Permeability of technical and biological tissues.

The permeability of a material is described by the amount of substances (gases, liquids, particles) passing through pores and/or interstices of the material in a certain time. In medicine and biotechnology the permeability is given usually as the amount of water (ml x cm(-2) x min(-1)) permeating per area and time unit through the material. Vascular prostheses are described e.g. as high porous prostheses (e.g. Dacron: 1500-4000 (ml x cm(-2) x min(-1)) or as low porous prostheses (e.g. ePTFE: 200-1000 (ml x cm(-2) x min(-1)). The permeability of blood capillaries is characterized by the exchange of nutrients, metabolites and breathing gases. Capillary permeability and the transport of the permeates through tissues are the key processes for the supply of organs and tissues where especially the protein transport through tissues is described by diffusive and/or convective terms. The vascular permeability is governed by the permeability of the intimal endothelial cells. The major influence is exerted by the interendothelial binding which can change drastically in a very short time. This is demonstrated by the fast development of interstitial lung oedema in case of septical shock. The permeability is an integral indicator of tissue and organ function. It is possible to assess the permeability of native and engineered tissues precisely with a recently developed system. First results will be shown.