A perspective on medical and biotechnological applications of membrane systems

The combination of artificial membranes with macromolecules or cells allows obtaining hybrid systems capable to imitate what nature has fine tune through aeons of evolution. In fact, these systems, based on their selective transport and catalytic properties, are able to carry out chemical reactions, selective separation and waste removal. The use of polymeric semipermeable membranes with different physico-chemical and transport properties is appealing in tissue engineering and bioartificial organs since these and biomembranes share similarities such as the selective transport of molecules, resistances and protection. Furthermore, synthetic membranes can easily be mass produced modulating their morphological and physico-chemical properties for specific applications [1]. Membranes in bioreactors containing cells act as means to perfuse oxygen and nutrients into a reactor or to withdraw waste and specific products, offering the possibility to create a continuous process. In these devices membrane acts also as support for adhesion of anchorage-dependent cells improving their metabolic functions. Bio-artificial hybrid systems can be formed by loading biomolecules such as enzymes to membranes for improving traditional production systems and for maintaining a sustainable growth. Typical examples include novel pharmaceutical products with well-defined enantiomeric composition; new foods with improved nutritive properties and the treatment of wastes [2]. When the biomolecule is an enzyme immobilized in a membrane, the overall performance of the biocatalytic membrane reactor is due to the preserved functional conformation of the enzyme as well as to the transport of reagent and product, through the membrane, to and from the enzyme, respectively. The biocatalyst can either be loaded to the membrane or just compartmentalized by the membrane. The aims of immobilizing enzymes are to increase the stability and productivity of the reactors, to improve the purity and quality of products and to reduce waste. In this paper we will report on some examples of membrane bio-artificial hybrid systems used in medical and biotechnological applications. In the first part we will discuss on membrane bioreactors using isolated mammalian cells (i.e., liver cells, lymphocytes) as physiological in vitro model to be used for screening of drugs alternatively to animal experimentation, for evaluation of drug individual sensitivity of patients and for studying of diseases. In the second part we will focus on membrane bioreactors using biocatalysts such as enzymes for the production of biological molecules and/or for separation of pharmaceutical products.