Abstract
The term 4D printing is used to describe the 3D printing of systems that through their design and functional materials are responsive to the environment. The goal of 4D printed systems is to establish them as low-energy, lightweight, and functionally integrated alternatives to conventional automation systems. Numerous new materials, fabrication processes and proof-of-concepts for 4D printed actuators and structures have been developed since the emergence of the field in 2014. Many possibilities to combine and leverage different actuation principles have been explored with the vision to create structures that function autonomously in reaction to environmental changes, their reaction embedded into the material and structural design. Systematic design knowledge is needed to consider environment-responsive actuation from an early design stage and integrate it effectively into a system. Since a main goal of this approach is to reduce required energy, an estimation of both functional and environmental performance, in terms of embodied energy and activation energy, needs to be known for different actuation principles and materials to select among them.
While new actuator designs are regularly published, the publications rarely include a performance characterization that considers both functional and environmental performance. This paper provides a first comparison of both functional and energy aspects of environment-responsive actuators. For this purpose, thermo-responsive actuator designs in literature are screened and eight actuators are compared according to their functional material, working principle, actuation force and stroke length. Further design characteristics of weight, materials, embodied and actuation energy are also estimated for the selected actuators. Based on the compiled data, the embodied material energy of the actuators and energy in use are compared and evaluated. The paper concludes with a discussion of the various options and implications for their integration in low-energy design of environment-responsive structures.
