Microrobots and other miniature machines all have the same problem: Where do you plug them in?

Mar 28, 2005
Bennett Daviss

Courtesy of Nature Materials

Microrobots and other miniature machines all have the same problem: Where do you plug them in? Even the best fuel cells and microscale batteries can't store much power for long periods. Now UCLA's Carlo Montemagno, a biomedical engineer, has shown that all you have to do to solve this power problem is to put a little muscle into it.1

A research team led by Montemagno has developed a unique way to grow bundles of muscle cells on silicon chips and attach them to fabricated devices such as tiny levers or switches. When the muscles contract, the devices move. No manufactured power source is needed; all that's required is nourishment for the muscles.

Typically, tissue cultured on silicon is micropatterned along a solid surface. "But a muscle cell has to be free to contract," explains UCLA team member Jianzhong Xi. "That's a conflict."

The group solved the problem by combining existing fabrication and patterning techniques with a polymer whose properties make it uniquely suited for this application. The polymer, poly-N-isopropylacrylamide, is a solid at 37°C but a liquid at 32°C, a temperature easily tolerated by the cells. Thus, it can be removed following cell culture. Mon-temagno's team used the polymer to coat micromanufactured switches, levers, and other equipment. They then patterned the polymer with thin, precisely patterned strips of gold that guide cell growth, thereby defining how the growing muscle cells would connect with the micromachined devices.

Once the cells had grown and attached themselves to the device, knitting their extracellular matrix of collagen, fibronectin, and other materials to the gold, the team could remove the polymer, allowing the cells to contract freely. As a result, these devices grow and assemble themselves without the need for microsurgery or human intervention. The technique is flexible enough to allow the integration of any kind of micromanufactured device with muscle tissue.

To demonstrate the method's practicality, the group built a W-shaped metal device lined with rat cardiac muscle cells. The cardiac cells spontaneously expand and relax in a heartbeat rhythm that moves the device's hinged legs and enables it to take crude steps. The researchers have also built devices lined with skeletal muscle tissue that can be controlled by electric current.

Coupled to a piezoelectric material that converts mechanical force into electrical energy, the muscle bundles could some day drive an internal power-generation system for micromachines, according to Xi.

"What the UCLA group has done is unique," says Robert Dennis, a biomedical engineer at the University of North Carolina at Chapel Hill, who has developed a tiny pump powered by cardiac tissue. "Bits and pieces have been done by others, but Carlo's group is the first to put it all together."