I.V. Khaydukova – Post-graduate Student, Department “Biomedical engineering systems”, Bauman Moscow State Technical University 

E-mail: irina.khaydukova@mail.ru

N.V. Belikov – Assistant, Department “Biomedical engineering systems”, Bauman Moscow State Technical University 

E-mail: aneox@list.ru

A.S. Borde – Post-graduate Student, Department “Biomedical engineering systems”, Bauman Moscow State Technical University 

E-mail: aenea.doerb@mail.ru

G.V. Savrasov – D.Sc.(Eng.), Professor, Department “Biomedical engineering systems”, Bauman Moscow State Technical University 

E-mail: savrasov2000@mail.ru

The force-displacement dependence during mechanical testing of biological tissues under uniaxial loading and unloading is different and forms a hysteresis loop. The diagram will also be different during cyclic testing, and therefore the registration of the mechanical parameters of the blood vessels immediately after sample fixation in the testing machine is incorrect. Therefore, it is necessary to carry out preliminary cyclic tests, during which there is a continuous tissue softening until a certain saturated state is reached, to obtain reproducible mechanical test results that are close to the tissue in vivo parameters. The area of the hysteresis loop decreases with each preprocessing cycle and its rate also decreases which is called the stress softening effect. After a certain number of cycles, the hysteresis becomes constant. The purpose of this work is to analyze the cyclic preprocessing techniques for registration of mechanical characteristics of blood vessels. In a literature review the existing methods of cyclic preprocessing of blood vessels are described, including such parameters as the controlled characteristics, the number of preprocessing cycles, the shape of the samples and tests conditions. Most often, the vascular tissue testing is carried out using non-destructive tests that do not provide information on any threshold values. The remaining tests determine only the maximum stress value. Considering the variation of the cyclic preprocessing parameters in measurement of the mechanical characteristics of the vascular wall in different studies, it is necessary to develop a unified method that takes into account their effect. The technique should include the study of the onset of microscopic damages (elastic limit), because after this point irreversible changes in the tissue structure occurs, leading to the weakening of the tissue and larger deformations. The maximum stress or deformation preprocessing value should always be less than the elastic limit. The most informative technique should provide the values of the mechanical characteristics of vessels over the entire stress range up to rupture. In this case, the preprocessing should be repeated if the level of stress or deformation changes. Thus, the most reproducible parameters of the target tissue are obtained. The evaluation of the onset of microscopic damages can be performed histologically or by repeated testing at the physiological level of stress. For determination of the required number of cycles for a certain type of tissue it is necessary to provide a quantitative criterion and its threshold value, according to which a decision is made whether two subsequent stress-strain curves fit sufficiently to consider the preprocessing completed. A preliminary determination of in situ stretching of veins and arteries is also recommended before their removal.

