Biotechnology and Applied Biochemistry Surface modiﬁcation of POSS- nanocomposite biomaterials using reactive oxygen plasma treatment for cardiovascular surgical implant applications Atefeh Solouk, 1,2 Brian G. Cousins, 1∗ Hamid Mirzadeh, 3 Mehran Solati-Hashtjin, 2 Siamak Najarian, 2 and Alexander M. Seifalian 1,4 1 Centre for Nanotechnology and Regenerative Medicine, Division of Surgery and Interventional Science, University College London (UCL), London, UK 2 Biomedical Engineering Faculty, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran 3 Polymer Engineering Faculty, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran 4 Royal Free Hampstead NHS Trust Hospital, London, UK Abstract. In this study, central composite design (CCD) was used to develop predictive models to optimize operating conditions of plasma surface modiﬁcation. It was concluded that out of the two process variables, power and duration of plasma exposure, the latter was signiﬁcantly affecting the surface energy (γ s ), chemistry, and topography of polyhedral oligomeric silsesquioxane–poly(carbonate-urea)urethane (POSS-PCU) ﬁlms. On the basis of experimental data, CCD was used to model the γ s using a quadratic modeling of the process variables to achieve optimum surface energy to improve the interaction between endothelial cells (ECs). It was found that optimal water θ for EC adhesion and retention, which was reported 55 ◦ from supporting literature (equivalent to γ s = 51 mN/m), was easily achievable using the following experimental conditions: (1) power output at 30 W for 75 Sec, (2) 90 W for 40 Sec, and (3) 90 W for 55 Sec in oxygen. In vitro cell culture and metabolic activity studies on optimized ﬁlms [as in (1)] demonstrate increased adhesion, coverage, and growth of human umbilical vein endothelial cells that were conﬂuent over a shorter time period (<24 H) than controls. Such materials enhanced the EC response and promoted endothelialization on optimized ﬁlms, thus demonstrating their use as bypass graft materials. C  2011 International Union of Biochemistry and Molecular Biology, Inc. Volume 58, Number 3, May/June 2011, Pages 147–161 • E-mail: b.cousins@medsch.ucl.ac.uk Keywords: blood–biomaterial interactions, coronary artery bypass surgery, endothelial cells, nanocomposite, plasma surface modiﬁcation, statistical modeling 1. Introduction There is an increasing demand for coronary artery bypass grafts for patients due to circulatory disease, which remains the pre- dominant cause of morbidity in the 21st century. Life-saving treatments are often performed by autologous bypass graft- ing from either the saphenous vein or the radial (or mammary) Abbreviations: AFM, atomic force microscope; ATR–FTIR, attenuated total reﬂection–Fourier transform infrared; CCD, central composite design; DOE, design of experiments; EC, endothelial cell; EDX, energy dispersive X-ray; IH, intimal hyperplasia; LF, low frequency; POSS, polyhedral oligomeric silsesquioxane; PSM, plasma surface modiﬁcation; PCU, poly(carbonate-urea)urethane; PUs, polyurethanes; RSM, response surface methodology; SEM, scanning electron microscope; R a , mean surface roughness; RMS, root mean square; R z , average maximum height of the proﬁle; EPSRC, Engineering and Physical Sciences Research Council; NCBI, National Cell Bank of Iran; RF, radio frequency. ∗ Address for correspondence: Dr. Brian G. Cousins, MRes, PhD, Centre for Nanotechnology and Regenerative Medicine, Division of Surgery and Interventional Science, University College London (UCL), London, UK. Tel.: + 20 7794 0500x35375; e-mail: b.cousins@medsch.ucl.ac.uk. Received 1 December 2010; accepted 4 March 2011 DOI: 10.1002/bab.22 Published online 2 June 2011 in Wiley Online Library (wileyonlinelibrary.com) artery for both macro- and microvascular repair. Complications arise due to the removal of vessels from the native tissue and positioning of the bypass graft creating a diameter mismatch; further revision surgery has led to developments in the use of bi- ological and synthetic bypass grafts [1]. Synthetic grafts reduce operating time and avoid donor site morbidity. The most com- mon are fabricated from expanded poly(tetraﬂuoroethylene) or poly(ethylene tetrapthalate) (Dacron TM , Invista., Wichita, KS, USA); however, they are not suitable for small-diameter ar- teries (≤5 mm), in which occlusion rates are high and of- ten associated with thrombosis and intimal hyperplasia (IH) [2],[3]. Such materials show poor patency rates clinically and are rigid when compared with the viscoelastic properties of the host artery [4]. Alternative polymeric materials have been used, including polyurethanes (PUs), in an attempt to improve graft patency [5]. PU has been used for cardiovascular repair since the 1960s [6]. However, chronic in vivo instability during prolonged implantation presents a major disadvantage. This led to the development of hydrolytic- and oxidative-resistant polycarbonate-based PU [6]. More recently, we have developed 147