Humans started making body armour more than 3000 years ago but have never managed to produce anything that reaches the combination of protection and flexibility that’s evolved many times in nature.
Recent advancements in the development of bio-inspired flexible armour have used parametric modelling and three-dimensional (3D) printing to investigate the mechanical behaviour of both biological and bio-inspired materials and structures.
Most previous research on biological flexible armours has focused on fish scales (which consist of a mineralised collagen-based plywood-like structure) or osteoderms (porous bony plates).
The study team – drawn from several US universities and one in Germany – examined how chitons have evolved to protect themselves from attack while maintaining a range of motion.
“We studied this biological material in a very detailed way,” says Ling Li, from Virginia Tech, US. “We quantified its internal microstructure, chemical composition, nano-mechanical properties, and three-dimensional geometry.”
Chitons can flex upward as needs when they’re moving over uneven surfaces; their armour’s so flexible they can curl up into a ball if they’re dislodged from rocks.
They have eight large shell plates on their backs for protection, and an array of mineralised scales to protect the girdle skirt that encircles the plates.
The authors report that these scales are unlike fish scales or reptilian osteoderms in that they are almost pure mineral – they lack any significant quantities of organic material.
Individual scales are rigid, but the scaled girdles are extremely flexible and capable of conforming to rough surfaces, while also locally wrinkling along the margins to form channels for the circulation of seawater.
The authors explored the structure and function of the mineralised scales from different species of chiton using a range of different techniques.
They then designed and 3D printed synthetic polymer armour to further analyse the scales’ structure and function. They also demonstrated how the 3D printed flexible armour can be used as knee pads to protect against broken glass.