  4D printing is a new manufacturing paradigm that combines stimuli-responsive
materials, mathematics, and multi-material additive manufacturing to yield
encoded multi-material structures with intelligent behavior over time. This
emerging field has received growing interests from various disciplines such as
space exploration, renewable energy, bioengineering, textile industry,
infrastructures, soft robotics, and so on. Here, as a first attempt, we
consider the energy aspect of 4D printing. By a thermodynamic analysis, we
obtain the theoretical limit of energy consumption in 4D printing and prove
that 4D printing can be the most energy-efficient manufacturing process. Before
that, we clearly underpin 4D printing as a new manufacturing process and
identify its unique attributes.
