Electrochemically designed interfaces: Electrical properties and morphology of micro-nanostructured Titania implant surfaces

Accepted Manuscript Electrochemically designed interfaces: Electrical properties and morphology of micro-nanostructured Titania implant surfaces

F.S. Utku PII: DOI: Reference:

S0257-8972(17)30444-9 doi: 10.1016/j.surfcoat.2017.04.069 SCT 22313

To appear in:

Surface & Coatings Technology

Received date: Revised date: Accepted date:

31 January 2017 24 April 2017 25 April 2017

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ACCEPTED MANUSCRIPT Electrochemically Designed Interfaces: Electrical Properties and Morphology of MicroNanostructured Titania Implant Surfaces F.S. Utku Yeditepe University, Department of Biomedical Engineering, Istanbul, Turkey

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Corresponding author: F.S. Utku

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Telephone: 0090-216-5780433

Complete permanent postal address:

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E-mail address: [email protected]

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Fax Number: 0090-216-5780244

26 Agustos Yerlesimi, Inonu Mahallesi, Kayisdagi Caddesi, 34755, Atasehir, Istanbul,

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Turkiye. (Dear Editor and Reviewer(s),

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I have included a revised version of the submitted research article. Following your comments, I have made many changes in the paper. Most of them are small grammatical corrections. Others are more significant changes in the abstract, results and discussion sections as you

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Yeditepe University, Faculty of Engineering, Department of Biomedical Engineering,

have requested. The small changes are many and thus are hard to mark on the article unless I mark them with track changes. If you want it to be carried out using track changes, I will submit a new revision in a short time. However, the larger and more significant changes in the abstract and results sections have been highlighted as requested. Deletions have been marked as crossed out yellow sections, additions/revisions are green in the text. I have written the action taken in pink highlight. Thank you for reviewing/editing and for your time and effort.)

ACCEPTED MANUSCRIPT Manuscript Abstract: Designing Titanium implant interfaces is essential not only for the prevention of corrosion, but also for the promotion of osteointegration. Surface morphology and surface charge are

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crucial determinants in the construction of biocompatible osteoconductive orthopedic and dental implants. Thus, generation of surfaces with optimal topographic and electrical

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properties for cellular growth has been aimed. In this study, surface chemistry and

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morphology of cp Titanium plates were modified by anodization at 30V for 60 minutes, in dual acidic solution (48wt% H2SO4-18wt% HCl) at 40°C and in alkaline solution (5M KOH)

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at 40°, 60° and 80°C. Titanium surfaces were characterized for morphology, crystallography,

Morphological characterization using FE-SEM revealed micro-to-nanoscale porosity, with

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nanosized pores formed within the micropores, generating a hierarchically arranged micro-

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nano network on Titanium surfaces anodized under all thermal conditions. Hydrophilicity decreased with increasing alkaline anodization temperature (control, 100±0.7°; 40°C, 23.3±3.0°; 60°C, 43.5±2.1°; 80°C, 55.3±2.3°). The XRD analysis displayed only Ti peaks at

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34.5°, 38°, 40°, 53° and 63° 2θ. Increasing alkaline anodization temperature modified the electrical properties of Titanium plates. Mott-Schottky analysis displayed an increase in

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wettability, bulk resistivity, corrosion resistance, surface conductivity and capacitance.

capacitance as indicated by steeper slopes and linearity extending over a greater potential range with increasing temperature. Corrosion current density (Icorr) was experimentally determined as 1.05×10−7A/cm2, 5.95×10−8A/cm2, 3.79×10−9A/cm2, 3.92×10−9A/cm2 while charge carrier density was calculated as 3.44×1020/cm3, 3.50×1019/cm3, 2.05×1019/cm3, 1.01×1019/cm3 respectively for the control, 40°C, 60°C and 80°C samples. All things considered, samples modified in 5M KOH solution at 60°C displayed optimal micro-tonanoporosity, lowest corrosion current density and anodic voltage. The electrical properties

ACCEPTED MANUSCRIPT of modified Titanium surfaces have indicated that it may be more suitable to use Potassium hydroxide in the anodization of biomedical implants which require a biocompatible, osteoconductive topography, high capacitance and high corrosion resistance. 1. Introduction

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Titanium (Ti) and its alloys, when compared with other metallic orthopedic and dental implant materials, display superior mechanical and physical properties, such as high

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toughness, specific strength, corrosion resistance, inertness and biocompatibility, properties

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which have led to their wide-spread use in the biomedical field [1-3]. In order to increase surface adhesion and osseointegration, while preventing fibrous tissue encapsulation and

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rejection of [4-5], the functional properties of Ti implant surfaces can be modified through

polishing [6], atmospheric plasma and vacuum plasma spraying of Ca-P and TiO2 coatings,

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sputtering of thin films and thermo-chemical surface treatment [2,7-10].

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Chemical methods, such as chemical vapor deposition, hydrogen peroxide, sol-gel and acidic/alkaline treatment and anodization can be used in surface functionalization. The

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bioactivity of medical Ti can be improved by generating hierarchically porous surface structures using acidic and alkaline solutions. The chemical treatment used in this study, i.e. dual-acid anodization, entails the use of strong acids to remove the surface oxide, to

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mechanical, physical and chemical means, such as micro/machining, sand/grit blasting, rough

clean/polish the implant surface, thus providing a larger surface area than untreated Ti with a uniform roughness of 0.5-2 μm [11-15]. Acid type-concentration, temperature and length of treatment determine the extent of polishing and production of microporous TiO2 surface. Using the dual acid-etching method, different mixtures of acids, such as concentrated HNO3 and HF or concentrated HCl and H2SO4, at temperature above 100 °C have been employed [6,12,16] to promote attachment of

ACCEPTED MANUSCRIPT fibrin and osteogenic cells, ECM production, direct bone formation on implant surface [17] and promotion of osseointegration with less bone resorption [18-20]. Alkaline treatment involves the use of NaOH or KOH that results in the formation of a bioactive, rough TiO2 surface layer, displaying higher biocompatibility, increased cell attachment and proliferation [21]. The oxide layer thickness and morphology obtained by

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alkaline anodization can be modulated by adjusting the electrochemical process parameters,

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such as, current density, electrolyte solution concentration, composition and temperature.

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Sodium hydroxide, used in alkaline electrochemical anodization of Ti has been shown to grow micro-mesoporous Ti surfaces with a bone-like hierarchical porosity [6,22-24]. The

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cation that constitutes the alkaline solution has been shown to affect the morphology of the porous layers formed on Ti, such that, using 5M aqueous KOH, well-defined, large pores,

In this study, Ti surfaces were fabricated using sulphuric-chloric acid based dual-acidic

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anodization at 40°C and KOH based alkaline anodization at 40°, 60°, and 80°C. Therefore, to

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the best of our knowledge, the effect of both temperature and potassium as the cation constituent of the alkaline anodization on the morphological, crystallographic, electrical and

2. Experimental

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wetting properties of the plates has been studied here for the first time [23].

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correlating with treatment time have been obtained [23].

2.1. Materials

Titanium Plates: Twelve commercially available pure Ti Grade IV (250 mm:500 mm:1 mm) plates were metallographically ground and polished using #120 grit down to #1200 grit Emery paper and finally one micrometer diamond paste until a mirror-like finish of roughness was obtained. Samples were then rinsed with distilled water and sonicated in acetone, anhydrous alcohol, and finally in distilled water for 10 min each [24].

ACCEPTED MANUSCRIPT Electrolyte Solution: Hanks’ solution was used for both I-V polarization tests and Mott Schottky capacitance analysis. Hank’s solution was prepared using 8 g/L NaCl, 0.4 g/L KCl, 0.14 g/L CaCl2, 0.35 g/L NaHCO3, 0.06 g/L Na2HPO4•2H2O, 0.1 g/L MgCl2•6H2O, 0.06 g/L KH2PO4, 0.06 g/L MgSO4•7H2O and 1.0 g/L glucose in autoclaved ultra pure water and buffered at 7.40 [24].

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2.2. Method

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2.2.1. Surface Functionalization

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Unprocessed Ti plates were used as controls. All solutions were prepared using analytical-

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grade chemicals. All Ti samples were anodized in 48wt%H2SO4:18wt%HCl aqueous solution at 30V, at 40°C for 60 minutes and then rinsed thoroughly with distilled water [24].

polished Ti samples were divided into three groups for anodization in 5M KOH at 40°C

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(40/40), 60°C (40/60) and 80°C (40/80). Anodization was conducted in an electrochemical

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cell, using a stainless steel cathode electrode at an anodic voltage of 30V for 60 minutes and then rinsed thoroughly in distilled water. After anodization, the Ti plates were annealed in a

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muffle furnace at 450°C for 4 hrs.

