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Investigation on

aDepartment of Chemistry, Periyar Univ

dhanaraj_gopi@yahoo.com; Fax: +91-427-2bCentre for Nanoscience and NanotechnologycDepartment of Physics, School of Basic an

Tamilnadu, Thiruvarur 610101, IndiadIndustrial Accelerator Section, Raja Ram

Indore 452013, India

Cite this: RSC Adv., 2014, 4, 34751

Received 13th May 2014Accepted 23rd July 2014

DOI: 10.1039/c4ra04484c

www.rsc.org/advances

This journal is © The Royal Society of C

corrosion protection andmechanical performance of minerals substitutedhydroxyapatite coating on HELCDEB-treatedtitanium using pulsed electrodeposition method

D. Gopi,*ab A. Karthika,a D. Rajeswari,ac L. Kavitha,c R. Pramodd and Jishnu Dwivedid

The present work aims to investigate the effects of minerals (strontium, magnesium and zinc) substituted

hydroxyapatite (M-HAP) coating on high-energy low-current DC electron beam (HELCDEB)-treated

titanium (Ti). The M-HAP coating was developed over the untreated and HELCDEB-treated Ti by pulsed

electrodeposition, and was characterized by scanning electron microscopy, X-ray diffraction, Fourier

transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and

electrochemical techniques. The M-HAP coating was obtained on Ti treated at 500 and 700 keV

HELCDEB. The coating on the 700 keV HELCDEB-treated Ti showed better corrosion resistance

properties than the coating obtained on the 500 keV HELCDEB-treated and untreated Ti. The M-HAP

coating on the HELCDEB-treated Ti showed typical flower-like morphology, and exhibited better

resistance to corrosion in simulated body fluid (SBF), along with increased microhardness and decreased

contact angle. An in vitro study of the coating was conducted by immersion in the SBF solution for 1–7

days. The results clearly showed that the M-HAP coating on 700 keV HELCDEB-treated Ti enhanced its

corrosion resistivity and mechanical properties. The coating may have many applications in orthopedics

because it could improve implant fixation in human bone.

1. Introduction

The development of biocompatible implant material is one ofthe most important research areas in medical science. Metallicimplants, such as Ti and its alloys, have gained signicantattention in the eld of orthopedic and dental prostheses.However, due to their bioinertness,1 the contact between theseimplants and bone tissue is solely a mechanical connection.Furthermore, their direct implantation into the human bodycan cause many problems, including low strength connectionswith bone, poor bioactivity, long curing time and metallic ionsmigrating into the body in physiological environments.2 Hence,metallic implants are coated with osteoconductive bioceramics,especially HAP [Ca10(PO4)6(OH)2]. HAP can develop a tight bondwith bone tissue, which is stable towards bioresorption and hasno adverse effects on the human body.3 The natural HAPpresent in bone contains different elements, which play a keyrole in bone formation and the normal function of bone tissue.

ersity, Salem 636011, India. E-mail:

345124; Tel: +91-427-2345766

, Periyar University, Salem 636011, India

d Applied Sciences, Central University of

anna Centre for Advanced Technology,

hemistry 2014

Synthetic HAP can undergo metal ion substitution and a smallquantity of these ions improves its performance in clinicalapplications. Of the many mineral ions,4,5 strontium (Sr),magnesium (Mg) and zinc (Zn) have recently attracted greatinterest.

Sr is an important trace element in the human body and alow dose of Sr diminishes the risk of fractures in post-menopausal osteoporotic patients.6 In addition to promotingbone formation, Sr favors bone healing.7,8 Sr has been shown toenhance preosteoblast proliferation and decrease bone resorp-tion by inhibiting osteoclast resorbing activity and osteoclasticdifferentiation.8 Many reports have shown that Sr-HAPenhances the bioactivity and biocompatibility of HAP by therelease of Sr2+ ions,9–11 and also improves its mechanicalproperties.12

Similarly, Mg is essential for bone metabolism, because thedepletion of Mg adversely affects skeletal metabolism andcauses the cessation of bone growth.13,14 Mg is the fourth mostabundant cation in the human body and is thought to interactwith osteoblast integrins, which are responsible for cell adhe-sion and stability.15,16 Zn occurs naturally in human bone andhas roles in enzyme regulation, cell division and bone forma-tion, which is strongly associated with the growth, develop-ment, and maintenance of healthy bones.17 Zn hasantibacterial activity, thus it minimizes the bacterial load on

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the implant surface aer orthopedic implantation18 andimproves the mechanical strength.19 Bone growth impedimentand defects are commonly observed in humans and animalsbecause of Zn deciency.20,21 Zinc has been reported to have astimulatory effect on bone formation and mineralization.22

