“We showed how functional and structural principles from biology could be transferred to technical material systems… Our work constitutes an important step in expanding the design space and tunable functionality of bio-inspired solutions.”Tiffany Cheng
A new approach to producing movable and self-adjusting materials systems has been developed by a team from the University of Freiburg and the University of Stuttgart in Germany. The systems can undergo complex shape changes where they contract and expand due to the influence of moisture in a pre-programmed way, and could lead to new orthotic devices able to adapt to specific patient anatomies and pathologies.
The system was inspired by the movement mechanisms of a plant called the air potato (Dioscorea bulbifera), which climbs trees by applying pressure to the trunk of the host plant by first winding loosely around the tree trunk and then sprouting “stipules”. These are basal outgrowths of the leaves that work to increase the space between the winding stem and the host plant, creating tension in the stem.
As described in the journal Advanced Science [Cheng et al. Adv. Sci. (2021) DOI: 10.1002/advs.202100411], computational design and 3D printing helped the team emulate the complex structural organization of the climbing plant to develop a functional prototype of a self-adjusting orthotic wrist splint that self-tightens like the plant and adapts to the wearer.
This new biomimetic design strategy used changes in moisture to produce shape changes, with a number of swelling and stabilizing layers combining to achieve a complicated movement mechanism that allows it to bend in different directions and by different degrees, producing coiling and forming a helix structure. “Pockets” on the surface cause the helix to be pushed outwards and put under tension, which results in the entire material system contracting.
In an interdisciplinary collaborative effort, such predetermined shape changes were shown to be triggered by a stimulus due the chemical composition of the materials, which consist of stimuli-responsive polymers. As co-leader Tiffany Cheng told Materials Today, “We showed how functional and structural principles from biology could be transferred to technical material systems… Our work constitutes an important step in expanding the design space and tunable functionality of bio-inspired solutions.”
3D printing is being increasingly utilized to produce intelligent material systems that stay in motion after printing, and also autonomously change their shape due to external stimuli, an approach known as 4D printing. As well as wearables for medical and sports applications, bio-inspired 4D printing has potential for adaptive architecture.
While the process is currently limited to existing base materials that respond to moisture, it is hoped one day there will be a wider array of bio-inspired adaptive designs materials that respond to other stimuli, although widespread adoption would require further research into controlling the timing and sequence of self-shaping.
Climbing plant inspires wearable materials systems