Fig. 4.

Measured (A) and calculated (B) equilibrium O₂ gradient in the bioreactor, using agar and water instead of Matrigel and culture media, as a function of distance away from a flat silicone hydrogel membrane. A) Experimental points are the values of oxygen concentration measured by a stationary sensor after equilibration (Fig S2), with horizontal error bars reflecting uncertainty due to sensor position and size, and vertical error bars reflecting long time-scale drift in measurement, likely mostly due to differences between liquid temperature and gas temperature. Other sources of error are not included. B) Average equilibrium oxygen gradient calculated for a 5 mm diameter cylindrical volume at the center the bioreactor, using a 2-D axisymmetric finite element model as described in text. Physical constants are D_O2,SiHy = 5×10⁻⁹ m²/s, D_O2,water = 3×10⁻⁹ m²/s, SiHy/water partition coefficient = 8, O₂ mass transfer coefficient at the water/gas interface = 7 × 10⁻⁶ m/s. Nominal position of boundary between agar layer and water shown as a vertical dashed line in both graphs.