Biomimetic tendrils by 4D-Printing bimorph springs with torsion and contraction properties based on bio-compatible graphene/silk fibroin and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Taking inspiration from plant tendril geometry, in this study, 4D bimorph coiled structures with an internal core of graphene nanoplatelets-modified regenerated silk and an external shell of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) are fabricated by 4D printing. Finite element simulations and experimental tests demonstrate that integrating these biomaterials with different coefficients of thermal expansion results in the temperature induced self-compression and torsion of the structure. The bimorph spring also exhibits reversible contractive actuation after exposure to water environment that paves its exploitation in regenerative medicine, since core materials also have been proven to be biocompatible. Finally, the authors validate their findings with experimental measurements using such springs for temperaturemediated lengthening of an artificial intestine.