Characterisation of carapace composition in developing and adult ostracods (Skogsbergia lerneri) and its potential for biomaterials

Abstract

The protective carapace of Skogsbergia lerneri, a marine ostracod, is scratch-resistant and transparent. The compositional and structural organisation of the carapace that underlies these properties is unknown. In this study, we aimed to quantify and determine the distribution of chemical elements and chitin within the carapace of adult ostracods, as well as at different stages of ostracod development, to gain insight into its composition. Elemental analyses included X-ray absorption near-edge structure, X-ray fluorescence and X-ray diffraction. Nonlinear microscopy and spectral imaging were performed to determine chitin distribution within the carapace. High levels of calcium (20.3%) and substantial levels of magnesium (1.89%) were identified throughout development. Amorphous calcium carbonate (ACC) was detected in carapaces of all developmental stages, with the polymorph, aragonite, identified in A-1 and adult carapaces. Novel chitin-derived second harmonic generation signals (430/5 nm) were detected. Quantification of relative chitin content within the developing and adult carapaces identified negligible differences in chitin content between developmental stages and adult carapaces, except for the lower chitin contribution in A-2 (66.8 ± 7.6%) compared to A-5 (85.5 ± 10%) (p = 0.03). Skogsbergia lerneri carapace calcium carbonate composition was distinct to other myodocopid ostracods. These calcium polymorphs and ACC are described in other biological transparent materials, and with the consistent chitin distribution throughout S. lerneri development, may imply a biological adaptation to preserve carapace physical properties. Realisation of S. lerneri carapace synthesis and structural organisation will enable exploitation to manufacture biomaterials and biomimetics with huge potential in industrial and military applications.

Organic Controls over Biomineral Ca–Mg Carbonate Compositions and Morphologies

“…Previous studies have demonstrated that acidic proteins promote calcium carbonate nucleation when on solid templates and inhibit crystal growth in solution. ,− In nature, acidic proteins are commonly associated with the biomineralization of carbonates that make up shells, skeletons, and spicules. ,, Aspartic acids in particular were shown to modify calcite crystal morphology by altering the surface energy at certain crystallographic facies. ,− As a consequence, aspartic acid exerts a strong influence on crystal morphology . Chitin also wields a significant influence on ACC and calcium carbonate growth. , Chitin is known to be widespread in biocalcifiers and likely contributes to the formation of calcium carbonates in coralline algae, , crustaceans, ostracods, and mollusks . Laboratory experiments have also demonstrated that chitin has the ability to promote heterogeneous nucleation of calcite at room temperature without the presence of magnesium. , …”

“…46 Chitin also wields a significant influence on ACC and calcium carbonate growth. 47,48 Chitin is known to be widespread in biocalcifiers and likely contributes to the formation of calcium carbonates in coralline algae, 49,50 crustaceans, 51 ostracods, 52 and mollusks. 53 Laboratory experiments have also demonstrated that chitin has the ability to promote heterogeneous nucleation of calcite at room temperature without the presence of magnesium.…”