applied along the long axis of the honeycomb, the cells contracted, whereas if it was applied along the perpendicular axis, the cells did not contract so readily. “You could see the cells ‘beating’ on the scaffold,” says project member George Engelmayr.
The technology could initially be used to grow artificial heart tissue in labs in order to screen new drugs designed to regulate heart activity, the team say. In the future, the scaffold could be inserted into damaged hearts and seeded with stem cells to help repair tissue. Since the honeycomb is flexible and stretches to the same degree and in the same directions as heart tissue, the patch should be integrated without causing additional damage, they say.
