Surface modification and bare metal functionalization of cobalt chromium alloys for biomolecule grafting

Abstract

Event Abstract Back to Event Surface modification and bare metal functionalization of cobalt chromium alloys for biomolecule grafting Sergio Diaz-Rodriguez1, Carlo Paternoster1, Pascale Chevallier1 and Diego Mantovani1 1 CHU de Québec Research Center, Laval University, Lab. Biomaterials and Bioengineering, CRC-I, Dept Min-Met-Materials Eng, Canada Introduction: L605 Co-Cr alloy is often used in cardiovascular applications due to its mechanical properties and resistance to corrosion [1],[2]. The biocompatibility of these devices and the reduction of adverse events (for example restenosis) associated to endovascular procedures are issues that still need to be assessed with a thorough approach. An effective one is the use of a multistep process aimed at: (1) modifying the metallic surface, to hinder the release of toxic ions (Cr, Ni) and to enhance the performance of the following modification process; (2) functionalizing the material by plasma amination directly on the metal, and (3) grafting suitable bioactive molecules for cardiovascular applications. Nevertheless, the mechanical properties of the layer formed during the first stage have to match those of the deforming substrate during device deployment. The object of this work is a preliminary study of the properties of an oxide layer produced on L605, with special emphasis to its effect on the following stages of the above mentioned strategy. Materials and Methods: L605 round samples of 15mm diameter, previously cleaned in an ultrasonic bath, were electropolished (EP) before thermal treatment (TT) in an air furnace. The effects of three temperatures (400, 500 and 600°C) and two duration times (1 or 2 hours) on the amination step effectiveness and on the coating mechanical properties [3] were investigated. The alloy amination was performed in a N2/H2 microwave plasma at 300 W during 10 min at 100 mTorr with a 5/5 sccm flow. Amination efficiency was assessed by chemical derivatization with chlorobenzaldehyde [4]. X-ray photoelectron spectroscopy (XPS), optical and scanning electron microscopy, and contact angle (CA) were used for surface characterization, before and after amination. Results and discussion: Chromium oxide is the surface main constituent of EP samples, while cobalt oxide (Fig. 1a) is the main one for TT specimens. Both temperature and exposition time induced changes in the oxide layer composition, as evidenced by XPS analyses. The surface functionalization was correlated to the initial oxide layer composition, as shown in fig. 1b: the selectivity, depict by %NH2/%N ratios, was enhanced by higher Co/Cr % at. ratios. Increasing TT temperatures and times promote surface features compatible with the formation of bigger oxide crystals. Deformed samples showed delamination and cracks for higher temperature treatments (Fig. 2). CA analyses displayed no significant difference all having a hydrophobic character (90 to 110°). Conclusion: Bare metal samples were successfully functionalized with amine groups using plasma treatment, as evidenced by chemical derivatization. Furthermore, TT increased the effectiveness of surface functionalization, obtaining more amino groups on the surface and also a better selectivity. However, high temperature samples evidenced a poor adhered and cracked oxide layer after deformation. Though, the TT at 400°C appeared promising due to its stability to deformation and its good amination yield. This work was partially supported by NSERC-Canada, CIHR-Canada, CFI-Canada, FRQ-NT-Quebec, and MRI-Quebec. SD-R was awarded of a doctoral scholarship from the NSERC CREATE program for regenerative medicine (NCPRM).