2.2.2. Characterization of Morphological, Hydrophilic and Crystallographic Properties of Anodized Surfaces

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Consequently, in order to determine the thermal effect of alkaline anodization, the acid

Samples were characterized using electron microscopic imaging, contact angle testing and X-Ray diffraction analysis. The surface morphology of the specimen was characterized using field emission scanning electron microscopy (FE-SEM) (JEOL JSM 7000F FEI). The Ti plates, cleaned in acetone, anhydrous alcohol and distilled water and oven-dried at 100°C for an hour, were tested for hydrophilicity using the sessile-drop method on a contact angle goniometer (KSV, CAM200, Finland). After a 5 µl drop of distilled water was placed on the

ACCEPTED MANUSCRIPT substrate surface using a needle and syringe, the advancing angle was measured for 15–45 seconds throughout the final visible advance of the water contact line displaying the slow absorption of water by the surface, where the final angle was indicative of the hydrophilicity of the substrate. The X-Ray Diffraction spectra of the samples were acquired using a glancing X-Ray Diffractometer (Philips, PW 3710) with Cu Kα radiation source at 40 kV and 30 mA

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2.2.3. Characterization of Electrical Properties of Surfaces

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at the grazing angle of 1°, at a step size of 0.2° 2θ and at the scattering angle of 20-70° 2θ.

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The electrical properties of Ti plates were characterized for their bulk resistivity, I-V

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polarization and capacitance behavior.

Bulk Resistivity: The bulk resistivity of Ti surfaces was determined using the four-point

of the anodized plates at an initial current of 10 mA and increased at an increment of 5mA

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upto 30 mA. The voltage generated between the two inner probes arranged in a straight line

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with the outer electrodes at an equal spacing of 15 mm. was measured using needle electrodes and a voltmeter. Separate current and voltage contacts were used to eliminate problems with

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contact resistance. The electrical resistance was determined as the relative resistance change (R/R0) as a function of change in direct current (i), with R0 as the initial resistance [25]. I-V Polarization Behavior: The Ti sample surfaces were coated with epoxy glue, leaving

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measurement method. Using a constant DC current source, current was applied to the corners

a 1cm2 uncoated surface to be exposed to Hank’s solution. The experimental set-up consisted of an electrochemical workstation (WonATech, Zive SP2, Korea), a three-electrode system with a working electrode (Ti sample), a reference electrode (SCE) and a counter electrode (graphite rod) in a covered glass cell containing 200 ml of Hank’s solution. The working and counter electrodes were placed 2 cm. apart from each other. The open circuit potential (OCP) of all controls and samples were determined prior to measurement. The I-V behavior of the

ACCEPTED MANUSCRIPT anodized surfaces was determined at a scan rate of 0.5 mV/s in a potential range of ±120 mV with respect to the open circuit potential and plotted as logarithmic changes in current density versus the electrochemical potential. Tafel extrapolation of polarization resistance was determined from the intersection of the tangent lines to the logarithm of the anodic and

slope of the current versus potential of the intersection [24].

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cathodic current, which were used to obtain Ecorr and Icorr. Resistance was calculated as the

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Capacitance: The capacitance of Ti plates, placed at 2 cm. from the counter electrode, was

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determined in Hank’s solution using a Potentiostat (WonATech, Zive SP2, Korea) with a fixed frequency of 1 kHz, at a 5 mV/s sweeping rate towards the anodic direction. The carrier

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density of the anodized surfaces was determined from the slope of Mott–Schottky plots

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according to equation,

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where ND is the carrier density, C is the space charge capacitance, ε is the dielectric constant,

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ε0 is the vacuum permittivity, EFB is the flat band potential, k is the Boltzmann constant, T is

3. Results

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the absolute temperature and, e the is the elementary charge [24].

