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Applied Surface Science 257 (2011) 2134–2141

Contents lists available at ScienceDirect

Applied Surface Science

journa l homepage: www.e lsev ier .com/ locate /apsusc

25 MeV Si9+ ion irradiation of calcium phosphate thin film coated byf-magnetron sputtering technique

. Elayarajaa, M.I. Ahymah Joshya, R.V. Suganthia, S. Narayana Kalkuraa,∗, M. Palanichamyb,. Ashokc, V.V. Sivakumard, P.K. Kulriyad, I. Sulaniad, D. Kanjilald, K. Asokand

Crystal Growth Centre, Anna University, Sardar Patel Road, Chennai 600025, Tamil Nadu, IndiaDepartment of Chemistry, Anna University, Chennai 600025, Tamil Nadu, IndiaDepartment of Physics, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu, IndiaInter-University Accelerator Center, Aruna Asaf Ali Marg, New Delhi 110067, India

r t i c l e i n f o

rticle history:eceived 13 January 2010eceived in revised form 4 September 2010ccepted 21 September 2010

a b s t r a c t

Titanium substrate was coated with hydroxyapatite by radiofrequency magnetron sputtering (rf-magnetron sputtering) technique and subjected to swift heavy ion (SHI) irradiation of 125 MeV with Si9+

at fluences of 1 × 1010, 1 × 1011 and 1 × 1012 ions/cm2. The glancing incidence X-ray diffraction (GIXRD)analysis confirmed the HAp phase of the irradiated film. There was a considerable decrease in crystallinity

vailable online 25 September 2010

eywords:iomaterialsf-magnetron sputteringon beam irradiation

and particle size after irradiation. In addition, DRS-UV reflectance spectra revealed a decrease in opti-cal band gap (Eg) from 5.2 to 4.6 eV. Wettability of biocompatible materials plays an important role inbiological cells proliferation for tissue engineering, drug delivery, gene transfer and bone growth. HApthin films irradiated with 1 × 1011 ions/cm2 fluence showed significant increase in wettability. While theSHI irradiated samples exhibited enhanced bioactivity, there was no significant variation in cell viability.

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Surface roughness, pores

. Introduction

Hydroxyapatite (HAp, Ca10(PO4)6(OH)2) is the main inorganiconstituent of bone and teeth [1]. Synthetically prepared HAperamics are used as artificial bone and dental replacement mate-ials [1–3]. It has excellent biocompatibility and has the ability toirectly bond with bone tissues. Bulk form of HAp cannot be useds implant to replace large bone defects due to its poor mechan-cal strength [4]. HAp coated on titanium substrates is used foroad bearing application (orthopedic and dental implant) [5]. Itas very good mechanical properties and low binding ability with

iving cell. The surface properties of implant materials, such asurface roughness, electrical charge and wettability play an impor-ant role in binding with the living cells [6]. Various methods aresed to modify the surface of implants viz., chemical etching [7]

icrowave [8], laser irradiation [9], electron [10], plasma and ion

eam implantation/irradiation [11,12]. Ion beam irradiation is aell known method for surface modification of polymers, solid

nd thin films [13]. This method provides selective surface mod-fication without affecting the bulk properties of the materials.

∗ Corresponding author. Tel.: +91 44 22203577; fax: +91 44 22352870.E-mail addresses: kalkura@annauniv.edu, kalkura@yahoo.com (S.N. Kalkura).

169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.apsusc.2010.09.062

verage particle size were analyzed by atomic force microscopy (AFM).© 2010 Elsevier B.V. All rights reserved.

