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Applied Surface Science 355 (2015) 104–111

Contents lists available at ScienceDirect

Applied Surface Science

journa l h om epa ge: www.elsev ier .com/ locate /apsusc

aser surface textured titanium alloy (Ti–6Al–4V): Part 1 – Surfaceharacterization

ilhelm Pflegingb,d, Renu Kumaria, Heino Besserb, Tim Scharnweberc,yotsna Dutta Majumdara,∗

Department of Metal. and Maters. Eng., I. I. T. Kharagpur, WB 721302, IndiaKarlsruhe Institute of Technology, IAM-AWP, P.O. Box 3640, 76021 Karlsruhe, GermanyKarlsruhe Institute of Technology, IBG-1, P.O. Box 3640, 76021 Karlsruhe, GermanyKarlsruhe Nano Micro Facility, H.-von-Helmholtz-Pl. 1, 76344 Egg.-Leopoldshafen, Germany

r t i c l e i n f o

rticle history:eceived 8 April 2015eceived in revised form 15 June 2015ccepted 26 June 2015vailable online 10 July 2015

eywords:

a b s t r a c t

In the present study, a detailed study of the characterization of laser-surface textured titanium alloy(Ti–6Al–4V) with line and dimple geometry developed by using an ArF excimer laser operating at awavelength of 193 nm with a pulse length of 5 ns is undertaken. The characterization of the texturedsurface (both the top surface and cross section) is carried out by scanning electron microscopy, elec-tron back scattered diffraction (EBSD) technique and X-ray diffraction techniques. There is refinementof microstructure along with presence of titanium oxides (rutile, anatase and few Ti2O3 phase) in the

aser surface texturingicrostructureRDurface roughnessurface energy

textured surface as compared to as-received one. The area fractions of linear texture and dimple texturemeasured by image analysis software are 45% and 20%, respectively. The wettability is increased afterlaser texturing. The total surface energy is decreased due to linear (29.6 mN/m) texturing and increaseddue to dimple (67.6 mN/m) texturing as compared to as-received Ti–6Al–4V (37 mN/m). The effect ofpolar component is more in influencing the surface energy of textured surface.

. Introduction

Titanium and its alloys are used for bio-implant applicationue to its high strength to weight ratio, good corrosion resistance,

ow density and relatively low Young’s modulus [1]. However,ts bio-inertness and poor adhesion at the interface due to for-

ation of porous titanium oxide create problems for long termse of Ti–6Al–4V as bio-implant [2,3]. In the past, several stud-

es had been undertaken to improve bio-compatibility of titaniumnd its alloys by physical, chemical or electro-chemical routes4]. Laser surface modification is a promising route for improvinghe surface dependent engineering properties of metallic com-onents [5]. Laser surface melting and laser gas alloying withitrogen are successfully attempted to tailor hardness, corrosionesistance and biocompatibility of titanium and its alloy [6,7].esides surface chemistry, surface topography also plays an impor-ant role in influencing the bio-compatibility of any component

nd may be preferentially introduced by physical, chemical andechanical means [8–10]. Laser surface texturing is an environ-ental friendly technique, where, a high energy density pulsed

∗ Corresponding author.E-mail address: jyotsna@metal.iitkgp.ernet.in (J.D. Majumdar).

ttp://dx.doi.org/10.1016/j.apsusc.2015.06.175169-4332/© 2015 Elsevier B.V. All rights reserved.

© 2015 Elsevier B.V. All rights reserved.

laser beam is applied on the surface to ablate material from thesurface and thereby, introducing the surface roughness with pre-ferred orientation [10]. Laser surface texturing can be appliedfor adjustment of surface topography and chemical propertieson a nanometer scale, which in turn has an impact on wettabil-ity, protein and cell adhesion [11,12]. In the past, studies havebeen undertaken to understand the effect of texture dimensionand orientation on cell attachments on to Ti–6Al–4V surfaces[13–16]. Yu et al. [13] reported that the average coefficient offriction is minimum when the dimple depth is in the range of8–10 �m [13]. On the other hand, grooves with a dimensionof 11 �m width and 10 �m depth offers a positive correlationbetween cell orientation and cell adhesion [14,15]. The adhesionstrength measurement shows that a highest cell retention wason linear textured surface with 20 �m spacing [15]. In addition,a detailed comparison between linear pattern and wave patternshows that linear pattern offers a higher rate of cell retention[16]. Chen et al. [17] also reported that microgrooves providecontact guidance and promote cell adhesion with an enhancedinteractions between the focal adhesions and the extra-cellular

matrix (ECM) proteins. Branemark et al. [18] reported that microand nano scale topography as well as surface oxides inducedby laser treatment, improved bone-implant interface anchor-age.

rface Science 355 (2015) 104–111 105

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Table 1Dispersion energy, polar energy and total surface energy at 20 ◦C of the liquids usedin this study.

