Fig. 3: Mechanical properties investigation of rTRM7 fiber.

a A typical strain-stress curve of the rTRM7 fiber stretched to rupture in wet condition. Inside images are an rTRM7 fiber before and after stretching. b Strain-stress curves of the rTRM7 fiber under cyclic tensile test at maximum strain of 200%. c Length change recording for rTRM7 fibers (n = 5) referring to initial state in a cyclic tensile test corresponding to the cyclic tensile test shown in figure b. S1 is unstrained state of fresh rTRM7 fiber. S2 is rTRM7 fiber after first stretch cycle. S3 is recovered rTRM7 fiber after a 2-h incubation in CaCl₂ buffer. d Micro images (left) and SEM images (right) of side view (top) and sectional view (bottom) of the rTRM7 fibers in untrained, strained, and relaxed state corresponding to S1, S2, and S3 in figure c. e Representative strain-stress curves of rTRM7, dehydrated and rehydrated rTRM7 fibers. f Representative strain-stress curves of rTRM7 and rTRM7’ fiber stretched to rupture in wet condition. g Raman spectra of rTRM7 and rTRM7’ fibers corresponding to f. h Representative strain-stress curves of rTRM7, rTRM7”, and Ca²⁺ recovered rTRM7” fibers stretched to rupture in wet condition. i FTIR adsorption spectrum of rTRM7 fiber, rTRM7” fiber, and Ca²⁺ recovered rTRM7” fiber corresponding to h. The band of carboxy in rTRM7” fiber at 1073 cm⁻¹ blue shifted to 1111 cm⁻¹ indicated calcium-carboxy coordination was removed in rTRM7” and recovered in Ca²⁺ recovery rTRM7” fiber. arb. units, arbitrary unit. j Schematic illustration of lamellar structure and chemical bonds of recombinant protein fiber.