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Miniaturisation and integration represent the biggest challenges in the biomedical devices of the last generation. Particularly blood oxygenators have been successfully used for the last decades as components of the heart-lung machines but still don’t offer in the traditional configuration an alternative for the middle and long-term treatment of the acute lung failure. Innovative systems with reduced blood contact surface, priming volume and number of components are developed with the aim of lower risk of infection, blood clotting and cell damage. In this context the possibility of blood oxygenation through membranes in the limited space within the vena cava in the venous system has been investigated for the last two decades. The limitations are of anatomical and physiological nature. The anatomy of the venous system makes the introduction of fibers in a defined configuration difficult and limits the implantable fiber surface. Moreover, flow resistance within the system should not disturb the physiology of the venous system. This work describes the conception, the development and the investigation of a high-integrated intravascular membrane oxygenator (HIMOX) which took place in the last years at the Helmholtz Institut for biomedical engineering at the RWTH Aachen. The system is aimed to provide the maximal performance without detrimental effect on the physiological functions. An innovative fiber configuration represents the core of the proposed concept. Compact flexible fiber bundles slide on a middle catheter and fit to the anatomy of the venous system. In the folded configuration the diameter of the system is reduced and implantation through a narrow peripheral vessel possible. The compression and the expansion of the fiber bundles lead to a filling of the space within the vena cava and to an increased fiber surface. Resulting cross flow fiber configuration results in enhanced blood mixing and thus increased gas exchange. The first test samples were manufactured in a wide range of construction parameters. The effect of the fiber configuration on the flow conditions was mathematical modelled and experimental evaluated. Further components of the system were developed under consideration of the anatomical and physiological conditions of the venous system. The integration of a micro-axial blood pump compensates for fiber resistance to blood flow. A deformable cover guarantees the separation between the blood within the system and the blood outside. This leads to physiological blood pressure in the organs and blood flow to the heart. The integration of the pump in a housing as well as the construction of a cover in form of a coated stent are presented. The gas supply to the bundles within the limited available space takes place partially serial, partially parallel. This makes a high gas flow with a reduced pressure drop possible. The realisation of this concept through slides and elastic components is described. In vitro as well as animal experiments with the first test samples lead to the first conclusions about the potential performance of the system and allow an outlook in the future of the project.

Membranes in medical process engineering. Synthetic membranes not only represent the essential components of an artificial kidney or an artificial lung but are also used as wound dressing and in systems for controlled release of drugs in certain long-term therapeutic measures or as part of an artificial pancreas. By far the greatest present economic significance of membranes is their use in the so-called artificial kidney. Considerable cost saving would result if patients could undertake „home dialysis”. This requires the development of new, simpler artificial kidneys and thus higher-performance membranes. The latest trend in „artificial kidneys”, the so-called method of „hemodiafiltration” warants special mention. The separation process is no longer effected only by diffusion but also by convection, i.e. the driving force is the pressure difference between the two sides of the membrane. This paper addresses problems encountered in the development and use of membranes in medicine, recent applications such as the controlled release of active components, or plasma separation, and demonstrates the potential of membranes in medicine.