Structure and composition of the cuticle of the goose barnacle Pollicipes pollicipes: a flexible composite biomaterial

Arthropods, the largest animal phylum, including insects, spiders and crustaceans, are characterized by their bodies being covered primarily in chitin. Besides being a source of this biopolymer, crustaceans have also attracted attention from biotechnology given their cuticlesâ remarkable and diverse mechanical properties. The goose barnacle, Pollicipes pollicipes, is a sessile crustacean characterized by their body parts covered with calcified plates and a peduncle attached to a substrate covered with a cuticle. In this work, the composition and structure of these plates and cuticle were characterized. The morphology of the tergum plate revealed a compact homogeneous structure of calcium carbonate, a typical composition among marine invertebrate hard structures. The cuticle consisted of an outer zone covered with scales and an inner homogenous zone, predominantly organic, composed of successive layers parallel to the surface. The scales are similar to the tergum plate and are arranged in parallel and oriented semi-vertically. Structural and biochemical characterization confirmed a bulk composition of É -chitin and suggested the presence of elastin-based proteins and collagen. The mechanical properties of the cuticle showed that the stiffness values are within the range of values described in elastomers and soft crustacean cuticles resulting from molting. The removal of calcified components exposed round holes, detailed the structure of the lamina, and changed the protein properties, increasing the rigidity of the material. This flexible cuticle, predominantly inorganic, can provide bioinspiration for developing biocompatible and mechanically suitable biomaterials for diverse applications, including in tissue engineering approaches. The authors acknowledge the funding from the European Regional Development Fund (ERDF) through the North Portugal Regional Operational Programme (NORTE2020), part of the Portugal2020 Partnership Agreement, under the scope of the structured program of R&D&I ATLANTIDA— Platform for the monitoring of the North Atlantic Ocean and tools for the sustainable exploitation of the marine resources (reference NORTE-01-0145-FEDER-000040) and through the Research Infrastructure TERM RES-Hub PINFRA/22190/2016 (reference Norte-01-0145-FEDER-022190), with the latter also being funded by the Portuguese Foundation for Science and Technology (FCT). FCT is also acknowledged for Ph.D. scholarships granted to Flávia C.M. Lobo (2021.07421.BD) and Rita