Predicting the multiscale mechanics of gelatin-based and freeze-dried hydrogels: from cyclic behaviour to damage mechanisms

PhD project

To do so, four major steps are envisaged:

• Step 1 will aim at processing new microstructured gelatin-based hydrogels using recent freezedrying techniques. These hydrogels will be elaborated to “mimic” the essential microstructural descriptors of many living soft tissues (e.g. preferential orientations of the solid phase, tortuosity at zero-stress state, multi-layered structure with gradients of solid volume fraction), which drive their mechanical properties at upper scales (e.g. non-linearity, anisotropy) as well as their ability to absorb/desorb liquids.
• Step 2 will aim at characterising the various 3D architectures generated in the solid phase of each material processed in step 1, using advanced micro-imaging techniques and quantitative analyses; and at investigating how such tailored microstructures can interact with the liquid phase and impact the absorption/desorption properties of the gels at rest (ante-mortem) and after a loading history (post-mortem).
• Step 3 will aim at characterising the mechanical properties of the materials elaborated in step 1 at different spatial scales (micrometer-scale, centimer-scale) and loading frequencies (from 10-5 Hz to 1.5 kHz), thereby covering the range of spatio-temporal scales relevant to the biomimetic study of many living tissues (including vocal folds). All tests will be progressively carried out from the linear regime at small strains upon finite strains, to investigate damage micro-mechanisms.
• Step 4 will be devoted to proposing an appropriate micro-to-macro mechanical model able to predict the overall mechanical behaviour of the hydrogels elaborated in step 1, and characterized in depth in step 3 in response to complex cyclic paths. All the information obtained at the microscopic scale concerning the internal structure (step 2) and mechanics (step 3) will serve as physical input data to properly identify the modelling. Multiscale predictions of viscoelastic, damping and damage properties of the gels evidenced in step 3b are expected as results of the enriched modelling.

Therefore, this program will participate to advance scientific knowledge acquired in microstructured hydrogels, which are promising current candidates to mimic the complex structure, multi-phasic nature and mechanics of living matter, but whose physics is still poorly understood so far.