Browsing by Author "Liu, Yingtao"

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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.
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    Thermomechanical data of polyurethane shape memory polymer: Considering varying compositions
    (Elsevier, 2020-09-09) Fisher, Hailey; Woolard, Payton; Ross, Colton; Kunkel, Robert; Bohnstedt, Bradley N.; Liu, Yingtao; Lee, Chung-Hao; Neurological Surgery, School of Medicine
    This article presents data from the investigation of the thermal characteristics and mechanical behaviors of twelve different compositions of a polyurethane shape memory polymer (SMP). Each of the SMP compositions has a unique molar ratio of three monomers: (i) hexamethylene diisocyanate (HDI), (ii) N,N,N′,N′-Tetrakis(2-Hydroxypropyl)ethylenediamine (HPED), and (iii) Triethanolamine (TEA). The thermal characteristic datasets for each composition include the glass transition temperatures, as obtained from differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), and the thermal degradation thresholds, as found from thermogravimetric analysis (TGA). The mechanical behaviors of the SMPs are represented by the failure stresses and strains, as obtained by cyclic tensile testing and failure testing, respectively. The interpretation of these measurements as well as a discussion of the potential usage of candidate SMP compositions for medical devices can be found in the companion article by Kunkel et al. (2018) [1], “Synthesis and characterization of bio-compatible shape memory polymers with potential applications to endovascular embolization of intracranial aneurysms.”