Gelatin yarns inspired by tendons - Structural and mechanical perspectives

Tendons are among the most robust structures in nature. Using the structural properties of natural tendon as a foundation for the development of micro-yarns may lead to innovative composite materials. Gelatin monofilaments were prepared by casting and spinning and small yarns-with up to ten filaments-were assembled into either parallel or 15° twisted yarns. The latter were intended as an attempt to generate mechanical effects similar to those arising from the crimp pattern in tendon. The mechanical properties of parallel and 15° twisted gelatin yarns were compared. The effect of an increasing number of filaments per yarn was also examined. The mechanical properties were mostly affected by the increasing number of filaments, and no benefit arose from twisting small yarns by 15°. However, since gelatin filaments are elasto-plastic rather than fully elastic, much increased toughness (by up to a factor of five for a ten filament yarn) can be achieved with yarns made of elasto-plastic filaments, as demonstrated by experiments and numerical simulations. The resulting effect shows some resemblance to the effect of crimp in tendons. Finally, we developed a dependable procedure to measure the toughness of single filaments based on the test of a yarn rather than on a large number of individual filament tests.