How should we measure and report elasticity in aortic tissue?

Area of Science:

• Biomedical Engineering
• Materials Science
• Cardiovascular Research

Background:

• Discrepancies exist in stress-strain definitions for measuring aortic tissue elastic modulus.
• Lack of consensus on the optimal stress-strain definition hinders consistent research findings.

Purpose of the Study:

• To evaluate the impact of various stress-strain definitions on elastic modulus measurements in aortic tissue.
• To recommend a standardized stress-strain definition for consistent analysis of aortic tissue mechanics.

Main Methods:

• Tensile properties of circumferential aortic specimens from patients with ascending thoracic aortic aneurysm (ATAA) were tested uniaxially.
• Multiple stress (second Piola-Kirchhoff, engineering, true) and strain (Almansi-Hamel, Green-St. Venant, engineering, true) definitions were applied.
• Elastic modulus was determined using combinations of these stress and strain definitions.

Main Results:

• The Almansi-Hamel strain definition resulted in the highest non-linear stress-strain relation, potentially overestimating the elastic modulus.
• The Green-St. Venant strain definition showed the lowest non-linear relation, possibly underestimating the elastic modulus.
• Engineering stress and strain are unsuitable for soft tissues due to limitations with large strains and displacements. Definition choice significantly impacts maximum elastic modulus but not hypertensive elastic modulus.

Conclusions:

• The selection of stress-strain definitions significantly influences elastic modulus outcomes in soft tissue analysis.
• The true stress-true strain definition, despite its non-linearity, is favored for its accuracy in capturing instantaneous material response.
• Standardizing stress-strain definitions is essential for reliable and reproducible research in aortic tissue mechanics.