Figure 3.

Real-time oxygen monitoring system. (a) To measure oxygen tension and gradients, we use commercially available invasive and noninvasive oxygen sensors. (b) Using invasive oxygen sensors (e.g., needle-type microsensors), we can measure oxygen tension and gradients throughout the hydrogel matrices by controlling the height of the sensors (0–3 mm; mean ± s.d.; n = 3). (c) Using noninvasive oxygen sensors, we can monitor the oxygen tension at the bottom of the hydrogels during culture periods. PC, personal computer. Adapted from with permission from Park and Gerecht³⁸, Nature Publishing Group.