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Using dual-acid anodization at 40°C and KOH anodization at 40°, 60° and 80°C, cp Grade IV Ti plate surfaces with hierarchically arranged macro-to-nanoscale porosity were produced and characterized for their morphological, physical and electrical properties. The results showed that an increase in alkaline anodization temperature correlated with an increase in porosity, where nanosized pores were formed within the micropores, generating a hierarchically arranged micro-nano network of pores. The change in surface porosity also correlated with the electrical properties of the samples, displaying a decrease in electrical conductivity and an increase in capacitance.

ACCEPTED MANUSCRIPT 3.1. Characterization of Morphological, Hydrophilic and Crystallographic Properties of Anodized Surfaces The TiO2 layer (Fig. 1) contained 0.050-1.0 micrometer wide pores with inhomogenously distributed mesopores, where pore size and density varied with alkaline anodization temperature. Micro-nanofunctionalized samples with large micropores (40/40), contained a

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high density of mesopores (Fig. 1a) and displayed the lowest contact angle of 23.3±3.0°

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(Table 1). Micro-nanofunctionalized samples with smaller micropores (40/60) contained a

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higher density of mesopores with thicker pore walls (Fig. 1b) and displayed slightly higher contact angle of 43.5±2.1° (Table 1). Nanofunctionalized samples (40/80) containing micron

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sized pits scarcely distributed within the nanoporosity (Fig. 1c) displayed even higher contact angle 55.3±2.3° (Table 1). The untreated control Ti plates had the highest contact angle of

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(XRD peaks at 34.5, 38, 40, 53 and 63° 2θ) (Fig. 2) [24-25].

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3.2. Characterization of Electrical Properties of Surfaces The bulk resistivity of the Ti samples varied with alkaline anodization temperature (Fig.

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3). A positive correlation between an increase in conducted current and voltage measured was displayed in the control and samples, except the 40/80 sample group, which displayed a steady voltage despite the increase in current to above 20 mA, indicating a decrease in bulk

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100±0.7° (Table 1). The crystallographic analysis of the samples displayed only Ti peaks

resistivity in this sample group. The corrosion current density (Icorr) of the anodized plates was determined from the linear polarization curves (Fig. 4) as 1.05×10−7 A/cm2, 5.95×10−8 A/cm2, 3.79×10−9 A/cm2 and 3.92×10−9 A/cm2 for the blank control Ti surface, 40/40, 40/60 and 40/80 samples respectively (Table 1). The Mott-Schottky plots for the anodized surfaces (Fig. 5) and the calculated charge carrier densities (Table 1) indicated that the samples produced at the higher alkaline anodization temperature displayed higher capacitance, i.e. steeper slopes, and linearity extending over a greater potential range. Using a dielectric

ACCEPTED MANUSCRIPT constant of 31 for TiO2 [26], the carrier density (ND) was calculated to be 3.44 × 1020/cm3, 3.50 × 1019/cm3, 2.05 × 1019/cm3 and 1.01 × 1019/cm3 for the blank Ti surface, 40/40, 40/80 and 40/60 samples (Table 1). 4. Discussion

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4.1. Morphological and Crystallographic Changes and Hydrophilicity of Anodized Ti

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Surfaces

Chemical surface modification of Ti aims to alter surface roughness and composition,

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enhancing wettability of the implant and deposition of Ca-P by effectively providing

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nucleation points for calcium phosphate precipitation. Acidic and alkaline treatment is a rutine process for the removal of debris and oxide scales, during which Ti is oxidized to a

generate a porous TiO2 layer [6,23-24].

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Thus, the porosity introduced into Ti is due to oxidation and reduction reactions taking

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place simultaneously. When Ti is immersed in alkaline solutions, Ti oxide and alkali titanate may be formed as a surface passive layer on Ti, grow to a limiting thickness and then cease to

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grow due to the compact layer formed as a barrier to the ionic species [23]. In addition, an active surface layer containing H may form and grow on the entire surface layer, forming a solid-state hydrogen solution (metal hydride), which, through dissolution in an alkaline

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bivalent state with the generation of oxygen ions, which react with the Ti+2 cations to

environment, generates a porous structure [23]. The sequential acidic and alkaline anodization has enabled formation of Ti surface with interconnected porosity, enhancing surface hydrophilicity significantly in comparison with the control plates. The results of this study indicate that hydrophilicity has been increased with anodization; however, it has decreased with the introduction of nanostructures at the higher anodization temperature. Although the FE-SEM images of the 40/40 and 40/60

ACCEPTED MANUSCRIPT samples display comparable porosity, the lower hydrophilicity of 40/60 may be due to the thicker pore walls in these samples.

