Strain rate viscoelastic analysis of soft and highly hydrated biomaterials

Abstract

Measuring the viscoelastic behavior of highly hydrated biological materials is challenging because of their intrinsic softness and labile nature. In these materials, it is difficult to avoid prestress and therefore to establish precise initial stress and strain conditions for lumped parameter estimation using creep or stress-relaxation (SR) tests. We describe a method ( or epsilon dot method) for deriving the viscoelastic parameters of soft hydrated biomaterials which avoids prestress and can be used to rapidly test degradable samples. Standard mechanical tests are first performed compressing samples using different strain rates. The dataset obtained is then analyzed to mathematically derive the material's viscoelastic parameters. In this work a stable elastomer, polydimethylsiloxane, and a labile hydrogel, gelatin, were first tested using the, in parallel SR was used to compare lumped parameter estimation. After demonstrating that the elastic parameters are equivalent and that the estimation of short-time constants is more precise using the proposed method, the viscoelastic behavior of porcine liver was investigated using this approach. The results show that the constitutive parameters of hepatic tissue can be quickly quantified without the application of any prestress and before the onset of time-dependent degradation phenomena. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 3352–3360, 2014

Tissue perfusion rate estimation with compression-based photoacoustic-ultrasound imaging

“…However, the impact of these effects should be minimal as compression and relaxation are performed on timescales faster than tissue viscoelastic relaxation rates, typically several seconds. [28][29][30] Future work should investigate the impact of tissue viscoelastic properties on perfusion-rate estimation and account for heterogeneity in tissue mechanical properties. …”

Sample, testing and analysis variables affecting liver mechanical properties: A review

“…Moreover, they often require a long testing phase which may result in significant sample deterioration in case of highly hydrated and labile specimens [23]. To address these issues we proposed the epsilon dot method ( _ eM) to derive material viscoelastic constants through measurements performed rapidly at different strain rates within the linear viscoelastic region [10]. As it avoids sample pre-stress and/or degradation during measurements, the _ eM is particularly suited for hepatic and other soft tissues.…”

“…Therefore, we suggest that tissue and soft material characterisation for in-vitro applications be performed on equilibrium swollen samples at physiological temperature (or at least at the same temperature at which the biomimetic material is tested) using methods which are non force-or strain-triggered and rapid measurements (e.g. _ eM [10], nano-_ eM [90]). Equilibrium swelling ensures that the samples are in a physiologically relevant, stable and reproducible state before the experiment, while quick, non-triggered testing avoids sample pre-stress and minimises status alterations during testing [23].…”

“…Moreover, environmental conditions and pre-load can significantly affect the status of these materials (e.g. they may degrade, change water content over time, or deform irreversibly under small pre-loads) and hence their resultant mechanical properties [10]. Indeed, the identification of a suitable experimental testing method that does not alter the native material behaviour before or during testing is crucial to obtain repeatable results that can be mathematically modelled to derive a unique and meaningful set of constitutive parameters.…”

Modified Modal Strain Energy Method for Analyzing the Dynamic Damping Behavior of Constrained Viscoelastic Structures

“…Kinetics modeling, including loss factor and nature frequency, is a key issue [3]. In recent years, many researchers have investigated the kinetics parameters of damping structures [4][5][6][7][8]. However, viscoelastic dynamic performance is difficult to precisely predict owing to the complex stiffness matrix of viscoelastic structures.…”