Experimental Continuum Mechanics
The study of the mechanical behavior of living tissues is a fascinating and challenging application of continuum mechanics: soft biological tissues are inhomogeneous, viscoelastic, anisotropic and are typically subjected to large deformations. The definition of mathematical models for the description of their mechanical behavior requires the application of sophisticated experimental techniques. The construction, execution, analysis and interpretation of advanced experiments for the characterization and understanding of the mechanical behaviour of soft biological tissue represent our main contribution to this field.
We use the “aspiration device” for quasi-static measurements in-vivo, the “torsional resonator device” for in-situ high frequency shear testing, the “inflation device” and the biaxial materials testing machine for multiaxial experiments with bio-membranes (e.g. liver capsule, fetal membranes). Our studies are motivated by medical applications:
- diagnosis (detection of liver pathologies; malfunctioning, “incompetent” uterine cervix; premature rupture of fetal membranes,
- surgery planning (facial tissue models for plastic surgery simulations, transapical aortic valve implantation),
- tissue replacement and implant development (e.g. supportive implant meshes for hernia or laxity, stents for cardiovascular applications).
Intra-operative application of our devices provides information on the in vivo mechanical behavior of human organs (as opposed to more common observations on specimen from animal organs or extracted from the human body). We have performed a large number of in vivo aspiration experiments on human liver, thus building a unique set of quantitative data on the in vivo mechanical response of this organ. Our measurements on the uterine cervix of pregnant women provided first objective data on the evolution of the compliance of the cervix during the gestation. These measurements might represent the starting point for a new medical procedure for predicting pre-term delivery.
The experimental observations are analyzed using nonlinear viscoelastic constitutive models (inverse problem). Different model formulations are evaluated in their capability of describing soft tissue response under uniaxial and multiaxial loading states. Recent efforts were towards a correlation between mechanical parameters and histological observations or biochemical indices characterizing tissues microstructure (e.g. for human liver and fetal membranes). In-situ experiments in the multi-photon microscope provide information on distribution and orientation of collagen fibers to inform the formulation of corresponding random network models.