A Multilevel Finite Element Approach to Study Pressure Ulcer Aetiology

A pressure ulcer is a form of tissue degeneration as a result of sustained mechanical loading. In the last 3 decades a lot of research has been done to understand the aetiology of pressure ulcers. It has become clear that the initial signs of tissue damage are found at the cell scale. That is where the damage process starts that eventually leads to severe wounds. In order to define damage thresholds or to understand what cells “feel” it is necessary to have information on the mechanical status of cells at a scale in the order of micrometres. How the external loading, that is gravitational body forces and reaction forces at supporting surfaces on patients in a bed or a wheel chair, is transferred to a local mechanical state within tissues depends on tissue morphology, mechanical properties and other boundary conditions and requires an analysis at the scale of the order of centimetres to a meter. This cannot be done in one single analysis covering the entire range of scales. This chapter summarizes some work that our group has done in the last 10 years on multi-scale modelling of soft tissues that was aimed at understanding some of the phenomena that play a role in pressure ulcer development. The work has shown the potential of multi-scale modelling to gain insight in the very complex interactions at cell level. It was shown that the heterogeneity in the microstructure has a profound impact on the way cells deform as well as the mechanical property changes of the cell after they become damaged.