Recently, our research group has reported the synthesis ofminerals (Sr, Mg and Zn) substituted HAP with improvedbioactivity23 and also the development of Sr- and Mg-substituted HAP coating on polymer protected 316L SS forimproved biocompatibility.24 In addition, Gopi et al. reportedthe development of CNT/CMC/M-HAP composite and its bio-logical activity on HOS MG63 osteoblast cells.25 Furthermore,Aina et al. investigated the effect of the addition of Sr and Mgions to the HAP structure on its physico-chemical properties.26

Cox et al. performed a live/dead assay using the MC3T3 oste-oblast precursor cells against the as-synthesized Sr, Mg, andZn-substituted HAP.27

An important requirement of a bioceramic coating is its goodadhesion to the implant material. In order to obtain an adhesivecoating with enhanced corrosion resistance, and to achievebetter osseointegrated implants, the surface of the titanium isusually modied. This can induce new bone growth on theimplant.

The surface properties of bioimplant materials, such assurface roughness and wettability, play an essential role inbonding with living cells.28 Many surface modication tech-niques are used to modify the surface of implants, includingchemical etching, alkaline heat treatment, laser, microwave,and electron beam irradiation, and plasma and ion beam irra-diation/implantation.29 In particular, electron beam treatmenthas been proven to be an efficient method for the surfacemodication of metallic materials.30 Energetic electron beamtreatments improve the microhardness and corrosion resis-tance of the implants. Dong et al.29 and Proskurovsky et al.31

have reported that pulsed electron beam treatment improvedthe physical, chemical and mechanical properties of the metal,which may be because of the metastable states in the surfacelayers of the metal. This technique has several advantages, suchas protecting the surface of the implant from oxidation, forminga strong bond between the substrate and the melted surface,and preventing cracks and pores in the surface of the implant.32

Recently Gopi et al.32,33 developed HAP and Sr-HAP coating witha ower-like morphology on HELCDEB-treated Ti and 316Lstainless steel by pulsed electrodeposition and electrodeposi-tion, respectively. During HELCDEB irradiation, the surfaceundergoes superfast heating, melting and solidication toprovide improved physicochemical properties and bondingstrength to the material, which cannot be achieved with othersurface treatments.33

Many methods have been developed to obtain bioactivepure and substituted HAP coatings, such as biomimeticprocesses,34,35 pulsed laser deposition,36 electrochemical depo-sition,37–40 micro arc oxidation,41 and plasma spraying.42 Elec-trodeposition can be used to deposit HAP on any complexgeometry substrates. However, in this method, H2O is reducedto OH� and large amounts of H2 are produced. The H2 gasprevents the nucleation and growth of HAP on the metallic

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surface, which results a loose, porous coating with low adhe-sion.43 However, pulsed electrodeposition has advantagesincluding higher deposition rate, control of depositioncomposition, improved coating quality with the desired struc-ture, and regulation of the coating thickness. During pulsedelectrodeposition, hydrogen peroxide (H2O2) inclusion in theelectrolyte restricts the evolution of H2 bubbles, whichenhances the ionic mobility and allows the deposition ofmineral ions on the implant material.44,45

The present work aims to study the effect of the M-HAPcoating obtained on HELCDEB-treated Ti under different irra-diation conditions. The corrosion resistive performance andmechanical properties of the M-HAP coating on HELCDEB-treated Ti were evaluated. Along with this, the in vitro dissolu-tion of the M-HAP coating was examined in simulated bodyuid (SBF) in order study the reactivity and reliability of theM-HAP coating.

2. Experimental2.1. Preparation of Ti substrate

Pieces of pure Ti metal (99.99%) with a size of 10 � 10 � 3 mmwere used as the substrates for the pulsed electrodeposition.The substrates were abraded using 400–1200 grit silicon carbidesheets and subsequently polished with 1.5 mm diamond paste.In between polishing and aer polishing, the substrates werewashed and ultrasonically cleaned with acetone to prevent thecross contamination of abrasive particles.

2.2. High-energy low-current DC electron beam treatmenton Ti

The specimens were surface treated using a 700 keV DC accel-erator with an electron beam with a current of 1.5 mA at anenergy of 500 or 700 keV to enhance the mechanical propertiesand corrosion resistance of the Ti metal. The procedure of theirradiation process was followed as per our previous report.33

2.3. Preparation and pulsed electrodeposition of M-HAP

Analytical grade 0.294MCa(NO3)2$2H2O, 0.042M Sr(NO3)2$6H2O,0.042 MMg(NO3)2$6H2O and 0.042 M Zn(NO3)2 were dissolved indeionized water and 0.25 M (NH4)2HPO4 was prepared separately.Then, the phosphate ion solution was added dropwise to thecationic solution keeping the target ratio of (Ca + Sr + Mg + Zn)/Pas 1.67. The electrolyte was deaerated with N2 for 30 min and thepH of the electrolyte was adjusted to 4.5 using NH4OH. Theelectrolyte temperature was maintained at 65 �C using a ther-mostat, and amagnetic stirrer was used to keep the concentrationof the electrolyte uniform at a speed of 180 rpm. Prior to startingthe coating procedure, hydrogen peroxide (2000 ppm) was addedto the electrolyte solution in order to decrease the hydrogen gasevolution.33

