(d) A flow perfusion bioreactor is being used to provide shear flow to mesenchymal stem cells seeded into a cylindrical polylactic acid scaffold fabricated via a salt-leaching process. The scaffold has a radius of 30 mm, a porosity of 70% and an average pore-size of 250 um. If a volumetric flow rate of 111 mm?/s is applied and the dynamic viscosity of the perfusion media is 7.8 x 10-4 Pa·s, estimate the wall shear stress imparted to the cells at the scaffold surface. [30 marks]