Research led by Ling Li, associate professor at the Department of Mechanical Engineering, Virginia Polytechnic Institute and State University (VT), has developed 3D printed flexible scaled armor inspired by the chitons, a group of marine mollusks.
The study, featured in the journal Nature Communications, sought to improve on the rigid structures used in man-made armors, which typically compromise on flexibility and maneuverability. Thus, using parametric computational modeling and multi-material 3D printing, flexible, scaled ceramic armor components were created.
“Most mollusks have a single rigid shell, such as the abalone, or two shells, such as clams,” explained Professor Li. “But the chiton has eight mineralized plates covering the top of the creature and around its base, it has a girdle of very small scales assembled like fish scales, that provide flexibility as well as protection.”
The researchers included members from MIT, Harvard Medical School, California State University, Max Planck Institute of Colloids and Interfaces, and the Wyss Institute.
3D printed girdle scale armor
The chiton species possess hundreds of small, mineralized scales arrayed on the soft girdle that surrounds their overlapping shell plates. According to the researchers, this ensures flexibility for locomotion and protection for its underlying soft body and is an excellent model for multifunctional armor design. Moreover, chiton’s girdle scales had not been studied in-depth prior to this study, the team noted.
“We studied this [girdle scales] in a very detailed way,” said Professor Li. “We quantified its internal microstructure, chemical composition, nano-mechanical properties, and three-dimensional geometry. We studied the geometrical variations of the scales across multiple chiton species, and we also investigated how the scales assemble together through 3D tomography analysis.”
As a result, a parametric 3D modeling methodology replicating the geometry of individual scales was developed. This was used to assemble individual scale units on flat or curved substrates, which could then be additively manufactured. Prior to this, scientists from VT developed a way to 3D print piezoelectric materials, which convert mechanical energy into electric current.
Protection-flexibility armor systems
The stiffness of the 3D printed armor derives from the arrangement of the scales which has been further emphasized using computational modeling. This was said to reveal how the scale armor becomes interlocked and rigid when the external load reaches a critical value. When it comes in contact with a force, the scales converge inward upon one another to form a solid barrier.
It was also observed that when the 3D printed scales were not under force, they can move on top of one another to provide differing amounts of flexibility dependent upon shape and placement. Professor Li added, “With these physical prototypes of controlled specimen geometries and sizes, the team conducted direct mechanical testing on them with controlled loading conditions.”
Following these tests, the researchers concluded that the dual protection-flexibility performance of the biological armor system would be suitable for the production of 3D printed protective gear such as kneepads.
“Bioinspired design of flexible armor based on chiton scales” is co-authored by Matthew Connors, Ting Yang, Ahmed Hosny, Zhifei Deng, Fatemeh Yazdandoost, Hajar Massaadi, Douglas Eernisse, Reza Mirzaeifar, Mason N. Dean, James C. Weaver, Christine Ortiz, and Ling Li.
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Featured image shows the 3D printed flexible armor inspired by the chiton mollusk. Photo via Virginia Tech.
