Artificial mimosa leaves made of plain paper respond to touch using a paper actuation technology. (Credit: Carnegie Mellon University)

A thin layer of conducting thermoplastic, applied to common paper with an inexpensive 3D printer or even painted by hand, serves as a low-cost, reversible actuator. When an electrical current is applied, the thermoplastic heats and expands, causing the paper to bend or fold; when the current is removed, the paper returns to a pre-determined shape.

Creating a paper actuator is a relatively simple process that employs the least expensive type of 3D printer, an FDM printer that lays down a continuous filament of melted thermoplastic. An off-the-shelf printing filament was used that conducts electricity.