Fig. 1: Structure and mechanical properties of the native scallop byssal thread.

a Photographs of marine scallop adheres to a given substrate through a byssus with a bundle of threads before and after stretching. b Photographs of a complete byssus derived from scallop. The thread region of scallop byssus is marked in dotted box. c Morphological characterization of the microscopic structure of the byssal thread by SEM. The byssal thread is composed of films folded loosely and aligned along the axis of macroscopic byssus. The insert image refers to X-ray fiber diffraction pattern of the byssal thread. The byssal thread shows a typical diffraction pattern of cross-β strands, in which the meridional reflection is ~4.65 Å (corresponding to the inter-sheet distance within the same layer) and the equatorial reflection is ~9.80 Å (corresponding to the inter-sheet distance between adjacent layers). d A representative strain-stress curve of scallop byssal thread stretched in wet condition (relative humidity ~90% and tensile speed 0.2 mm/s). The byssal thread shows high extensibility reaching up to 327 ± 32%. The insert images show the byssal thread before and after stretching. e The extensibility comparison of scallop byssal thread and several biogenic threads derived from diverse of creatures underwater or on the earth. The scallop byssal thread shows the highest extensibility, which serves a benchmark for high extensible materials. f Quantitively analysis of metal elements in the byssal thread by ICP-MS. Among these polyvalent metals, calcium accounts for the largest proportion in thread region (55.75%). Data are presented as mean values ± SEM. n = 3 biologically independent experiments.