Sample Dispersiveenergy (� lv

d)(mN/m)

Polar (� lvp)

(mN/m)Surface energy(� lv) (mN/m)

W. Pfleging et al. / Applied Su

In this regard, it is relevant to mention that though the effectf laser surface texturing on the cell adherence has been studied,owever, an extensive studies of the microstructures developedue to laser surface texturing has not been undertaken in details.

n the present study, laser surface texturing of titanium alloyTi–6Al–4V) has been undertaken using ArF excimer laser oper-ting at a wavelength of 193 nm with a pulse length of 5 ns. Inhis regard, it is relevant to mention that ns laser is used in theresent study as it is known to offer a good combinations of nar-ow heat effected zone, more penetration depth, less overall timeequired and of relatively lower cost as compared to femtosec-nd pulsed laser [19]. In addition to that the use of excimer laseradiation is also of great interest because of its flat top intensityrofile which enables very precise material removal and the for-ation of flat ablation craters within one laser pulse. Using special

ptics, structure sizes down to 300–400 nm can be achieved [11].he high photon energy (6.4 eV) of excimer laser radiation is alsof great interest especially for selective material removal or forblation processes. The combination of high photon energy andigh resolution mask imaging technology makes the use of excimer

aser radiation attractive for surface modification. Laser pattern-ng is applied by using a mask imaging technique. In general, laser

achining can be achieved in two modes; (a) in serial mode, where,urface is moved relative to the laser beam. Serial machining isdvantageous for prototyping because there is no requirement for

mask. For deep structures, layer-by-layer ablation becomes neces-ary and an appropriate process strategy has to be applied in ordero reduce the surface roughness in the ablated region; (b) in the par-llel mode, the laser beam is imaged (projected) through a mask orptical beam shaping system onto the workpiece, generally using

demagnifying projection lens. Mask projection or parallel beamrocessing is generally preferred for large area material processingnd for achieving structure details in the range down to 300 nm11]. For the presented work, the second approach was appliedor the development of linear and dimple geometry. Followed byaser surface texturing, an extensive characterization of the tex-ured surface has been carried out by scanning electron microscopySEM), electron back scattered diffraction (EBSD) technique and-ray diffraction technique (XRD). The effect of laser surface

exturing on the wettability and surface energy has also been stud-ed in details.

. Experimental

In the present investigation, samples made of Ti–6Al–4V eachith a dimension of 10 mm × 10 mm × 5 mm are mechanically pol-

shed up to a surface roughness (RZ) of 3 �m and subsequently,ubjected to laser texturing using a ArF excimer laser (ATLEX-00-SI, ATL GmbH, Wermelskirchen, Germany) at a wavelength of93 nm (pulse length 5 ns). Laser patterning is applied by using aask imaging technique where, a mask made of steel is illuminated

y the flat intensity profile of the excimer laser beam. An objectiveens with a demagnification factor of 14:1 is applied which providesaser fluences up to 10 J/cm2. For this purpose structuring is per-ormed with a laser workstation Light Shot V2 (Optec s.a., Belgium).ifferent mask designs and a motorized mask selector are used inrder to achieve textures of linear and dimple geometry. Linearexturing is achieved at a laser fluence of 2.4 J/cm2, a laser pulseepetition rate of 200 Hz and 50 laser pulses. On the other hand,he dimple texture is achieved using a laser fluence of 3.2 J/cm2, aepetition rate of 200 Hz and 100 laser pulses. The obtained sur-

ace structure is measured by laser scanning profilometry using0 nW He–Ne laser. The microstructures of the top surface andross section of the laser treated surface are characterized by

