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Bioreactors are important inevitable part of any tissue engineering (TE) strategy as they aid the construction of three-dimensional functional tissues. Since the ultimate aim of a bioreactor is to create a biological product, the engineering parameters, for example, internal and external mass transfer, fluid velocity, shear stress, electrical current distribution, and so forth, are worth to be thoroughly investigated. The effects of such engineering parameters on biological cultures have been addressed in only a few preceding studies. Furthermore, it would be highly inefficient to determine the optimal engineering parameters by trial and error method. A solution is provided by emerging modeling and computational tools and by analyzing oxygen, carbon dioxide, and nutrient and metabolism waste material transports, which can simulate and predict the experimental results. Discovering the optimal engineering parameters is crucial not only to reduce the cost and time of experiments, but also to enhance efficacy and functionality of the tissue construct. This review intends to provide an inclusive package of the engineering parameters together with their calculation procedure in addition to the modeling techniques in TE bioreactors.

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Geometric data are fundamental to the design of a contactor. The efficiency of a membrane contactor is mainly defined by its mass-transfer coefficient. However, design modifications also have significant effects on the performance of membrane contactors. In a hollow-fiber membrane oxygenator (HFMO), properties such as priming volume and effective membrane surface area (referred to as design specifications) can be determined. In this study, an extensive theoretical model for calculation of geometric data and configuration properties, and, consequently, optimization of the design of an HFMO, is presented. Calculations were performed for Oxyphan(®) hollow-fiber micro-porous membranes, which are frequently used in current HFMOs because of their high gas exchange performance. The results reveal how to regulate both the transverse and longitudinal pitches of fiber bundles to obtain a lower rand width and a greater number of windings. Such modifications assist optimization of module design and, consequently, substantially increase the efficiency of an HFMO. On the basis of these considerations, three values, called efficiency factors, are proposed for evaluation of the design specifications of an HFMO with regard with its performance characteristics (i.e. oxygen-transfer rate and blood pressure drop). Moreover, the performance characteristics of six different commercial HFMOs were measured experimentally, in vitro, under the same standard conditions. Comparison of calculated efficiency factors reveals Quadrox(®) is the oxygenator with the most efficient design with regard with its performance among the oxygenators tested.

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Carbon dioxide transfer rate (CTR) is an important performance characteristic of a hollow fiber membrane oxygenator (HFMO), which is used as an artificial lung in clinical practices. In vitro measurement of CTR through HFMOs is challenging specifically in investigations with natural blood. In this study, a straightforward and applicable method is presented in order to simulate blood CO 2 exchange through HFMOs and consequently calculate the corresponding CTR. The method is based on CO 2 dissociation in deionized water resulting in pH drop of the aqueous solution. The results of proposed method are then validated comparing with in vitro investigations using native porcine blood (NPB) in two types of commercially available HFMOs. Moreover, an innovative relationship between effective membrane surface area, blood retention time, and mixing ratio of CO 2 and N 2 gases in pH drop experiment is introduced in order to simulate the CTR of complicated NPB investigations. The results reveal a good agreement between pH-based calculated CTRs and those investigated conventionally using NPB. This method would be principally applicable not only for other cylindrical HFMOs but also for other configurations of hollow fiber membrane contactors.