A New Cryo-jaw Designed For In Vitro Biomechanical Evaluation Of Rat Achilles Tendon

Achilles tendon problems are most often caused by overuse or repeated movements.These movements can happen during sports, work, or other activities, thus, increasingthe number of affected people with Achilles tendon issues. It’s a task for bioengineers tolook for an immediate solution to this problem. In this present study, a new, simple andsecure set of Cryo-jaw are designed for the in vitro tensile testing of the Achilles tendonin rats, in order to solve the problems, the other researchers are facing. The new designCryo-jaw are specified to avoid the problems of slipping and stress concentration bypre-freezing the muscle at-20oC and keep it frozen during the experiment time bypouring liquid nitrogen into the vessel part of the upper fix clamp. This makes sure thatthe muscle remains rigid since the outer part (vessel part of the upper fix clamp) is incongelation. Also the new designs mimic the in vivo condition by submerging theAchilles tendon in37oC saline water during the process of stretching.A biomechanical test was performed with20specimens of native rats’ Achillestendons. The20specimens were dividing into four groups (A, B, C, D) Group A andgroup B each had5specimens frozen in different ways.(Group A) pre-froze the sampleat-20oC for one week. Group B froze the fresh sample by putting it in liquid nitrogenfor1minute. In both groups, the tendons were submerged in37oC saline water duringthe process of stretching; the displacement was set at10mm/min. In (group A), theaverage of the maximum load was determined at (119.2±25N), the displacement tofailure was (1.868±0.174mm), and the Young’s modules mean values were(264.64±108.78MPa). While in (group B), the average of the maximum load wasdetermined to be (90.5±13N), the displacement to failure was (3.6838±0.8825mm), andthe Young’s modules mean values were (66.926±24.743MPa). Group C and D eachgroup had5specimens, the same way used to freeze the sample by fixing the freshsample on the upper clamp device then adding liquid nitrogen into the vessel part, thenthe tendon is stretched without using saline water. Each group was set at differentdisplacement. In (Group C), the displacement was set at10mm/min, while in (group D),the displacement was set at500mm/min. In (group C), the average of the maximumload was determined to be (70±20N), the displacement to failure was (2.966±1.279mm), and the Young’s modules mean values were (86.822±27.915MPa). While in-group D,the average of the maximum load was (53±10N), the displacement to failure was(2.130±0.719mm), and the Young’s modules mean values were (38.078±9.765MPa).