These systems have both electrical and mechanical components.
Today there are many more fabrication techniques and materials available.
Sensors are non-invasive while actuators modify the environment. Micro sensors are useful because their physical size allows them to be less invasive. Micro actuators are useful because the amount of work they perform on the environment is small and therefore can be very precise. Central Microstructure Facility at the UK's Rutherford Appleton Laboratory. Cornell's MEMS Lab is run by Dr. Noel C. MacDonald and is affiliated with the Cornell Nanofabrication Facility.