Figure Boundary conditions of the CFD model. In the dynamic seeding cells are injected at the inlet whereas in the static seeding they are injected from the green surface on top of the chamber where the scaffold is located. The fluid velocity is imposed at the inlet and outlet boundaries with a UDF to alternate the direction of the flow in the dynamic seeding. Regarding the cell-scaffold interactions, cells were trapped in the scaffold wall boundary as soon as they contacted the scaffold wall. The same condition was applied in the chamber walls with the exception of the inlet and outlet boundaries where the cells were subjected to reflection. The coordinates of the trapped cells in the scaffold surface and chamber walls were registered in text files during simulations for further post-processing. Numerical calculations For the static seeding, the fluid flow was previously resolved and then the cells were advanced every second in the steady flow until they were trapped either in the scaffold or at the bottom of the chamber. In the dynamic seeding, transient simulations were applied to inject cells and calculate cell path along the fluid domain. At every time step, the continuous phase was calculated with 100 iterations which was sufficient for the residuals to stabilise. Then, the cells were advanced in the resolved fluid flow at the end of the time step. The time step during the injection time was set to every 15, 1.25 and 0.35 seconds for the 12, 120 and 600 µl/min flow rate cases respectively. Once the injections were completed, the time step was set to 2,500, 250 and 50 seconds corresponding to the time to change the direction of the flow. Two hours were simulated as that was the seeding time employed in the laboratory experiments. These models were resolved in Fluent Ansys 15.0. The continuum phase was solved using the pressure-based coupled solver to calculate the continuous phase where the continuity and momentum equations are solved simultaneously. The second
Figure Boundary conditions of the CFD model. In the dynamic seeding cells are injected at the inlet whereas in the static seeding they are injected from the green surface on top of the chamber where the scaffold is located. The fluid velocity is imposed at the inlet and outlet boundaries with a UDF to alternate the direction of the flow in the dynamic seeding. Regarding the cell-scaffold interactions, cells were trapped in the scaffold wall boundary as soon as they contacted the scaffold wall. The same condition was applied in the chamber walls with the exception of the inlet and outlet boundaries where the cells were subjected to reflection. The coordinates of the trapped cells in the scaffold surface and chamber walls were registered in text files during simulations for further post-processing. Numerical calculations For the static seeding, the fluid flow was previously resolved and then the cells were advanced every second in the steady flow until they were trapped either in the scaffold or at the bottom of the chamber. In the dynamic seeding, transient simulations were applied to inject cells and calculate cell path along the fluid domain. At every time step, the continuous phase was calculated with 100 iterations which was sufficient for the residuals to stabilise. Then, the cells were advanced in the resolved fluid flow at the end of the time step. The time step during the injection time was set to every 15, 1.25 and 0.35 seconds for the 12, 120 and 600 µl/min flow rate cases respectively. Once the injections were completed, the time step was set to 2,500, 250 and 50 seconds corresponding to the time to change the direction of the flow. Two hours were simulated as that was the seeding time employed in the laboratory experiments. These models were resolved in Fluent Ansys 15.0. The continuum phase was solved using the pressure-based coupled solver to calculate the continuous phase where the continuity and momentum equations are solved simultaneously. The second
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