Bioabsorbable zinc alloys for use in urological surgery

Purpose Non-absorbable clips are widely used in urologic surgery and they may come in contact with an open urinary tract intraoperatively. As a result, stray clips in the urinary tract and associated intractable infections have been reported. We developed a bioabsorbable metal and evaluated whether it would dissolve if it strayed into the urinary tract. Methods We prepared four types of alloys mainly comprising zinc (Zn) with small amounts of magnesium (Mg) and strontium (Sr), and the biological effects, degradability, strength, and ductility were investigated. Each alloy was implanted in the bladder of five rats for 4, 8, and 12 weeks. The alloys were removed and evaluated for degradability, stone adhesion, and tissue changes. The Zn–Mg–Sr alloy had degradability and no stone adhesion in the rat experiments, and it was implanted in the bladders of five pigs for 24 weeks. The Mg and Zn levels in the blood were measured, and staple changes were confirmed by cystoscopy. Results Zn–Mg–Sr alloys showed the best degradability of 6.51% at 12 weeks. In pig experiments, the degradation rate was 3.72% at 24 weeks. None of the pigs had changes in the Zn or Mg concentrations in the blood. Overall, the bladder incision was healed and the gross pathology showed wound healing. Conclusions The Zn–Mg–Sr alloys were safely used in animal experiments. Furthermore, the alloys are easy to process and can be formed into various shapes, such as staples, making them useful in robotic surgery.