Manufacturing and Automation Research Center, Koc University, Istanbul, 34450, Turkey.
Manufacturing and Automation Research Center, Koc University, Istanbul, 34450, Turkey.
J Mech Behav Biomed Mater. 2020 Jul;107:103770. doi: 10.1016/j.jmbbm.2020.103770. Epub 2020 Apr 7.
Superelastic Nitinol staples, utilized routinely in foot surgeries, are proposed to be used for sternal closure application in this study. It is hypothesized that the shape memory induced superelasticity will allow multiple staples placed along the sternum to promote fast and safe recovery by maintaining constant clamping pressure at the sternotomy midline.
Two different Nitinol staples of different alloying compositions, one representing the metal formed wire geometry and, the other, powder metallurgy manufactured rectangular geometry, are chosen from the literature. Austenite finish temperatures of both materials are confirmed to be appropriately below the body temperature for superelastic shape memory activation. The adopted finite element superelasticity model is first validated and, via design optimization of parametrized dimensions, the staple geometries for producing maximal clamping forces are identified. The performances of the optimized staples for full trans-sternal closure (seven staples for each) are then tested under lateral sternal loading in separate computational models.
The optimized metal formed staple exerts 70.2 N and the optimized powder metallurgy manufactured staple exerts 245 N clamping force, while keeping the maximum localized stresses under the yield threshold for 90° leg bending. Testing the staple-sternum constructs under lateral sternal loading revealed that the former staple can be utilized for small-chested patients with lower expected physiological loading, while the latter staple can be used for high-risk patients, for which high magnitude valsalva maneuver is expected.
Computational results prove that superelastic Nitinol staples are promising candidates as alternatives to routinely performed techniques for sternal closure.
超弹性 Nitinol 钉通常用于足部手术，本研究拟将其用于胸骨闭合应用。假设形状记忆诱导的超弹性将允许在胸骨上放置多个钉，通过在胸骨切开中线保持恒定的夹紧压力来促进快速和安全的恢复。
从文献中选择了两种不同合金成分的不同 Nitinol 钉，一种代表金属成型线几何形状，另一种代表粉末冶金制造的矩形几何形状。两种材料的奥氏体完成温度都被确认为适当低于体温，以激活超弹性形状记忆。采用的有限元超弹性模型首先进行验证，并通过参数化尺寸的设计优化，确定了产生最大夹紧力的钉几何形状。然后，在单独的计算模型中，对用于完全跨胸骨闭合的优化钉（每个 7 个）进行侧向胸骨加载下的性能测试。
优化后的金属成型钉施加 70.2 N 的夹紧力，优化后的粉末冶金制造的钉施加 245 N 的夹紧力，同时保持 90°腿弯曲的屈服阈值下的最大局部应力。在侧向胸骨加载下测试钉-胸骨结构表明，前者钉可用于预计生理负荷较低的小胸患者，而后者钉可用于预计会进行高强度瓦氏动作的高危患者。
计算结果证明，超弹性 Nitinol 钉是替代常规胸骨闭合技术的有前途的候选者。
