Cell Culture Finite Element Analysis Shear Stress Fluid Flow NUTRIENT MEDIUM REACTIVE STRESSES IN A CELL CULTURE MECHANOSTIMULUS SYSTEM DELIVERING HOMOGENEOUS EQUIBIAXIAL STRAINS

INTRODUCTION: Several novel cell culture mechanostimulus designs [1,2,3] have recently been introduced to obviate the strain field inhomogeneity and anisotropy seen with earlier designs [4,5] reliant on transmural pressure differentials applied across a diaphragmatic culture substrate. Despite the apparent improvement in substrate kinematic uniformity, these new designs introduce heretofore unencountered patterns of fluid motion in the overlying liquid medium, thereby developing novel patterns of reactive normal and shear stresses at the culture surface. We here report how duty cycle parameters influence the reactive fluid stresses in one increasingly popular such design, involving a membrane-like circular substrate which is radially stretched as it is distended by pulsatile motions of a lubricated, flat circular platen. METHOD: The apparatus considered is that originally introduced by Schaffer et al. [2], in which axisymmetric substrate distentions are achieved by cam-driven vertical excursions of a flat-ended, rounded-lipped cylindrical platen contacting the substrate undersurface (Fig 1). Nutrient medium flow fields were determined by finite element solution of the Navier-Stokes equations [6], the nutrient medium being modeled as a Newtonian fluid of density ρ and viscosity μ. Ranges of variation for the system operational parameters were: 0.180 to 3.97 mm for A (corresponding to peak substrate strains from 0.29 to 6.43%), 0.25 to 4 Hz for f, and 3 to 9 mm for the resting depth h of the nutrient. Each of these three parameters was individually perturbed in two increments, both upward and downward, from baseline (A,f,h) = (1.11, 1, 6).