Researchers studying the jaws of the ancient sea worm Perinereis cultrifera have identified a new class of materials they call “bio-metals” — substances built from structural proteins and metal ions that behave like neither purely metallic nor purely biological materials.

Scientists from TU Wien and the University of Vienna examined the worm’s jaws using nanoindentation, chemical analysis, and imaging, identifying three defining qualities of bio-metals: hardness, strain mechanics, and ion-protein structure.

The research found that metal ion concentration is higher at the jaw tips, explaining their increased hardness. The jaws also displayed the Nix-Gao nanoindentation size effect, a phenomenon typically seen in metals like copper and silver, in which smaller regions prove harder to indent.

Yet the jaws also showed “size-dependent elasticity — this is a distinguishing feature of bio-metals when compared to standard crystalline metals like copper or silver,” according to researcher Christian Hellmich.

Journal: Biophysics Reviews
DOI: 10.1063/5.0325367
Article Title: “‘Bio-metals’: Ancient biological materials with nanoindentation size effects: Experiments and elements of manifold micromechanics”
Publication Date: July 14, 2026

Source: EurekAlert