Shape memory polymer -- gold nanocomposite materials for transcatheter cardiovascular devices

Modern trans-catheter cardiovascular devices (TCDs) include coils and particulates for embolization of aneurysms and other vascular malformations, patches for cardiac septal defect closure, coronary and peripheral artery stents, and filters designed to catch blood clots. Today, the vast majority are fabricated using metal alloys, since they are normally visible using X-ray based imaging modalities and possess adequate, if sub-optimal, mechanical properties for their intended application. However, synthetic polymers offer a far more attractive palette of features, including reduced device costs, decreased or absent magnetic resonance and computed tomography imaging artifacts, and the ability to tune stiffness, surface interactions with blood components, and biodegradation. A class of polymers called shape memory polymers (SMPs) is particularly promising, since they can recover almost any pre-defined 3D shape following deployment from a vascular catheter.;Nevertheless, while their fundamental material properties are very encouraging, traditional SMPs are not ideal; they are X-ray invisible and still may not offer enough flexibility to span the broad range in bulk mechanical and surface properties required to fabricate ideal TCDs. To overcome these obstacles, we aimed to engineer and evaluate a new composite SMP which incorporates gold nanoparticles (GNPs). GNPs are excellent additives for a variety of reasons. First, due to gold's high atomic mass, GNPs attenuate X-rays very well in the diagnostic energy range and can make SMPs radio-opaque for device visualization. Moreover, compared to traditional contrast agents like iodine, gold can be imaged at even higher X-ray energies, for which bone and soft-tissue absorption are minimized, improving contrast and reducing radiation dose to the patient. Second, by varying their size, concentration, and surface chemistry, the bulk properties of the resulting composite material can be tailored to a very fine degree. Third, GNPs are very well characterized in the literature and numerous methods already exist to synthesize and functionalize them for dispersion in polymer environments.;Ultimately, the objective of this study was to develop a customizable GNP-SMP composite material that preserves the best properties of both metals and polymers and to evaluate its utility for the design of next-generation TCDs. To achieve this, a variety of synthetic challenges needed to be addressed, such as identifying the best surface-modifiers for GNPs to ensure uniform and maximum incorporation into SMPs. After a protocol was developed for reproducible production of GNP-SMP composites, their thermo-mechanical, radiographic, and photo-thermal, and degradative properties were studied. Though additional development is necessary, this research yielded a material that is radio-opaque, produces minimal MRI and CT artifacts, retains important shape recovery characteristics, and can be heated indirectly with green light. It could potentially improve patient outcomes for transcatheter therapies, while reducing associated costs.