Surface chemistry of the biomedical implants has been modifiedto enhance the osseointegration [7,14]. Recently, ion beam irradi-ation is used to modify the HAp surface [14]. Mechanical, thermaland morphological behaviors of gamma irradiated HAp compositeswere already reported [15,16]. Miro et al. [17] studied the effect ofSHI on fluroapatite (FAp) pellets. The irradiation of 30 MeV clusterbeams of C60 produced tracks on FAp [18]. The mechanical prop-erties of nitrogen and argon implanted HAp film was reported byPelletier et al. [19]. The hardness elastic modulus of HAp layer wasfound to increase on irradiation of Ni and Ar implanted HAp thinfilms. Density of hydroxyapatite thin film was enhanced by lowenergy (1–2 MeV) silicon ion irradiation [12]. Effect of irradiationof HAp with 100 MeV oxygen ions was recently reported [20–22].These studies revealed the enhancement of bioactivity and lumi-nescence after irradiation. Irradiation with argon and oxygen ionenhanced wettability and cell adhesion of the HAp thin films [23].Silicon is one of the trace elements known to be essential in bio-logical processes. It enhances the bone growth rates of bioactiveprosthetic materials, while its incorporation in the HAp lattice isconsidered to be a potential method for improving the bioactiv-

ity of HAp [24]. Previous studies reported irradiation of ion beamsof light (O and Ar) ions on HAp. Hence, in the present study themain aim was to examine the surface properties of HAp thin filmsby irradiating silicon (125 MeV Si9+ ion) and its effect on biologicalresponse.

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. Materials and methods

.1. Materials

Reagents, calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) andiammonium hydrogen phosphate ((NH4)2HPO4) and ammoniaolution (AR grade, Merck) were used for the synthesis. Stoichio-etric amount of calcium nitrate tetrahydrate and diammonium

ydrogen phosphate salt were taken and dissolved separately in50 ml deionized water. Before mixing, the pH value of the solutionas adjusted to 11.0 for calcium nitrate and 10.5 for diammoniumydrogen phosphate using ammonia solution. These two solutionsere mixed together at constant flow rate (2 ml/min) and keptnder vigorous stirring for 3 h. The pH of the mixture was main-ained at 10.5. Then, the mixture was autoclaved at 150 ◦C for 12 hnder a pressure of 120 psi. The crystallized HAp product was col-

ected, washed using deionized water and dried at 90 ◦C. The HApowder was used as rf sputter target. The target (50 mm in diameternd 5 mm thick) was prepared by hydraulic pressing HAp pow-er at 200 MPa (Lawrence & Mayo) for 5 min then it was sinteredt 1000 ◦C for 1 h in air. Titanium plates (Ti 99.7%, Aldrich Chemi-al Company Inc., USA) of dimensions 10 mm × 10 mm × 0.25 mmere used as substrate. The substrate was ultrasonically cleaned

or 30 min successively with ethanol, acetone and deionized water.

.2. Thin film preparation and irradiation

Films were deposited in a custom-built rf-magnetron sputtereposition chamber. An operating frequency of 13.56 MHz and

ncident power of 150 W was applied from the rf generator. Theistance between magnetron target and substrate was 30 mm andrgon was used as working gas. The sputtering chamber was evac-ated to 4.3 × 10−5 Torr and then argon gas was introduced at aow rate of 1.5 s cm3. The deposition was performed at 150 W

or 3 h with substrate temperature of 500 ◦C and working pres-ure 60 mTorr. Irradiation was carried out at the Inter-Universityccelerator Centre (IUAC), New Delhi using 15UD pelletron accel-rator, using 125 MeV silicon ions with a charge state of 9+

nd fluences range from 1 × 1010, 1 × 1011 and 1 × 1012 ions/cm2.he ion beam current was about 1 pnA (1 (pnA) particle nanompere = 6.25 × 109 ions/s) was used during irradiation. Initially,

he area of beam scan was ensured by illuminating on a quartzafer which was fixed at the end of copper holder. The dimensions

f the ion beam irradiation area were typically 10 mm × 10 mm.he ion beam was scanned over an area of 10 mm × 10 mm on thinlm surface using magnetic scanner. All samples were identical andelonged to the same batch of preparation.

