Visible vs. Non-Visible Mesh in Underlay Positon After Repair of Umbilical Hernias

The purpose of this study is to determine the exact position of a mesh which is placed in underlay position in umbilical hernia in vitro. The investigators want to gain information if the mesh lays directly next to the abdominal wall fascia or if there´s fat tissue between mesh and fascia. Furthermore they hope to get some information about the tissue incorporation.