Production of zinc wire for use as a high strength biodegradable surgical threads

摘要

Zinc along with magnesium and iron is one of the promising materials for creating high strength biodegradable surgical threads. However, for the production of zinc threads, it is necessary to study and optimize the atypical properties of the material: mechanical properties of the wire tied into a surgical knots, stress relaxation, biocorrosion. Additionally, traditional studies of tensile stress, elongation, and the number of kinks are needed. The paper explores the technology of drawing of zinc wire and changes in its properties at various parameters of drawing. As a workpiece, a wire with a diameter of 1.6 mm obtained by the Properzi method with standards DIN EN ISO 14919 and EN 1179 was used. The preform used is ductile (elongation about 40%), but has a low strength (about 100 MPa). The surface of the workpiece contains a noticeable number of defects associated with pre-treatment by metal forming. To improve the surface quality, a pattern was used in die with an angle atypical for zinc (5°). FEM modelling showed that for such die angle, shear strain on the wire surface is less than for large die angles, characteristic of traditional zinc drawing. The use of drawing in die with a reduced angle improved surface quality. In this work, wires of two diameters, 1 mm and 0.5 mm, were obtained and investigated. The study of the strength of the wire tied with a surgical knot made it possible to reveal the exceptional mechanical effectiveness of zinc as a material for surgical threads. The results of tensile tests showed that strength of the wire with a knot (effective strength) practically does not differ from the standard strength of the wire. For comparison, existing polymer threads and threads from magnesium alloys, when tied into a knot, lose more than 50% of their strength. This fact allows us to state that the effective strength of zinc threads (with a knot) approximately corresponds to the effective strength of threads from magnesium alloys. The relaxation of the resulting Zn wire was investigated on a Zwick250 machine. The obtained relaxation intensity of zinc is quite high and exceeds the relaxation intensity of magnesium and polymer filaments. However, after tying into a knot, the relaxation intensity of the obtained Zn wire practically did not change, while for other materials it accelerated significantly. Thus, the effective relaxation of the zinc wire is only slightly different from the relaxation of the polymer material. The results of an in vitro corrosion study showed that zinc, after drawing according to the scheme proposed in the work, has a corrosion rate of 40% less than the Properzi workpiece. This effect is a result of improving the surface quality of the wire. This is also the desired result and corresponds to the required corrosion rate of the surgical sutures. Thus, the zinc wire obtained by the proposed method of drawing well meets the requirements for high strength biodegradable surgical threads. However, obtaining threads with a diameter less than 0.5 mm is limited by the low strength of pure zinc and requires the search for new materials.