.3. Phase, thickness and optical properties analysis

GIXRD analysis was carried out using Rigaku X-ray diffractome-er applying maximum power of 30 Kv/40 mA with CuK� radiation� = 1.5406 A) with increment step of 0.02 and scan speed of 1◦/minrom 25◦ to 45◦. The glancing angle was fixed at 2◦. Thickness ofhe film was measured by reflection method using filmetrics F20.eflection spectrum of pure and irradiated HAp films was recorded

n the wavelength range from 190 nm to 1100 nm at room temper-ture using Shimadzu UV-spectrophotometer (Model-1801).

.4. Wettability characteristics analysis

Wettability measurement was carried out on pristine and irradi-ted samples by measuring their contact angle with a sessile dropf deionized water (10 �l) deposited on the sample surface. Theptical wettability inspection was performed by Euromex opticalicroscope with inbuilt color charge coupled device (CCD) camera

cience 257 (2011) 2134–2141 2135

and it was examined in normal atmospheric condition at a roomtemperature (27 ◦C). The wetting profile photograph of the sessiledrop was obtained every fifteen seconds up to 3 min. The contactangles were analyzed in the digital image with help of “imageJ”software and the standard deviation due to experimental error wascalculated as ±3◦.

2.5. Morphology and chemical analysis

The surface morphology of pristine and irradiated samples werestudied using multimode atomic force microscope (AFM, DigitalInstruments Nanoscope IIIa controller) by tapping mode over thescanned area of 10 �m2 × 10 �m2 on thin film surface. The particlesize, porosity and surface roughness were analyzed from the area ofX and Y axis of 2.5 �m2 × 2.5 �m2 surface (AFM) topography withhelp of Nanoscope software [25]. All the 3D AFM image, X and Y axiswas 0.5 �m × 0.5 �m of each division and Z axis value was variedfor each sample. The surface morphology of pristine and irradiatedsamples was observed by scanning electron microscope (SEM, LEO440 STEREOSCAN, Leica). Compositional analysis of thin films wasdone by energy dispersive X-ray analysis (EDAX, Hitachi S-3400N).

2.6. In vitro bioactivity and cell viability study

Simulated body fluid (SBF) solution was used for the invitro bioactivity studies. Reagent grade chemicals were dissolvedin the order NaCl, NaHCO3, KCl, Na2HPO4·2H2O, MgCl2·6H2O,CaCl2·2H2O, Na2SO4, TRIS buffer and 1 M HCl in deionized water.Finally, HCl was used to adjust the solution pH to 7.4 at 37 ◦C [26].The pristine and irradiated HAp thin films were immersed in 20 mlof SBF in plastic containers at 37 ◦C. The samples were immersedin SBF for a period of three weeks and the solution was renewedonce in two days. The cell viability test was performed using MTTassay. MDAMB231 cell was cultured in Dulbecco’s modified Eagle’smedium (DMEM) supplemented with 10% fetal bovine serum (FBS)and 1% penicillin/streptomycin (P/S) at 37 ◦C. This cell was seededon pristine and irradiated HAp thin film using polystyrene 48well plates. It was incubated for 24 h to allow cell adherence at37 ◦C. Then, 10 �L of MTT reagent (10 �g/ml) was added to eachwell plate and incubated for 30 min at the same condition. Finally,dimethylsulfoxide was added for dissolving the formasan crystalsand absorbance was measured at 595 nm in an ELISA reader. Thesamples verse optical density graph was plotted (Fig. 10).

3. Results and discussion

Swift heavy ions traveling through a material lose their energythrough interactions with electrons (electronic energy loss, Se) andatomic nuclei (nuclear energy loss, Sn). The electronic energy losscauses excitation and ionization of target atoms, while nuclearenergy loss takes place by displacement of target atoms. The pro-jected range of Si9+ ions, into HAp thin film was 33.12 �m anddistribution of energy losses of electronic and nuclear energylosses were 3.057 × 103 eV/nm and 2.173 eV/nm respectively asobtained by SRIM-2008 program [27]. It was found that most ofthe ions passed through the film (thickness 850 nm) and cameto rest in the substrate (Fig. 1). In addition, most of the energylost traversing through the film was due to electronic energylosses.