Pulsed electrodeposition was carried out in a regular threeelectrode system using an electrochemical workstation (CHI760C, CH Instruments, USA) in which the untreated Ti andHELCDEB treated Ti specimens acted as working electrode. Aplatinum electrode and a saturated calomel electrode (SCE)

This journal is © The Royal Society of Chemistry 2014

Fig. 1 FT-IR spectra of the M-HAP coating on (a) untreated Ti, (b) 500keV HELCDEB-treated Ti and (c) 700 keV HELCDEB treated Ti.

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were used as counter and reference electrodes, respectively. Thedeposition was performed for 1 h on untreated and surface-irradiated Ti samples in galvanostatic mode with a constantcurrent density of 1.0 mA cm�2. The pulse on and off time waskept constant as per our previous study,33 and the optimumconditions were 1 s pulse on time and 4 s pulse off time forcurrent densities of 1.0 and 0 mA cm�2. Aer the coatingprocess, the specimens were removed from the electrolyte andwashed with deionized water, then dried in a desiccator for 4 h.

2.4. Structural characterizations

The FT-IR spectra were obtained using a Perkin Elmer RX1 FT-IR spectrometer and were recorded in the 4000–400 cm�1 regionwith 4 cm�1 resolution by using KBr pellet technique. TheRaman spectra of M-HAP coatings were obtained with a Ramanspectrometer (Horiba-Jobin, LabRAM HR) with the scan rangeof 50–3000 cm�1. All the spectra were recorded at ambienttemperature.

The X-ray diffraction (XRD) patterns of the pure Ti, pureHAP, and as-coated samples were obtained using a PANalyticalX'Pert PRO diffractometer in the range 20� # 2q # 60� with CuKa radiation (1.5406 A).

The surface morphology and actual composition of the as-deposited samples were observed by high-resolution scanningelectron microscopy (HRSEM, JSM 840A Scanning microscope,JEOL – Japan) equipped with energy dispersive X-ray analysis(EDAX). Cross-sectional HRSEM analysis of all the coatedsamples was also carried out. The average thickness of eachcoating was obtained from three measurements at differentpositions.

X-ray photoelectron spectroscopy (XPS; Omicron Nano-Technology instrument) with a focused monochromatic Al Kasource (1486.6 eV) for excitation was used for chemicalcomposition analysis of the M-HAP coating. The electron takeoff angle was 54.7� and the XPS survey spectrum over a bindingenergy range of 0–1100 eV was acquired with an analyzer passenergy of 50 and 20 eV for high-resolution elemental scans. Thevacuum pressure was around 3.5 � 10�10 mbar during spectralacquisition. Data analysis was carried out with EIS-Spherasoware provided by the manufacturer.25

2.5. Contact angle measurements

The contact angle measurement of the untreated, 500 and700 keV HELCDEB-treated Ti specimens were analyzed usinga video-based contact angle meter (OCA 15EC, Data PhysicsInstruments, Germany). An equal volume of distilled waterwas placed on every sample with a micropipette, forming adrop or spreading on the surface. Photos were takenthroughout to record the shape of the drops and the contactangle was measured. Five measurements were taken atdifferent locations on each specimen and an average contactangle was calculated.

2.6. Mechanical properties of the M-HAP coating

2.6.1. Adhesion strength. The adhesion strength of theM-HAP coatings on untreated, 500 and 700 keV HELCDEB-

This journal is © The Royal Society of Chemistry 2014

treated Ti was evaluated by a pull-out test according to theAmerican Society for Testing Materials (ASTM) internationalstandard F1044-05 (ref. 46) with ve experiments for eachsample carried out. The specimens were subjected to tests at aconstant crosshead speed using a universal testing machine(Model 5569, Instron).

2.6.2. Vickers hardness test. The surface Vickersmicrohardness was measured at the top surface of the M-HAPcoatings on the untreated and HELCDEB-treated Ti samples.The hardness value is an average of eight different hardnesstest measurements.

2.7. Electrochemical characterizations

The potentiodynamic polarization study was performed on theuntreated, HELCDEB-treated and M-HAP coatings on theuntreated and HELCDEB treated Ti samples using the electro-chemical workstation (CHI 760C, USA) in SBF solution. These Tisamples with an exposed surface area of 1 cm2 were used as theworking electrode. The SBF solution was prepared at pH 7.4 andthe temperature was kept at 37 �C.47 Potentiodynamic polari-zation studies were performed in a potential range of �1 to 1 Vat a scan rate of 0.001 V s�1. The potentiodynamic polarizationwas repeated at least three times in order to obtain averagevalues.

