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Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎

Contents lists available at SciVerse ScienceDirect

Materials Letters

0167-57http://d

n Corr636011,

E-m

Pleaspulse

journal homepage: www.elsevier.com/locate/matlet

Development of lotus-like hydroxyapatite coating on HELCDEB treatedtitanium by pulsed electrodeposition

D. Gopi a,b,n, A. Karthika a, M. Sekar a,c, L. Kavitha b,c, R Pramod d, Jishnu Dwivedi d

a Department of Chemistry, Periyar University, Salem 636011, Indiab Centre for Nanoscience and Nanotechnology, Periyar University, Salem 636011, Indiac Department of Physics, Periyar University, Salem 636011, Indiad Industrial and Medical Accelerator Section, Raja Ramanna Centre for Advanced Technology, Indore 452013, India

a r t i c l e i n f o

Article history:Received 4 January 2013Accepted 6 April 2013

Keywords:BioceramicsSurfacesFTIRElectrodeposition

7X/$ - see front matter & 2013 Published by Ex.doi.org/10.1016/j.matlet.2013.04.019

esponding author at: Department of ChemistIndia. Tel.: +91 427 2345766; fax: +91 427 23ail address: dhanaraj_gopi@yahoo.com (D. Go

e cite this article as: Gopi D, etd electrodeposition. Mater Lett (201

a b s t r a c t

Pure titanium (Ti) was irradiated using high energy low current electron beam (HELCDEB) with aconcentrated energy flow of 500 keV at 1.5 mA beam current. The irradiated Ti surface was coated withhydroxyapatite (HAP) by pulsed electrodeposition (PED) with the optimum concentration of 2000 ppmH2O2 at current density 1 mA/cm2. The HRSEM characterization of HAP coating on the HELCDEB treatedTi substrate exhibited lotus flower-like morphology. The corrosion resistivity of HAP coating on theHELCDEB treated Ti was investigated by the potentiodynamic polarization technique, which showsdesired bioresistivity in simulated body fluid (SBF). The as-coated HAP can immensely serve as apotential candidate for biomedical applications.

& 2013 Published by Elsevier B.V.

676869707172737475767778798081828384858687888990919293

1. Introduction

A significant factor for triumphant fixation of implants utilizedfor bone reconstruction is the enhancement of a stable interfacebetween the implant and bone. This property could be achieved bythe coating of active bioceramic material like HAP on implantmaterials. HAP [Ca10(PO4)6(OH)2] can bond to the bony tissue dueto its excellent biocompatibility [1,2]. However, the HAP coatingscould not sustain long-term stability, and may delaminate fromthe implant due to their insufficient chemical stability, which leadto many medical complications. Surface modifications of implantprior to coating can overcome these defects. Recently, the electronbeam irradiation technique is prominently used for surface mod-ification of implants, in which low energy high current pulsedelectron beam treatment was reported elsewhere [3,4]. Herein, wehave utilized HELCDEB to modify the surface of Ti and enhance itsbioresistivity in SBF. In HELCDEB irradiation, the surface undergoessuperfast heating, melting and solidification to provide improvedphysicochemical properties and bonding strength to the materialwhich are unachievable with other surface treatments. It holdsseveral advantages like impeding the surface of implant fromoxidation, forms strong bond between the substrate and meltedsurface, and prevents the surface of the implant from cracks andpores. Our present study is aimed for the development of HAP

lsevier B.V.

ry, Periyar University, Salem45124.pi).

al. Development of lotus-3), http://dx.doi.org/10.1016

coating on HELCDEB treated Ti. So far, several techniques havebeen adopted for HAP coating on metallic implants [5–9]. Recently,we achieved HAP coating on 316L SS by PED [10]. It has manyadvantages like higher deposition rate, improved coating qualitywith desired structure, and also regulates the composition andcoating thickness. Thus, this study describes the development oflotus flower-like structured HAP coating on HELCDEB treated Ti byPED that significantly improved the uniform flower arrangementby nucleation on the erupted Ti surface, which facilitates betterbone regeneration.

9495969798

2. Materials and methods

The pure Ti substrates (99.99%) each with a size of 10�10�3 mm3 was abraded with different grades of SiC sheets from400 to 1200 grits, finally polished with 1.5 μm of diamond paste,degreased with acetone and ultrasonicated using deionized water.The specimens were surface treated at 500 keV electron beamenergy and 1.5 mA beam current using 700 keV DC acceleratordeveloped at Raja Rammanna Centre for Advanced Technology(RRCAT), Indore (MP) to enhance corrosion resistance of Ti. Thesample was placed on the conveyor system in air. The HELCDEBfrom the accelerator is scanned in scan horn with frequency of50 Hz. This scanned beam is transmitted in air through 50 μm thintitanium foil. The sample to be irradiated was placed 100 mmbelow the titanium foil in air. The elliptical beam of dimension100 mm�120 mm falls on the sample. The sample was movedwith velocity of 20 m/min in beam path so as to avoid excessive

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Fig. 1. (a) FTIR spectrum and (b) XRD pattern of HAP deposited on HELCDEB treated Ti at optimum condition.