3.1. Phase analysis

The GIXRD pattern of HAp standard data (JCPDS 09-0432), pris-tine and irradiated HAp thin film are shown in Fig. 2a–e. Thepristine and irradiated samples showed the presence of pure phaseof HAp. In the case of irradiated samples, there was a reduction

2136 K. Elayaraja et al. / Applied Surface Science 257 (2011) 2134–2141

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Table 1Crystallite size and crystallinity of (2 1 1) plane of pristine and irradiated HAp thinfilms.

Fluence Crystallinity (Xc)(±0.01)

Crystallite size(L) (±1 nm)

Pristine 0.910 50

Fig. 1. Plot of ion projected range in HAp layer and Ti substrate.

n the peak intensity corresponding to the (2 1 1) plane at theuences from 1 × 1010 to 1 × 1012 ions/cm2. The intensity varia-ion in XRD patterns indicated a decrease in crystallinity due toefects created by the SHI in the HAp lattice [28]. The crystal-

ite size was calculated from XRD spectra using Scherrer formula29]. L = K�/ˇ1/2 cos �, where L is the crystallite size, � the X-rayavelength (� = 1.5406 A), � the diffraction angle, ˇ the full width

t half maximum and K a constant (0.9). The full width at halfaximum of the major HAp peak (2 1 1) and particle size were cal-

ulated. The crystallite size of the irradiated samples decreased by0–50% compared to the pristine sample (Table 1). Crystallinity ofhese samples was calculated from an empirical relation betweenc and ˇ2 1 1 of plane. ˇ2 1 1 × (Xc)1/3 = KA, where Xc is the degreef crystallinity, ˇ0 0 2 the full width of the peak at half intensityf (2 1 1) reflection in (◦), K a constant set at 0.24. Crystallinity

Af the irradiated samples decreased when compared with pristineTable 1).

ig. 2. GIXRD spectra of HAp surface: (a) standard HAp data (09-0432), (b) pris-ine, (c) 1 × 1010 ions/cm2, (d) 1 × 1011 ions/cm2, and (e) 1 × 1012 ions/cm2 irradiatedamples.

1 × 1010 ions/cm2 0.390 281 × 1011 ions/cm2 0.471 351 × 1012 ions/cm2 0.492 38

3.2. Optical properties and band gap analysis

Thickness of the pristine HAp film was found to be 850 nm whichwas much smaller than the projected range (33.1 �m) of 125 MeV Siion beam. As per SRIM calculation no significant change is expectedin thickness as after irradiation in addition the ion beam passesthrough the HAp films. The reflectance spectra showed good inter-ference patterns indicating that the films were of uniform thickness(Fig. 3) [30]. Here interference pattern was formed due to elec-tromagnetic wave traveled through film and air media. About 58%reflectance was observed for the pristine sample, whereas, for theirradiated samples, the reflectance value varied from 10 to 80%depending on ion fluences. The wide variation in reflectance onirradiation may be attributed to the surface modification, ion beammelting and subsequent rapid quenching to aggregation of clus-ter on the surface of the films. The reflectance edges varied withincrease in ion fluences (Fig. 3). However, the reflectance of higherfluence (1 × 1011 and 1 × 1012 ions/cm2) irradiated samples dis-played significant red shift.

