pubs.acs.org/Langmuir © 2010 American Chemical Society
A “Clickable” Titanium Surface Platform )
:: Matthew A. Watson,†,‡ Joel Lyskawa,†,‡,§ Cedric Zobrist,†,‡,§ David Fournier,†,‡,§ †,‡,§ Maude Jimenez, Michel Traisnel,†,‡,§ Leon Gengembre,†, and Patrice Woisel*,†,‡,§,^ Universit e Lille Nord de France, F-59000 Lille, France, ‡USTL, Unit e des Mat eriaux et Transformations (UMET, UMR 8207), Equipe Ing enierie des Syst emes Polym eres (ISP), F-59655 Villeneuve d’Ascq Cedex, France, §F ed eration Biomat eriaux et Dispositifs M edicaux Fonctionnalis es (BDMF/FED 4123), F-59655 Villeneuve d’Ascq Cedex, France, Unit e de Catalyse et de Chimie du Solide, UCCS UMR CNRS-8181, F-59655 Villeneuve d’Ascq, France, and ^ENSCL, F-59655 Villeneuve d’Ascq, France )
†
Received July 5, 2010. Revised Manuscript Received September 1, 2010 A straightforward functionalization of a titanium surface using “click” chemistry is reported. A “clickable” titanium surface platform was prepared by the immobilization of an azide-functionalized electroactive catechol anchor and was subsequently derivatized with an electroactive or fluorinated probe via the CuAAC (copper-catalyzed azide-alkyne cycloaddition) reaction. The course of the reaction was investigated by contact angle, XPS, and electrochemical measurements.
Introduction Titanium and its alloys have attracted enormous attention because of their remarkable mechanical, thermal, electrical, and biocompatible properties. Titanium’s applications include nanoelectronics, sensors, energy storage devices, photovoltaics, and biomaterials.1 Many applications utilizing titanium require chemical modification of the titanium surfaces to confer desirable and improved functional properties. For example, for biomedical applications, the functionalization of titanium surfaces is essential in allowing them to interact selectively with cells or biomolecules or, in contrast, in avoiding nonspecific physical absorption on the surface2 (e.g. improved biocompatibility, biointegration or cell adhesion). Several techniques for manipulating the chemical composition of titanium surfaces have evolved in the past decade. To date, the most common methodologies for the covalent attachment of target molecules onto titanium surfaces have involved the formation of monolayers with organofunctional silanes,3,4 phosphonic acids,5-7 and phosphonates,8 followed by the covalent attachment of a target molecule onto the newly introduced functional group on the surface. However, these strategies usually require multistep organic synthesis involving protecting groups7 to elaborate appropriate organofunctional anchors; otherwise, harsh conditions7-9 are necessary to immobilize anchors onto the *Corresponding author. E-mail:
[email protected]. (1) Brunette, D. M.; Tengvall, P.; Textor, M.; Thomsen, P. Titanium in Medicine: Material Science, Surface Science, Engineering, Biological Responses, and Medical Applications; Springer: Berlin, 2001; p 14. (2) Textor, M.; Tosatti, S.; Wieland, M.; Brunette, D. M. Bio-Implant Interface: Improving Biomaterials and Tissue Reactions; CRC Press: London, 2003; p 341. (3) Porte-Durieu, M. C.; Guillemot, F.; Pallu, S.; Labrugere, C.; Brouillaud, B.; Bareille, R.; Amedee, J.; Barthe, N.; Dard, M.; Baquey, Ch. Biomaterials 2004, 25, 4837–4846. (4) Jia, X.; Jiang, X.; Liu, R.; Yin, J. Macromol. Chem. Phys. 2009, 210, 1876– 1882. (5) Viornery, C.; Chevolot, Y.; Leonard, D.; Aronsson, B. O.; Pechy, P.; Mathieu, H. J.; Descouts, P.; Gr€atzel, M. Langmuir 2002, 18, 2582–2589. (6) Zoulalian, V.; Monge, S.; Z€urcher, S.; Textor, M.; Robin, J. J.; Tosatti, S. J. Phys. Chem. B 2006, 110, 25603–25605. (7) Adden, N.; Gamble, L. J.; Castner, D. G.; Hoffmann, A.; Gross, G.; Menzel, H. Langmuir 2006, 22, 8197–8204. (8) White, M. A.; Maliakal, A.; Turro, N. J.; Koberstein, J. Macromol. Rapid Commun. 2008, 29, 1544–1548. (9) Tchoul, M. N.; Fillery, S. P.; Koerner, H.; Drummy, L. F.; Oyerokun, F. T.; Mirau, P. A.; Durstock, M. F.; Vaia, R. A. Chem. Mater. 2010, 22, 1749–1759.
