electrolyte solutions with high electrochemical potential (1.5 V), which cause gas generation in the electrolyte. The released gas dramatically increases the actuator stroke from the carbon nanotube sheet. Thickness of the carbon nanotube sheet expands by ≈300% and the sheet plane contracts by 3%. Artificial muscles and giant strokes by MWNT aerogel sheets Highly ordered free-standing aerogel sheets of MWNTs can be realized by simply drawing the sheet from the sidewalls of CVD-grown MWNT forests. UT Dallas researchers came up with the conventional method where they attach an adhesive tape to the sidewalls of MWNT forests and pull the tape at a constant rate as fast as to get 3–5 cm wide aerogel sheets of aligned MWNTs which have exceptional mechanical and optical properties. The aerogel sheets have a density of ≈1.5 mg/cm3, an areal density of 1-3 µg/cm2, and a thickness of ≈20 µm. The thickness is decreased to ≈50 nm by liquid-based densification to decrease the volume. The aerogel sheets can be stretched as much as three times along the width while low-modulus rubber like behavior is remained. Having aerogel sheets of MWNTs, UT researchers fabricated actuators with giant strokes (≈180% actuation along the width) with 5 ms delay time between applying the potential and observing the maximum stroke. Therefore, the actuation rate is slightly better than that of the human muscle. This is a very important achievement considering the actuation rate for artificial muscles used in robots is typically much slower. Furthermore, the use of carbon nanotubes as the building blocks as an artificial muscle also helps in terms of strength and robustness by making the artificial muscle stronger than steel in one direction and more flexible than rubber in the other two directions. The lack of electrolyte solution and temperature robustness of the aerogel sheet in inert ambient makes high temperature operation possible. The actuation stroke decreases by only 50% from its room-temperature value to . Thus, this design of artificial muscles can be quite useful for many industrial applications with the drawback of high-voltage operation for giant strokes. Challenges and future applications As a result, carbon nanotubes have been shown to be great materials for actuation-related applications. The subfield of carbon nanotube actuators have been quite successful and ready for scalable applications, considering there are quite a few conventional and scalable methods for the synthesis of large-scale carbon nanotubes. Carbon nanotube sheets used as electrodes