UC San Diego

This thesis aims to further the understanding on the structure and mechanical properties of the dermal armor of the boxfish (Lactoria cornuta). Structural differences between collagen regions underlying the hexagonal scutes was observed with confocal microscopy and microcomputed tomography (µ-CT). µ-CT revealed a tapering of the mineral plate from the center of the scute to the interface between scutes, suggesting the structure allows for more flexibility at the interface. High-resolution µ-CT revealed, for the first time, a 3D image of the dermal armor’s complex collagen structure. Helical interfibrillar gaps in the collagen base were found that are structurally similar to micron-sized canals found in the twisted plywood, or Bouligand-type, structure of the lobster, Homarus americanus; thereby, suggesting the collagen in the boxfish is also of a Bouligand-type structure. Nanoindentation further corroborates a Bouligand-type structure by mapping the hardness and reduced modulus of the collagen along the helical axis. Lastly, in-situ scanning electron microscopy and small-angle X-ray scattering tests were performed in shear and tension between two connected scutes. Final failure occurred at the interfacial collagen with all tests, suggesting that this region is structurally designed to preferentially absorb energy during deformation to protect the internal collagen. These findings further the understanding of the structure and mechanics of the dermal armor of the boxfish which help provide a basis to synthesize bioinspired composites for impact-resistant materials, specifically with bioinspired Bouligand-type structures to create novel fiber-reinforced composites.