No abstract

Biaxial tests are commonly used to investigate the mechanical behaviour of anisotropic soft biological tissues such as cardiovascular tissues. However, there is still no clear understanding of the influence that the biaxial test setup conditions may have on the computing material stress of the experimental results. The aim of the present study is to further investigate the accuracy of calculated material stress from measured force during biaxial tests using Finite Element Methods (FEM). The biaxial mechanical response of ascending aorta and pulmonary artery tissue samples was obtained by FEM simulation under two different gripping methods: (i) a system with noodle clamps and (ii) a clamped system with needles which leave the specimen's edges free to expand laterally.The results show that the clamped method whose joints allow free movement in the lateral direction produces stresses closer to the universally accepted formulation of biaxial material stress in the central region. However, the system with noodle clamps, commonly used to grip the sample, produces an alteration of the measurement stresses. Our simulations show results giving an inaccurate estimation of the stress at the centre of the sample. In some cases the stresses are overestimated, and in others underestimated depending on the anisotropy of the sample. We can conclude that the clamped system with needles which leave the specimen's edges free to expand laterally should be used as an efficient methodology to other commonly used gripping methods for biological tissues with anisotropic materials.

Active commuting to school has health implications for young people. Previous research has shown the need to consistently define the concept of “active commuter”, given that assessment as well as comparison between studies may be hindered by current discrepancies in frequency criteria. Using a sample of 158 Spanish students (12th–13th grade, 60.8% girls), the current study aimed to compare several cut-off criteria to rigorously identify the frequency of weekly active trips to school in order to categorize adolescents as active or passive commuters, and to analyze whether the threshold living distance to school is associated with the different trip cut-off criteria. Percentages of active commuters ranged from 75% to 88.6%, varying significantly depending on the cut-off criteria (5–10 active trips/week) used. The results also support the need to be stricter in the selection of a cut-off criterion when the distance to the school becomes shorter. Our findings highlight the importance of following a standard criterion to classify individuals as active or passive commuters, considering the characteristics of the context in which each study is conducted.