field emission scanning electron microscopic (SUPRA 40, Zeiss

Ethylene glycol 29 19 48Diethylene glycol 31.7 12.7 44.4

SMT AG, Germany) coupled with energy dispersive X-ray (EDX)micro-analyzer. Compositional analysis is carried out using energydispersive spectroscopic analysis. Texture and crystallographic ori-entation are examined by electron backscattered diffraction (EBSD)technique using a system HKL-OXFORD INSTRUMENTS being partof a SEM (SUPRA 40, Zeiss SMT AG, Germany system) with EDAXEBSD camera operated at 20 keV. EBSD uses inelastic scatteringof electrons to generate Kikuchi patterns which can be comparedto Kikuchi patterns of known crystal orientations. The sample ismounted onto an aluminum holder and tilted to 70◦. The scan-ning step size for EBSD is 0.5 �m. Data are processed using theFlemco software of acquisition and data analysis is done by usingHKL software. By using orientation distribution function sectionplot, with the application of the Bunge symbolic definition system,the relationship between Euler angle (ϕ1, ϕ, ϕ2) and {hkil}<uvtw>,texture component is calculated [20]. The phases present on thetreated surface are analyzed by XRD (Philips X’Pert PRO Diffrac-tometer, PANalytical, Almelo, Netherlands) technique operated ataccelerating voltage of 40 kV and current equal to 30 mA usingCo-K� radiation. Average lattice strain developed in the texturedsurface is measured from the analysis of peak broadening usingScherrer’s formula [21]. Residual stress developed on the surface iscarefully measured by XRD technique using a stress Goniometry formacro-stress (PW 3040/60, Panalytical X’pert Pro, The Netherland)by using the sin2 � method [21]. Finally, the wettability of Hank’ssolution on the surface of as-received and laser textured surface ofTi–6Al–4V alloy is evaluated by sessile-drop technique [22]. Dur-ing the measurement a drop (of diameter 0.5–1 mm) of SBF isreleased from a tip of syringe on a sample surface and the con-tact angle the drop makes with the surface is measured by takingthe digital image of the drop. The accuracy of the contact anglemeasurements is within ±1◦. Total surface energy, as well as thedispersive and polar components of surface energy for as receivedand laser textured (with line and dimple geometry) surfaces aredetermined by using Young–Dupre equation and Harmonic meansmethod [23–25] (Table 1).

3. Results and discussions

Fig. 1 shows the scanning electron micrographs of as receivedTi–6Al–4V alloy, consisted of equiaxed �-Ti grains (4–10 �m) andpresence of �-Ti. Fig. 2(a–d) shows the scanning electron micro-graphs of the top surface of laser surface textured Ti–6Al–4V laserprocessed in air with (a) linear geometry (lased with a laser flu-ence (ε) of 2.4 J/cm2, repetition rate (�rep) of 200 Hz, number oflaser pulses (N) of 50 (pulse overlap in laser scan direction)) (b)high magnification view of textured zone 1 of Fig. 2(a) and (c)dimple geometry (ε = 3.2 J/cm2, �rep = 200 Hz, N = 100) (d) high mag-nification view of textured zone 1 of Fig. 2(c). Fig. 2(a) reveals thepresence of periodic linear texture with a width of 25 �m at aninterval of 20 �m. Fig. 2(c) reveals the presence of an array of dim-ples each with a diameter of about 60 �m. From Fig. 2(a) and (c)

it can be seen that there are formation of defect free periodic tex-tures with uniform dimensions. The area fractions of linear textureand dimple textured zones measured by image analysis softwareare 45% and 20%, respectively. The high magnification views of the

106 W. Pfleging et al. / Applied Surface Science 355 (2015) 104–111

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Fig. 2. Scanning electron micrographs of top surface of laser surface texturedTi–6Al–4V lased with excimer laser (ArF) with (a) linear geometry (b) high mag-

Fig. 1. Scanning electron micrographs of as received Ti–6Al–4V alloy.