The Tauc plots were drawn to estimate the optical band gap (Eg)of these films, i.e. (�h�)1/n = 0, where � is the absorption coefficientand h� is the photon energy. Absorption coefficient, � was deter-mined from 2�t = ln [(Rmax − Rmin)/(R −Rmin)] where t, Rmax, Rminand R are the thickness of film, maximum reflectance, minimumreflectance and any intermediate photon energy [31]. The plot ofphoton energy (h�) vs. (�h�)2 by assuming n = 2 [32] is shown inFig. 4. The band gap values estimated from the plots are 5.2, 5.25,5.05 and 4.6 eV for pristine, 1 × 1010, 1 × 1011 and 1 × 1012 ions/cm2

irradiated samples. There was a significant decrease in band gap at

higher fluences. When thin film or solid samples are irradiated withSHI, the band gap reduction is expected either due to increased crys-tallization or the formation of defect states in the forbidden energyband. The analysis of optical properties revealed a reduction in band

Fig. 3. UV reflectance spectrum of pristine and irradiated (fluences1 × 1010 ions/cm2, 1 × 1011 ions/cm2, and 1 × 1012 ions/cm2) samples.

K. Elayaraja et al. / Applied Surface Science 257 (2011) 2134–2141 2137

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Table 2AFM results of pristine and irradiated samples.

Fluence Mediandistribution ofthe particles inAFM micrograph(nm)

Roughness(±1 nm)

Pore size(±1 nm)

Pristine 80–100 7.9 –

ig. 4. Tauc plot of pristine and irradiated (fluences 1 × 1010 ions/cm2,× 1011 ions/cm2 and 1 × 1012 ions/cm2) samples.

ap due to irradiation at fluence of 1 × 1012 ions/cm2. This reduc-ion in band gap may be due to the creation of defect levels due torradiation of the samples. This reduction in band gap may make ituitable for biosensor applications [33].

.3. Morphology, wettability and in vitro bioactivity test

AFM topography of pristine and irradiated HAp thin film ishown in Fig. 5(a–d). The pristine sample consisted of a dense

ayer of spherical HAp with median distribution of the particlen distribution graph about 80–100 nm and surface roughnessnm (Fig. 5a and Table 2). The sample irradiated at lower fluence

1 × 1010 ions/cm2) had 10% increase in the particle size, due togglomeration along with an increase in its roughness (Fig. 5b).

Fig. 5. AFM 3D images of (a) pristine, (b) 1 × 1010 ions/cm2, (c) 1 ×

1 × 1010 ions/cm2 100–120 11.7 1511 × 1011 ions/cm2 60–80 11.4 1801 × 1012 ions/cm2 60–80 12.6 172

At the fluence of 1 × 1011 ions/cm2 and 1 × 1012 ions/cm2, the par-ticle size decreased due to grain splitting (Fig. 5c and d) [28] whencompared with 1 × 1010 ions/cm2 [Fig. 6]. In addition, random dis-tribution of conical shaped hillocks was observed on the surface(Fig. 5d). The change in surface roughness on irradiation (Table 2)was due to the high electronic energy loss. The surface modifi-cations produced by SHI depend upon the energy loss on targetmaterial. The ions with energy of the order of a few keV interactwith the atoms of the target by elastic collisions. In case of ions withenergies greater than 100 keV, the dominant energy loss occursvia inelastic collisions with the atomic electrons. The irradiationof 125 MeV Si9+ ions on HAp thin films led to surface modifica-tion and ionization mainly due to electronic energy loss (Se). Thisenergy loss occurred on the target due to inelastic process [39].Further, analysis by SRIM 2008 program [27] indicated a higherelectronic energy loss (Se ∼ 3.057 × 103 eV/nm) then nuclear energyloss (Sn ∼ 2.173 eV/nm). Formation of pores (150–180 nm) was alsoobserved on the irradiated samples (Fig. 5b–d). SEM observation ofthe pristine sample had shown uniform smooth surface (Fig. 7a).On irradiation, samples developed cracks along with the formationof pores (Fig. 7b–d).

Wettability of pristine and irradiated HAp thin films wasas illustrated in Fig. 8. Wetting is the contact between a liq-uid and a solid surface due to intermolecular interactions. Thecontact angle between substrate and liquid drop was 60 ± 3◦

1011 ions/cm2, and (d) 1 × 1012 ions/cm2 irradiated sample.

