# Capturing Strain Stiffening Using Volume Controlled Cavity Expansion

## TL;DR

This paper introduces the Volume Controlled Cavity Expansion (VCCE) technique for in-vivo measurement of strain stiffening and shear modulus in soft biological materials, enabling better characterization of nonlinear elastic responses.

## Contribution

The paper presents a novel VCCE method that allows in-vivo measurement of strain stiffening and shear modulus using minimal constitutive models.

## Key findings

- VCCE accurately captures shear modulus in PDMS samples.
- VCCE reliably measures strain stiffening behavior.
- The method is applicable for in-vivo characterization of biological tissues.

## Abstract

Strain-stiffening is a well-documented behavior in soft biological materials such as liver and brain tissue. Measuring and characterizing this nonlinear response, which is commonly considered as a mechanism for damage prevention, is of great interest to engineers for design of better biomimetic materials, and to physicians for diagnostic purposes. However, probing the elastic response of soft or biological materials at large deformation in their natural habitat, is an arduous task. Here, we present the Volume Controlled Cavity Expansion (VCCE) technique as an in-vivo measurement method that offers the ability of characterizing the stiffening response of materials in addition to identifying their shear modulus. By employing minimal constitutive representations involving only two constants (Mooney-Rivlin, Gent, and Ogden) we show that for the conventional PDMS samples, this technique and an accompanying data analysis method capture the shear modulus, as well as providing reliable measures of the stiffening behavior of the samples.