1. Fratzl P. Collagen. Structure and mechanics, an introduction // Collagen. Springer, Boston, MA. 2008. P. 1–13. 
2. Holzapfel G.A., Gasser T.C., Ogden R.W. A new constitutive framework for arterial wall mechanics and a comparative study of materi-al models // Journal of elasticity and the physical science of solids. 2000. V. 61. № 1–3. P. 1–48.
3. Peña E. On the Microstructural Modeling of Vascular Tissues // Computational and Experimental Biomedical Sciences: Methods and Applications. Springer, Cham. 2015. P. 19–47. 
4. Raghavan M.L., Webster M.W., Vorp D.A. Ex vivo biomechanical behavior of abdominal aortic aneurysm: assessment using a new mathematical model // Annals of biomedical engineering. 1996. V. 24. № 5. P. 573–582. 
5. Pasquesi S.A., Liu Y., Margulies S.S. Repeated loading behavior of pediatric porcine common carotid arteries // Journal of biomechanical engineering. 2016. V. 138. № 12. P. 124502.
6. Holzapfel G.A., Sommer G., Gasser C.T. et al. Determination of layer-specific mechanical properties of human coronary arteries with nonatherosclerotic intimal thickening and related constitutive modeling // American Journal of Physiology-Heart and Circulatory Physi-ology. 2005. V. 289. №. 5.  P. H2048–H2058. 
7. Savrasov G.V., Belikov N.V., Hajdukova I.V. Issledovanie mekhanicheskih svojstv protezov krovenosnyh sosudov pri izmene-nii parametrov okruzhayushchej sredy // Medicinskaya tekhnika. 2017. № 2. S. 9–12. 
8. Fung Y. Biomechanics: mechanical properties of living tissues. Springer Science & Business Media, 2013. 
9. Schulze-Bauer C.A.J., Regitnig P., Holzapfel G.A. Mechanics of the human femoral adventitia including the high-pressure response // American Journal of Physiology-Heart and Circulatory Physiology. 2002. V. 282. № 6. P. H2427–H2440.
10. Holzapfel G.A., Fereidoonnezhad B. Modeling of damage in soft biological tissues // Biomechanics of Living Organs. 2017. 
11. P. 101–123. 
12. Donovan D.L., Schmidt, S.P., Townshend S.P. et al. Material and structural characterization of human saphenous vein // Journal of vas-cular surgery. 1990. V. 12. № 5. P. 531–537. 
13. Sokolis D.P. Passive mechanical properties and constitutive modeling of blood vessels in relation to microstructure // Medical & biologi-cal engineering & computing. 2008. V. 46. № 12. P. 1187–1199. 
14. Alastrué V., Peña, E., Martínez, M.A. et al. Experimental study and constitutive modelling of the passive mechanical properties of the ovine infrarenal vena cava tissue // Journal of biomechanics. 2008. V. 41. № 14. P. 3038–3045.
15. Karimi A., Navidbakhsh M., Alizadeh M. et al. A comparative study on the mechanical properties of the umbilical vein and umbilical ar-tery under uniaxial loading // Artery Research. 2014. V. 8. № 2. P. 51–56. 
16. Sommer G., Regitnig P., Kö ltringer L. et al. Biaxial mechanical properties of intact and layer-dissected human carotid arteries at physio-logical and supraphysiological loadings // American Journal of Physiology-Heart and Circulatory Physiology. 2009. 
17. V. 298. № 3. P. H898–H912. 
18. Kang T., Resar J., Humphrey J.D. Heat-induced changes in the mechanical behavior of passive coronary arteries // Journal of biome-chanical engineering. 1995. V. 117. № 1. P. 86–93.
19. Desch G.W., Weizsäcker H.W. A model for passive elastic properties of rat vena cava // Journal of biomechanics. 2007. V. 40. 
20. № 14. P. 3130–3145.
21. Rezakhaniha R., Stergiopulos N. A structural model of the venous wall considering elastin anisotropy // Journal of biomechanical engi-neering. 2008. V. 130. № 3. P. 031017.
22. Veselý J., Horný L., Chlup H. et al. Constitutive modeling of human saphenous veins at overloading pressures // Journal of the mechan-ical behavior of biomedical materials. 2015. V. 45. P. 101–108. 
23. Zhao J., Andreasen J.J., Yang J. et al. Manual pressure distension of the human saphenous vein changes its biomechanical properties – implication for coronary artery bypass grafting //Journal of biomechanics. 2007. V. 40. № 10. P. 2268–2276.
24. Sokolis D.P. Passive mechanical properties and constitutive modeling of blood vessels in relation to microstructure // Medical & biologi-cal engineering & computing. 2008. V. 46. № 12. P. 1187–1199. 
25. Zhou J., Fung Y.C. The degree of nonlinearity and anisotropy of blood vessel elasticity //Proceedings of the National Academy of Sci-ences. 1997.  V. 94. № 26. P. 14255–14260. 
26. Belikov N.V., Borde A.S., Volchenkova A.M. Opredelenie biomekhanicheskih harakteristik krovenosnyh sosudov pri odnoosnom rastyazhenii // Molodezhnyj nauchno-tekhnicheskij vestnik. 2016. № 2 (http://sntbul.bmstu.ru/doc/835845.html)