The Sturdy Chiton Girdle

Once again, mollusks have taken center stage in the research discipline of Biomimetics, also known as Bioinspiration. Biomimetics is a branch of engineering that derives design ideas and inspiration from special structures, materials, and substances in animals and plants. Matthews Connors of the Massachusetts Institute of Technology and his colleagues described, in a recent issue of Nature Communications, the engineering and material properties of the girdle and girdle scales in the chiton Rhissoplax canariensis. Chitons are members of the class Polyplacophora, marine mollusks that live mostly on hard surfaces and that have eight, or rarely seven, shell plates. The girdle is the structure that surrounds the shell plates. Quite often, the girdle is formed by overlapping scales, like tiles on a roof, or a medieval coat-of-mail. (The classic common name for chitons in England is “coat-of-mail shells.”) The mineralized scales in the chiton girdle provide protection to the underlying soft body combined with the flexibility needed for locomotion on irregular, hard surfaces.

The chiton Rhyssoplax canariensis under a scanning electron microscope. PP = primary shell plates; G = girdle. Rectangle indicates area of detail in illustration below. This is Figure 1a in Connors et al. (2019). 1 mm = 0.04 inch.

Using complex techniques such as electron microscopy, instrumented nanoindentation, and micro-computed tomography, Connors and his collaborators studied the girdle’s material composition, biomechanical properties, and its potential for the design of light, strong, and flexible armor. Individual scales consist of a composite material that includes a fibrous organic matrix surrounded by calcium carbonate, which renders the scales extremely hard and resilient. Relying on sophisticated computer models and 3-D printing, Connors and his collaborators created a synthetic, bio-inspired flexible scaled armor that mimicks the properties of the chiton girdle. For those of you who are more technically inclined, here is a copy of the article.

Detail of the girdle scales in Rhyssoplax canariensis under a scanning electron microscope. Adapted from Figure 1c in Connors et al. (2019). 1 mm = 0.04 inch.

Connors, M., T. Yang, A. Hosny, Z. Deng, F. Yazdandoost, H. Massaadi, D. Eernisse, R. Mirzaeifar, M.N. Dean, J.C. Weaver, C. Ortiz, and L. Li. 2019. Bioinspired design of flexible armor based on chiton scales. Nature Communications 10: 5413. doi.org/10.1038/s41467-019-13215-0