Scientific Method / Science & Exploration

Muscle-powered films create a micro-cyborg

New work reported in this week's edition of Science illustrates how to create …

Tissue- and bio-engineering promise some of the biggest breakthroughs science and engineering will deliver in the next few years. Today a paper appears in Science that reports on the creation of a biohybrid device that uses plastics and muscle cells to enable autonomous walking and swimming. These devices, created by a pair of research groups at Harvard University, are termed muscular thin films (MTFs).

These MTFs use a combination of neonatal rat ventricular cardiomyocytes for muscles and polydimethylsiloxane as the plastic.  They we created by incubating some seed cells on the plastic for a few days; the cells grow into a thin layer of muscle coating the plastic. Muscles gain their strength from the alignment of their constituent cells—when all the components of the muscles, from the sarcomeres up to muscle fibers, act together, they are capable of doing a large amount of work. To achieve this, the researchers caused the cells to grow along specified axes by laying down a prepattern of the protein fibronectin that the cells have an affinity for.

The contraction and relaxation of the muscle cells, coupled with the geometry of the plastic surface, allowed the team to engineer a variety of what they termed "soft robotic actuators." The devices reported in the paper include a cylindrical MTF that would decrease its radius drastically during contraction of the muscle cells, and subsequently increase it as the cells relaxed. A similar setup, one where the muscle cells were aligned off-axis from the rectangular plastic sheet, resulted in a helical configuration for the MTF. Contraction of the cells here would result in the elongation of the helix by up to a few hundred microns. Both of these devices could see potential use as valveless pumps for biological fluids.

The final robotic actuator mentioned is a "gripper," which is constructed of an arc of muscle cells and plastic. It could be forced to close and open at various frequencies via the application of varying external electric fields. This could hold promise for applications such as grabbing and holding a single cell in a small biological sample.

With the ability to create devices that can 'pump,' 'poke,' and 'grab,' the researchers allowed their creations to take it a step forward. They engineered a material geometry that allowed an MTF to autonomously walk along a petri dish. The motion was more akin to a dog scooting his butt across a floor, but the biohybrid device was able to move on its own at a speed of about 8mm per minute. In a similar setup, they found that a triangular geometry was capable of swimming. The swimming was accomplished through a burst-and-coast type motion through the water where the device would fold and unfold to propel itself forward at about 24mm per minute. The researchers also found that a device could swim even if the muscles cells were not aligned, although this configuration could only travel at about one-fifth the speed of the device with the aligned cells.

The authors conclude the paper by asking the question "Can we leverage these capabilities to build more advanced soft robotic actuators and devices?" Since these MTFs represent fairly simple modes of motion, they suggest looking at creatures that rely on soft muscular appendages to move around. As an example, the authors point out that an octopus is capable of complex locomotive methods without the need for a skeletal structure and articulated joints. They say that more powerful motions could be achieved by either using multiple MTFs in parallel or by growing thicker muscle layers on the patterned surface. Both methods would have their challenges, but the payoffs for such devices could be huge.

For high resolution images of these devices as well as video of the various locomotive modes, check out the online supporting material at Science's web site. Subscription NOT needed. 

Science, 2007. DOI: 10.1126/science.1146885

Expand full story

You must to comment.