09/1 Physically based constitutive models of biological tissues

		In vivo testing of human liver Histological analysis of tissue (red is fibrosis)

This subproject is focused on detailed mechanical modelling and experimental characterisation of soft biological tissues. In particular, the purpose is the formulation and experimental validation of physically based constitutive models representative of tissues microstructure and related biophysical processes. Research will aim at clinical applications (e.g. diagnostics).

Vascularised tissues are very soft composite structures (typically elastin, collagen, GAG, fluids, etc.). They constitute the inner organs of the body. The in vivo mechanical response of vascularised tissue is influenced by biochemical, growth and aging processes. When excised, these tissues rapidly alter their mechanical properties, so that their mechanical behaviour has to be characterised in vivo. In Co-Me phase 1 analysis of such measurements showed that existing constitutive models (based on quasi-linear viscoelasticity) are inadequate to fully explain the observed mechanical response. To overcome this, microstructural and phenomenological models have been proposed recently (e.g. Rubin and Hurschler).

In the present project physically based constitutive equations will be developed to include terms, reflecting the contribution of specific constituents and structural features to the mechanical behaviour of biological tissues. For a physically appropriate model, the layered structure of inner organs will be accounted for. Integration into a finite element framework enables then direct comparison with experiments.

In vivo measurements will be performed using the experimental techniques developed and applied in COME phase 1 (aspiration and torsional resonator experiment), and the existent devices will be further improved. In particular, a miniaturisation shall facilitate the in vivo application (laparoscopy) and enable local tissue characterisation of the mechanical response.