Fig. 2. HRSEMmicrographs of untreated (a), HELCDEB treated (b), HAP coating on untreated Ti at condition II (c), and HAP coating on HELCDEB treated Ti at condition I (d), atcondition II (e), and the magnified SEM image (f).

D. Gopi et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎2

heating of the sample. Required number of electrons were depos-ited by bringing sample again and again in the beam path. Thusapproximately 1016 number of electrons were deposited on thesurface of the sample in 6 s (beam interaction time). The PED was

Please cite this article as: Gopi D, et al. Development of lotus-pulsed electrodeposition. Mater Lett (2013), http://dx.doi.org/10.1016

performed in a regular three electrode system using an electro-chemical workstation (CHI 760C, USA). The electrolyte used wasprepared by dissolving the analytical grade 0.42 M CaCl2 �2 H2Oand 0.25 M K2HPO4 in deionized water with 2000 ppm of H2O2 to

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Fig. 3. Chronopotentiometric curves of HAP coating on HELCDEB treated Ti at (a) condition I (c) condition II, (b,d) the magnified view of “curve a and c” up to 40 s.

D. Gopi et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎ 3

reduce H2 evolution and other deposition parameters were sameas our previous report [9]. Deposition was performed in agalvanostatic mode for 1 h. Both the pulsed on time and off timeare varied in such a way that (I) ton¼4 s andtoff ¼1 s and (II) ton¼1 s and toff ¼4 s at current densitiesjon¼1.0 mA/cm2 and joff¼0 mA/cm2. The treated and as-coatedspecimens were characterized by various analytical techniqueslike Fourier transform infrared spectroscopy (FTIR), X-ray diffrac-tion (XRD) and high resolution scanning electron microscopy(HRSEM). Potentiodynamic polarization studies were performedin SBF environment [11] for untreated, HELCDEB treated and HAPcoated on HELCDEB treated Ti with an exposed surface area of1 cm2 at potential range of −1000 to 1000 mV and at a scan rate of

Please cite this article as: Gopi D, et al. Development of lotus-pulsed electrodeposition. Mater Lett (2013), http://dx.doi.org/10.1016

1 mV/s. The experiments were performed in triplicate to ensurereproducibility.

3. Results and discussion

The FTIR spectrum of HAP coating obtained on HELCDEBtreated Ti (Fig. 1(a)) shows absorption in two regions: (i) the bandat 3573 cm−1 and the libration band at 632 cm−1 are originatedfrom OH− group, and (ii) the bands of PO4

3− ions are obtained at956, 1093, 1032, 583 and 603 cm−1. The results indicate theformation of HAP coating on the treated Ti. The XRD pattern ofthe as-coated Ti shown in Fig. 1(b) is in good agreement with the

like hydroxyapatite coating on HELCDEB treated titanium by/j.matlet.2013.04.019i

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Fig. 4. Potentiodynamic polarization curves of untreated, HELCDEB treated andHAP coated on HELCDEB treated Ti.

D. Gopi et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎4

standard data for HAP (ICDD file no. 09-0432). The main diffrac-tion peaks of HAP appear at 2θ values of 25.21, 31.91 and 34.01confirm the formation of pure HAP coating on treated Ti surface.

The morphological features of untreated, HELCDEB treated,HAP coatings on the substrates before and after HELCDEBtreatment were shown in Fig. 2(a–f). The Fig. 2(a) shows themorphology of the untreated Ti and Fig. 2(b) represents themodified surface of the HELCDEB treated Ti which consists of thehomogeneous micro-structured eruptions formed during the rapidsolidification of the surface melted layer. It involves the generationof dynamic thermal cycle in the treated surface, including a rapidheating process (absorption of beam energy) and a subsequent fastcooling process (heat conduction towards the bulk matrix)together with the formation of thermal stresses and the evapora-tion of impure ions. The flake-like structured HAP is obtained onuntreated Ti metal at condition (II) exposed in Fig. 2(c). At condition(I), a partial formation of flower-like agglomerated HAP is evidencedfrom Fig. 2(d). An exact lotus flower-like structure consisting ofaround 1 mm thick petals originated and organized from the centre ofthe erupted site at condition (II) is shown in Fig. 2(e) and themagnified image shows the clear lotus-like structure in Fig. 2(f).Hence, the surface treatment and PED technique has found toinfluence the formation and uniformity of flower-like structured HAP.