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2.8. Inductively coupled plasma atomic emissionspectroscopy

The SBF dissolution study of the M-HAP coating was performedby inductively coupled plasma-atomic emission spectroscopy(ICP-AES, Thermo Electron IRIS INTREPID II XSP DUO, USA).The fresh SBF was maintained by immersing the coated spec-imen for 1, 4 and 7 days.

3. Results and discussion3.1. Functional group analysis

The FT-IR spectra of the M-HAP coating on untreated Ti, and500 and 700 keV HELCDEB-treated Ti are given in Fig. 1(a)–(c).The characteristic peaks observed at 480.89 (n2), 563.00 and601.34 (n4), 977.89 (n1), 1028.75 and 1098.26 (n3) cm

�1 corre-spond to the PO3

4� group. The peaks at 3427.87 and 1642.93cm�1 were assigned to the stretching and bending mode of theadsorbed water. Moreover, the characteristic –OH peaks of HAPat around 3569.41 and 633.12 cm�1 correspond to the stretch-ing and bending modes.48 Thus, the FT-IR spectra conrmed

Fig. 2 Raman spectra showing (a) n2 and n4 signals and (b) n1 and n4signals of the M-HAP coating on (A and A0) untreated Ti, (B and B0) 500keV HELCDEB-treated Ti, and (C and C0) 700 keV HELCDEB-treated Ti.

Fig. 3 XRD pattern of (a) the pure Ti substrate, (b) the HAP coating onuntreated Ti, and the M-HAP coating on (c) untreated Ti, (d) 500 keVHELCDEB-treated Ti and (e) 700 keV HELCDEB-treated Ti.

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the formation of the M-HAP coating by pulsed electrodepositionand no other impurities were identied.

The Raman spectra of the M-HAP coatings that containbands arising from the four phosphate internal vibrationmodes are shown in Fig. 2(a) and (b). The bands for thestretching and librational modes of the hydroxyl ions are weakand provide little information on the mineral environment inthe Raman spectrum.49 Therefore, we focused on the phosphatemodes. The most intense bands at 964 cm�1 are caused by thesymmetric n1 (PO4) stretching mode of the free tetrahedralphosphate ion. The n1 (PO4), n2 (PO4) bands at 447 and432 cm�1, the n3 (PO4) bands at 1082, 1073, 1047, and1026 cm�1, and the n4 (PO4) bands at 611, 603, and 587 cm�1

were assigned (Fig. 2(a) and (b)). The Raman spectra of the M-HAP coating contain the typical stretching frequency of thephosphate ion, which conrms the presence of the calciumphosphate phase. No other additional bands were observed andthis conrms the absence of impurities, which is consistentwith the FT-IR results.

3.2. Diffraction studies

The XRD patterns of the Ti substrate, the pure HAP coating onuntreated Ti, and the M-HAP coating on untreated Ti, and 500and 700 keV HELCDEB-treated Ti are shown in Fig. 3(a)–(e). TheXRD pattern of pure Ti showed no diffraction peaks apart fromthe Ti peak (Fig. 3(a)). The pattern in Fig. 3(c) is less intense andshowed a slight shi compared with that of pure HAP (Fig. 3(b)),

This journal is © The Royal Society of Chemistry 2014

Fig. 4 SEM images of (a) untreated Ti, (b) the M-HAP coating on untreated Ti [inset: magnified view], (c) cross-sectional image of (b), (d) 500 keVHELCDEB-treated Ti, (e) the M-HAP coating on 500 keV HELCDEB-treated Ti [inset: magnified view], (f) cross-sectional image of (d), (g) 700 keVHELCDEB-treated Ti, (h) the M-HAP coating on 700 keV HELCDEB-treated Ti [inset: magnified view], (i) cross-sectional image of (h), and (j) EDAXspectrum of the M-HAP coating on 700 keV HELCDEB-treated Ti.

Fig. 5 XPS survey spectrum of the M-HAP coating on 700 keVHELCDEB-treated Ti.

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which agrees well with ICDD no. 09-0432.33 In this regard, themain diffraction peaks of HAP obtained at 25.9�, 31.7�, 32.2�

and 32.9� are shied to the le by the substitution of mineralions because of the expansion and contraction in the HAPlattices26,50,51. Fig. 3(d) and (e) show the intense peaks for theM-HAP coating obtained on 500 and 700 keV HELCDEB-treatedTi, which indicated that the crystallinity of the coating is high.These patterns reveal the presence of Sr, Mg and Zn in theM-HAP coating.48

3.3. Morphological studies

The SEM images of untreated, 500 and 700 keV HELCDEB-treated Ti, and M-HAP coatings on the Ti metal before andaer HELCDEB treatments are displayed in Fig. 4(a)–(f). Themorphology of the polished Ti is shown in Fig. 4(a). The M-HAPcoating on the untreated Ti exhibits spherical morphology at 1 spulse on time and 4 s pulse off time (Fig. 4(b)). The modied

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Fig. 6 Contact angle measurement of (a) untreated Ti, (b) 500 keVHELCDEB-treated Ti and (c) 700 keV HELCDEB-treated Ti.

Fig. 7 Adhesion strength measurements of the M-HAP coating on (a)untreated Ti, (b) 500 keV HELCDEB-treated Ti and (c) 700 keVHELCDEB-treated Ti.

Fig. 8 Vickers microhardness measurements of the M-HAP coatingon (a) untreated Ti, (b) 500 keV HELCDEB-treated Ti and (c) 700 keVHELCDEB-treated Ti.

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surface of the 500 and 700 keV HELCDEB-treated Ti specimensare shown in Fig. 4(d) and (g), respectively, and consist of thehomogeneous micro-structured eruptions formed during therapid solidication of the surface melted layer. The magniedviews of the surface-treated Ti are given as insets in Fig. 4(d) and(g). A uniformly arranged ower-like coating (Fig. 4(e)) which

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covers the entire surface was observed for the 500 keVHELCDEB-treated Ti substrate. The ower-like structure mayhave originated from the centre of the erupted spot, which had adiameter of few micrometers (�8 mm), shown in the inset inFig. 4(e). Fig. 4(h) also shows the formation of a ower-like M-HAP coating over the 700 keV HELCDEB-treated Ti. Themagnied image also had a ower-like structure (inset inFig. 4(h)). Hence, the morphological studies clearly show thatthe surface treatment played a major role in the formation anduniformity of the ower-like structure of the M-HAPcoating. Fig. 4(c), (f) and (i) shows the cross-sectional view ofthe as-developed coatings. The thickness of the M-HAP coatingon untreated Ti (Fig. 3(c)), 500 keV HELCDEB-treated Ti(Fig. 3(f)) and 700 keV HELCDEB-treated Ti (Fig. 3(i)) rangedfrom 27–29 mm.

The Fig. 4(j) shows the EDAX spectrum of the M-HAP coatingon the HELCDEB-treated Ti. The distribution of Sr, Mg, Zn, Ca,P and O ions is shown in Fig. 4(j) and supports the presence ofthe mineral ions in the surface-treated Ti. Furthermore, thequantitative measurement of theM-HAP coating is shown in theinset in Fig. 4(j).

3.4. X-ray photoelectron spectroscopic study

XPS is a widely used surface analytical technique that is usefulfor detecting the elements present in a material. The XPS surveyspectrum of the M-HAP coating on 700 keV HELCDEB-treated Tiis shown in Fig. 5. The survey spectrum identied Ca, P, Sr, Mg,Zn, and O as the major constituents of the M-HAP coating onthe 700 keV HELCDEB-treated Ti substrate. The observed peaksnear 347.5 and 350.7 eV are attributed to Ca 2p3/2 and Ca 2p1/2,respectively.52 The binding energy of P 2s is 190.2 eV and thepeak at 133.2 eV is the overlap of the Sr 3d and P 2p peaks,because the Sr 3d5/2 (133 � 0.5 eV) and the P 2p (132–133 eV)lines were located close to the Sr peak.53 The O 1s peak observed

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with a binding energy of 530.8 and 532.2 eV are attributed tooxygen associated with the phosphate group and adsorbedwater in the M-HAP, respectively.54 The peak at 49.9 eV isattributed to Mg and the typical binding energy of Zn 2p is1022.0 eV.55 Therefore, the XPS data clearly indicates the pres-ence of minerals that conrms the formation of M-HAP.25

3.5. Contact angle measurements

The contact angle between the deionized water and 500 keVHELCDEB-treated Ti was 53.09�, whereas that for 700 keVHELCDEB-treated Ti was 49.05� (Fig. 6(b) and (c)). Thesecontact angles suggested that the hydrophobic surface ofuntreated Ti (75.70�) (Fig. 6a) becomes hydrophilic aertreatment.

3.6. Adhesion strength

Fig. 7 summarizes the adhesion strength of the M-HAP coatingon untreated Ti, and 500 and 700 keV HELCDEB-treated Ti. Theadhesion strength of the M-HAP coating on untreated Ti wasmeasured as 20.4 � 1.3 MPa. The M-HAP coating on 700 keVHELCDEB-treated Ti exhibits a slightly higher adhesionstrength (22.1 � 1.1 MPa) than that of the coating obtained on500 keV HELCDEB-treated Ti (21.6 � 0.7 MPa). These resultsfulll the main requirement of the coating for the prolonged lifeof the implant.

