Effect of elastin degradation of patellar tendon on the quasi-static tensile mechanical properties
Liu Xiaoyun1, Deng Yuping1, 2, 3, Li Feifei1, Zhao Dongliang3, 4, Yang Yang1, Huang Tao1, 5, Tan Wenchang3, 4, Wu Yaobin1, Huang Wenhua1, 6, Li Yanbing1
1Guangdong Engineering Research Center for Translation of Medical 3D Printing Application; 2Department of Orthopedics and Traumatology, Integrated Hospital of Traditional Chinese Medicine and Western Medicine, Southern Medical University; 3Institute of Biomedical Engineering, Shenzhen Bay Laboratory; 4School of Chemical Biology and Biotechnology; 5The Third Affiliated Hospital of Guangzhou University of Chinese Medicine; 6The Third Affiliated Hospital of Southern Medical University
Abstract: BACKGROUND: Patellar tendon is an important structure to maintain the stability of the knee joint and exhibits unique nonlinear mechanical properties under tension, but the effect of elastin on the mechanical behavior of the patellar tendon under tensile loading is still unclear.
OBJECTIVE: To study the effect of elastin on the mechanical properties of patellar tendon through targeted enzyme treatment of elastin.
METHODS: (1) Thirty fresh porcine patellar tendons, weighing 40–50 mg, were evenly divided into five different elastase concentrations (0, 1, 5, 10, 20 U/mL) or incubated in elastase solutions for five different times (0, 1, 4, 6, 12 hours), and finally the elastin content was detected. (2) Patellar tendon was treated in PBS or 5 U/mL elastase for 8 hours, then Verhoeff Van Gieson (VVG) staining and Masson staining were performed. (3) Twenty fresh porcine patellar tendons were randomly divided into PBS control group and elastase-treated group. After 9 points were marked on the sample surface, the longitudinal tensile test and stress relaxation test were carried out. The displacement of the marked points was calculated by optical non-contact method for subsequent strain analysis and stress calculation. The samples were incubated in PBS or 5 U/mL elastase for 8 hours, and the same mechanical test was performed again.
RESULTS AND CONCLUSION: (1) Incubating in 5 U/mL elastase for 8 hours could meet the requirements of this experiment. (2) Compared with pre-treatment, tissue tensile stress was significantly reduced in the PBS and elastase-treated groups, which were both decreased by about 40% (P < 0.001, P < 0.01). Compared with pre-treatment, the relaxation percentage after treatment increased significantly, with a difference of about 12% (P < 0.05). On the normalized average stress-time curve, the stress of elastase-treated treatment group decreased more than that of PBS group, with a difference of about 16% (P < 0.0001). (3) The above results showed that elastin played an important role in the tensile mechanical properties and viscoelastic properties of patellar tendon, further supplementing the understanding of the multiscale tendon structure-function relationships, which would be beneficial to the development and improvement of microstructure constitutive model in the future to simulate patellar tendon lesions and surgical intervention.
Key words: patellar tendon, biomechanics, stress relaxation, elastin, quasi-static tensile, elastase, viscoelasticity, enzyme treatment