Characterization of plasma deposited hydrocarbon diffusion barriers for embolic foam devices

Shape memory polymer (SMP) containing medical implants that are delivered through catheters require controlled expansion times to prevent the device from binding in the delivery catheter. Delayed expansion can be accomplished using body temperature and moisture plasticization from the aqueous environment of the blood. Although bulk material approaches are effective at delaying the expansion rate, they often compromise the ultimate expansion volume, or necessitate temperatures above body temperature for actuation. These factors motivate material refinement beyond bulk chemistry changes to achieve nonlinear passive actuation profiles. In this work, plasma deposited hydrocarbon diffusion barriers enable a second degree of material expansion control, facilitating extended catheter delivery times for endovascular medical devices. Hydrocarbon plasma films polymerized from mixtures of acetylene, ethylene and propylene were deposited on silicon wafers and characterized using ellipsometry, static water contact angles, and x-ray photoelectron spectroscopy. Selected plasma processes were applied to polyurethane SMP foams and material performance was characterized using differential scanning calorimetry and unconstrained foam expansion in 37 °C water. These plasma films were found to increase surface hydrophobicity and delay the moisture plasticization rate of shape memory polymer embolic foams without altering bulk thermo-mechanical properties.