Isolating Poroelastic and Viscoelastic Mechanisms of Soft Tissues and Hydrogels Through Sequential Microscale Indentation Testing: New Applications of Indentation Theory for Microscale Characterization

Abstract

Soft hydrated materials, including biological tissues and hydrogels, exhibit complex time-dependent mechanical behaviors due to their poroelastic and viscoelastic properties. These properties often manifest on overlapping time scales, making it challenging to isolate the individual contributions of poroelasticity and viscoelasticity to the overall mechanical response. This study presents a novel semi-analytical model for characterizing these properties through sequential microscale load relaxation indentation testing. By extending existing theories, we developed a poroviscoelastic framework that enables the deconvolution of poroelastic and viscoelastic effects. Using this model to fit sequential microscale indentation data, we characterized porcine heart and liver tissues, as well as collagen and GelMA hydrogels, revealing distinct differences in their poroelastic and viscoelastic parameters. Our findings demonstrate that this approach not only provides rapid and detailed insights into the mechanical properties at the microscale but also offers significant advantages over traditional methods in terms of speed, computational efficiency, and practicality. This methodology has broad implications for advancing the understanding of tissue mechanics and the design of biomimetic materials for tissue engineering applications.Statement of SignificanceThis study introduces a novel approach to understanding the mechanical behavior of soft hydrated materials, like tissues and hydrogels. This study introduces a semi-analytical model to describe the time dependent behavior and a practical approach to distinguish between poroelasticity and viscoelasticity at the microscale. By providing this model along with a rapid and efficient characterization method, our approach enhances understanding of time-dependent mechanical behaviors critical for soft tissue mechanics and biomaterials design.