## 2 Materials and Methods  
### FEA of Screw Structure  
Our framework included two FEA simulations: displacement and force control. The prescribed motion was simulated in displacement control for validation, and the results were compared with those obtained in mechanical testing. Force control using the von Mises criterion was performed to investigate the contributions of design parameters and determine the optimal design for the pullout tests. All FEA simulations were conducted using the implicit method to address quasistatic problems during pullout. Our geometrical models comprised a suture anchor and a polyurethane (PU) block corresponding to the configuration in ASTM F-543. Preprocessing of the FE models was performed using ANSYS/LS-Dyna (ANSYS Inc., Canonsburg, PA, USA). Twenty-four computer-aided design models were manually meshed using FE preprocessing software. Ten-node tetrahedral elements were applied to the FE models (Figure 3a). To accurately investigate the effects of contact areas, for the test block, a fine mesh (0.22 mm) was applied to the screw-bone interface; a coarse mesh (0.7-3.5 mm) was used in more distant regions of the test foam. For the suture anchor, the size of the elements in the whole structure was consistent with that of the elements in the contact areas. The convergence test was conducted first. The variance of the maximum von Mises stress value between consecutive groups was less than 3%. Moreover, when the size of suture anchor meshes was smaller than 0.22 mm, the number of elements was 102,000, and the number of elements in the PU blocks was 118,000, we observed that the quality of the elements was high [11]. Accordingly, the number of elements in the testing model was determined to be approximately 220,000. Figure 2: Dimensional characteristics of the proposed suture anchor design. Four design parameters, tapered angle (TA), upper thread pitch (UP), groove width (W), and lower thread angle (LA) are indicated. Outer (OR) and internal radii (IR) are also shown. The suture anchor was set to move along the longitudinal axis by referencing the displacement curve in the prescribed motion form for displacement control. Moreover, a pullout force, which was vertical to the insertion plane, was loaded for force control. All peripheral nodes of the test blocks were constrained in all directions, and the suture anchor nodes were free in the axial direction. Contact between the screw-block interface was set to a penalty-based surface-to-surface contact, with a friction coefficient of 0.2. Different types of material properties were derived from the literature and applied to the models [27]. Previously determined linear elastic properties of a common magnesium alloy (AM 1004-T61) were applied to the suture anchors (Table 1) [28]. For the PU blocks, the properties of a piecewise linear elastic material were applied, in addition to the application of the mechanical properties of two types of bone, namely a normal bone and an osteoporotic one [29]. These properties were compared with those of solid foam (solid rigid polyurethane foam, Sawbones, USA) measuring 20 pounds per cubic foot (PCF; representing normal bone) and 10 PCF (representing osteoporotic bone) for validation. In the displacement-controlled simulation, the pullout strength of the suture anchor was evaluated to assess the stability of the design under a single pullout procedure, and the results were compared with the mechanical testing results for validation. A constant velocity of 0.1 mm/s was applied to the bottom nodes of the suture anchor. Pullout strength was defined as the maximum value of the reaction force at the bone-screw interface. In the force-controlled simulation, the stress distribution of the suture anchor, which could provide information on material failure, was investigated by applying an upward loading to the bottom of the suture loop (Figure 3b). The stress distribution and maximum von Mises stress were estimated to evaluate the structural factors and determine the optimal design.