Characterization and haemocompatibility of fluorinated DLC and Si interlayer on Ti6Al4V Chau-Chang Chou a, ⁎, Yi-Yang Wu a , Jyh-Wei Lee b, c , Chi-Hsiao Yeh d , Jen-Ching Huang e a Department of Mechanical & Mechatronic Engineering, National Taiwan Ocean University, No.2 Pei-Ning Rd., Keelung 20224, Taiwan, ROC b Department of Materials Engineering, Ming Chi University of Technology, No.84 Gongzhuan Rd., Taishan Dist., New Taipei City 24301, Taiwan, ROC c Center for Thin Film Technologies and Applications, Ming Chi University of Technology, No.84 Gongzhuan Rd., Taishan Dist., New Taipei City 24301, Taiwan, ROC d Division of Thoracic and Cardiovascular Surgery, Chang Gung Memorial Hospital, Keelung 204, Taiwan, ROC e Institute of Mechatronic Engineering, Tungnan University, No. 152 Sec.2 Pei-Shen Rd., Shen-Ken Dist., New Taipei City 222, Taiwan, ROC abstract article info Available online 18 January 2012 Keywords: Fluorinated diamond-like carbon Titanium alloy PECVD Blood compatibility Fluorinated diamond-like carbon (F-DLC) films were deposited on Ti6Al4V substrates by radio frequency plasma enhanced chemical vapor deposition (rf PECVD) technique using a mixture of methane (CH 4 ) and tet- rafluoromethane (CF 4 ) gasses. A 100 nm Si interlayer was coated in advance by physical vapor deposition (PVD) to improve the adhesion between F-DLC and Ti alloy. A 200 nm TiN-coated specimen with the same Ti6Al4V substrate was also built by PVD as a benchmark. The structure and surface properties of F-DLC coat- ings, prepared with various fluorine flow ratios, were investigated by using X-ray photoelectron spectrosco- py, scanning electron microscopy, atomic force microscopy, liquid drop goniometry, and electrochemical corrosion tests. The blood compatibility was evaluated by measuring haemolysis ratio and platelet-covered area in vitro. The films' spectroscopic results show that the CF x group and fluorine atomic concentration in- crease as CF 4 flow ratio is promoted in the mixture. The surface energy is reduced due to the increased fluo- rine content. The modified surfaces are characterized by higher hydrophobicity, lower thrombogenicity, and better corrosive protection than the virgin and TiN ones. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Thrombosis and haemolysis are two major concerns in the blood compatibility of prosthetic heart valves, blood pump, stent, and other blood contacting cardiovascular devices. For mechanical heart valves (MHVs), pyrolytic-carbon (PyC) is widely used, but it does not have adequate thromboresistant properties, and its failure due to crack propagation originated from the material's brittleness also results in problems with durability [1,2]. Biomedical Ti alloys with modified coatings [3–6] are a promising solution. TiN, TiC, Ta, TaN, diamond-like-carbon (DLC) and the multilayers of these films are common coatings for the enhancement of blood compatibility [7]. Among these coatings, the bio- and haemo-compatibility of diamond-like-carbon (DLC) films have been widely investigated and reported [1,8–18]. Besides, the outstanding wear-resistance of various DLC films [1,16,17,19,20] makes them the most effective candidates for dynamic blood contact. Fluorinated DLC (F-DLC) film, compared with other DLC derivatives, has attracted extensive interest due to its superiorly low friction coefficient, smooth surface, good chemical inertness, low dielectric constant, and wide optical band [21–23]. Freire et al. [24] discussed the transformation of the DLC's microstructure with increasing fluorine content. Yu et al. [25] found that the F content leads to a reduction in surface energy of the samples as compared with that of diamond-like carbon (DLC) film. Sui et al. [26] demonstrated the relationship between the corrosion resistance and the F-DLC structure as well as the surface hydrophilicity of the films. Hasebe et al. [27] concluded from their human platelet incubation study that the localized fluorine in the top- most thin layer is one of the key factors in the promotion of the non- thrombogenicity of F-DLC film. Marciano et al. [10] also verified that the reduced compressive stress and increased I D /I G ratio, hydrogen con- tent, and water contact angle of F-DLC enhance the DLC antibacterial ac- tivity. The aim of this work is to study the effect of a process parameter, i.e. mixtures with various CF 4 /CH 4 ratios, on the surface characteristics of F-DLC films with an amorphous Si (a-Si) interlayer on Ti6Al4V sub- strates. The anticorrosion capability and blood compatibility were in- vestigated and compared with the original Ti alloy and a sample with a 200 nm TiN coating as benchmarks. 2. Experimental procedure Ti6Al4V substrates with dimensions of 20 × 20 × 6 mm were ground and polished down to 0.09 nm (Ra). The substrates were washed in distilled water, ultrasonically degreased in acetone Surface & Coatings Technology 231 (2013) 418–422 ⁎ Corresponding author. Tel.: + 886 2 24622192x3224; fax: + 886 2 2462 0836. E-mail address: cchou@mail.ntou.edu.tw (C.-C. Chou). 0257-8972/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2012.01.020 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat