Development and Characterization of Biodegradable Zinc Vascular Ligation Clips

Vascular clips, made from inert materials such as titanium or stainless steel, are currently used for surgeries requiring transection of a blood vessel or duct. Hemostatic clips allow for quick application, as well as maneuverability in narrow spaces during laparoscopic surgeries, without the need for external power sources. However, commercially-available materials are biologically-inert and, after implantation, are fibrously encapsulated by the patient’s foreign body response. With the use of biodegradable materials, implanted clips could degrade after a surgical procedure, instead of being an unnecessarily permanent implant. Zinc has been previously explored as a biodegradable metal, due to its high ductility and acceptable biocompatibility, for stent applications. However, its use for hemostatic clips had not yet been investigated. Experimentation consisted of parallel tracks of work, in vitro and in vivo studies, in order to provide a holistic evaluation of the performance of zinc. Hemostatic clips were fabricated from flattened zinc wire (99.99+ wt.%) and applied to surrogate blood vessels. Initial results showed a bursting pressure of 660 ± 60 mmHg and 350 ± 40 mmHg, when applied to vessels with a diameter of 1 and 2 mm, respectively. After 21 days of immersion in corrosive media, these pressures were reduced to 320 ± 40 mmHg and 450 ± 60 mmHg for 1 and 2 mm vessels within simulated body fluid (pH 7.4); 690 ± 20 mmHg and 600 ± 290 mmHg for 1 and 2 mm vessels within MES-buffered saline (pH 6.0). Explanted tissue from the in vivo work showed that zinc maintained a persistent inflammatory response, consistent with an unresolved foreign body response, while platinum was encapsulated within a fibrous matrix. These histological results were further confirmed with DAPI/CD68 immunostaining, which showed higher cell densities and CD68-expressing cells at the zinc implant, and lower cell densities with decreased CD68-expressing cells at the platinum implant. Investigations into the zinc retention of the heart, kidney, liver, and blood serum showed no significant accumulation across all time intervals