Aging of plasma treated surfaces and their effects on platelet adhesion and activation Martina Modic, Ita Junkar, Alenka Vesel, Miran Mozetic ⁎ Department of Surface Engineering, Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia abstract article info Article history: Received 29 May 2012 Accepted in revised form 11 October 2012 Available online 22 October 2012 Keywords: Plasma treatment Aging effect Platelet adhesion ICP plasma Surface modification Improving hemocompatibility of blood connecting devices is one of the key issues in biomaterial science. To prevent and study the effects of platelet adhesion and activation on polyethylene terephthalate (PET), a high- ly non-equilibrium oxygen plasma was used. Surface analyzing techniques confirmed that incorporation of oxygen functional groups, achieved by treatment with oxygen plasma, changed the surface character of PET from hydrophobic to hydrophilic. Moreover, plasma modifies the surface morphology and increases sur- face roughness of PET. It was shown that such surface modification has a significant effect on platelet adhe- sion and activation. Even a short exposure of PET surface to highly non-equilibrium plasma reduced adhesion and activation of platelets mainly through oxygen surface functionalization. However effects of plasma treat- ment diminish with time and many oxygen functional groups are lost from the surface within 3 h of aging. It was shown that aging of plasma treated PET is highly affected by the storage conditions. Thus the main objective of our work was to study these aging effects on platelet adhesion after storage of PET in the air, in deionized water and in phosphate buffered saline. According to the surface analysis, the samples stored in the air showed the least aging effects, as they contained the lowest number of adhered platelets. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Application of physical techniques for modification of solid materials has become an attractive field for applied physics. A technique of partic- ular importance is the application of non-equilibrium gaseous plasma. It has been known for decades that cold gaseous plasma can modify sur- face properties of polymeric materials. Even highly hydrophobic po- lymers can be made hydrophilic or even super-hydrophilic after treatment with cold oxygen plasma. The change in the surface free en- ergy after treatment with plasma is due to incorporation of polar func- tional groups, formation of dangling bonds, modification of surface roughness, or the combination of these effects. Thus this technique gained significant importance not only in adhesion of paints or other coatings in the electrical and chemical industries but also in the bio- medical field [1]. Numerous authors have shown modification of poly- mers for biomedical applications such as poly(dimethyl siloxane) [2,3], polyurethane [4], polytetrafluoroethylene [3,5], high-density polyethylene [6] diamond-like carbon films [7–9], polyethylene tere- phthalate [10–13] and many others [14,15]. Although many efforts have been made to improve compatibility of surfaces with blood, a truly hemocompatible surface does not yet exist. Even polymers com- monly employed as blood connecting devices exhibit suboptimal hemocompatibility. For example, polyethylene terephthalate (PET) is commercially employed in the biomedical field for sutures, vascular grafts or heart valves, because of its mechanical properties and satisfactory biocompatibility. The only drawback being poor hemo- compatibility, which often causes the undesired thrombus reactions. Since the biological interactions with materials occur on the surface, there have been many attempts to improve compatibility with blood fo- cusing on surface modification by wet chemical treatment or plasma treatment in combination with chemical grafting and surface deposi- tion of various coatings with known antithrombogenic materials, such as gelatin or albumin [16,17]. Plasma treatment is a promising tech- nique that enables a uniform modification of various geometries such as long and narrow tubes used for vascular implants. However the drawback of plasma treatment alone is that the effects of plasma treat- ment can be lost with time (aging effects). The stability of the plasma in- duced changes strongly depends on the type of polymer, storage conditions and treatment parameters such as; working gas, treatment time, power and pressure [18–24]. Thus the main objective of our work was to study effects of aging of oxygen plasma treated PET sur- faces after storage in different environments and its effects on adhesion and activation of platelets. The effects of surface properties after plasma modification and after aging in different environments were analyzed by atomic force microscopy (AFM), water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS), while the in vitro biological response was determined from images taken by confocal optical microscopy. 2. Experimental Samples of PET foils (DuPont, Contern, Luxembourg) 250 μm thick were cut into small disks 11 mm in diameter. These were carefully Surface & Coatings Technology 213 (2012) 98–104 ⁎ Corresponding author. Tel.: +386 14773504; fax: +386 14773440. E-mail address: miran.mozetic@ijs.si (M. Mozetic). 0257-8972/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.surfcoat.2012.10.026 Contents lists available at SciVerse ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat