Creating objects showing the same dexterity of Nature's product is extremely difficult. We have invented motors to move parts of objects and over time we have seen a shrinking of these motors but still achieving motion, strength and lightness mimicking a finger is still a dream. Problem is, shrinking motors is decreasing the strength and creating a system that can move in three directions like a finger can't be done with motors.
Researchers are experimenting with elastomers, sort of plastics, and are looking for ways to modify the elastomer shape, thus creating movement.
The challenge is to create a correct mix of elastomers in the appropriate architecture that would result in the desired shape change and hence the movements.
At Cornell a team of researchers have developed a process to create an artificial tentacle by 3D printing the elastomers. A computer directs the 3D printer to create elastomers along three axes, longitudinal, transverse and helical. The 3D printer can accurately create antagonistic pair of pleated actuators in the three axes, something that would be impossible to do with normal construction methods. The elastomers material is commercially available, the innovation here is in the 3D printing process to create the needed architecture.
This is another example where a 3D printing process can create something that would be impossible using standard manufacturing processes.
The Cornell team feels this is the right path to create an artificial finger as prosthetic.However, it is likely that the first application will happen in robotics.