Residual stress and strain in aortic segments

Area of Science:

• Biomedical Engineering
• Cardiovascular Research
• Materials Science

Background:

• The assumption of a stress-free state for vascular segments in their natural configuration is widely accepted.
• This assumption simplifies biomechanical models of arterial function.
• However, the validity of this stress-free assumption requires empirical investigation.

Purpose of the Study:

• To quantify residual strains in vascular segments.
• To determine the extent to which the unloaded arterial wall deviates from a truly stress-free state.
• To assess the implications of these residual stresses on overall arterial biomechanics.

Main Methods:

• Excising 286 oval rings from bovine and porcine aortas.
• Photographically documenting intact rings and radially cut rings that opened into horseshoe shapes.
• Measuring intimal and adventitial boundary lengths from images to compute residual strains.

Main Results:

• Significant residual strains were found in both intimal (average max -0.082) and adventitial (average max 0.085) layers.
• The intima exhibits compressive residual strain, while the adventitia shows tensile residual strain.
• These strains translate to estimated average stresses: -0.188 x 10^5 Pa (compressive) in the intima and 0.195 x 10^5 Pa (tensile) in the adventitia.

Conclusions:

• The traction-free configuration of vascular segments is not truly stress-free.
• Residual intimal compression may counteract in vivo tensile stress, while adventitial tension adds to it.
• These initial stresses, though small, are significant and must be considered in detailed arterial stress analyses.