Nanotechnology research yields high strength, chemically powered artificial muscles

Citation

(2006), "Nanotechnology research yields high strength, chemically powered artificial muscles", Assembly Automation, Vol. 26 No. 3. https://doi.org/10.1108/aa.2006.03326caf.003

Nanotechnology research yields high strength, chemically powered artificial muscles

Nanotechnology research yields high strength, chemically powered artificial muscles

Keywords: Muscles, Nanotechnology, Robotics

In March 2006, a research group from the University of Texas at Dallas (UTD) announced the development of chemically-powered artificial muscles in the journal Science (Vol. 311, no. 2767). Conducted at the UTD's NanoTech Institute this research was stimulated by a visit to the Institute by John Main from the Defence Advanced Projects Agency (DARPA) who described his visions of a future that would include technological advances such as artificial muscles for autonomous humanoid robots, artificial limbs that act like natural limbs and exoskeletons that could provide super-human strength to fire fighters, astronauts and soldiers. The less futuristic of these concepts reflect a major limitation of today's robots: those that are mains-powered cannot move freely and autonomous types are limited by their batteries which store too little energy and deliver it at too low a rate for prolonged or intense activity.

In an attempt to solve these problems, and with funding from DAPRA, the UTD team have developed two different types of artificial muscles that, like natural muscles, convert directly the chemical energy of a fuel source into mechanical energy. They simultaneously function as both fuel cells and muscles and in one type, fabricated from a strip of carbon nanotube (CNT) sheet, a catalyst- containing CNT electrode acts as a fuel cell electrode to convert chemical energy to electrical energy; as a super- capacitor electrode to store this electrical energy; and as a muscle electrode to transform the electrical energy into mechanical energy. Chemical fuel-powered charge injection in a CNT electrode produces the dimensional changes required for actuation due to a combination of quantum mechanical and electrostatic effects which are present at the nanoscale.

In the second type, presently the most powerful, being able to support stresses of at least 150MPa, the chemical energy in the fuel (methanol, hydrogen or formic acid) is converted to heat by a catalytic reaction between a mixture of fuel and oxygen in the air. The resulting temperature increase in this “continuously shorted fuel cell” muscle causes the contraction of a NiTi (nickel/titanium) shape-memory metal wire that supports a platinum catalyst. Subsequent cooling completes the work cycle by causing expansion of the muscle. These types of muscles should be easy to deploy in robotic devices, since they comprise commercially available shape-memory wires that are coated with a conventional metal catalyst. According to the researchers, the major challenges have been attaching the catalyst to the wires to provide long muscle lifetimes and controlling muscle actuation rate and stroke. A longer term possibility could be to replace the metal catalysts with tethered enzymes which might ultimately lead to artificial muscles powered by food-derived fuels for actuation in the human body – perhaps even for artificial hearts.

These artificial muscles are 100 times stronger than natural muscles, able to do 100 times greater work per cycle and produce, at reduced strengths, larger contractions. Potential applications are diverse and range from advanced, autonomous robots, smart skins and morphing structures for use on space, air and marine craft, to dynamic Braille displays. Significantly, the properties of the two muscle types can be merged to exploit the benefits of both and as all muscles would not be used at the same time, temporarily inactive ones of the first type could be used as ordinary fuel cells and super-capacitors to provide the electrical needs of, for example, autonomous robots and prosthetic limbs. Most importantly, the energy density of chemical fuels such as methanol is more than 30 times higher than that from the most advanced batteries and this can translate into long operational lifetimes without refuelling for autonomous robots. Whilst this research is still at an early stage, the ability to generate significant mechanical forces from chemically- powered artificial muscles is a major break-through which may ultimately pave the way for highly mobile autonomous robots with the capacity to conduct arduous and physically demanding tasks.

Further reading

Von Howard, Ebron, Zhiwei, Yang, Daniel, J.Seyer, Mikhail, E.Kozlov, Jiyoung, Oh, Hui, Xie, Joselito, Razal, Lee, J.Hall, John, P.Ferraris, Alan, G.MacDiarmid and Ray, H.Baughman (2006), “Fuel-Powered Artificial Muscles”, Science, Vol. 311 No. 5767, pp. 1580-3.

Contact: ray.baughman@utdallas.edu