The XRD analysis has displayed only Ti peaks, indicating that either an anatase oxide

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layer too thin to be detected by XRD has been formed on the Ti samples (with XRD peaks at (101) 25.2° and (200) 48° 2θ) [23-24] or the surfaces have been amorphous with potassium

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titanate (K2Ti6O13) hydrogel attracting water into the porosity [25] and thus broadening the

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4.2. Fundamental Electrical Properties of Surfaces

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diffraction peaks and lowering their intensities (Fig. 2) [24-25].

Ti has an enthalpy of formation ∆fH°(TiO2) of -944.7 kJ/mol [27]. Ti, having a highly

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moisture [23]. When immersed in an aqueous solution, the Ti will adsorb OH− to form TiOH

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groups at the solid-liquid interaction interface, where these groups exhibit acidic or basic

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behavior according to solution pH. When the solution pH is <4, a positively charged surface is formed by the protonated [TiOH]+; and, when the solution pH is >9, a negatively charged

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surface is formed by the hydroxylated [TiOH]−. At pH between 4 and 9, both protonated and hydroxylated TiOH groups coexist on the Ti surface [23]. In SBF, at pH 7.4, with an isoelectric point of about 5–6, the TiO2 surface is slightly negative due to presence of

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negative electrochemical potential, easily oxidizes to yield TiO2(s), upon exposure to air or

deprotonated acidic hydroxides. The linear polarization (I-V) curves of the samples, obtained in Hank’s solution, indicated that the control was more anodic than the samples, which demonstrated a positive potential shift and displayed better corrosion resistance compared with the blank Ti control (Fig. 4). The polarization curves displayed a typical Tafel relationship with two linear regions, a

ACCEPTED MANUSCRIPT characteristic diffusion controlled Her (hydrogen evolution reaction) and an Orr (oxygen reduction reaction) regions. The positive slopes of all curves in Mott–Schottky plots suggested that the oxide films formed on Ti exhibited a typical n-type semiconductor behavior. The lower charge carrier density indicated a lower mass transport of ions and a higher corrosion resistance as a result

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of less number of oxygen vacancies on anodized Ti [3]. The initial formation of TiO2 on the

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Ti surface with an O/Ti concentration ratio of 2 may be decreased, making the oxide layer

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oxygen deficient [22,24].

The bulk resistivity of the Ti samples varied with anodization temperature (Fig. 3).

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However, the 40/80 sample group displayed a steady voltage despite the increase in current to above 20 mA and demonstrating a decrease in bulk resistivity. In the literature, a gradual

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in a study on resistance (R) per initial resistance (R0) vs t for KOH treated Ti [25]. A change

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in electrical resistance (R) may be due to either a reduction in the material dimensions, i.e.

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metal dissolution through corrosion, or a modification of electrical resistivity, i.e. compositional changes, such as hydrogen absorption [28]. The decrease in bulk resistivity

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over time has thus been explained as a flux of Habs, facilitating the partial reduction of the semiconducting passive layer (TiO2) to a more conducting lower state Ti species (Ti2+ or Ti3+) [29]. After absorption of Hads to Habs and dissolution of the Habs forming pores, the R/Ro

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increase of R/R0 within the first hour without reaching any limiting value has been obtained

values increase over time. 4.3 Effect of Cation Type on the Electrical Properties of Ti The acidic and alkaline anodization resembles a corrosion process with local cathodic and anodic regions in the metal. In the cathodic region, the reduction reaction undergoes a hydrogen evolution reaction (Her) through a reaction intermediate, H adsorbed to the surface, Hads, which diffuses and is absorbed into the bulk of the metal to form a metal hydride (Habs)

ACCEPTED MANUSCRIPT through a concentration gradient. In an alkaline solution, Habs containing surface layer dissolves partially to form a porous structure [23]. In the anodic region, the oxidation reaction produces an oxide layer. However, anodization in alkaline solutions of various concentrations and the subsequent heat treatment can produce a thicker and denser oxide layer on Ti surfaces [25]. The thickness of the porous oxide layer

