In silico analysis of Superelastic Nitinol staples for trans-sternal closure

• Published in: Journal of the mechanical behavior of biomedical materials Vol. 107; p. 103770
• Main Authors: Subasi, Omer, Torabnia, Shams, Lazoglu, Ismail
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01.07.2020
• Subjects: Alloys; Computer Simulation; Humans; Nitinol staple; Shape memory alloy; Sternal closure; Sternum; Superelasticity; Sutures; Nitinol staple; Sternum; Shape memory alloy; Superelasticity; Sternal closure
• ISSN: 1751-6161; 1878-0180
• DOI: 10.1016/j.jmbbm.2020.103770

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. [Display omitted] •Superelastic Nitinol staples are proposed for trans-sternal closure.•Shape memory triggered clamping force promotes osteosynthesis at sternotomy midline.•Parametric design optimization is carried out for the staple dimensions.•Successful in silico performance is observed for lateral sternal loading.•Advantages over the routinely used stainless steel suturing technique are realized.