DOI 10.1515/ejnm-2014-0006 Eur. J. Nanomed. 2014; 6(1): 37–46 Prabitha Urwyler a , Xue Zhao b , Alfons Pascual, Helmut Schift and Bert Müller* Tailoring surface nanostructures on polyaryletherketones for load-bearing implants Abstract: High-performance thermoplastics including polyetheretherketone (PEEK) are key biomaterials for load-bearing implants. Plasma treatment of implants surfaces has been shown to chemically activate its sur- face, which is a prerequisite to achieve proper cell attach- ment. Oxygen plasma treatment of PEEK films results in very reproducible surface nanostructures and has been reported in the literature. Our goal is to apply the plasma treatment to another promising polymer, polyetherk- etoneketone (PEKK), and compare its characteristics to the ones of PEEK. Oxygen plasma treatments of plasma powers between 25 and 150 W were applied on 60 μm- thick PEKK and 100 μm-thick PEEK films. Analysis of the nanostructures by atomic force microscopy showed that the roughness increased and island density decreased with plasma power for both PEKK and PEEK films cor- relating with contact angle values without affecting bulk properties of the used films. Thermal analysis of the plasma-treated films shows that the plasma treatment does not change the bulk properties of the PEKK and PEEK films. Keywords: Polyetheretherketone (PEEK); polyetherke- toneketone (PEKK); oxygen plasma treatment; atomic force microscopy; differential scanning calorimetry. a Present address: University of Bern, Gerontechnology and Rehabilitation group, 3010 Bern, Switzerland. b Present address: EMPA, Laboratory for Nanoscale Materials Science, 8600 Dübendorf, Switzerland. *Corresponding author: Bert Müller, Biomaterials Science Center (BMC), University of Basel, c/o University Hospital Basel, 4031 Basel, Switzerland, Phone: +41 61 265 9660, Fax: +41 61 265 9699, E-mail: bert.mueller@unibas.ch Prabitha Urwyler: Biomaterials Science Center (BMC), University of Basel, c/o University Hospital Basel, 4031 Basel, Switzerland; and Paul Scherrer Institute (PSI), Laboratory for Micro- and Nanotechnology, 5232 Villigen PSI, Switzerland Xue Zhao: Biomaterials Science Center (BMC), University of Basel, c/o University Hospital Basel, 4031 Basel, Switzerland Alfons Pascual: University of Applied Sciences Northwestern Switzerland FHNW, Institute of Polymer Engineering (IKT), 5210 Windisch, Switzerland Helmut Schift: Paul Scherrer Institute (PSI), Laboratory for Micro- and Nanotechnology, 5232 Villigen PSI, Switzerland Introduction Polyaryletherketones are semi-crystalline thermoplastics, which are thermally stable up to at least 250°C and exhibit high mechanical strengths compared to other polymers. While polyetheretherketone (PEEK) has been established as a high-performance polymer in the orthopedics (1, 2) and further medical implants (1, 3–6), polyetherketonek- etone (PEKK) is only at the transition to medical appli- cations. The structure of PEKK and PEEK, reproduced in Figure 1, is very similar. Both polymers, PEKK and PEEK, belong to the polyaryletherketone family, where benzene rings are linked via ether and ketone groups. The ratio and sequence of ethers to ketones affect the thermal properties including glass transition temperature, melting point, heat resistance, and processing temperature of the polymer. PEKK has a higher ratio of ketones than PEEK making the polymer chain more rigid. As a consequence, the reported glass transition temperature of PEKK (T g = 162°C) and the melting point of PEKK (T m = 395°) (7, 8) are significantly higher than the ones of PEEK (T g = 143°C, T m = 343°C) (9). In comparison to PEEK, PEKK has an extremely slow rate of crystallization leading to improved flow characteristics, lower mold-in stresses, and greater dimensional stability (10). PEKK also exhibits lower melt viscosity than PEEK (11) rendering easier processing of injection-molded prod- ucts. Even more important for load-bearing implants are the mechanical properties of PEKK with respect to the established PEEK. The compressive yield strength of PEKK (205 MPa), for example, is twice as large as the one of PEEK (118 MPa). The density of PEKK (1.3 g/cm 3 ) and of PEEK (1.3 g/cm 3 ) (9) is closer to bone (1.9 g/cm 3 ) (12) than that of the metals in use for load-bearing implants. The thermo-mechanical properties of PEKK superior to the ones of PEEK are a clear advantage when working with thin film or thin-walled products. Nevertheless, as PEEK, PEKK is radiolucent, compatible to magnetic reso- nance imaging and chemically inert and, therefore, quali- fies as a promising biomaterial for a variety of medical implants. Several manufacturing processes including inject- ing molding are in use to produce medical implants from PEEK (13, 14). For osteointegration, the PEEK surfaces Bereitgestellt von | Lib4RI Angemeldet | 192.33.118.37 Heruntergeladen am | 06.03.14 09:32