A theoretical model to study the effects of cellular stiffening on the damage evolution in deep tissue injury

Pressure induced deep tissue injury (DTI) is a severe form of pressure ulcers that is hard to detect in early stages and difficult to prevent and treat. High prevalence figures are partly due to a lack of understanding of pathological pathways involved in DTI. The aim of this study was to investigate, whether changes in material properties of damaged tissue can play a role in DTI aetiology. A numerical model was developed based on muscle microstructure and tissue engineering experiments. A time dependent damage law was proposed and stiffening of dead cells incorporated. The results obtained in the microstructural investigations were used to include the stiffening information in a pre-existing macroscopic model based on animal experiments, which correlated strains to tissue damage measured in the tibialis anterior muscle in rat limbs. With the modelling approach employed in this paper, the damaged area in the rat limb models increased up to 1.65-fold and the rate of damage progression was up to 2.1 times higher in microstructural simulations when stiffening was included.