Irritable bowel syndrome afflicts 10-20% of the global population, causing visceral pain with increased sensitivity to colorectal distension and normal bowel movements. Understanding and predicting these biomechanics will further advance our understanding of visceral pain and complement the existing literature on visceral neurophysiology. We recently performed a series of experiments at three longitudinal segments (colonic, intermediate, and rectal) of the distal 30 mm of colorectums of mice. We also established and fitted constitutive models addressing mechanical heterogeneity in both the through-thickness and longitudinal directions of the colorectum. Afferent nerve endings, strategically located within the submucosa, are likely nociceptors that detect concentrations of mechanical stresses to evoke the perception of pain from the viscera. In this study we aim to: (1) establish and validate a method for incorporating residual stresses into models of colorectums, and (2) predict the effects of residual stresses on the intra-tissue mechanics within the colorectum, and (3) establish intra-tissue distributions of stretches and stresses within the colorectum in vivo. To these ends we developed two-layered, composite finite element models of the colorectum based on our experimental evidence and validated our approaches against independent experimental data. We included layer- and segment-specific residual stretches/stresses in our simulations via the pre-strain algorithm built into the finite element software FEBio. Our models and modeling approaches allow researchers to predict both organ and intra-tissue biomechanics of the colorectum, and may facilitate better understanding of the underlying mechanical mechanisms of visceral pain.

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