Imagine a piece of paper that would move and have the shape of a fish. A Harvard team led by biomedical engineer Kit Parker has developed thin sheets of elastic film studded with rat heart muscle cells that can turn this into reality. The muscle-bound sheets react to electricity, as muscles contract, bend and flex the polymer layers.

Sometimes the films kept on moving spontaneously; in other cases, they did it just in tandem with the electrical impulses. The material could be cut out in whatever form (like triangles or rectangular strips) that could move. The new research could lead to sophisticated "soft robots," organ replacement and improved prosthetic devices.

Triangular pieces moved like zebrafish, which swim by swinging their tailfin to one side and then straightening their tail and coasting, but the speed was low, just a fraction of the material's length (an inch or 2.4 cm) per minute. But the muscular thin films could flex quickly and powerfully.

The team also created a crawling mini-machine with a rounded body and a "leg" at the back that flexes to push the whole "body" along.

"We also made a spontaneously coiling strip as well as a clawlike gripper that could grab tightly enough to move individual cells," said study co-author Adam Feinberg.

Parker believes the greatest achievement was to line up the muscle cells properly.

"In order to have rhythmic contraction, you need to have proper alignment of the muscle cells. To date, that is what has vexed tissue engineers." said Parker.

To overcome this issue, the team stamped their elastic films with a pattern of stripes built of fibronectin, a type of protein along which the heart muscle cells grew. The cells arranged themselves into functional muscle sheets.
"If you put down a pattern, you automatically get a tissue," said Parker.

Other animal muscles could lead to more complex devices.

"An octopus can deform itself to get through obstacles and can also bend its arms in all directions. Getting the muscular films to work in a similar way could lead to the development of "soft robotics"," said Parker.

"The first application of these [rat muscle films] might be in drug assays that look at the benefits and side effects of particular drugs on heart cells. We need to try to get human cells to grow on the films, because this would open up another possibility-making replacement tissues and organs," said Parker.

Lab grown muscle sheets could fix holes in the diseased heart or intestines.

"What's really nice is they focus on the mechanics of single cells, controlling how these cells attach to one another and work together." said Gordana Vunjak-Novakovic of Columbia University, not involved in this research.

She believes that the technique could lead to artificial arms or legs.

"It is conceivable [that] prosthetic devices would be very substantially advanced if you could make these [engineered muscles] work for you," she said.

"This study will change the way that people think about the interaction between the synthetic and biological materials and how they can work together to produce machines." said Keith Baar, biochemist at the University of Dundee in Scotland.