Biomacromolecules in recent phosphate-shelled brachiopods: identification and characterization of chitin matrix

• Published in: Journal of materials science Vol. 56; no. 36; pp. 19884 - 19898
• Main Authors: Agbaje, Oluwatoosin B. A., Brock, Glenn A., Zhang, Zhifei, Duru, Kingsley C., Liang, Yue, George, Simon C., Holmer, Lars E.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.12.2021; Springer; Springer Nature B.V
• Subjects: Analysis; animals; biocompatible materials; Biological products; Biomedical materials; Biopolymers; Calcium phosphate; Calcium phosphates; Characterization and Evaluation of Materials; Chemistry and Materials Science; Chitin; Classical Mechanics; Composites & Nanocomposites; Crystallography and Scattering Methods; Earth Science with specialization in Historical Geology and Palaeontology; Geovetenskap med inriktning mot historisk geologi och paleontologi; Gravimetric analysis; lifestyle; Marine animals; Marine environment; Materials Science; Organic fibers; Polymer Sciences; Polysaccharides; Sheets; Shells; Solid Mechanics; spectral analysis; Spectroscopic analysis; spectroscopy; thermogravimetry
• ISSN: 0022-2461; 1573-4803; 1573-4803
• DOI: 10.1007/s10853-021-06487-9

Phosphate-shelled brachiopods differ in filter-feeding lifestyle, with Lingula anatina an active infaunal burrower, and Discinisca tenuis a shallow marine epibenthic animal. The shells of these animals are built of organophosphatic constituents, the organic fibres/sheets reinforced with calcium phosphate to provide a sophisticated ultrastructural robustness. This investigation examined the nature of the organic fibres in order to improve understanding of how living organisms produce hierarchically structured biomaterials. Unlike powdered samples commonly used in previous studies, organic fibres were isolated for the first time and the shell fractions were purified, in order to study the content and nature of the biopolymer fibres. Biochemical methods including Calcofluor staining revealed a chitin matrix. Ultrastructural analysis, thermal gravimetric analysis, and spectroscopic analyses show that the core polysaccharide framework is composed of layers of β -chitin sheets and/or fibrils that are coated with a fibrous organic matrix. There is more chitin matrix in the L. anatina shells (26.6 wt.%) compared to the D. tenuis shells (12.9 wt.%). Taken together, the data show that the chitin matrix contributes to increased skeletal strength, making L. anatina highly adapted for life as an active burrower. In comparison, D. tenuis contains less chitin and lives as attached epibenthos in a shallow marine environment. Graphical abstract First spectroscopic evidence of β-chitin sheets in recent organophosphatic brachiopods