Colloids and Surfaces B: Biointerfaces 117 (2014) 89–97 Contents lists available at ScienceDirect Colloids and Surfaces B: Biointerfaces j o ur nal ho me pa ge: www.elsevier.com/locate/colsurfb Enhanced osteoblast responses to poly ether ether ketone surface modified by water plasma immersion ion implantation Heying Wang, Tao Lu, Fanhao Meng, Hongqin Zhu, Xuanyong Liu ∗ State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China a r t i c l e i n f o Article history: Received 13 December 2013 Received in revised form 25 January 2014 Accepted 8 February 2014 Available online 18 February 2014 Keywords: PEEK Plasma immersion ion implantation Nanostructure Hydroxyl groups Osteoblast a b s t r a c t Poly ether ether ketone (PEEK) offers a set of characteristics superior for human implants; however, its application is limited by the bio-inert surface property. In this work, PEEK surface was modified using single step plasma immersion ion implantation (PIII) treatment with a gas mixture of water vapor as a plasma resource and argon as an ionization assistant. Field emission scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy were used to investigate the microstructure and composition of the modified PEEK surface. The water contact angle and zeta-potential of the surfaces were also measured. Osteoblast precursor cells MC3T3-E1 and rat bone mesenchymal stem cells were cultured on the PEEK samples to evaluate their cytocompatibility. The obtained results show that the hydroxyl groups as well as a “ravined structure” are constructed on water PIII modified PEEK. Compared with pristine PEEK, the water PIII treated PEEK is more favorable for osteoblast adhesion, spreading and proliferation, besides, early osteogenic differentiation indicated by the alkaline phosphatase activity is also up-regulated. Our study illustrates enhanced osteoblast responses to the PEEK surface modified by water PIII, which gives positive information in terms of future biomedical applications. © 2014 Elsevier B.V. All rights reserved. 1. Introduction As a substitute for titanium and its alloys, poly ether ether ketone (PEEK) was highlighted in the 1980s [1]. PEEK is a linear polyaromatic thermoplastic (chemical structure shown in Fig. S1) with a crystallinity of 30–35% typically and offers a set of charac- teristics superior for biomaterials including excellent mechanical properties [2], non-toxicity [3], good chemical and sterilization resistance [4], and natural radiolucency. More importantly, com- pared with titanium and its alloys, PEEK has a relatively low elastic modulus which is closer to that of cortical bone [5,6]. This contributes to the minimization of stress shielding effect and peri- implant bone resorption [7,8], avoiding the possible loosening of implants. However, the stable chemical structure makes PEEK inert and keeps it from binding to bone directly [9], resulting in inferior osseointegration [10]. It is known that surface properties, both chemical and topographical, are important in tissue response and wound healing [11]. Surface modification may make it more attractive for osteoblast growth, which leads to improved bone ∗ Corresponding author. Tel.: +86 21 52412409. E-mail address: xyliu@mail.sic.ac.cn (X. Liu). integration. Various modification methods have been developed to alter the surface properties of PEEK [12–14]. Han et al. [15] coated PEEK surface with a titanium layer using electron beam deposi- tion method. In vitro cellular responses were enhanced and the in vivo animal tests also showed a higher bone-in-contact ratio. Noiset et al. [16] employed wet-chemistry technique to selectively reduce PEEK and covalently fixed amine and carboxyl groups on the surface. The cultivation of CaCo 2 epithelial cells demonstrated the cellular adhesion and growth were improved. Nevertheless, these methods have some drawbacks such as poor bonding, complex operation and time-consuming post-treatment. As an important surface modification technique, plasma immer- sion ion implantation (PIII) has drawn much attention due to its simple operation and non-light-of-sight characteristics which bode well for biomedical implants with a complex shape [17]. Moreover, surface properties can be selectively modified using PIII technique without affecting the bulk characteristics [18]. In the PIII process, the sample is immersed in a plasma and negative high voltage pulses are applied to it. When the sample is negatively biased, the electrons around it are repelled and a positive ion sheath is estab- lished. Ions are accelerated by the electric field in the sheath and implanted into the sample surface vertically from all directions. Surface physical states such as roughness and hydrophilicity can be adjusted flexibly by PIII method [19,20]. Meantime, by using http://dx.doi.org/10.1016/j.colsurfb.2014.02.019 0927-7765/© 2014 Elsevier B.V. All rights reserved.