Development of water stable N-rich butadiene based plasma polymer films for endovascular coiling

Abstract

Event Abstract Back to Event Development of water stable N-rich butadiene based plasma polymer films for endovascular coiling Madhuwanthi Buddhadasa1, Sophie Lerouge2 and Pierre-Luc Girard-Lauriault1 1 McGill University, Plasma Processing Laboratory, Department of Chemical Engineering, Canada 2 ÉTS, Laboratory of Endovascular Biomaterials, CHUM research Centre & Department of Mechanical Engineering, Canada Introduction: Endovascular coiling is the minimally invasive treatment for brain aneurysms. It involves inserting a coil into the aneurysm through a microcatheter, promoting blood coagulation around the coil and inside the aneurysm in order to help healing, exclude aneurysm from blood flow and prevent it from rupture. Stimulating coagulation is therefore a key feature of endovascular coils, which limits the use of synthetic polymers owing to their ineffective biological-reactivity. Both platelet adhesion and activation of the coagulation cascade are mediated by adsorbed plasma proteins, which are well known to depend on biomaterials surface properties. On account of their highly tunable surface properties and easy adhesion to almost any substrate, plasma polymer (PP) films are potential candidates to promote blood coagulation. Primary amine-rich PP coatings were shown to promote fibrinogen (Fg) adsorption and platelet adhesion and activation[1]. In this project, we propose to use 1,3-butadiene based PP films, stable in aqueous media and rich in amine groups, to promote protein adsorption, platelet activation and coagulation around polymeric coils. Materials and Methods: PP films were deposited on silicon wafer, as the substrate, using a Plasma Enhanced Chemical Vapor Deposition (PECVD) system. The precursor gases used were 1,3-butadiene, ethylene and ammonia, used at various ratios. Total hydrocarbon (HC) flow rate, FT, was maintained at 10 sccm and gas pressure at 80 Pa. X-ray Photoelectron Spectroscopy (XPS) and chemical derivatisation with 4-trifluoromethylebenzaldehyde XPS were used to determine the N and amine content [-NH2]. Film water stability, defined as % loss in film thickness after 24 h immersion in DI water, was determined by profilometric measurements. Nanoscratch and nanoindentation tests were performed to study the adhesion and the elastic modulus and hardness of the films, respectively. Fg adsorption on films after the 24 h immersion was investigated by scan- and time-measurements of Surface Plasmon Resonance (SPR) spectroscopy. Results and Discussion: The first step in the development of a bio-functional PP film is to optimise the plasma process parameters such as, power, gas flow ratio (R) and HC gas flow ratio (RHC), in order to produce both stable and amine-rich films. This requires an extensive set of experiments, due to the fact that high amine contents tend to lead to increased film solubility, owing to the high affinity of amine-rich surfaces towards polar solvents. Figure 1 shows the effect of RHC and power on the film amine content and stability. Deposition at 20 W results in an increased amine incorporation (Fig 1a) which is attributed to the higher energy input that has led to higher reaction rates. The increase in RHC resulting in a decrease in [-NH2] (Fig 1a) is explained by the increased availability of butadiene that has a lower bond dissociation energy. The high degree of cross-linking introduced by the more unsaturated structure of butadiene results in a more stable PP film (Fig 1b). Once the plasma parameters were optimised, protein adsorption on selected films was investigated and Fg adsorption on these different surfaces was compared. Figure 2 shows the adhesion of Fg on a pure butadiene PP film which was already previously exposed to water for 24 h. The shift in the SPR peak in Fig 2a confirms the successful adsorption of the protein and the time-measurement (Fig 2b) shows that the process stabilises within ~10 min. The concentration of Fg solution used was 2 mg/ml, equivalent to that of blood plasma. Nanoindentation studies of these films show an elastic modulus and hardness of ~10 GPa and ~0.35 GPa, respectively. Conclusion: Butadiene based PP films with reasonably high amine content are found to be fully stable in aqueous media and to promote Fg adsorption. The highly cross-linked nature of butadiene based PP films and relatively high elastic modulus, renders them not only insoluble but also resilient and durable candidates for endovascular coiling applications. Work in progress and future work involves study of mechanical properties, platelet activation and blood coagulation. Natural Sciences and Engineering Research Council of Canada (NSERC); Canada Foundation for Innovation (CFI); Fonds de Recherche du Québec — Nature et Technologies (FRQNT)