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may be determined by the hydroxide ion concentration, while the morphology and

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composition of the porous oxide layer may be determined by the cation type. Compared with

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Na+, K+, with an ionic radius of 1.33 Å [23] has a weaker electric field and thus a lower hydration number of only 2-4 water molecules [23]. The ability to form a porous titanate

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layer K2Ti6O13 and a solid-state hydrogen solution (metal hydride) is thus affected. With a lower hydration number than Na+, both Ti+4 and O-2 ions display a highly stable and porous

The differences between the K+ and Na+ cation may be validated when the electrical

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properties of the TiO2 substrates are compared. In the literature, using the same procedure

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with K+ as the source of alkalinity, similar charge transfer densities have been obtained; however, corrosion current densities, Icorr, lower at two logarithmic scales with the corrosion

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voltage migrating cathodically have been realized [24]. The two logarithmic scale reduction in Icorr is significant as it allows less current flow through the implant, affecting its surface energy, chemistry and crystallinity and modulating the adsorption of organic biomolecules

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crystallographic network in presence of alkaline solutions.

and ions in the tissue fluid. Therefore, the macro-to-nanoscale porosity generated by the coordinated acidic and alkaline chemical anodization has enabled formation of more hydrophilic surfaces with improved adhesive surface properties, which may also affect both the amount and composition of adsorbed protein [22]. The organic and inorganic compounds deposited by the cells contain groups that make both ionic and hydrogen bonds as well as

ACCEPTED MANUSCRIPT weak van der Waals forces which may improve the mechanical properties and the adhesion strength of the newly deposited tissue to the implant. Osteointegration [30] through increased mechanical stability [31-32] has been shown to be affected by implant surface topography [33], morphology, chemistry, charge, roughness

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[4,6,30,34] and substrate stiffness, dictating tissue-implant surface mechanical compatability [35] and cellular attachment [36]. In the literature, surfaces with microfunctionalized porosity

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have demonstrated enhanced osteoblast attachment, differentiation, local factor production

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and wound healing [17], promoting osteoblast attachment, differentiation and successful bone-to-implant contact in vivo, without osteoblast proliferation and bone mass formation

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[36]. Hierarchically arranged micro-to-nanoscale structures, with larger surface area and

mechanical concerns related to interfacial interactions at the implant- host level and enabled anchorage of extracellular proteins and subsequent attachment, spreading and proliferation of

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bone cells [30-33,36]. 5. Conclusions

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Anodic and cathodic electrochemical processes have been used to introduce porosity on Ti, expected to biomimick bone surfaces and enhance osteointegration through the provision and improvement of fundamental mechanical, biological and chemical elements of fixation. Using

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wettability, have been shown to dissipate bonding energy [24,36]. They have overcome the

dual-acid anodization at 40°C and KOH alkaline anodization at 40°, 60° and 80°C, hierarchically arranged macro-to-nanoscale porous surfaces have been produced on cp Grade IV Ti plates and characterized for their morphological and electrical properties. The results indicate that an increase in alkaline anodization temperature correlates with an increase in porosity and wettability which then affects the electrical properties of the samples, displaying a decrease in electrical conductivity and an increase in capacitance. With the Potassium

ACCEPTED MANUSCRIPT cation used as the source of alkalinity, the Icorr has been found to be two logarithmic scales lower than Sodium cation results with the corrosion voltage migrating cathodically. Thus, the macro-to-nanoscale porous surfaces may be potential implant-ceramic-hard tissue interfaces for future biomedical applications.

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Acknowledgements We would like to thank Prof. Mustafa Urgen, Prof. Mustafa Culha, Prof. Necdet Yazar,

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Prof. Gultekin Goller, Huseyin Sezer, Sena Salta, Sibel Sofuoglu, Secil Goncuoglu, Caglar

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Caymaz, Ibrahim Kapici and Muhammed Aydin for their help in the conduction of this

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research.

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19. D. Buser, N. Broggini, M. Wieland, R.K. Schenk, A.J. Denzer, D.L. Cochran, B.

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20. Gupta, M. Dhanraj, G. Sivagami, Status of surface treatment in endosseous implant: a literary overview, Indian J. Dental Res. 21 (2010) 433-438.