2138 K. Elayaraja et al. / Applied Surface Science 257 (2011) 2134–2141

Fig. 6. Particle size distribution of pristine and irradiated samples.

Fig. 7. SEM micrograph shows the irradiated surface of (a) pristine, (b) 1 × 1010 (c) 1 × 1011 and (d) 1 × 1012 ions/cm2 samples.

K. Elayaraja et al. / Applied Surface Science 257 (2011) 2134–2141 2139

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Fig. 8. Different wettability states of the HAp thin films: (a) pristin

or pristine sample which implies intermediate hydrophilic stateFig. 8a). The contact angles of 1 × 1010 and 1 × 1011 ions/cm2

rradiated HAp thin films were 38 ± 3◦ and 33 ± 3◦ respectivelyhich indicates an increased hydrophilic state (Fig. 8b and c).t higher fluence (1 × 1012 ions/cm2) the contact angle was

Fig. 9. SEM micrograph of the HAp layer deposited in SBF on the surface of (a

1 × 1010, (c) 1 × 1011 and (d) 1 × 1012 ions/cm2 irradiated samples.

◦

78 ± 3 which revealed a well-defined weak hydrophilic surface(Fig. 8d).

The bone bonding ability of a material depends on the prop-erty of HAp surface when immersed in simulated body fluids (SBF)with the ion concentration nearly equal to that of human blood

) pristine, (b) 1 × 1010, (c) 1 × 1011, and (d) 1 × 1012 ions/cm2 samples.

2140 K. Elayaraja et al. / Applied Surface Science 257 (2011) 2134–2141

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protein absorption and DNA prefers more hydrophilic surface dueto phosphate group’s presence in the bone [42]. The above wettabil-ity results correlate with the growth of HAp on surface of irradiatedsamples: the sample irradiated at fluence of 1 × 1010 and 1 × 1011

Fig. 10. EDX spectra shows the elemental composition meas

lasma [26]. The channels due to partial dissolution were visi-le along with irregular formation of HAp, when pristine samplesere immersed in SBF (Fig. 9a) [34]. In the case of irradiated

ample, initially all the samples undergo partial dissolution as indi-ated by the formation of channels. Subsequently over a periodf time apatite layers are found to grow on the surface of all theamples immersed in SBF solution. The samples irradiated with flu-nce of 1 × 1012 ions/cm2 immersed in SBF revealed formation ofpherulites of size about 13 �m (Fig. 9d). EDX spectrum of pristinend 1 × 1012 ions/cm2 – SBF soaked HAp thin film showed peaksorresponding to the substrate elements (Ti, Al). Signals corre-ponding to Ca, P and O peaks were found to be weak. Ca/P ratio wasalculated to be 1.60 (Fig. 10a) and 1.80 (Fig. 10b) for pristine andSBF tested (1 × 1012 ions/cm2 irradiated) samples respectively.

he higher value of Ca/P may be spherical shape of Ca-rich apatiteormation on the surface [21].

.4. Relation between bioactivity and wettability

The enhancement of wettability and bioactivity on HAp thinlms are based on surface properties viz., roughness, chemical com-osition, surface charge and porosity and these properties help

n the binding of living cells on the implants [35]. Recent reportsevealed that cell proliferation, wettability and biomimetic growthn biomedical implants were influenced by surface roughness,olar component of the surface energy and oxygen content on theurface [35,36]. Here, the irradiated samples exhibited increasedettability (1 × 1010, 1 × 1011 ions/cm2). In the case of higher flu-

nce, wettability decreased considerably (Fig. 8d). This indicatesignificant change in the surface property of the film on irradiation.s the irradiation does not produce material loss, enhancement inettability might be attributed to surface energy variation [37] and

