| dc.description.abstract | Shape memory polymers (SMPs) are a class of materials that can be programmed into a secondary, metastable geometry and subsequently stimulated to return to their original geometry. These biocompatible materials enable the delivery and subsequent expansion of multiple catheter-based medical devices, including low density foams for embolic applications. In this work, cold plasma surface modifications and bulk compositional changes were used to address three design limitations of previous SMP systems: controlled foam expansion, controlled foam membrane removal, and inherent x-ray visibility.
SMP parameters including glass transition temperature, foam pore size, expansion rate in water, and x-ray contrast can be modified by altering the SMP composition or by using particulate additives to form an SMP composite. However, aggressive changes in bulk material chemistry can also affect properties associated with the surface, such as biocompatibility or hydrophobicity. To address the current limitations of SMP devices, this dissertation investigates the use of cold gas plasma techniques as an additional tool to alter surface material properties independent of bulk material composition.
The material modifications imparted by plasma processes or changes in composition were first analyzed on simple film and bulk substrates using techniques such as ellipsometry, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, uniaxial tensile testing, and goniometry. After material characterization, each process was applied to a specific medical device application and characterized based on device performance criteria. Device-specific characteristics, including cell-material interactions, x-ray visibility, fluid permeability, and expansion kinetics, were conducted on device prototypes using confocal microscopy, fluoroscopic imaging, flow system analysis, and isothermal expansion imaging, respectively.
Cold plasma film deposition using hydrocarbon gases was proven to influence SMP foam expansion kinetics by modulating the rate of moisture plasticization. Additionally, oxygen and tetrafluoromethane cold plasmas preferentially removed foam membranes to increase the interconnected porosity and fluid permeability of embolic SMP scaffolds with minimal impacts on material toughness. Finally, chemically incorporating triiodobenzene containing monomers not only provided x-ray visibility, but also significantly improved tensile toughness. | en |
