Browsing by Subject "Shape memory polymers"

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    CFD investigations of a shape-memory polymer foam-based endovascular embolization device for the treatment of intracranial aneurysms
    (Research Square, 2024-10-18) Cabaniss, Tanner; Bodlak, Ryan; Liu, Yingtao; Colby, Geoffrey; Lee, Hyowon; Bohnstedt, Bradley; Garziera, Rinaldo; Holzapfel, Gerhard; Lee, Chung-Hao; Neurological Surgery, School of Medicine
    The hemodynamic and convective heat transfer effects of a patient-specific endovascular therapeutic agent based on shape memory polymer foam (SMPf) are evaluated using computational fluid dynamics studies for six patient-specific aneurysm geometries. The SMPf device is modeled as a continuous porous medium with full expansion for the flow studies and with various degrees of expansion for the heat transfer studies. The flow simulation parameters were qualitatively validated based on the existing literature. Further, a mesh independence study was conducted to verify an optimal cell size and reduce the computational costs. For convective heat transfer, a worst-case scenario is evaluated where the minimum volumetric flow rate is applied alongside the zero-flux boundary conditions. In the flow simulations, we found a reduction of the average intra-aneurysmal flow of > 85% and a reduction of the maximum intra-aneurysmal flow of > 45% for all presented geometries. These findings were compared with the literature on numerical simulations of hemodynamic and heat transfer of SMPf devices. The results obtained from this study can serve as a guide for optimizing the design and development of patient-specific SMPf devices aimed at personalized endovascular embolization of intracranial aneurysms.
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    Potential Application of 4D Technology in Fabrication of Orthodontic Aligners
    (Frontiers Media, 2022) Elshazly, Tarek M.; Keilig, Ludger; Alkabani, Yasmine; Ghoneima, Ahmed; Abuzayda, Moosa; Talaat, Wael; Talaat, Sameh; Bourauel, Christoph P.; Orthodontics and Oral Facial Genetics, School of Dentistry
    Objectives: To investigate and quantify forces generated by three-dimensional-printed aligners made of shape memory polymers (four-dimensional [4D] aligner). Methods: Clear X v1.1 material was used in this study. On a custom-made typodont model, correction of maxillary central incisor (tooth 21) malposition by 4D aligners with thicknesses of 0.8 and 1.0 mm was measured by superimposition of subsequent scans. Maximum deflection forces generated by foil sheet specimens were measured at different temperatures in three-point bending (3-PB) tests. In a biomechanical system (orthodontic measurement and simulation system [OMSS]), forces generated on movements of tooth 21 by the 4D aligners were measured at different temperatures. Results: 4D aligners succeeded to achieve a significant tooth movement (2.5 ± 0.5 mm) on the typodont, with insignificant difference between different thicknesses. In the 3-PB test, the maximum deflection forces measured at 20, 30, 37, 45, and 55°C, were 3.8 ± 1.1, 2.5 ± 0.9, 1.7 ± 0.6, 1.0 ± 0.4, and 0.5 ± 0.4 N, respectively. Forces delivered on palatal displacement of tooth 21 at 37, 45, and 55°C by 0.8-mm aligners were 0.3 ± 0.1, 0.2 ± 0.1, and 0.7 ± 0.2 N, respectively, whereas those by 1.0-mm aligners were 0.3 ± 0.1, 0.3 ± 0.1, and 0.6 ± 0.2 N, respectively. A good concordance with movement on the typodont model was shown in OMSS. Conclusion: An initial study of 4D-printed aligner shows its ability to move a tooth by biocompatible orthodontic forces, after a suitable thermal stimulus within the oral temperature range.
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    Shape Memory Polymer-Based Endovascular Devices: Design Criteria and Future Perspective
    (MDPI, 2022-06-21) Pineda-Castillo, Sergio A.; Stiles, Aryn M.; Bohnstedt, Bradley N.; Lee, Hyowon; Liu, Yingtao; Lee, Chung-Hao; Neurological Surgery, School of Medicine
    Devices for the endovascular embolization of intracranial aneurysms (ICAs) face limitations related to suboptimal rates of lasting complete occlusion. Incomplete occlusion frequently leads to residual flow within the aneurysm sac, which subsequently causes aneurysm recurrence needing surgical re-operation. An emerging method for improving the rates of complete occlusion both immediately after implant and in the longer run can be the fabrication of patient-specific materials for ICA embolization. Shape memory polymers (SMPs) are materials with great potential for this application, owing to their versatile and tunable shape memory properties that can be tailored to a patient's aneurysm geometry and flow condition. In this review, we first present the state-of-the-art endovascular devices and their limitations in providing long-term complete occlusion. Then, we present methods for the fabrication of SMPs, the most prominent actuation methods for their shape recovery, and the potential of SMPs as endovascular devices for ICA embolization. Although SMPs are a promising alternative for the patient-specific treatment of ICAs, there are still limitations that need to be addressed for their application as an effective coil-free endovascular therapy.