During parental development, the umbilical cord is physiologically and genetically part of the fetus and, in humans, normally contains a pair of arteries and a vein. The umbilical vein (UV) supplies the fetus with oxygenated, nutrient-rich blood from the placenta. In contrast, the fetal heart pumps deoxygenated, nutrient-depleted blood through the umbilical arteries (UA) back to the placenta. Although the extreme importance of the mechanical properties of the UA and UV, such as linear elasticity and non-linear hyperelasticity, is fully recognized, detailed viscoelastic, time-dependent, mechanical behavior of umbilical cord components is still lacking. A deep investigation on the quasilinear, viscoelastic (QLV), time-dependent, mechanical behavior of the UV could help to understand its long-term patency for the treatment of coronary artery disease (CAD) as a coronary artery bypass graft (CABG).

In the present study, the mechanical properties during tension of the human umbilical artery and umbilical vein were evaluated using a QLV approach. A ramp of stress-relaxation tests were performed on UA and UV samples extracted from term Caesarian deliveries, after uncomplicated pregnancies, from eight female umbilical cords. The QLV coefficients were calculated by fitting the experimental stress-relaxation data to the material model.

The results revealed that the peak stress in UA samples is significantly higher than that of UV samples. In addition, the equilibrium stress was reached in about 50 seconds for both the UAs and UVs in tension.

The findings of this study could have implications, not only for understanding the viscoelastic, time-dependent, mechanical behavior of UAs and UVs, but also for interventions and surgeries, including balloon-angioplasty, bypass and stenting.