Hydraulics are sometimes looked at as an alternative to electric motors. Hydraulic systems use an incompressible liquid (as opposed to pneumatics that use a compressible gas) to transfer force from one place to another. Since the hydraulic system will be a closed system (ignore relief valves for now) when you apply a force to one end of the system that force is transferred to another part of that system. By manipulating the volume of fluid in different parts of the system you can change the forces in different parts of the system (Remember Pascal's Law from high school??). So here are some of the basic components used (or needed) to develop a hydraulic system.

We live in a society where human health is increasingly enhanced by artificial augmentation and implantation including hip replacements and hearing aids. French company Carmat have been working for 15 years on the artificial heart, a device that completely replaces the human heart in people with end stage heart disease and a life expectancy of less than two weeks without the surgery. They've recently announced their second trial, commencing in 2017 with the aim to achieve European approval for their device. The Carmat device differs to other robotic heart devices as it is meant to be used in cases of terminal heart failure, instead of being used as a bridge device while the patient awaits a transplant. In Carmat's design, two chambers are each divided by a membrane that holds hydraulic fluid on one side.