3.7. Vickers microhardness

The results of the microhardness for the M-HAP coatings onuntreated Ti, and M-HAP coatings on 500 and 700 keVHELCDEB-treated Ti are shown in Fig. 8. The microhardness isgreater for the M-HAP coating on HELCDEB-treated Ti samplescompared with the coating on untreated Ti (6.31 � 0.42 GPa).The M-HAP coating on the 700 keV HELCDEB-treated Ti sample(7.16 � 0.6 GPa) exhibits a slightly higher hardness value than

Fig. 9 Potentiodynamic polarization curves of (a) untreated Ti, (b) 500keV HELCDEB-treated Ti, and (c) 700 keV HELCDEB-treated Ti, andthe M-HAP coating on (d) untreated Ti, (e) 500 keV HELCDEB-treatedTi, and (f) 700 keV HELCDEB-treated Ti.

This journal is © The Royal Society of Chemistry 2014

the 500 keV HELCDEB-treated sample (7.02 � 0.35 GPa). Thisindicates that the as-formed coating remained intact on theHELCDEB-treated Ti substrate.

3.8. Potentiodynamic polarization studies

Representative potentiodynamic polarization curves of theuntreated Ti, and 500 and 700 keV HELCDEB-treated Ti, and M-HAP coatings on the untreated Ti, and 500 and 700 keVHELCDEB-treated Ti are shown in Fig. 9. The values of Ecorr andIcorr for the untreated Ti were �0.57 V and 0.54 mA cm�2, for the500 keV HELCDEB-treated Ti they were �0.148 V and 0.09 mAcm�2, and for the 700 keV HELCDEB-treated Ti they were �0.09V and 0.08 mA cm�2, respectively. The surface treated samplesshowed higher Ecorr and Icorr values than the untreated Tisample. For the samples coated with M-HAP, the Ecorr valueswere �0.023, 0.088, and 0.245 V, whereas the correspondingIcorr values were 0.42, 0.34, and 0.22 mA cm�2, respectively. TheEcorr values for the coated samples were higher than that of theuntreated Ti sample, which indicates the passive nature of thecoatings. Compared with the M-HAP coating on untreated Ti,the Ecorr and Icorr values of the M-HAP coating on HELCDEB-treated Ti specimens showed better shi towards the noblerdirection. In particular, the M-HAP coating on 700 keVHELCDEB-treated Ti showed a larger positive shi than the M-HAP coating on the 500 keV HELCDEB-treated Ti.

3.9. SBF dissolution study

ICP-AES analysis showed that the dissolution of mineral ionsoccurred from the M-HAP coating during the rst day. Theaverage Ca ion concentration in the solution increased rapidlyfrom �1.2 to �26.9 ppm, which is the difference between thecontrol value and leach out value, from 0 to 1 day. Likewise, therelease of Sr, Mg, Zn and P ions in the solution slightlyincreased as shown in Fig. 10. However, the concentration ofions released decreased slightly aer 4 and 7 days. This

Fig. 10 ICP-AES analysis of M-HAP coating on 700 keV HELCDEB-treated Ti at different immersion times.

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situation indicated that the coating only dissolved during therst day of immersion, and subsequently HAP deposition tookplace on the surface of the M-HAP coating.56

4. Conclusions

In this study, a Sr, Mg and Zn-substituted HAP coating wasobtained on HELCDEB-treated Ti by pulsed electrodeposition.The results are summarized as follows.

1. The presence of functional groups in the M-HAP coatingwas conrmed by the FT-IR and Raman results and the effect ofSr, Mg and Zn substitution on the M-HAP was conrmed byXRD studies.

2. SEM images exhibited typical ower-like morphology withdiameters of a few micrometers (�8 mm) on the HELCDEB-treated Ti samples. The EDAX and XPS studies revealed thepresence of mineral ions (Sr, Mg, Zn, Ca, P and O) in theresultant coating.

3. The M-HAP coating on the 700 keV HELCDEB-treated Tipossesses a higher adhesion strength than the M-HAP coatingon 500 keV HELECDEB-treated Ti and on untreated Ti.

4. The electrochemical results revealed that the M-HAPcoating on 700 keV HELCDEB-treated Ti showed higher corro-sion protection compared with the untreated Ti and the othercoatings.

5. The ICP-AES results showed that no large-scale dissolutionoccurred from the M-HAP coating in the SBF environment for 7days, which proved the stability of the coating.

In summary, the HELCDEB treatment of Ti enhances thecorrosion and mechanical properties of the M-HAP coating andit may be suitable for use in orthopedics. The biological studiesof the resultant coating will be published later.

Acknowledgements

One of the authors D. Gopi acknowledges the major nancialsupport from the Department of Science and Technology, NewDelhi, India (DST) and Council of Scientic and IndustrialResearch, New Delhi, India (CSIR) in the form of major researchprojects. D. Gopi and L. Kavitha also acknowledge UGC, NewDelhi, India for the Research Award (Ref. no. F. 30-1/2013(SA-II)/RA-2012-14-NEW-SC-TAM-3240 and F. 30-1/2013(SA-II)/RA-2012-14-NEW-GE-TAM-3228) (2012–2014), respectively.

