Replicating the shimmering iridescence of a butterfly wing, the hammer-like hardness of a mantis shrimp claw or the strength of mammalian cortical bone is no simple matter.
But a chemical engineering scientist and her research team at the University of South Carolina are pioneering 3D-printing methods to create novel soft materials that mimic the intricate nanostructures found in nature.
“Most of the research we do is nature-inspired,” says Sanaz (Monirosadat) Sadati, an assistant professor in the College of Engineering and Computing whose research prowess on the crystallization of chiral liquid crystals was recognized last year with a CAREER award from the National Science Foundation. “In this research, we’re particularly interested in replicating Bouligand structures found in nature, which are layers of micro- and nano fibers that are slightly twisted with respect to their adjacent layers, resulting in a helicoidal/chiral structure.”
Iridescent beetles and marble berries contain Bouligand structures in their outer layers — chitin in beetles and cellulose in berries — and the chiral or twisted assembly of those layers selectively reflects light at particular wavelengths. As a result, they display eye-catching colors without pigmentation.
Bouligand structures in mantis shrimp claws and mammalian cortical bones exhibit exceptional mechanical properties, owing to the twisted arrangement of chitin or collagen fibers.
Drawing inspiration from these biomaterials, Sadati’s research is focused on developing 3D-printing methods to replicate the micro and nanoscale architecture of the light-reflecting and high-strength structures. To do this, Sadati’s team employs tiny needles as 3D-printing nozzles that inject cellulosic materials as “ink.”
“To design our ink and adjust 3D-printing parameters, we first needed to learn how shear forces in the printing process interact with the Bouligand/chiral structure in inks,” Sadati says. “We discovered that when shear forces are applied — in this case, the force with which the printer pushes the materials through the printer nozzle — the Bouligand structure of cellulosic components is disturbed. So, we had to design our inks in a way that ensures they ultimately regain the helical assembly found in the natural Bouligand material after printing.”
Sadati’s team has recently published papers on their 3D-printing experiments in PNAS (Proceedings of the National Academy of Sciences) and in Small, where it was the featured cover of the May 10, 2023, edition. These two works were led by two of Sadati’s graduate students, Kyle George and Mohsen Esmaeili.
“We are interested in designing these structures for photonic and for mechanical applications,” Sadati says, noting that much work lies ahead, including extensive testing of the physical and mechanical properties of the 3D-printed materials. Her research has been supported with university funding and has been submitted for federal funding.