A Viscosity Model for Viscoelastic Deformable Objects

(Semester Project)

Virtual Reality Lab



The CO-ME, Computer Aided and Image Guided Medical Interventions, is an NCCR long-term project that involves many Swiss Institutes and Universities. The aim of the project is to use the potential of information technology for the optimization of medical interventions in order to improve both the treatment of individual patients and overall health care for the whole society.

Our lab is contributing to the project by creating a biomechanical model of joints. In this model, joint postures are calculated based on contact between different tissues, rather than traditional approaches based on transformations. In this case, it’s important to have a correct behavior of each comprised tissue in order to obtain realistic postures.

The problem

We are working on a physically based deformation model of soft tissues to represent biological tissues like cartilage and ligament. Such tissues have a complex behavior involving viscoelasticity and anisotropy among other features.

A viscoelastic material is one which the elasticity coeficient is time dependent, i.e., the strain on the tissue varies according to the duration of the applied elongation. For example, if the tissue is submitted to a certain elongation and imediately released, the deformation back to the original elongation will be faster than if the elongation is kept for some time before releasing.
In its current state, our model ignores viscous behavior, focusing only on the linear-elastic part of the viscoelastic deformation. However, our project issues require that viscous behavior is considered.

Thus, the problem is to include a vicscous function as a new component of the existing elastic model to make it vicsoelastic.

Student’s work
Our approach to solve the problem will be based on the physiology of joint tissues deformation. In tissues like cartilage, viscosity is caracterized by the flow of liquid from the tissue to the joint capsule space and vice-versa according to the applied stress; just like when you squish a sponge in the water. We will control this fluid equilibrium in our model in order to obtain a similar effect.

The student is asked to use and update the existent C++ classes and methods, and implement a new set of methods to compute viscoelastic behavior of cartilage and other bio-tissues. To evaluate results, we will compare data measured on the model considering viscosity with data obtained regardless viscosity and possibly with data measured on real tissue available on literature. The first approach to compare may be the Stress x Time graph, like shown in the image bellow (bottom-right):



PC, C++.

Good knowledge in C++.

References :
CO-ME : http://co-me.ch
Hip Joint: HipJoint_summary.pdf
Viscoelasticity: viscoelastic_EJM2000.pdf
Deformation model: paper.pdf (mainly  until section 3.2)

Note: Project can be done either in English or French.

Responsible: Anderson Maciel  Tel: 5248,  Room: INJ 118, Dept: DI