The phytomimetic potential of three types of hydration motors that drive nastic plant movements

Phytomimetics deals with plant-inspired materials, structures and movements and as such has been only a minor part of biomimetics. Here we analyze and summarize the basic motors and mechanisms of plant mobility and their potential for inspiring future phytomimetic designs. Like other organisms plants have subcellular micromotors in the form of proteins (e.g., P-proteins or forisomes that expand and contract in dependence of external calcium ions). Macromovements of plants, however, are significantly different from those in animals. Lacking endoskeleton and contracting “muscle” cells, mobile plant structures resemble multi-chambered inflatables with elastic walls and internal pressures exceeding those of car tires. They are powered by hydration motors of osmotic, colloid or fibrous design. These motors are not externally attached to a lever-based joint (as in many animals and machines) but are an integrated and often inconspicuous part of the mobile structure. While early phyto-inspired designs such as barbed wire, coiled extension wires, Velcro and low-speed airplane wings were based on easily deduced, passive plant features, future designs are likely to derive from less obvious characteristics. They require a new level of cooperative efforts from both biologists and engineers to understand and use the time-tested structures and machines that plants have developed and perfected over millions of years of evolution. Reviewing basic principles of power generation and transmission in plant movements, the present paper intends to broaden the interest in phytomimetics.