Tailoring the microstructure of biodegradable Zn-Cu-Li wires via thermo-mechanical processing towards high-performance surgical staples.

Abstract

Although biodegradable Zn alloy fine wires are promising for staples, most exhibit inadequate mechanical properties, and current studies remain preliminary. In this work, Zn-2Cu-0.8Li (wt%) alloy fine wires (0.22 mm) for staples with outstanding mechanical properties were fabricated via hot extrusion, multi-pass drawing at room temperature and annealing. The microstructure, property evolutions and application feasibility for staples were systematically studied. The drawing process induces dramatic elongation of the <i>β</i>-LiZn₄ matrix, accompanied by dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX). The low-angle grain boundary fractions significantly increase and the average grain sizes dramatically decrease. The <i>η</i>-Zn distributes as fine equiaxed grain bands due to DRX. The tensile yield strength (TYS) and ultimate tensile strength (UTS) increase from 376 MPa and 423 MPa to 596 MPa and 631 MPa, respectively, due to grain boundary (GB) and texture strengthening. Meanwhile, the deformability remains good with fracture elongation (EL) of 25.4% owing to DRV, CDRX and the presence of <i>η</i>-Zn. The wires annealed at 120 °C for 1 h show optimal mechanical properties (TYS: 492 MPa, UTS: 537 MPa and EL: 44.2%). The wires exhibit uniform degradation mode with a higher degradation rate of 327 μm∙year^-1 than as-extruded wires due to increased GB densities. The fabricated staples show an ultimate tensile force of 1.86 N comparable to Ti staples. They can achieve satisfactory anastomosis of beagle gastric tissue, and show appropriate degradation properties in vitro and in vivo. These findings indicate that Zn-2Cu-0.8Li fine wires and staples are promising for clinical applications.