The disclosure relates to devices and methods for extracorporeal conditioning of blood. Extracorporeal blood oxygenators and blood oxygenator components, such as conditioning modules, are described. An extracorporeal blood oxygenator includes a conditioning module having an external frame, an inlet cover, an outlet cover, and an internal chamber. A fiber assembly is disposed within the internal chamber and a potting material on the fiber assembly creates a circumferential seal that defines a passageway through the fiber assembly having a substantially circular cross-sectional shape. A fluid inlet is in fluid communication with the passageway, has a lumen that extends along an axis that is substantially perpendicular to the fiber assembly, and has an internal curvilinear surface adjacent the fiber assembly. A fluid outlet on the opposite side of the fiber assembly also has a lumen that extends along an axis that is substantially perpendicular to the fiber assembly.

Disclosed is a blood oxygenator for a premature fetus comprising a housing defining a cavity therein, wherein the housing comprises a blood inlet, a blood outlet, a gas inlet, and a gas outlet; and a gas exchanger disposed within the cavity, wherein the gas exchanger comprises a plurality of hollow fibers arranged in a pattern allowing blood to flow past the hollow fibers when in contact with the hollow fibers, wherein the hollow fibers comprise a receiving end in communication with the gas inlet for receiving a sweep gas and an emitting end in communication with the gas outlet from which the sweep gas exits, wherein the oxygenator is designed to rely on the fetal heart as sole blood pump.

A hollow fiber membrane module includes a pair of plate-shaped portions for forming a passage for a fluid that flows through exteriors of a plurality of hollow fiber membranes between an inner circumferential surface of a case and the plurality of hollow fiber membranes, the pair of plate-shaped portions are provided with a plurality of through holes that serve as a passage for the fluid that flows through the exteriors, and in a region where the plurality of through holes are provided in the pair of plate-shaped portions, a proportion of a total area of the plurality of through holes relative to a total surface area of a side, where the plurality of hollow fiber membranes are disposed, is 30% or more, and a width of each through hole in a direction parallel to the plurality of hollow fiber membranes is 10 mm or less.