Robotic materials are composite materials that combine sensing, actuation, computation, and communication in a repeatable or amorphous pattern.[1] Robotic materials can be considered computational metamaterials in that they extend the original definition of a metamaterial[2] as "macroscopic composites having a man-made, three-dimensional, periodic cellular architecture designed to produce an optimized combination, not available in nature, of two or more responses to specific excitation" by being fully programmable. That is, unlike in a conventional metamaterial, the relationship between a specific excitation and response is governed by sensing, actuation, and a computer program that implements the desired logic.[citation needed]