apillary action [38] of the pores on the spreading of water. WhenHI like 125 MeV Si9+ ion beam penetrates HAp thin film, it losesnergy mainly through interactions with electrons which are raisedo excited states or ejected from the atoms. The HAp atoms do notet ejected because of the stable HAp lattice. Part of the excitationnergy gets transferred to the lattice and cause substantial modi-cation in the target material as described by Coulomb-explosionCE) and electro-phonon (e-ph) coupling or thermal spike (TS) [39]

odels. As per the CE model, a swift heavy ion passing through aAp film leads to ionization of the medium along its path. Due

o the strong electrostatic repulsive Coulomb force, the ionizedAp atoms are pushed out of this track and generate a cylinderf reduced atomic density along the ion path. Whereas accordingo the TS model, the energy is transferred to the lattice subsystemia e-ph coupling, which leads to an increase of the lattice temper-

n (a) pristine and. (b) SBF tested (1 × 1012 ions/cm2) sample

ature along the ion path, and may result in a molten track. Due tothis reason, HAp atoms get excited by ion beam irradiation leadingto modification of the surface energy. In addition, TRIM program ofionization plot also confirmed that the surface atoms are ionizedby the incident ions. The energy loss due to the recoiling ions isnegligible. Fine pores (150 to 180 nm) were formed on the surfaceof the HAp film due to irradiation (Figs. 5 and 7). In addition tovariation in surface energy, the pore formatting on the irradiatedsurface also contributed to the change in wettability. At higher flu-ence of 1 × 1012 ions/cm2, there was a decrease in number of poresdue to local heating [40], leading to a decrease in wettability [41].Further, as there was no significant change in surface roughness,their influence on wettability might have been minimal (Table 2).The decrease in wettability at higher fluence compared to the pris-tine samples may be due to the non-availability of the polar OHgroups on their surface. The various types of surface interactions,the origin of proteins and cells adhesion on biomaterial surface inorthopedic implants and tissues engineering are mainly attributedto wettability of the biological substrates considering hydropho-bic/hydrophilic properties. Hydrophobic interaction is favorable to

Fig. 11. Cell viability study of pristine and irradiated (fluences 1 × 1010 ions/cm2,1 × 1011 ions/cm2, and 1 × 1012 ions/cm2) samples.

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ons/cm2 aided deposition of HAp in SBF, whereas at higher fluence,here was no significant bioactivity on the samples (Fig. 8). At theuence 1 × 1012 ions/cm2, the irradiated sample surface displayed

ow bioactivity with deposition of spherulites of HAp. It is ascribedo the loss of hydrophilic nature of the surface due to high fluencef the irradiating ion beams.

.5. Cell viability

Cell viability of pristine and irradiated samples was as shownn Fig. 11. The irradiation does not significantly affect cell viabil-ty. The optical density of the pristine and irradiated samples hadhown almost similar values after one day incubation of cells whichevealed the non toxic nature of the irradiated films.

. Conclusions

The effect of swift heavy silicon ion irradiation (125 MeV) onAp thin films, prepared by rf magnetron sputtering, was studied.he irradiation caused variation of surface roughness and parti-le size on the surface without modifying its phase along withdecrease in its optical band gap energy. Here, HAp thin films

rradiated with fluence of 1 × 1011 ions/cm2 showed enhanced wet-ability and aided the deposition of a layer of bone like apatite whenmmersed in SBF. This apatite deposition on HAp surface may be dueo the negative surface charge, which attracts calcium ions from theBF solution, as described in our previous report [21]. Irradiatedamples showed no cytotoxicity. Therefore, SHI irradiation withi9+ ion beams can be an ideal technique to enhance the wettabilitynd bioactivity of the related HAp biomaterials.

cknowledgments

The authors thank IUAC, New Delhi through research projecto. UFUP 31317 and financial support of DST, New Delhi through

esearch project No. SR/SO/HS-05/2005. One of the authors KEcknowledges CSIR, India for the award of SRF fellowship (File no:9/468(0413)/2009-EMR-I).

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