The chronopotentiometric curves comprised of 720 cycles forthe PED of HAP for 1 h at the condition (I) and (II) are shown inFig. 3(,c). The magnified view of the curves for both depositionconditions up to 40 s is shown in Fig. 3(b,d). The polarizationbehaviour of the untreated, HELCDEB treated and HAP coated onHELCDEB treated Ti samples in SBF are depicted in Fig. 4.

On comparing the corrosion potential (Ecorr) and corrosioncurrent density (icorr) values, the results obtained for HELCDEBtreated Ti (Ecorr¼−0.148 V and icorr¼0.09 μA/cm2) showed a better

Please cite this article as: Gopi D, et al. Development of lotus-pulsed electrodeposition. Mater Lett (2013), http://dx.doi.org/10.1016

shift in anodic region than that of untreated Ti (Ecorr¼−0.57 V andicorr¼0.54 μA/cm2). For HAP coated on HELCDEB treated Ti(Ecorr¼−0.02 V and icorr¼0.05 μA/cm2), the further positive shiftin the Ecorr value emphasize the enhanced protective effect thanthat obtained for the surfaces treated and untreated Ti in SBF. Theimproved corrosion resistance was obtained by the HELCDEBtreatment in which there is a redistribution of impurities andremoval of top surface contaminants along with the formation ofprotective oxide layer [3].

4. Conclusion

The lotus flower-like structured HAP coating was successfullydeveloped on HELCDEB treated Ti surface by PED at 1 mA/cm2. TheSEM results clearly revealed that the equally sized flower-likeapatite uniformly oriented at the desired site of erupted titaniumis formed at prolonged pulse off time. The polarization studiesexposed that the HAP on HELCDEB treated Ti showed betterbioresistivity in SBF than the untreated Ti. Thus, the as-formedcoating can immensely serve as a potential candidate for biome-dical applications.

Acknowledgements

DG acknowledges DST-SERC, DST-TSD, DST WOS-A, ICMR, CSIR,and UGC in the form of major research projects. Authors are alsoacknowledging RRCAT for providing DC Accelerator facility.

References

[1] Dorozhkin SV. Biphasic, triphasic and multiphasic calcium orthophosphates.Acta Biomater 2012;8:963–77.

[2] Narayanan R, Seshadri SK, Kwon TY, Kim KH. Calcium phosphate-basedcoatings on titanium and its alloys. J Biomed Mater Res 2008;85B:279–99.

[3] Zhang XD, Hao SZ, Li XN, Dong C, Grosdidier T. Surface modification of puretitanium by pulsed electron beam. Appl Surf Sci 2011;257:5899–902.

[4] Hao Y, Gao B, Tu GF, Li SW, Hao SZ, Dong C. Surface modification of Al–-20Sialloy by high current pulsed electron beam. Appl Surf Sci 2011;257:3913–9.

[5] Zheng X, Huang M, Ding C. Bond strength of plasma sprayed hydroxyapatite/Ticomposite coatings. Biomaterials 2000;21:841–9.

[6] Gopi D, Collins Arun Prakash V, Kavitha L. Evaluation of hydroxyapatitecoating on borate passivated 316L SS in Ringer's solution. Mater Sci Eng C2009;29:955–8.

[7] Wang C, Ma J, Cheng W, Zhang R. Thick hydroxyapatite coatings by electro-phoretic deposition. Mater Lett 2002;57:99–105.

[8] Gopi D, Collins Arun Prakash V, Kavitha L, Kannan S, Bhalaji PR, Shinyjoy E,et al. A facile electrodeposition of hydroxyapatite onto borate passivatedsurgical grade stainless steel. Corros Sci 2011;53:2328–34.

[9] Song YW, Shan DY, Han EH. Electrodeposition of hydroxyapatite coating onAZ91D magnesium alloy for biomaterial application. Mater Lett 2008;62:3276–9.

[10] Gopi D, Indira J, Kavitha L. A comparative study on the direct and pulsedcurrent electrodeposition of hydroxyapatite coatings on surgical grade stain-less steel. Surf Coat Technol 2012;206:2859–69.

[11] Kokubo T, Kushitani H, Sakka S, Kitsugi T, Yamamuto T. Solutions able toreproduce in vivo surface-structure changes in bioactive glass–ceramic A–W3. JBiomed Mater Res 1990;24:721–34.

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