Learning from Self‐Sealing Deformations of Plant Leaves: The Biomimetic Multilayer Actuator

Abstract

During evolution, plants have developed various functional principles for sealing and healing wounds. Prime examples are succulent leaves of Delosperma cooperi that seal external injuries within 60 min. Cross sections of intact leaves show a centripetal multilayer structure consisting of five tissues alternately under tensile and compressive prestress. Injuries destroy this mechanical equilibrium causing a deformation of the entire leaf until a new equilibrium is reached, and the wound edges meet, thereby sealing the fissure. Following this functional principle of D. cooperi leaves, a planar three‐layer materials system consisting of a sheet of shape memory polymer (SMP) with programmed temporary geometry sandwiched between two polydimethylsiloxane (PDMS) sheets is developed. After the individual sheets are bonded at room temperature, the application of heat treatment without mechanical constraints results in a prestressed multilayer system. The damage‐triggered bending behavior of the three‐layer system is described by means of an analytical model and feasibility tests establishing the self‐sealing functionality of the system. Thus, a biomimetic materials system with a self‐sealing function within the framework of a biomimetic biology push process is developed. However, the discussion herein has gone beyond the biological model, because the self‐sealing three‐layer materials system can additionally serve as an actuator.