The artificial muscle

The android will not exist without artificial muscles. Currently robots have a rather mechanical approach, however, the artificial muscle exists and is effective.

February 2014: Creating a muscle with fishing line

The principle is simple and is described in a video. Using plain synthetic yarn, we arrive at a more stronger fiber than that of biological muscle, 100 times stronger. To achieve this the fishing line is wire is rolled up, more and more, until you can not squeeze again. When the tension is released, it tends to return to the spiral shape itself. To loosen it takes a little heat. At the same time, it contracts. So far it is not very interesting, because heating and cooling the fibers to active or relax the muscle takes some time ... But it was also found that placing the fibers in a sheath that conducts electricity, one can manage to control the muscle and make movements by sending current.
It is true that the idea of ​​using a twisted cord is not entirely new, it is described in this document released in 2010: Twisted String Actuation. But in this case, the twist is induced by an actuator, we do not use a fiber already twisted, this is slower.

The manufacturing process is very inexpensive, and therefore it is expected to see the artificial muscle for sale very soon. This will significantly advance robotics.
Ref Science Mag: Artificial muscles from fishing line and sewing thread.

Wax and carbon nanotubes

The latest advance in the field is to use a compound of carbon nanotubes and wax for making an artificial fiber able to relax or contract under the effect of an electrical pulse. The artificial muscle fiber is almost 100 times more potent than the natural fiber and react in a quarter of a second. The solution devised by the University of Dallas has been to fill the nanotube with wax then braid them to make a fiber. This structure allows both rotations and contractions.
Reference:

"Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles" by Sciencemag.

Electroactive polymer: A muscle for surgery

There are plans to use artificial muscles to compensate for disabilities, and the same technology should be functional for robots with a mixed format as the form of exoskeleton to reduce the effort of physical force or leverage.
The Archives of Facial Plastic Surgery describe a method which is a combination of silicon and electrodes to complement biological deficient muscles.
This process called EPAM (electroactive polymer Artificial Muscle) contracts or relaxes the muscles in silicon based on the voltage applied.

Aerogel

This method takes the form of leaf Aerogel composed of carbon nanotubes, ultra light and flexible as rubber and that can relax up to ten times its length. It can withstand temperatures as low as -200 ° or as high as 1500 °!

Very effective, it can contract to 1000 times faster than a biological muscle to 30,000 times per second. According to the electric voltage applied to this material, it contracts or relaxes, as do our muscles.

This material currently lacks strength to equip robots while electroactive polymers are stronger than human muscles.

Reference:

UT Dallas Alan G. MacDiarmid NanoTech Institute.

Muscle in fibers of carbon nanotubes

This new material allows flexibility 1000 times greater than the achievements of polymer. It works the same way as natural muscles, reacting to the stimulation of an electric current.
It is more flexible than rubber and 100 times stronger than human muscle.

The applications are numerous, but the most important are the creation of prosthetics and robotics, finally with something closer to and even better than what nature provides.

The Jamming Gripper, a cheap alternative

An entirely different approach is to use the phase of a material as a source of movement and grip means, and it is effective.

MIT has shown in a Video how could operate such a device. It needs upgrading to meet the fineness of the fingers, but it is fully functional. It is composed of a pipe filled with any substrate provided it is granulated. It become smooth when air is blown and becomes rigid when it is aspirated. Control of air flow in different parts of the "member", enable to create the desired movements ...