References

1 J. Cizek, K. A. Khor and Z. Prochazka, Mater. Sci. Eng., C,2007, 27, 340.

2 A. Letic-Gavrilovic, R. Scandurra and K. Abe, Dent. Mater. J.,2000, 19, 99.

3 C. G. Ambrose and T. O. Clanton, Ann. Biomed. Eng., 2004, 32,171.

4 M. Vallet-Regi and J. M. Gonzalez-Calbet, Prog. Solid StateChem., 2004, 41, 3130.

5 S. V. Dorozhkin and M. Epple, Angew. Chem., Int. Ed., 2002,41, 1.

34758 | RSC Adv., 2014, 4, 34751–34759

6 J. Yan, J. Sun, P. K. Chu, Y. Han and Y. Zhang, J. Biomed.Mater. Res., Part A, 2013, 101, 2465.

7 E. Canalis, M. Hott, P. Deloffre, Y. Tsouderos and P. J. Marie,Bone, 1996, 18, 517.

8 E. Bonnelye, A. Chabadel, F. Saltel and P. Jurdic, Bone, 2008,42, 129.

9 K. K. Johal, G. M. Suarez and J. I. E. Garcia, J. Mater. Sci.:Mater. Med., 2002, 13, 375.

10 S. Pina, P. M. Torres, F. G. Neunhoeffer, J. Neubauer andJ. M. F. Ferreira, Acta Biomater., 2010, 6, 928.

11 E. Buache, F. Velard, E. Bauden, C. Guillaume, E. Jallot,J. M. Nedelec, D. L. Maquin and P. Laquerriere, ActaBiomater., 2012, 8, 3113.

12 N. D. Ravi, R. Balu and T. S. Sampath Kumar, J. Am. Ceram.Soc., 2012, 95, 2700.

13 S. Wallach, Magnesium Trace Elem., 1990, 9, 1.14 J. E. Sojka and C. M. Weaver, Nutr. Rev., 1995, 53, 71.15 H. Zreiqat, C. R. Howlett, A. Zannettino, P. Evans,

G. S. Tanzil, C. Knabe and M. Shakibaei, J. Biomed. Mater.Res., 2002, 62, 175.

16 M. Okazaki, Y. Yamasaki, Y. Yoshida, A. Shimazu, T. Uchida,T. Kubo, Y. Akagawa, Y. Hamada, J. Takahashi andN. Matsuura, J. Biomed. Mater. Res., 2002, 62, 99.

17 Y. Tang, H. F. Chappell, M. T. Dove, R. J. Reeder and Y. J. Lee,Biomaterials, 2009, 30, 2864.

18 V. Stanic, S. Dimitrijevi, J. A. Stankovic, M. Mitri, B. Joki,I. B. Plecas and S. Raicevi, Appl. Surf. Sci., 2010, 256, 6083.

19 S. Sutha, G. Karunakaran and V. Rajendran, Ceram. Int.,2013, 39, 5205.

20 H. S. Hsieh and J. M. Navia, J. Nutr., 1980, 110, 1581.21 J. T. Kim, S. H. Baek, S. H. Lee, E. K. Park, E. C. Kim,

I. S. Kwun and H. I. Shin, J. Med. Food, 2009, 12, 118.22 M. Yamaguchi, J. Trace Elem. Exp. Med., 1998, 11, 119.23 D. Gopi, S. Nithiya, E. Shinyjoy and L. Kavitha, Spectrochim.

Acta, Part A, 2012, 92, 194.24 D. Gopi, S. Ramya, D. Rajeswari, M. Surendiran and

L. Kavitha, Colloids Surf., B, 2014, 114, 234.25 D. Gopi, S. Nithiya, E. Shinyjoy, D. Rajeswari and L. Kavitha,

Ind. Eng. Chem. Res., 2014, 53, 7660.26 V. Aina, G. Lusvardi, B. Annaz, I. R. Gibson, F. E. Imrie,

G. Malavasi, L. Menabue, G. Cerrato and G. Martra, J.Mater. Sci.: Mater. Med., 2012, 23, 2867.

27 S. C. Cox, P. Jamshidi, L. M. Grover and K. K. Mallick,Mater.Sci. Eng., C, 2014, 35, 106.

28 K. Elayaraja, P. Rajesh, M. I. Ahymah Joshy, V. SarathChandra, R. V. Suganthi, J. Kennedy, P. K. Kulriya,I. Sulania, K. Asokan, D. Kanjilal, D. K. Avasthi,H. K. Varma and S. N. Kalkura, Mater. Chem. Phys., 2012,134, 464.

