The effect of different preconditioning protocols on repeatability of bovine ACL stress-relaxation response in tension

Abstract

Mechanical characterization of soft tissues such as ligaments remains challenging. There is variability in the measured material parameters of ligaments, most of which is related to natural tissue variability, but some of it can be a result of using different testing protocols. Generally preconditioning (cyclic loading-unloading) is performed prior to actual tests to reduce the experimental variability. Commonly, preconditioning protocols for ligaments with a small strain level and 10 sinusoidal loading-unloading cycles are used. The effect of preconditioning and its parameters including strain level, number of cycles and number of 1 contributed equally to this study. preconditioning repetitions on the repeatability of tensile stress-relaxation tests are poorly known for knee ligaments. In the present study, forty-eight dumbbell-shaped bovine anterior cruciate ligament (ACL) samples were used to evaluate the repeatability of stress-relaxation response. Different preconditioning protocols with 2% and 6% strain levels and 1, 5 or 10 preconditioning repetitions were applied. After preconditioning, one-step stress-relaxation test was carried out twice with an hour resting period in between the tests. The equilibrium stress showed no systematic bias when only one preconditioning repetition was applied (2.0±3.1% difference and p>0.05 between repeated tests). Systematic bias in the peak-toequilibrium stress ratio was not observed when higher strain level and number of repetitions were used (0.5±1.6% difference and p>0.05 between repeated tests). In conclusion, the commonly used preconditioning protocol is capable of producing repeatable equilibrium stress levels of bovine ACLs from stress-relaxation tests in tension. However, if repeatable peak-to-equilibrium stress ratio is desirable, higher strain and number of preconditioning repetitions are recommended.

Viscoelastic characteristics of the canine cranial cruciate ligament complex at slow strain rates

“…Application of the preload was then followed by preconditioning the CCLs to ensure that they were in a steady state and would produce comparable and reproducible load-elongation curves (Butler, Noyes & Grood, 1978;Fung, 1993;Savelberg et al, 1993). Preconditioning involved performing ten loading-unloading cycles up to a maximum load of 10 N at 10 %/min strain rate (Ebrahimi et al, 2019;Woo et al, 1991). Subsequently the CCL was subjected to cyclic tensile loading-unloading tests investigating stress-strain behaviour of the ligament at the toe region through the application of 10 N load at sequential slow strain rates of 0.1%, 1% and 10%/min.…”

Viscoelastic characteristics of the canine cranial cruciate ligament complex at slow strain rates

“…Application of the preload was then followed by preconditioning the CCLs to ensure that they were in a steady state and would produce comparable and reproducible load-elongation curves (Butler et al, 1978;Fung, 1993;Savelberg et al, 1993). Preconditioning involved performing ten loading-unloading cycles up to a maximum load of 10 N at 10 %/min strain rate (Ebrahimi et al, 2019;Woo et al, 1991). Subsequently the CCL was subjected to cyclic tensile loading-unloading tests investigating stress-strain behaviour of the ligament at the toe region through the application of 10 N load at sequential slow strain rates of 0.1, 1 and 10 %/min.…”

“…Each strain rate consisted of three loading-unloading cycles which allowed for reproducible results. Between each two cycles, including the preconditioning procedure, a period of six minutes recovery time was given (Ebrahimi et al, 2019;Viidik, 1968). From the paired stifle joints, the left CCLs were exposed to an ascending strain rate test in which the rate of strain was increased from 0.1 to 1 and to 10 %/min and the right CCLs were exposed 8 to a descending strain rate in which the CCL was tested under decreasing strain rates from 10 to and to 0.1 %/min (Pioletti et al, 1999;Pioletti and Rakotomanana, 2000).…”

Peer Review #1 of "Viscoelastic characteristics of the canine cranial cruciate ligament complex at slow strain rates (v0.1)"

“…Application of the preload was then followed by preconditioning the CCLs to ensure that they were in a steady state and would produce comparable and reproducible load-elongation curves (Butler et al, 1978;Fung, 1993;Savelberg et al, 1993). Preconditioning involved performing ten loadingunloading cycles up to a maximum load of 10 N at 10 %/min strain rate (Ebrahimi et al, 2019;Woo et al, 1991). Subsequently the CCL was subjected to cyclic tensile loading-unloading tests investigating stress-strain behaviour of the ligament at the toe region through the application of PeerJ reviewing PDF | (2020:09:52900:1:1:NEW 13 Nov 2020)…”