extured surface (cf. Fig. 2(b and d)) show similar features withhe presence of fine grained �-Ti (labeled as 1) with size 2–3 �miameter, �-Ti (labeled as 2) and oxides (labeled as 3). In addi-ion, grains are more refine in the range 0.3–1.3 �m in texturedone (cf. Fig. 2(b) and (d)) as compare to as received Ti–6Al–4V.e. 4–10 �m (cf. Fig. 1). Laser texturing at low fluencies follows thehoto thermal mechanism for ablation includes materials evapora-ion and sublimation [26]. From the microstructure of the texturedegions it is also evident that there is presence of very fine par-icles (debris), attributed to a redeposition of evoprated titanium.cf. Fig. 2(b) and (d)), Presence of oxides is due to reaction of tita-ium with oxygen during/after laser processing. The area fractionf these fine dispersed particles is higher in the linear textured zoneompared to those with dimple morphology. Fig. 3(a and b) showshe scanning electron micrographs of the cross section of laserurface textured Ti–6Al–4V with (a) linear geometry and (b) dim-le geometry. From Fig. 3, it may be clear that the microstructuref the surface of the cross-section is rough and wavy in appearanceith the presence of grain refined �-Ti and coarse �-Ti. The pres-

nce of waviness in the cross section is attributed to scanning ofhe laser beam over the sample surface during ablation of mate-ial. Presence of refined microstructure is partly due to depositionf ablated species and partly due to grain refinement associatedith rapid cooling from the molten state. On the other hand, pres-

nce of coarse �-phase in the microstructure is due to meltingf the material and preferential partitioning of vanadium caus-ng formation of solidified �-phase. From Fig. 3 it may be notedhat the depth of texturing and microstructure of the cross sectionf dimple textured zone is almost similar to the linear texturedone. Fig. 4 shows the surface topography of laser textured zonehowing (a) 3D topography of linear texturing, (b) 2D roughnessrofile of the same and (c) 3D topography of dimple texturing andd) 2D roughness profile of the same by a color 3D laser micro-cope (VK-9710, Keyence, Japan). The scanned area used for surfaceopography is 200 × 283 �m. From Fig. 4(a) it may be noted that for

linear textured surface the width of linear grooves is 20 �m andts depth is 8 �m. Furthermore, the average roughness on the ridges 2.5 �m and the same inside a groove is 2.4 �m. On the otherand, from Fig. 4(b) it is observed that for dimple textured surfacehe diameter of the dimples is about 60 �m and its depth is 8 �m.

Furthermore, it may also be noted that the average surfaceoughness inside a dimple is 2–2.5 �m. Hence, it may be concludedhat in the present study there is also micro-roughening of the

urface in addition to modification of surface topography due toaser surface texturing. Nishimoto et al. [27] showed roughed tita-ium surface exhibited better early cell attachment. Furthermore,ue to introduction of linear grooves and dimples there is also an

nification view of textured zone 1of Fig. 2(a), (c) dimple geometry and (d) highmagnification view of textured zone1of Fig. 2(c). Laser processing parameters aresummarized in the manuscript.

W. Pfleging et al. / Applied Surface Science 355 (2015) 104–111 107

Fig. 3. Scanning electron micrographs of the cross section of laser surface tex-tured Ti–6Al–4V with (a) linear geometry and (b) dimple geometry. Laser processingp

issead(pifohd

Fig. 4. Surface topography of laser textured zone showing (a) 3D topography of lin-ear texturing, (b) 2D roughness profile of the same and (c) 3D topography of dimple

TS

arameters are summarized in the manuscript.

ncrease in actual surface area, which is beneficial in enhancingurface properties like wettability and biocompatibility. Table 2ummarizes the percentage increase in surface area due to both lin-ar and dimple texturing. From Table 2 it may be noted that there is

significant increase in surface area and its magnitude is higher forimple textured surfaces (50%) as compared to linear textured ones30%). In the past numerous studied showed that surface topogra-hy, improve osseointegration, biocompatibility and mechanical

nterlocking of the bone implant interface of, due to enhance sur-ace area [28]. It was reported that dimple grooves act as reservoir

f wear debris and micro-hydrodynamic bearing, on the otherand parallel grooves provides cell contact guidance along theirection of the grooves and reduces the scar formation [17,29].

able 2ummary of surface characterizations of as-received and laser textured surface of Ti–6Al–

Texture geometry andits dimensions

Texturedimension

Area fraction oftextured zone (%)

Percentage incresurface area

As received – –

Dimple Diameter:58 �mDepth: 8 �m

20 50

Linear Line width:21–23 �mDepth: 8 �m

45 30

texturing and (d) 2D roughness profile of the same by laser scanning profilometerusing 10 nW He–Ne laser.

