Comprehensive characterisation of the compressive behaviour of hydrogels using a new modelling procedure and redefining compression testing

Abstract The aim of tissue engineering is the regeneration of damaged tissue or the production of representative tissue organoids in vitro. To achieve this, one approach is to use hydrogels, water-swollen hydrophilic and crosslinked polymer networks, that can accommodate encapsulation of living cells and help the regeneration process. Even though mechanically biomimicking target tissue is important for a favorable cell response, the mechanical characterisation of tissues or hydrogels is not yet a fully defined process with various possible models and methods existing. In this paper, for the first time, a specific procedure and model has been suggested for the discussion of the nonlinear stress-strain relationship in large deformations of hydrogels. Moreover, this approach has comprehensively characterised the compressive material performance of hydrogels in a theoretical framework. To present the performance and utility of the introduced procedure, it is used with two different compositions of bioamine crosslinked gellan gum hydrogel. In addition, a three-dimensional digital image correlation technique has been utilized together with compression testing to measure the actual force and deformation in unconfined compression. The material model parameters were obtained to represent nonlinear stress-strain behaviour and the viscoelastic response (relaxation) of gellan gum hydrogel in compression.