Different meshes caused specific histological reactions with changes of their mechanical properties after implantation in rodents. A new mesh with a reduced amount of polypropylene showed both less inflammation and less restriction in the mobility of the abdominal wall though it exceeded the required tensile strength of 16 N/cm.

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Meshes that contain a lot of polypropylene shrink to about 30%-50% of their original size after 4 weeks, requiring an overlap of at least 3 cm if implanted subfascially. Reduction in the polypropylene content decreases both the inflammatory response and the shrinkage. Meshes with big pores are less likely to fold and improve compatibility.

With more than 1 million implantations per year worldwide, mesh repair has become a standard procedure for the treatment of hernias. Apart from various technical problems, the type of material has been proven to be of considerable importance for the functional and histological outcome, particularly for long-term implantation. Whereas the advantageous application of low-weight, large-pore meshes based on multifilaments can be stated without doubt, it is still open whether similar results can be achieved on the basis of pure monofilaments. In the present study, a low-weight polypropylene mesh (LW) made purely of monofilaments was compared to a common heavy-weight polypropylene mesh (HW) in regard to the functional consequences and the tissue response. After implantation in rats as an inlay for 3--90 days, the abdominal-wall mobility of the implant region was recorded by 3D stereography, and the tensile strength of both the suture zone and the mesh was measured. The morphometry of the histological reaction in regard to the inflammatory infiltrate, the connective tissue, the number of granulocytes, macrophages, and fibroblasts served to reflect the tissue response. As parameters for the remodeling process at the interface the cellular activation was evaluated by TUNEL (DNA-strand breaks or apoptosis, respectively), Ki 67 (cell proliferation), and HSP 70 (cell stress). The measured tensile strength of the LW mesh confirmed a sufficient strength of the material-reduced mesh modification. After implantation the consecutive impairment of the abdominal-wall mobility was reduced compared to the HW mesh, concomitant to the reduced fibrotic level at the interface. At the end of the observation period the foreign-body reaction was significantly lowered for the LW mesh, almost reaching physiological values. In conclusion, these data confirm the improved biocompatibility of material-reduced mesh implants.

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