Synthesis and characterization of bio-compatible shape memory polymers with potential applications to endovascular embolization of intracranial aneurysms

Abstract

Intracranial aneurysms (ICAs) are focal dilations in the brain's arteries. When left untreated, ICAs can grow to the point of rupture, accounting for 50-80% of subarachnoid hemorrhage cases. Current treatments include surgical clipping and endovascular coil embolization to block circulation into the aneurysmal space for preventing aneurysm rupture. As for endovascular embolization, patients could experience aneurysm recurrence due to an incomplete coil filling or compaction over time. The use of shape memory polymers (SMPs) in place of conventional platinum coils could provide more control and predictability for mitigating these complications. This study was focused on characterization of an aliphatic urethane-based SMP to evaluate its potential as a novel biomaterial for endovascular embolization. Twelve compositions of the SMP were synthesized and their thermomechanical properties together with the shape recovery behavior were comprehensively investigated. Our results showed that the SMPs experienced a significant decrease in storage and loss moduli as heated above their glass transition temperatures (32.3-83.2 °C), and that all SMPs were thermally stable up to 265 °C. Moreover, the SMPs exhibited both composition-dependent stress relaxation and a decrease in elastic modulus during cyclic loading. The shape recovery time was less than 11 s for all SMP compositions, which is sufficiently short for shape changing during embolization procedures. Several candidate compositions were identified, which possess a glass transition temperature above body temperature (37 °C) and below the threshold of causing tissue damage (45 °C). They also exhibit high material strength and low stress relaxation behavior, suggesting their potential applicability to endovascular embolization of ICAs.

Thermomechanical data of polyurethane shape memory polymer: Considering varying compositions

“…For a detailed account of the SMP synthesis process, we refer the reader to Kunkel et al . [1] and Wilson et al . [3] .…”

“…To avoid slippage during testing, double-sided padded tape was added to both sides of the dog-bone specimen's gripping regions before mounting. The extension reading of the Instron mechanical testing machine was calibrated after each specimen was mounted and before testing began, according to the procedure described by Kunkel et al [1] .…”

“…The included data concerns the thermomechanical and tensile properties of twelve different SMP compositions with varied molar ratios of the monomers hexamethylene diisocyanate (HDI), N,N,N′,N′-tetrakis(2-hydroxypropyl) ethylenediamine (HPED), and triethanolamine (TEA). The molar ratios used in each composition, labelled SMP1-12, are found in Table 1 from the companion article [1] . The thermomechanical properties of each composition were examined by dynamic mechanical analysis (DMA), dynamic scanning calorimetry (DSC), and thermogravimetric analysis (TGA).…”

“…4 ). From the data contained in each .txt file, essential thermal characteristics for each SMP composition may be derived, such as the glass transition temperature (T g ), as shown in Table 2 in the companion article [1] . Specifically, T g for a sample may be found from the DMA data as the temperature corresponding to the maximum tan(δ) value.…”

“…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.”…”