Mini muscle machines take the strain

7 September 2007

Imagine tiny machines made from muscle cells, or living sticking plasters for damaged hearts. Scientists in the US have brought these breakthroughs a step closer by creating the world's most advanced artificial muscles. Antenna investigates...

This research was published in the journal Science on 7 September 2007.

Muscle cells, with their nuclei stained blue and communication channels between cells stained red.

Image: Disease Biophysics Group, Harvard University/Science

About half of your body weight is muscle, and it's powerful stuff. The muscles in your jaw are the strongest - the force of a single bite can be equivalent to more than your entire body weight pressing down on the ground.
Experts all over the world are working on building artificial muscles, and now scientists at Harvard University in the US have created some of the best yet. Their mini muscles can grip like a pair of tweezers, swim and even walk along the bottom of a glass dish.

Broadband Version

This little walking muscle, called a 'myopod', was made by folding down the top of a triangular-shaped artificial muscle to make a foot pad. Each time the muscle contracts, the foot pad is pushed forward.

Video: Disease Biophysics Group, Harvard University

Kit Parker, Harvard University

Image: Harvard University

The mini muscles might only be a centimetre or so long, but they're the biggest working artificial muscles ever made. 'We could build them a metre long, we just don't have a Petri dish big enough,' says Kit Parker, an artificial muscle expert at Harvard University.

This gripper is made out of a rectangular-shaped artificial muscle. When it contracts, the tips (yellow circles) pinch together.

Image: Disease Biophysics Group, Harvard University/Science

Kit and his team used different designs of artificial muscle to build a variety of living machine parts. One type can coil and uncoil as it contracts, while another has a helix shape that extends and rotates. 'The idea is to harness these muscles to build machines with nano-scale components,' says Kit.
Machines made out of muscle could have several advantages over their metallic counterparts. For example, a key challenge scientists face is how to make 'smart' materials that can be reprogrammed to do different things. By using living muscle, they can more easily achieve this.
What makes these muscles so special?
The muscles were made by growing cells from a rat heart on a thin elastic film. The key to making the muscles work properly was getting the cells to connect in straight lines, just like in a natural muscle.

These muscle cells have grown in a random arrangement, so pull in different directions when they contract.

Image: Disease Biophysics Group, Harvard University/Science

Kit and his team used lines of sticky proteins to 'draw' out a template of the muscle on the elastic film, and then added the muscle cells.
'The cells automatically aligned themselves on the surface,' explains Kit. 'In other artificial muscles the cells are thrown down randomly, whereas our muscles have nice, smooth, rhythmic contractions. If you get the right form, you get the right function.'

The cells in the top of this image have grown in straight lines. To create separate muscle fibres (bottom), Kit and his team added a substance to stop the cells sticking to the film in certain places.

Image: Disease Biophysics Group, Harvard University/Science

And their function doesn't just include machine parts - the muscles could be a medical breakthrough too. 'This research is amazing,' says tissue engineering expert Julia Polak from Imperial College London.
'Hopefully the technology could be used to make little patches to repair damaged hearts. It's a long way off from being used in humans, but it's a realistic aim.'

Julia Polak, Imperial College London

Image: Julia Polak

Kit's also excited by the medical possibilities. 'We're investigating using other types of muscle, such as the muscle in the walls of the uterus. The idea that you could reconstruct a uterus and build a replacement organ is quite possible.'

A triangular piece of muscle swimming through the liquid that provides it with nutrients.

Image: Disease Biophysics Group, Harvard University/Science

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