Control of oxygen tension and pH in a bioreactor for cartilage tissue engineering

Introduction (instead of abstract)<br/> Environmental parameters such as oxygen tension and extracellular pH are believed to play a crucial role in successful tissue engineering. Identifying the optimal values of such parameters and understanding the cellular mechanisms that they govern are essential steps in the tissue engineering process. Cartilage, for example, is well known for its avascularity and its naturally hypoxic state in vivo. However, mimicking this hypoxic state in vitro does not automatically translate to improved tissue engineering results. In fact, the effect of hypoxia on chondrocytes appears to differ between species, differentiation state and metabolic condition [1]. Similarly, while chondrocytes are generally believed to experience a slightly acidic environment, a pH of approximately 7.2 seems to be favored for matrix synthesis [2], as lower values appear to inhibit GAG deposition [3]. Unfortunately, the mechanism by which pH influences matrix synthesis remains unknown. Moreover, the effects of oxygen tension and pH can also vary with medium composition if they exert an effect on, for example, growth factor functionality. We investigated the functionality of a new bioreactor, that allows independent control of oxygen tension and pH in 24 individual wells, for tissue engineering purposes. Accuracy and consistency of control were examined and an experiment was performed with human articular chondrocytes using oxygen and pH control to evaluate this bioreactor in a relevant tissue engineering application.

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