Fig. 5 shows phase distribution in the linear textured zoneof laser surface treated Ti–6Al–4V. From Fig. 5 it may be notedthat presence of maximum mass fraction of �-Ti phase forma-tion (green colored and labeled as 1), 5–10% �-Ti (yellow coloredand labeled as 2) and only few TiO2 (red colored and labeled as3) is visible in textured surface. A detailed study of orientation

distribution of the individual phase is undertaken to understandthe effect of laser processing on the crystallographic texturing ofdifferent phases. Fig. 6(a and b) shows the orientation mapping

4V alloy.

ase Average SurfaceRoughness of texturedzone (�m)

Phases present andits mass fraction

Latticestrain

Residualstress

0.4 �-Ti-93%�-Ti-7%

0.27 –130

3.5 �-Ti-12%�-Ti-7%Ti2O3-12%Rutile-9%

.30 36

2.7 �-Ti-12%�-Ti-7%Ti2O3-12%Rutile-69%

.327 –78

108 W. Pfleging et al. / Applied Surface

Fig. 5. Phase distribution map in the textured zone of linear textured Ti–6Al–4V.(For interpretation of the references to color in text near the reference citation, thereader is referred to the web version of this article.)

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same with (b) linear texturing (c) dimple texturing. From Fig. 9(a) it

ig. 6. Orientation mapping of (a) �-Ti, and (b) �-Ti in the textured zone of linearextured Ti–6Al–4V.

f (a) �-Ti and (b) �-Ti in laser surface textured of Ti–6Al–4Vith linear geometry. The grains with different orientation are

abeled on both figures. The grain labeled as 1 are orientatedlong (0 1 0) plane, grain labeled as 2 are orientated (1 2 0) planend the grain labeled as 3 and 4 shows orientation mismatch

etween the grains in �-Ti of Fig. 6(a). From the orientation dis-ribution of �-phase as shown in Fig. 6(b), it is evident that a

aximum amount �-Ti phase orientated along (1 1 1) plane, only

Fig. 7. Pole figures of (a) �-Ti, and (b) �-Ti, in the

Science 355 (2015) 104–111

of few orientated along (0 0 1) plane and (101) plane. And restof �-Ti phase showing orientation mismatch between the grains.

A detailed study of pole figures of different phases, i.e. �-Ti and�-Ti present in textured zone are summarized in Fig. 7(a and b).From Fig. 7(a and b), it may be noted that there is no specific textureobserved in �-Ti or �-Ti. However, the strength of orientation of �-Ti grains is maximum along {0 0 0 1} plane as compared to {1120}and {1010} plane. On the other hand, strength of �-Ti grains is max-imum along {1 0 0} and {1 1 1} plane as compared to {1 1 0} plane.

Fig. 8 show the orientation distribution function (ODF) of (a) �-Ti and (b) �-Ti in the textured zone of linear textured Ti–6Al–4V.The Orientation distribution function plot of �-Ti shows the cer-tain degree of similarity of Euler angles = 0–9◦, = 14–19◦,

= 24–33◦, = 38–43◦, = 47–52◦ and = 57–90◦. The maxi-mum strength of orientation distribution function �-Ti grainsalong = 38◦ and = 43◦ and texture component is {0 0 0 1}{0 0 0 1} < 1 1 2 0 > basal texture. The orientation distributionfunction (ODF) plot of �-Ti also shows certain degree of similarityof ( = 14–19◦, = 24–33◦, = 38–43◦ and = 47–52◦). The max-imum strength of orientation distribution function of �-Ti grainsare along = 38–43◦ and texture component is {0 0 1} < 0 1 0 >.

From the pole figure and orientation distribution function study,we concluded that the strength of orientation of �-Ti grains ismaximum along {0 0 0 1} plane, which may improve the corrosionresistance and bioactivity. Crystallographic texture has a signifi-cant effect the biomaterials performance. The basal planes of theHCP structure are the most closely packed and therefore, they havethe lowest surface energy resulting in a higher corrosion resis-tance property [30]. It is known that the hydroxyapatite crystalsin bone are highly oriented such that the normal to (0 0 0 1) planesis parallel to the axis of collagen fibrils [31]. Mao et al. [32] haveshown that �-Ti substrate with (0 0 0 1) texture led to the orientedgrowth of HA through crystal matching between the substrateand HA, thereby mimicking the natural mineralization process.

