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The median- and long-term use of percutaneous devices is limited byinfections at the site of skin penetration. Thus it is very important tofind a suitable surface structure of the biomaterial which enables a betterprotection from infection by close contacts and undisturbed growth ofepithelial cells on the implant. The cell confluency as the sum ofadhesion, propagation and proliferation of he cells on the biomaterial wasmeasured on different silicones with the help of human keratinocytes of theimmortalized cell - line HaCaT. Silicones of the manufacturer Dow CorningSF Medical and NuSil were investigated. Smooth and "rough" materials fromthe firms Dow Corning and NuSil, and materials with surfaces functionalizedwith COO~, i.e. COO~ NH3+-groups from NuSil and SF Medical wereinvestigated The cell confluency on the different testing foils wasmeasured quantitativly with the help of imageprocessing and -evaluation inform of a screening system. The cell confluency of HaCaT - cells on thefoils was measured after an incubation of three days. The silicone modifiedwith carboxyl-groups from SF Medical showed a median cell confluency of97%. Approximately the same adhesion (96%) was measured on the smoothsilicones functionalized with COO-HN3+-groups from SF Medical and NuSil.The results with the other functionalized materials showed a median of cellconfluency of 89% with the "rough" and 83% withthe smooth silicone modifiedwith COO-groups from NuSil and 84% cell confluency with the"rough" siliconefrom his firm modified with COO-HN3+-groups. Within the group of materialswithunmodified surfaces, the "rough" silicone from Dow Corning showed thebest results with a cellconfluency of 84%, followed by the smooth siliconefrom the same manufacturer with 71%, thesmooth material from NuSil with54%, the silicone from SF Medical with 53%, and the "rough" silicone fromNuSil with only 37% cell confluency.These data provide evidence for theassumption that the surfaces modified with COO -Jo or withC00-P4H3+ groupsallow a better in vitro growth of the epithelial cells on the materials;therefore, it seems promising to improve the actually used unmodifiedsmooth surfaces.