gms | German Medical Science

Today for keratoplasty either single use or reusable metal trephines are commonly used. Because of the lack of donator corneae the preparation of the corneae becomes essential. Diamond trephines do not exist due to the complex geometry . Sharp metal cutting edges must exhibit a very small radius of curvature which however is less resistant to mechanical stress. It has been described that immediately after blades are exposed to tissue the cutting edge is immediately bent. As a result the cutting forces are raising. Inital SEM pictures of trephine cutting edges have shown that it is necessary to establish a reliable reproducible automated process for manufacturing of more reliable and mechanically stable cutting edges. The newly developed automated process for manufacturing microsurgical instruments with complex geometries and diamondlike features is described.

Different metal trephines are characterized using a SEM. The radius of curvature of the cutting edges are measured. After trepanation of pig corneas histological examination is performed. Selected trephines are ion forged in a newly developed reactor using highly accelerated ions which are concentrated by magnetic fields at low temperature. Following the process the cutting edges are characterized again using a SEM. In an additional step the treated cutting edges are coated with a nanostructured amorphous carbon. Again pig corneae are prepared and histologically evaluated. Additionally, the cutting forces of untreated as well as treated trephines were measured when penetrating into a PU foil.

The cutting edges of untreated trephines exhibited alteration of the cutting edge when examined by SEM. The SEM investigation following treatment with ion forging and coating with amorphous carbon displayed significantly better results. The histological characterization of the treated trephines exhibited much smoother surfaces and the measured forces were significantly reduced in the case of the treated cutting edge.

The newly developed ion forging in connection with nanostructured coatings can result in much more reliable and mechanically more stable cutting edges. The new technology enables us to produce more complex cutting edges with diamond like properties.