29 C. Dong, A. Wu, S. Hao, J. Zou, Z. Liu, P. Zhong, A. Zhang,T. Xu, J. Chen, J. Xu, Q. Liu and Z. Zhou, Surf. Coat.Technol., 2003, 163–164, 620.

30 Q. F. Guan, H. Zou, G. T. Zou, A. M. Wu, S. Z. Hao, J. X. Zou,Y. Qin, C. Dong and Q. Y. Zhang, Surf. Coat. Technol., 2005,196, 145.

This journal is © The Royal Society of Chemistry 2014

Paper RSC Advances

Publ

ishe

d on

23

July

201

4. D

ownl

oade

d by

Iow

a St

ate

Uni

vers

ity o

n 26

/09/

2014

05:

46:1

8.

View Article Online

31 D. I. Proskurovsky, V. P. Rotshtein, G. E. Ozur, A. B. Markov,D. S. Nazarov, V. A. Shulov, F. Yu, R. Ivanov and G. Buchheit,J. Vac. Sci. Technol., A, 1998, 16, 2480.

32 D. Gopi, D. Rajeswari, S. Ramya, M. Sekar, R. Pramod,J. Dwivedi, L. Kavitha and R. Ramaseshan, Appl. Surf. Sci.,2013, 286, 83.

33 D. Gopi, A. Karthika, M. Sekar, L. Kavitha, R. Pramod andJ. Dwivedi, Mater. Lett., 2013, 105, 216.

34 J. H. Lin, C. H. Chang, Y. S. Chen and G. T. Lin, Surf. Coat.Technol., 2006, 200, 3665.

35 W. Xia, C. Lindahl, J. Lausmaa, P. Borchardt, A. Ballo,P. Thomsen and H. Engqvist, Acta Biomater., 2010, 6, 1591.

36 D. Gopi, S. Ramya, D. Rajeswari and L. Kavitha, ColloidsSurf., B, 2013, 107, 130.

37 A. Kar, K. S. Raja and M. Misra, Surf. Coat. Technol., 2006,201, 3723.

38 D. Gopi, V. C. A. Prakash and L. Kavitha, Mater. Sci. Eng., C,2009, 29, 955.

39 Y. Han, T. Fu, J. Lu and K. Xu, J. Biomed. Mater. Res., 2001, 54,96.

40 D. Gopi, V. C. A. Prakash, L. Kavitha, S. Kannan, P. R. Bhalaji,E. Shinyjoy and J. M. F. Ferreira, Corros. Sci., 2011, 53, 2328.

41 M. Popa, E. Vasilescu, P. Drob, M. V. Popa, J. M. C. Moreno,C. Vasilescu and S. I. Drob, J. Am. Ceram. Soc., 2012, 95, 3807.

42 D. Gopi, J. Indira and L. Kavitha, J. Appl. Electrochem., 2013,43, 331.

This journal is © The Royal Society of Chemistry 2014

43 Y. Y. Zhang, J. Tao, Y.-C. Pang, W. Wang and T. Wang, Trans.Nonferrous Met. Soc. China, 2006, 16, 633.

44 Y. W. Gu, K. A. Khor, D. Pan and P. Cheang, Biomaterials,2004, 25, 3177.

45 R. Drevet, H. Benhayounea, L. Worthama, S. Potirona,J. Dougladeb and D. L. Maquina, Mater. Charact., 2010, 61,786.

46 ASTM standard F 1044-05, ASTM International, WestConshohocken, PA.

47 T. Kokubo and H. Takafama, Biomaterials, 2006, 27, 2907.48 D. Gopi, A. Karthika, S. Nithiya and L. Kavitha, Mater. Chem.

Phys., 2014, 144, 75.49 J. Guerra-Lopez, R. Pomes, C. O. D. Vedova, R. Vina and

G. Punte, J. Raman Spectrosc., 2001, 32, 255.50 L. Oliveira, R. L. Reis and P. Li, J. Biomed. Mater. Res., Part B,

2007, 83, 258.51 D. Guo, K. Xu, X. Zhao and Y. Han, Biomaterials, 2005, 26,

4073.52 R. N. Panda, H. Ming-Fa, R. J. Chung and T. S. Chin, J. Appl.

Phys., 2001, 40, 5030.53 W. Xia, C. Lindahl, J. Lausma, P. Borchardt, A. Ballo,

P. Thomsen and H. Engqvist, Acta Biomater., 2010, 6, 1591.54 J. Chen, Y. Song, D. Shan and E. H. Han, Corros. Sci., 2011,

53, 3281.55 J. Li, L. Zhang and Y. Zuo, Appl. Surf. Sci., 2008, 254, 2844.56 A. Dey and A. K. Mukhopadhyay, Int. J. Appl. Ceram. Technol.,

2014, 11, 65.

RSC Adv., 2014, 4, 34751–34759 | 34759