Fig. 9 shows the X-ray diffraction profiles of the surface ofTi–6Al–4V in (a) as-received condition and the textured zone of the

is relevant that as received Ti–6Al–4V contains both �-Ti and �-Tiphase. Surface texturing with both linear and dimple morphologyshows presence of �-Ti and �-Ti phase along with few oxide phases

textured zone of linear textured Ti–6Al–4V.

W. Pfleging et al. / Applied Surface Science 355 (2015) 104–111 109

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(eabist

ig. 8. Orientation distribution function (ODF) of (a) �-Ti and (b) �-Ti in the texturedone of linear textured Ti–6Al–4V.

predominantly rutile with one anatase peak and few Ti2O3). Pres-nce of oxide phase in textured surface is due to surface oxidations texturing was carried out in ambient air. Presence of oxides is

eneficial in enhancing both the wear resistance and biocompat-

bility. In addition to the presence few oxides peaks, there was aignificant broadening of the peaks in both line and dimple tex-ured surface which is attributed to introduction of lattice strain

Fig. 9. X-ray diffraction profiles of the top surface of Ti–6Al–4V in (a) as-receivedcondition and the textured zone of the same with (b) linear texture (c) dimpletexture.

and refinement of the grain size. Table 2 summarizes the latticestrain developed due to linear and dimple texturing of Ti–6Al–4V.From Table 2 it may be noted that lattice strain is marginallyincreased in textured surface (from 0.27 for as-received to 0.33for linear textured surfaces and 0.30 for dimple textured). Theincrease in lattice strain in textured surface is possibly attributedto incorporation of oxygen atom in the lattice and the introductionof lattice defect during texturing which is predominately abla-tion based. The residual stress introduced during laser texturingis evaluated by stress goniometer and is summarized in Table 2.From Table 2 it is observed that the as-received Ti–6Al–4V sampleshows a high magnitude of residual compressive stress (−130 MPa)which is possibly due to cold working operation applied for thedevelopment of this alloy. On the other hand, on the surface of lin-ear textured sample, magnitude of compressive stress decreaseswhich is mainly due to annealing effect during laser irradiation(−78 MPa). Furthermore, for the sample with dimple texture, theresidual stress is very low (36 MPa) and tensile in nature. Thedecrease of compressive residual stress is attributed to a very highrate of cooling followed by laser irradiation of the ablated surface.However, the low magnitude of residual tensile stress would not bedetrimental to its mechanical property. Robinson et al. [33] foundthe generation of tensile residual stress in laser melting process.

A detailed study of the wettability in terms of contact angle ofthe surface was measured by sessile drop techniques and the con-tact angle of as-received and laser textured with line and dimpletextured are summarized in Fig. 10. From Fig. 10, it may be notedthat there is marginal decrease in contact angle due to laser surfacetexturing. The contact angle decreases from 60◦ for as received sam-ple to 55◦ for dimple textured and 50◦ for liner textured surface(parallel to grooves direction) and 45◦ (perpendicular to groovesdirection) degree. Cunha et al. [34] showed the wetting behav-ior is anisotropic, reflecting the anisotropy of the surface textures.They reported that wettability is more in perpendicular directionof laser-induced periodic surface structures direction as compareto parallel direction. However, laser surface texturing improvesthe wettability. In the past it has been reported that that highhydrophilic surface of titanium alloy is more desirable for cell dif-

ferentiation and growth as compare to hydrophobic surface [35,36].

