Electrophoretic Deposition, Microstructure, and Corrosion Resistance of Porous Sol–Gel Glass/Polyetheretherketone Coatings on the Ti-13Nb-13Zr Alloy

Electrophoretic Deposition, Microstructure, and Corrosion Resistance of Porous Sol–Gel Glass/ Polyetheretherketone Coatings on the Ti-13Nb-13Zr Alloy TOMASZ MOSKALEWICZ, ANITA ZYCH, ALICJA ŁUKASZCZYK, KATARZYNA CHOLEWA-KOWALSKA, ADAM KRUK, BEATA DUBIEL, AGNIESZKA RADZISZEWSKA, KATARZYNA BERENT, and MARTA GAJEWSKA In this study, microporous composite sol–gel glass/polyetheretherketone (SGG/PEEK) coatings were produced on the Ti-13Nb-13Zr titanium alloy by electrophoretic deposition. Coatings with different levels of high open porosity were developed by introducing SGG particles of varying diameters into the PEEK matrix. The microstructure of the coatings was characterized by electron microscopy and X-ray diffractometry. The coatings with 40-50 lm thickness were composed of semicrystalline SGG particles consisting of hydroxyapatite, CaSiO3, some Ca2SiO4, and an amorphous phase containing Ca, Si, P, and O, homogeneously embedded in a semicrystalline PEEK matrix. The size of SGG particles present in the coatings strongly influenced the formation of microcracks and their adhesion to the underlying substrate. Microscratch tests showed that the coating containing SGG particles with a diameter smaller than 45 lm and open porosity of 45 pct exhibited good adhesion to the titanium alloy substrate, much better than the coating containing particles with a diameter smaller than 85 lm and total open porosity equal to 48 pct. The corrosion resistance was investigated in Ringer’s solution at a temperature of 310 K (37 C) for a pH equal to 7.4 and in deaerated solutions with the use of open-circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy. The SGG/PEEK-coated alloy indicated better electrochemical corrosion resistance compared with the uncoated alloy. DOI: 10.1007/s11661-017-4030-0  The Author(s) 2017. This article is published with open access at Springerlink.com I. INTRODUCTION TITANIUM alloys are the most frequently used metallic materials for biomedical applications due to their high strength-to-weight ratio, high fatigue resistance, and good biocompatibility.[1,2] Today, the most important titanium alloys, which have found applications in medicine, are b alloys. They exhibit low elastic modulus and density, high strength, and ductility as well as good electrochemical corrosion resistance.[3–5] However, their use in medicine is limited not only by their TOMASZ MOSKALEWICZ, ANITA ZYCH, ADAM KRUK, BEATA DUBIEL, and AGNIESZKA RADZISZEWSKA are with the Faculty of Metals Engineering and Industrial Computer Science, AGH University of Science and Technology, Czarnowiejska 66, 30-054 Kraków, Poland. Contact e-mail: ALICJA ŁUKASZCZYK is with the Faculty of Foundry Engineering, AGH University of Science and Technology, Reymonta 23, 30-059 Kraków, Poland. KATARZYNA CHOLEWA-KOWALSKA is with the Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Mickiewicza Av. 30, 30-059 Kraków, Poland. KATARZYNA BERENT and MARTA GAJEWSKA are with the Academic Centre for Materials and Nanotechnology, AGH University of Science and Technology, Mickiewicza Av. 30, 30-059 Kraków, Poland. Manuscript submitted December 5, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A relatively low hardness and poor tribological properties, but also by the very slow osseointegration between implants and surrounding bone tissues.[6,7] Titanium alloy osseointegration might be enhanced by surface treatment involving the deposition of porous coatings containing bioceramics, biopolymers, and their combinations. The porous coatings improve osseointegration by providing more space for bone growth. Moreover, the bond between the biomaterial and bone becomes stronger.[8,9] Porosity, pore diameter, distribution, and interconnectivity are important parameters, which determine the biomaterial bioactivity.[10] In general, open porosity higher than 50 pct and interconnected pores with a mean diameter of 100 lm or higher are considered to be the minimum requirements to permit tissue ingrowth.[11,12] For example, Hadjicharalambous et al.[13] showed that about 50 pct porosity and an average pore size of 150 lm are beneficial for cellular growth in zirconia ceramics. The important limitations to the use of materials, especially ceramics, with high porosity and pore size are their low mechanical properties.[14] Thus, a good response to the improvement of the mechanical properties of highly porous coatings may be the introduction of a polymer and the deposition of composite polymer-based coatings incorporating ceramic particles. Electrophoretic deposition (EPD) is a surface engineering method, which enables the codeposition of different ceramic or/and polymeric materials, producing dense or porous composite polymer-based coatings with high homogeneity and tailored thickness.[15,16] EPD consists of the movement of charged particles suspended in liquid and deposition onto a conducting substrate under the influence of an externally applied electrical field.[17,18] The advantages of this method are high purity, easy control of the coating thickness, high coating uniformity, the possibility of using complex shaped substrates, and the short deposition time of coatings.[19,20] One of the popular materials with useful properties for a relatively strong porous coating matrix is polyetheretherketone (PEEK). PEEK is a nontoxic and bioinert material.[16,21,22] It is a crystallizable aromatic polymer with very good thermal and mechanical properties. This polymer is used to replace metal implant components, especially in long-term orthopedic applications.[23] Furthermore, PEEK is noncytotoxic and can be repeatedly sterilized without evident deterioration of its mechanical properties.[21] The osseointegration process of titanium alloy might be enhanced by using a bioactive glass or glass-ceramic as a bioactive coating component. A typical feature common to all bioactive glasses, both melt or sol–gel derived, is the ability to interact with living tissue, in particular forming strong bonds to bone.[24] Bioactive glasses are amorphous silicate-based materials exhibiting osteoconductive/osteoinductive properties.[10,25,26] They are promising materials for bone tissue engineering applications due to their excellent bioactivity, biocompatibility, and osteogenicity properties.[27,28] Bioactive glass stimulates new bone growth and, once implanted in the body, can react with physiological fluids and form a strong bond with bones. Its bioactivity is associated with the formation of a carbonated hydroxyapatite layer (HCA) on its surface, similar to the bone mineral.[29,30] Glass-ceramics with crystalline or semicrystalline structures are produced by the transformation of the glass into a ceramic.[10] The sol–gel glasses offer several advantages compared with the melt-delivered glasses. Due to their nonporous texture, the sol–gel-derived glasses exhibit a high specific surface area in compariso (...truncated)