A New Laser Reflectance System Capable of Measuring Changing Cross-Sectional Area of Soft Tissues During Tensile Testing

Abstract

Determination of the biomechanical properties of soft tissues such as tendons and ligaments is dependent on the accurate measurement of their cross-sectional area (CSA). Measurement methods, which involve contact with the specimen, are problematic because soft tissues are easily deformed. Noncontact measurement methods are preferable in this regard, but may experience difficulty in dealing with the complex cross-sectional shapes and glistening surfaces seen in soft tissues. Additionally, existing CSA measurement systems are separated from the materials testing machine, resulting in the inability to measure CSA during testing. Furthermore, CSA measurements are usually made in a different orientation, and with a different preload, prior to testing. To overcome these problems, a noncontact laser reflectance system (LRS) was developed. Designed to fit in an Instron 8872 servohydraulic test machine, the system measures CSA by orbiting a laser transducer in a circular path around a soft tissue specimen held by tissue clamps. CSA measurements can be conducted before and during tensile testing. The system was validated using machined metallic specimens of various shapes and sizes, as well as different sizes of bovine tendons. The metallic specimens could be measured to within 4% accuracy, and the tendons to within an average error of 4.3%. Statistical analyses showed no significant differences between the measurements of the LRS and those of the casting method, an established measurement technique. The LRS was successfully used to measure the changing CSA of bovine tendons during uniaxial tensile testing. The LRS developed in this work represents a simple, quick, and accurate way of reconstructing complex cross-sectional profiles and calculating cross-sectional areas. In addition, the LRS represents the first system capable of automatically measuring changing CSA of soft tissues during tensile testing, facilitating the calculation of more accurate biomechanical properties.

Three-dimensional morphology and strain of the Achilles free tendon immediately following eccentric heel drop exercise

“…Increased strain of the Achilles free tendon measured at the same external load after exercise has been demonstrated following running (Lichtwark et al, 2013) and repeated eccentric heel drops (Obst et al, 2015), and is suggestive of early stage tendon fatigue due to mechanical creep (Fung et al, 2010). Because increased tendon longitudinal strain during tensile loading is closely associated with changes in tendon transverse morphology and strain (Obst et al, 2014b;Pokhai et al, 2009;Reeves and Cooper, 2014;Vergari et al, 2011), a similar relationship might be expected for the changes in tendon morphology and strain that occur in response to an exercise bout. In view of the high rate of exerciserelated injuries of the Achilles free tendon and the potential role short-term changes in tendon transverse dimensions could have on the local mechanical and biological environment (Heinemeier and Kjaer, 2011;Shim et al, 2014;Smith et al, 2013), there is a need to better understand the acute effects of exercise on the tendon 3D morphology and strain.…”

True stress and Poisson's ratio of tendons during loading

“…Pokhai et al (2009) reported a CSA decrease of 13.5 ± 1.9 % at 2.5 % axial strain for bovine deep and superficial digital flexor tendons. In the present study, a CSA decrease of about 10.7 ± 2.8 % was measured at tendon failure Poisson's ratio versus engineering strain for tendon #3.…”

“…Although accurate and not invasive, these systems require long acquisition times which are incompatible with dynamic or quasi-static measurements. A faster laser system (still requiring 20 s for each acquisition) was developed and applied to measure bovine tendons undergoing tensile loads (Pokhai et al, 2009); however, this system requires precise centering of the specimen in the measured zone, a task not easily performed with long specimens that can undergo tensile loads up to 20 kN. A linear scanner laser system, adapted to measurements of biological specimens CSA at rest or during mechanical testing, capable of performing fast acquisitions and not needing precise specimen centering, was recently developed (Vergari et al, 2010a).…”

Effects of gamma irradiation and repetitive freeze–thaw cycles on the biomechanical properties of human flexor digitorum superficialis tendons

“…The second limitation was the use of a micrometric caliper to measure the length and cross-sectional area of the grafts. Currently the laser micrometer system is the more common method to obtain the cross-sectional area of soft tissues (Moon et al, 2006a,b;Pokhai et al, 2009). However, we averaged the cross-sectional area of four levels along the tendons to eliminate any measurement errors.…”