In silico study of the mechanisms of cell deposition into 3D rapid prototyping scaffolds under in vitro hydrodynamic conditions

Tissue engineering scaffolds are potential candidates to develop bone grafts with autologous properties. Scaffolds mimic the bone extracellular matrix playing an active role in tissue formation. Scaffold architecture must be controlled to deliver the adequate mechanical stimuli onto cells. Rapid prototyping methods have been widely used to fabricate scaffolds with controlled regular internal microstructure. However, inaccuracies in the fabrication process could deviate the actual scaffold from its intended design leading to variations in the micromechanical cell environment and thereby final tissue properties. In this thesis, a computational inspection protocol was developed to evaluate the quality and the reproducibility of rapid prototyping scaffolds. A commercially available scaffold with three-dimensional regular microstructure was selected and none of the inspected samples replicated the intended design. In addition, variability among samples at the pore level in terms of wall shear stress and fluid velocities was found. This could potentially lead to perturbations in cell activity and affect the transport of cells during cell seeding. Scaffold cell seeding determines the initial conditions for tissue growth and the control of this process is essential towards the automatization and translation of scaffold-based therapies into clinical treatments. Micro-particle image velocimetry and cell tracking experiments were performed to characterise cell motion during hydrodynamic seeding. These experimental data were employed for the development of a computational model to predict cell transport and cell deposition onto 3D scaffolds under fluid flow. This computational model was applied to explore in vitro cell seeding experiments. It was found that cells tend to follow the fluid streamlines reducing the probability of cell interception with scaffold substrate and therefore cell adhesion. Force due to gravity and secondary flows were identified as the main mechanisms of cell deposition during cell seeding. Flow rate and geometry of the scaffold and the microfluidic chamber are key factors to control these mechanisms of cell deposition and enhance cell seeding efficiency.