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22. W.Q. Yu, X.Q. Jiang, F.Q. Zhang, L. Xu, The effect of anatase TiO2 nanotube layers

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on MC3T3-E1 preosteoblast adhesion, proliferation, and differentiation, Journal of Biomedical Materials Research Part A 94 (2010) 1012

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23. S. Tanaka, H. Tobimatsu, Y. Maruyama, T. Tanaki, G. Jerkiewicz, Preparation and characterization of microporous layers on Ti , ACS Appl Mater Interfaces 1 (2009) 2312-2319.

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ACCEPTED MANUSCRIPT 26. M. Ye, J. Gong, Y. Lai, C. Lin, Z. Lin, High-efficiency photoelectrocatalytic hydrogen generation enabled by palladium quantum dots-sensitized TiO2 nanotube arrays, J Am. Chem. Soc. 134 (2012) 15720-15723. 27. Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 0-618-94690-X.

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28. G. Jerkiewicz, B. Zhao, S. Hrapovic, B.L. Luan, Discovery of reversible switching of

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coloration f passive layers on titanium, Chem. Mater. 20 (2008) 1877–1880.

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29. X. Lu, G. Wang, T. Zhai, M. Yu, J. Gan, Y. Tong, Y. Li, Hydrogenated TiO2 nanotube arrays for supercapacitors, Nano Letters 12 (2012) 1690-1696.

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30. P.I. Branemark, Osseointegration and its experimental background, J. Pros. Dent. 59 (1983) 399-410.

nanoscale structure, Biomaterials 25 (2004) 3593.

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32. S.F. Hulbert, F.W. Cooke, J.J. Klawitte, R.B. Leonard, B.W. Sauer, D.D. Moyle, H.B.

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Skinner, Attachment of prostheses to musculoskeletal system by tissue ingrowth and mechanical interlocking, J. Biomed. Mater. Res. 7 (1973) 1-23.

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33. P.G. Coelho, T. Takayama, D. Yoo, R Jimbo, S. Karunagaran, N. Tovar, M.N. Janal, S. Yamano, Nanometer-scale features on micrometer-scale surface texturing: a bone histological, gene expression, and nanomechanical study, Bone, 65 (2014) 25-32.

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31. J. Tan, W.M. Saltzman, Biomaterials with hierarchically defined micro- and

34. F.S. Utku, E. Yuca, E. Seckin, G. Goller, A. Yazgan Karatas, M. Urgen, C. Tamerler, Protein mediated hydroxyapatite composite layer formation on nanotubular titania, Bioinspired Biomim. Nanobiomater. 4 (2015) 155-165. 35. Y. Zhou, M.L. Snead, C. Tamerler, Bio-inspired hard-to-soft interface for implant integration to bone, Nanomed. 11 (2015) 431-434.

ACCEPTED MANUSCRIPT 36. C.J. Bettinger, R. Langer, J.T. Borenstein, Engineering substrate topography at the micro and nanoscale to control cell function, Angew. Chem. Int. Ed. Engl. 48 (2009)

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ACCEPTED MANUSCRIPT Figures: Figure.1 The micro-meso structured surfaces of the control and sample plates. Magnification: 40K. Figure. 2 The XRD spectra of the control and sample plates.

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Figure. 3 Voltage response of the control and sample plates tested for bulk resistivity under

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Figure 4. I-V Polarization plots of the control and sample plates.

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Figure 5 Mott –Schottky plots of the control and sample plates.

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Table 1 Electrochemical and Physical Parameters of Titania Implant Surfaces. Control 40/40 40/60 40/80 100.7°±0.84° 23.3°±3.0° 43.5.0°±2.1° 55.3°±2.3° Contact Angle -0.292 -0.259 -0.145 -0.213 Ecorr vs SCE (V) 1.05E-07 5.95E-08 3.79E-09 3. 92E-09 Icorr (A) 2,77E+06 4.37E+06 3.83E+07 5.37E+07 R (Ω) 3.44E+20 3.5E+19 2.05E+19 1.01E+19 ND (cm-2)

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ACCEPTED MANUSCRIPT Highlights

a) the structural features of bone, macro-mesoporosity, have been biomimicked. b) the electrical conductivity has been compared for KOH vs. NaOH anodization.

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c) the electrical properties have been compared according to anodization temperature.

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