A multiphysics 3D model of tissue growth under interstitial perfusion in a tissue-engineering bioreactor

The main challenge in engineered cartilage consistsin understanding and controlling the growth processtowards a functional tissue. Mathematical and computationalmodelling can help in the optimal design of the bioreactorconfiguration and in a quantitative understanding ofimportant culture parameters. In this work, we present amultiphysics computational model for the prediction of cartilagetissue growth in an interstitial perfusion bioreactor.The model consists of two separate sub-models, one twodimensional(2D) sub-model and one three-dimensional (3D)sub-model, which are coupled between each other. Thesesub-models account both for the hydrodynamic microenvironmentimposed by the bioreactor, using a model based onthe Navier–Stokes equation, the mass transport equation andthe biomass growth. The biomass, assumed as a phase comprisingcells and the synthesised extracellular matrix, hasbeen modelled by using amoving boundary approach. In particular,the boundary at the fluid–biomass interface is movingwith a velocity depending from the local oxygen concentrationand viscous stress. In thiswork,we showthat all parameterspredicted, such as oxygen concentration and wall shearstress, by the 2Dsub-model with respect to the ones predictedby the 3D sub-model are systematically overestimated andthus the tissue growth, which directly depends on these parameters.This implies that further predictive models for tissuegrowth should take into account of the three dimensionalityof the problem for any scaffold microarchitecture.