Fig. 11 shows the variation of dispersion, polar and total sur-face energy of as-received and laser textured surface with linearand dimple geometry. From Fig. 11, it may be noted that total

110 W. Pfleging et al. / Applied Surface

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ig. 10. Bar charts showing the variation of contact angle of as received and laser tex-ured surface with dimple and linear along the parallel and perpendicular directionf the grooves in hank’s solution.

urface energy of laser textured surfaces significantly varies from9 to 67 mN/m as compared to as-received Ti6Al4V (37 mN/m). Aetailed comparison shows that a higher surface energy is observed

n dimple textured surface (67 mN/m) as compared to linear tex-ured surface (29 mN/m). Furthermore, the polar component ofhe surface energy is significantly higher in linear textured sur-ace as compared to as-received and dimple textured samples. Inontrast, the dispersive component of the surface energy is signifi-ant higher in dimple textured surface as compared to as-receivednd the linear textured surface. The surface energy of materialss influenced by several surface characteristics like chemical com-osition, surface charge and microstructural topography, thoughhe correlation among them is not clear [37]. High surface energynd increased wettability enhance interaction between the implanturface and the biological environment, cell spreading and celldherence [24,38–40]. Hallab et al. [24] showed that surface energys more important to induce cell adhesion and proliferation than

urface roughness values. Polar component has significant effect onettability; polar molecules interact with dipole force and hydro-

en bonds which is beneficial for enhancement wettability [24,41].allab et al. [24] reported the highest correlation occur between

ig. 11. Variation of dispersion, polar and total surface energy of as received andaser textured surface with linear and dimple textured.

Science 355 (2015) 104–111

the total surface energy or the polar component and cellular adhe-sion strength. On the other hand, less correlation was observedbetween the dispersion component and adhesion strength.

Hence, from the present study it may be concluded thatdimple texturing offered a higher surface energy, whichperhaps, would be beneficial in improving cell attachment.

4. Conclusions

The study presents laser surface texturing of titaniumalloy (Ti–6Al–4 V) with line and dimple geometry using ArFexcimer laser operating at a wavelength of 193 nm witha pulse length of 5 ns. A detailed characterization of thetextured surface has been undertaken. From the above men-tioned investigation the following conclusions may be drawn:

(1) Laser-assisted patterning of Ti–6Al–4V with linear and dimplestructure geometries are successfully developed with UV-laserradiation (wavelength 193 nm). Defect free and periodic tex-tured patterns are achieved.

(2) The area fraction of linear textured and dimple textured zonemeasured by image analysis software are 45% and 20%, respec-tively.

(3) The microstructure of textured region consists of refined grainsof �-Ti with presence of �-Ti particles on the grain boundary.X-ray diffraction analysis showed the presence of mainly �-Ti,and �-Ti. However, a few peaks of rutile, anatase and Ti2O3 werealso observed in the XRD profile.

(4) The phase distribution mapping in the textured zone by elec-tron back scattered imaging shows the presence of a maximummass fraction of �-Ti, 5–10% �-Ti and only few TiO2 (red coloredand labeled as 3) in textured surface.

(5) From the pole figure and orientation distribution functionstudy, it is concluded that the strength of orientation of �-Tigrains is maximum along {0 0 0 1} plane, which is beneficial inimproving corrosion resistance and bioactivity.

(6) The total surface energy of laser textured surfaces significantlyvaries from 29 to 67 mN/m as compared to as-received Ti6Al4V(37 mN/m). However, a higher surface energy is observed indimple textured surface (67 mN/m) as compared to linear tex-tured surface (29 mN/m). The higher surface energy due todimple texturing is beneficial in improving cell attachment.

(7) The polar component of the surface energy is significantlyhigher in linear textured surface as compared to as-receivedand dimple textured samples. In contrast, the dispersive com-ponent of the surface energy is significant higher in dimpletextured surface as compared to as-received and the linear tex-tured surface.

(8) Due to increased surface area, there was an increased wettabil-ity of the textured surface against simulated body fluid. Theimproved wettability has beneficial effect on cell attachment,cell differentiation and growth.

Acknowledgement

Partial financial supports from Alexander von HumboldtFoundation, Bonn (to J. Dutta Majumdar), German academicExchange Service, Bonn (to J. Dutta Majumdar), Departmentof Biotechnology, N. Delhi (to J. Dutta Majumdar) and Min-istry of Human Resource Development, N. Delhi (to Renu

Kumari) as well as the support for laser processing (to all theauthors) by the Karlsruhe Nano Micro Facility (KNMF, http://www.knmf.kit.edu) a Helmholtz research infrastructure at theKarlsruhe Institute of Technology are gratefully acknowledged.

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