Advances on the use of carbon based materials at the biological and surface interface for applications in medical implants James Andrew McLaughlin ⁎ , Paul Damian Maguire Nanotechnology and Integrated Bioengineering Centre, University of Ulster, Newtownabbey, BT37 OQB Northern Ireland Available online 1 November 2007 Abstract One of the setbacks of vascular stents is the potential development of a thick-smooth muscle tissue inside the lumen, which can be so severe as to re-occlude the vessel lumen leading to restenosis. Considerable improvements have been made, including the use of more bio-compatible materials, anti-inflammatory drug-eluting stents, re-sorbable stents, and now plasma coatings are being recognised as a potential way forward. This paper describes the role of 3-D plasma coatings of amorphous carbon and in particular low-stress a–C:H:Si overlayers. The high barrier nature of the amorphous carbon coating is examined by measuring oxygen and water diffusion across the ultra thin film. The stent coating is analysed by Raman Spectroscopy and the ID/IG ratio relates to the coating quality differences inside and outside of the stent cage. Published by Elsevier B.V. Keywords: Stent; Amorphous carbon; Plasma coated; Medical device. 1. Introduction It is well recognised that a single material approach will not provide the biomaterials for new improved medical devices [1,2]. The surface-bio-fluid interface is critical and therefore a new generation of surface-modifications such as plasma-coat- ings can dramatically tailor the functional nature of the device surface. Current implants use metals such as medical grade stainless steel, cobalt, titanium alloy; chromium and polymers such as polycarbonate, polyethylene and polyurethane (Table 1). Much interest has recently been shown in applying DLC (particularly amorphous hydrogenated carbon) films to medical devices and this has been addressed by various groups [3– 12,24–26]. Graphitic carbon is a well known implant material particularly in relation to heart valves and therefore the particular properties of thin film amorphous carbon in relation to its high hardness and wear, good lubricity, biocompatability, low roughness and surface energy have been addressed. The coatings are also inert to acids and alkalies. Being atomically dense means that they form an effective diffusion barrier. The films also adhere strongly to metals which form carbides and also to glasses and also most polymers. These properties are attractive to such medical devices as stents; dental roots; catheters; pacemakers; internal leads and electrodes; guidewires; prosthe- ses; inferior vena cava filters; heart valves; blood tubing; cannulae; dental instrument tips; scalpels. Also bio-sensors; anti-biofouling coatings for urinary and blood based implants; needles; orthopaedic pins; reducing bone cement wear; coatings on artificial heart organs; intraocular lens etc. There is therefore sufficient evidence to warrant interest in DLC as a general biocompatible material (Fig. 2a and b). The questions now are: (i) which DLC structure produces the “best” biocompatibility for implants, (ii) is the choice of structure application specific or can more general rules be determined and (iii) how sensitive is the biocompatibility to variations in structure and geometry? These are critical issues because applications involve difficult substrate materials and complex shapes, which may limit access to the full DLC property space. 2. Coronary stents This paper in particular focuses on the highly topical medical implant called a stent. Tubular scaffold structures called stents Available online at www.sciencedirect.com Diamond & Related Materials 17 (2008) 873 – 877 www.elsevier.com/locate/diamond ⁎ Corresponding author. Nanotechnology and Advanced Materials Institute and NIBEC, NIBEC Building, University of Ulster, Newtownabbey, BT37 OQB, Northern Ireland, Ireland. Tel.: +44 28 90368933; fax: +44 28 90366863. E-mail address: jad.mclaughlin@ulster.ac.uk (J.A. McLaughlin). 0925-9635/$ - see front matter. Published by Elsevier B.V. doi:10.1016/j.diamond.2007.10.025