A Data-Driven Memory-Dependent Modeling Framework for Anomalous Rheology: Application to Urinary Bladder Tissue

TL;DR

This paper presents a novel data-driven fractional viscoelastic modeling framework for bio-tissues, specifically urinary bladder, capturing complex relaxation behaviors across multiple time scales and strains with high accuracy.

Contribution

It introduces a two-stage fractional modeling approach combining linear and nonlinear viscoelasticity, tailored for bio-tissue rheology, validated on porcine urinary bladder data.

Findings

Fractional Maxwell model effectively captures short/long-term behaviors.

The fractional quasi-linear model achieves errors below 2%.

Model remains accurate across multiple strains without recalibration.

Abstract

We introduce a data-driven fractional modeling framework aimed at complex materials, and particularly bio-tissues. From multi-step relaxation experiments of distinct anatomical locations of porcine urinary bladder, we identify an anomalous relaxation character, with two power-law-like behaviors for short/long long times, and nonlinearity for strains greater than 25%. The first component of our framework is an existence study, to determine admissible fractional viscoelastic models that qualitatively describe the linear relaxation behavior. After the linear viscoelastic model is selected, the second stage adds large-strain effects to the framework through a fractional quasi-linear viscoelastic approach, given by a multiplicative kernel decomposition of the selected relaxation function and a nonlinear elastic response for the bio-tissue of interest. From single-relaxation data of the urinary bladder, a fractional Maxwell model captures both short/long-term behaviors with two fractional orders, being the most suitable model for small strains at the first stage. For the second stage, multi-step relaxation data under large strains were employed to calibrate a four-parameter fractional quasi-linear viscoelastic model, that combines a Scott-Blair relaxation function and an exponential instantaneous stress response, to describe the elastin/collagen phases of bladder rheology. Our obtained results demonstrate that the employed fractional quasi-linear model, with a single fractional order in the range $\alpha = 0.25 - 0.30$, is suitable for the porcine urinary bladder, producing errors below 2% without need for recalibration over subsequent applied strains. We conclude that fractional models are attractive tools to capture the bladder tissue behavior under small-to-large strains and multiple time scales, therefore being potential alternatives to describe multiple stages of bladder functionality.