State of current research
Computational Fluid Dynamics (CFD) supports the development process of oxygenators significantly. The Influence of design changes on the flow distribution in an oxygenator can be estimated early in the process. The fiber bundle of hollow-fiber-membrane oxygenators (HFMOs) used clinically, supports or replaces the gas exchange of the natural lung. The device consists of thousands of single membrane fibers, which separate gas inside the fibers and the blood flow on the outside. A numerical approach to model every fiber is not feasible due to the high number of elements required and therefore the high amount of time it would take to solve. The fiber bundle of an oxygenator is usually modeled as a porous media with assigned parameters, e.g. porosity and permeability, which represent the behavior of the actual fibers. As a result of research conducted for a dissertation at the CVE, a miniature oxygenator with only a few single membrane fibers was numerical implemented and validated in in-vitro-tests . This model helps to understand the blood flow around the fibers and the gas exchange on a microscopic level.
Aim of this project is to develop the numerical model further, as well as to validate it in vitro. Further improvements consist of implementing a pulsatile flow, different fiber materials and arrangements. This improvements allow the investigation of isolated parameters, e.g. material, fiber gaps, flow rate and so forth, which will help to evaluate alternative membrane materials.
Another aspect of this project is to implement and validate a multiphase blood model. In capillary diameters smaller than 300 µm erythrocytes migrate towards the center of the tube due to the Fåhræus–Lindqvist effect . This effect results in a cell-free boundary layer. The gaps between fibers in a fiber bundle are also in the range of 200-300 µm. The tube diameter is not constant, which results in acceleration and deceleration of the blood flow. Due to this irregular flow patterns, it is not proven that a cell-free layer exists in hollow-fiber-membrane oxygenators. A cell-free layer would increase the diffusion pathway between membrane and erythrocytes. The multiphase blood model will help to investigate the cell-free layer and gas exchange in oxygenators on a microscopic level.
 Marcus Hormes, Ralf Borchardt, Ilona Mager, Thomas Schmitz-Rode, Marek Behr, and Ulrich Steinseifer. A validated CFD model to predict O2 and CO2 transfer within hollow fiber membrane oxygenators. Int J Artif Organs, 34(3):317–325, Mar 2011.
 Robin Fahraeus and Torsten Lindqvist. The viscosity of the blood in narrow capillary tubes. American Journal of Physiology–Leg