Effect of strain rates on the mechanical response of whole muscle bundle.

Muscle injuries frequently happen during sports activities and exercise, which could have serious consequences if not diagnosed and treated promptly. This research aims to investigate the quasi-static and dynamic responses of over 30 fresh frog semitendinosus muscles utilizing Split Hopkinson Pressure Bars (SHPB) and a material testing system under strain rates between 0.001 ~ 200 s-1. To accommodate the special shape of muscle-tendon-bone samples, PLA clampers were produced by the 3D printer to properly hold and prevent slipping during the testing process. The mechanical characteristics of the whole muscle bundle, including Young's modulus and stress-strain curve, are illustrated at various strain rates. The findings showed that the muscle properties were sensitive to strain rate when under passive deformation. Both maximum stress and Young's modulus increased with the rise of strain rate, and modulus at 200 s-1 can be as high as 10 times compared with quasi-static conditions.

Dynamic tensile properties of porcine knee ligament.

BACKGROUND: The knee plays an essential role in movement. There are four major ligaments in the knee which all have crucial functionalities for human activities. The anterior cruciate ligament (ACL) is the most commonly injured ligament in the knee, especially in athletes. OBJECTIVE: The aim of this study was to investigate the dynamic tensile response of the porcine ACL at strain rates from 800 to 1500 s-1 for simulations of acute injury from sudden impact or collision. METHODS: Split Hopkinson Tension Bar (SHTB) was utilized to create a dynamic tensile wave on the ACL. Stress-strain curves of strain rates between 800 s-1 to 1500 s-1 were recorded. RESULTS: The results demonstrated that the elastic modulus of the porcine ACL at higher strain rates was six to eight times higher than that of porcine and human specimens at quasi-static strain rate. However, the failure stress was quite similar while the strain was much smaller than that at the lower strain rate. CONCLUSIONS: ACL is highly strain rate sensitive and easier to break with lower failure strain when the strain rates increased to more than 1000 s-1. The stress-strain curves indicated that the sketching crimps at the slack region did not happen but switched to the sliding process of collagen fibers and was accompanied by some ruptures, which can develop into tears when strain and stress were large enough. On the other hand, the viscoelastic properties of the ligament, depending on the proteoglycan matrix and the cross-link, showed a limited value in the studied strain rate range.