Viscoelastic and poroelastic mechanical characterization of hydrated gels

Abstract

Measurement of the mechanical behavior of hydrated gels is challenging due to a relatively small elastic modulus and dominant time-dependence compared with traditional engineering materials. Here polyacrylamide gel materials are examined using different techniques (indentation, unconfined compression, dynamic mechanical analysis) at different length-scales and considering both viscoelastic and poroelastic mechanical frameworks. Elastic modulus values were similar for nanoindentation and microindentation, but both indentation techniques overestimated elastic modulus values compared with homogeneous loading techniques. Hydraulic and intrinsic permeability values from microindentation tests, deconvoluted using a poroelastic finite element model, were consistent with literature values for gels of the same composition. Although elastic modulus values were comparable for viscoelastic and poroelastic analyses, timedependent behavior was length-scale dependent, supporting the use of a poroelastic, instead of a viscoelastic, framework for future studies of gel mechanical behavior under indentation.

Size effects in indentation of hydrated biological tissues

“…The average duration for constitutive parameter identification on a personal computer equipped with a dual core 2.16 GHz central processing unit was approximately 10 s, a negligible computational cost if compared to that of an analogous identification based on inverse finite element modeling (on the order of hours 20 ). There are some limitations to the poroelastic analysis, however.…”

“…Since indentation techniques are capable of testing even the smallest hierarchical length scales in biological materials, 9,10 there exists an opportunity to characterize a range of hierarchical features in tissues simply by varying the indentation load (or depth), tip geometry, and the physical instrument used to perform the testing. Data analysis techniques optimized for high-throughput, largescale investigations by indentation have been developed for examining time-dependent deformation during indentation contact, [20][21][22][23][24] but these have been used in only limited investigations of biological materials to date. 25 In the current study, nanoindentation and microindentation creep and load relaxation tests are performed on hydrated bone and cartilage tissue samples.…”

The role of material structure and mechanical properties in cell–matrix interactions

“…However, as it is a uid-saturated porous solid, polyacrylamide is probably best described as poroelastic rather than purely linearly elastic. 35 That is, polyacrylamide displays some time-dependent behaviour, but this results from uid moving through the pores of the elastic solid rather than due to time-dependent ow of the material itself. Polyacrylamide is not permissive for cell attachment.…”

Indentation of polydimethylsiloxane submerged in organic solvents

“…Indentation has long been used to characterize elasticity and plasticity of metals, 10 and has in recent years been used to characterize elasticity, 11 viscoelasticity 12,13 and poroelasticity [14][15][16][17][18][19][20] of gels. A challenge has been to relate the response of indentation to the properties of the material.…”