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The influence of annealing process in the fabrication of helical needles for sutures in deep-wound cavities

The standard procedure of a surgical suture can be very difficult to perform in deep-wound cavities because the available space is not enough to perform the complicated movements required for the knot or to handle the needle. To improve this situation a new kind of hollow, helical needle was developed and filed for patent. To ensure the manufacturability of this kind of needle, a prototype and a prototypical tool were designed and tested. As a prototypical basis, commercially available cannulas were selected. Coil winding was used as a forming process to bring the cannula into the helical form. The material properties of the surgical steel and the work hardening that the semi-finished products underwent lead to challenges for the forming process. The limitations of springback and low formability reduce the possible radius of the helix. Therefore, a soft annealing of the cannula was investigated. However, in surgical needles, stiffness is of great importance. Since hardening by quenching is not possible, annealing parameters were chosen to retain the necessary stiffness. Based on the data obtained from tests of annealing parameters, four final geometries of helical needles were designed and first prototypes were manufactured.