 Hi, welcome to this video abstract where we present a new technique for optimizing shear stresses inside a porous scaffold bioreactor. If you like to grow tissues in three dimensions, it's most likely that the distribution of shear stresses inside the bioreactor is suboptimal for various reasons, because of the shape of the bioreactor and also because of the properties of the fluid flow inside the bioreactor. Our technique uses a genetic algorithm to optimize the topology of channels that are patterned inside the bioreactor. We optimize for a target shear stress value and a narrow distribution of shear stress around this target value. We validate the technique using non-invasive MRI readouts and compare with the theoretical prediction. Our technique could be extended to situations where arbitrary shear stress patterns are prescribed to the bioreactor. If you'd like to grow tissues in three dimensions, you'd also like to optimize the mechanical forces that are acting on the cells that are growing in order to produce optimal growth. Now let's look at the details of our technique. Topology optimization consists of two parts, a systematic way to generate channels and an optimization method to achieve a target shear stress distribution. We used an inverse discrete cosine transform for generating the channels. Here we can see a randomly generated topology. Using a genetic algorithm, we can watch the topology evolve, yielding a more uniform shear stress distribution with progressing generations. Let's us Boltzmann method was used to computationally determine shear stress distributions through a porous media. The first simulation is a control case with no channels. In the next simulation, we demonstrate the flow field through an optimized channel topology. To validate the theoretical results, we fabricated porous polymer scaffolds via a porogen leaching method with the appropriate channel topologies embedded on the surface. A paste of sugar and polycaprolactone was added to Teflon molds. Post leaching in water, the porous polymer scaffolds could be stacked. The stacked scaffolds could then be placed in our custom designed Teflon bioreactor. To map shear stress distributions to the porous scaffolds, we use an NMR flow technique in order to experimentally measure velocity. From the velocity data, shear rate distributions could be determined for the three different scaffold topologies. In summary, we've presented a new technique that allows us to optimize flows inside a porous bioreactor. We've demonstrated it using a uniform shear stress distribution around target shear stress value, but this could be easily done for any arbitrary gradients of shear stress that may be desired. The technique was demonstrated in two dimensions, but it could also be extended to three dimensions using three-dimensional lattice Boltzmann flow simulations and also using techniques for prototyping scaffolds in three dimensions.