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Biodegradable Zn alloy interference screws are promising for anterior cruciate ligament reconstruction. However, previous in vitro studies not only predominantly focus on short-term (≤30 days) immersion, but also neglect influence of crevice corrosion in bone tunnel. This study develops a Zn-0.45Mn-0.2 Mg alloy with yield strength of 288.3 MPa, ultimate tensile strength of 325.4 MPa and elongation of 26.3 %. The alloy is fabricated into screws, inserted into polyurethane bone blocks and immersed in Hank's balanced salt solution for 180 days. The alloy degraded at a corrosion rate of 0.07 mm/y, with its yield strength and elongation eventually decreasing to 229 MPa and 4.3 %, respectively. Second phase detachment during long-term corrosion reduces alloy's surface fracture toughness ( K IC ) and increases stress intensity ( K I ) at corrosion pits. This causes premature fracture of the alloy ( K I > K IC ) and a larger decrease in the alloy's ductility (70 %) than that in strength (30 %). Crevice corrosion of the screws originates deep within the bone tunnel and spreads outward over time. Accumulation of Cl − ions exacerbates corrosion severity in the narrow thread tops of the screws. This study provides a foundation for quasi-equivalent in vitro studies of Zn alloy implants, and highlights the necessity of developing ductility-attenuation-resistant Zn alloys.
Li et al. (Sun,) studied this question.