Strain evaluation of axially loaded collateral ligaments: a comparison of digital image correlation and strain gauges

Abstract

The response of soft tissue to loading can be obtained by strain assessment. Typically, strain can be measured using electrical resistance with strain gauges (SG), or optical sensors based on the digital image correlation (DIC), among others. These sensor systems are already established in other areas of technology. However, sensors have a limited range of applications in medical technology due to various challenges in handling human soft materials. The aim of this study was to compare directly attached foil-type SG and 3D-DIC to determine the strain of axially loaded human ligament structures. Therefore, the medial (MCL) and lateral (LCL) collateral ligaments of 18 human knee joints underwent cyclic displacement-controlled loading at a rate of 20 mm/min in two test trials. In the first trial, strain was recorded with the 3D-DIC system and the reference strain of the testing machine. In the second trial, strain was additionally measured with a directly attached SG. The results of the strain measurement with the 3D-DIC system did not differ significantly from the reference strain in the first trial. The strains assessed in the second trial between reference and SG, as well as between reference and 3D-DIC showed significant differences. This suggests that using an optical system based on the DIC with a given unrestricted view is an effective method to measure the superficial strain of human ligaments. In contrast, directly attached SGs provide only qualitative comparable results. Therefore, their scope on human ligaments is limited to the evaluation of changes under different conditions.

Full-field strain distribution in hierarchical electrospun nanofibrous poly-L(lactic) acid/collagen scaffolds for tendon and ligament regeneration: A multiscale study

“…The DVC full-field strain distribution of SB and EHS produced a strain behavior similar to that experienced in the natural T/L tissue counterpart by using DVC [ 43 ], DIC [ [25] , [26] , [27] , [28] , [29] , [30] , 61 , 62 ] and finite element models [ 63 ]. The progressive stretching and reorganization of internal collagen fibrils/fascicles of T/L during physiological activities is responsible for the nonlinear behavior of their stress/strain curves.…”

“…The progressive stretching and reorganization of internal collagen fibrils/fascicles of T/L during physiological activities is responsible for the nonlinear behavior of their stress/strain curves. This characteristic is typically visible using DIC on T/L and resulting into inhomogeneous strain patterns that follow the local stretch/relaxation during tensile test, reaching mean values from 8% up to 25% depending on the T/L under investigation [ [25] , [26] , [27] , [28] , [29] , [30] , 61 , 62 ]. The inhomogeneous strain patterns were due to the internal rearrangement, and progressive failure, of groups of collagen fibrils of the T/L of interest.…”

Full-field strain distribution in hierarchical electrospun nanofibrous Poly-L(lactic) acid and Collagen based scaffolds for tendon and ligament tissue regeneration: a multiscale study

“…8D) in correspondence of their maximum sliding (εDmax = 10.75±1.30%). The DVC full-field strain distribution of SB and EHS produced a strain behavior similar to that experienced in the natural T/L tissue counterpart by using DVC [43], DIC [26,28,57,58] and finite element models [59]. The progressive stretching and reorganization of internal collagen fibrils/fascicles of T/L during physiological activities is responsible for the nonlinear behavior of their stress/strain curves.…”

“…The progressive stretching and reorganization of internal collagen fibrils/fascicles of T/L during physiological activities is responsible for the nonlinear behavior of their stress/strain curves. This characteristic is typically visible using DIC on T/L and resulting into inhomogeneous strain patterns that follow the local stretch/relaxation during tensile test [26,28,57,58]. Moreover, it is also well established that the collagen fibrils in T/L start damaging in the linear region of the stress/strain curve in a specific point defined as "inflection point" [60].…”