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titanium surface. Furthermore, the silanization approach leads to the formation of hydrolytically unstable and heterogeneous films.10 Moreover, the chemical modification of a functionalized monolayer appears to be an interesting way to generate functionalized surfaces, but the yields are often low,11 thus affording surfaces with low functionalization density. An ideal, simple, and effective method for functionalizing titanium surfaces could be based on the use of a readily accessible anchor incorporating both an anchoring group that is capable of forming, under mild conditions, a robust, hydrolytically stable monolayer and a “clickable” function8,9 allowing the modular and efficient postfunctionalization of the titanium surface. Recently, the catechol unit, because of its strong adhesive property, has become an important biomimetic ligand for surface immobilization. Indeed, catechols are subunits of mussel-adhesive proteins (MPAs), which are at the origin of the strong adhesion of mussels to surfaces.12,13 The ability of catechol derivatives to bind metal oxide surfaces has been exploited to tailor their physical-chemical surface properties such as wettability14 and biofouling.15,16 Although several surface derivatization schemes have been reported to modify titanium surfaces with catechol anchors, such as the absorption of functionalized 3,4-dihydroxyphenethylamine (dopamine)-based molecules or polymers and surface-initiated polymerization from the catechol initiator absorbed on TiO2,17,18 none have been devised so far using a click chemistry approach. Here, we report a simple and versatile strategy for titanium surface modification based on catechol surface modification that (10) Adden, N.; Gamble, L. J.; Castner, D. G.; Hoffman, A.; Gross, G.; Menzel, H. Biomacromolecules 2006, 7, 2552–2559. (11) Collman, J. P.; Devaraj, N. K.; Chidsey, C. E. D. Langmuir 2004, 20, 1051– 1053. (12) Lee, H.; Lee, B. P.; Messersmith, P. B. Nature 2007, 448, 338–341. (13) Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B. Science 2007, 318, 426–430. (14) Ting, G. G., II; Acton, O.; Ma, H.; Won, Ka, J.; Jen, A. K.-Y. Langmuir 2009, 25, 2140–2147. (15) Fan, X.; Lin, L.; Messersmith, P. B. Biomacromolecules 2006, 7, 2443–2446. (16) Dalsin, J. L.; Hu, B. H.; Lee, B. P.; Messersmith, P. B. J. Am. Chem. Soc. 2003, 125, 4253–4258. (17) Fan, X.; Lin, L.; Dalsin, J. L.; Messersmith, P. B. J. Am. Chem. Soc. 2005, 127, 15843–15847. (18) Fan, X.; Lin, L.; Messersmith, P. B. Compos. Sci. Technol. 2006, 66, 1195– 1201.
Published on Web 09/20/2010
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enables target molecules to be attached using the coppercatalyzed azide-alkyne cycloaddition (CuAAC) reaction.
Experimental Details Reagents. All reagents were purchased from Aldrich Chemical Co. and were used as received. Synthesis. Preparation of 1. 3-Azidopropan-1-ol (3g, 29 mmol), glutaric anhydride (3.38 g, 29 mmol), and DMAP (0.272 g, 2.2 mmol, 0.75 equiv) were dissolved in a 50 mL solution of anhydrous CH2Cl2, and the mixture was stirred vigorously overnight at room temperature. The organic solution was washed with HCl (0.5 M, 30 mL) and brine (15 mL) and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (SiO2/ethyl acetate/petroleum ether 4:6), affording 1 in 80% yield as a colorless oil. 1H NMR (300 MHz, CDCl3): 1.84 (m, 4H, 2 C-CH2-C), 2.35-2.37 (m, 4H, 2 C-CH2-CdO), 3.33 (t, 2H, CH2-N3), 4.11 (t, 2H, CH2-O-CO-), 9.67 (br s, 1H, COOH). 13 C NMR (75 MHz, CDCl3): 179.0, 172.8 (CdO); 61.4 (CH2-O); 48.2 (CH2-N3); 33.0, 32.9, 28.1, 19.7 (C-CH2-C). Preparation of 2. 1 (3.34 g, 15.5 mmol) and N-hydroxysuccinimide (23 mmol, 1.5 equiv) were dissolved in anhydrous CH2Cl2 (50 mL), and the mixture was cooled to -5 C. DCC (2.68 g, 23 mmol, 1.5 equiv) dissolved in 10 mL of CH2Cl2 was added dropwise to the solution of 1. The reaction was allowed to return to room temperature and was stirred vigorously overnight. The solution was filtered, and the solvent was evaporated. The product was obtained in 90% yield as a colorless oil. 1H NMR (300 MHz CDCl3): 1.85 (m, 2H, CH2-CH2-CH2-N3), 2.00 (m, 2H, CO-CH2-CH2-CH2-CO), 2.42 (t, 2H, CH2CO-O), 2.65 (t, 2H, CH2CO-O-N), 2.78 (s, 4H, CH2(NHS)), 3.34 (t, 2H, CH2-N3), 4.11 (t, 2H, CH2-O-CO-). 13C NMR (75 MHz, CDCl3): 178.6, 172.9 (CdO); 61.6 (CH2-O); 48.3 (CH2-N3); 32.9, 33.0 (CH2-CdO); 28.0, 19.8 (C-CH2-C). Preparation of 3. Dopamine hydrochloride (2.35 g, 0.015 mol) was dissolved in MeOH (50 mL), and 1.55 g of NEt3 (0.015 mol) was added. A solution of 2 (4.8 g, 0.015 mol) in MeOH (20 mL) was added dropwise to the first solution. The reaction was stirred vigorously for 48 h. The solvent was evaporated under reduced pressure, and the residue was dissolved in CH2Cl2 (100 mL). The organic phase was washed with HCl (0.5 M, 20 mL) and dried over Na2SO4. After filtration, the solvent was evaporated and the crude product was purified by column chromatography (SiO2/ CH2Cl2/methanol 10:1). The product was obtained as a lightbrown solid in 80% yield. 1H NMR (300 MHz, CDCl3): 1.85 (m, 4H, C-CH2-C), 2.15 (t, 2H, CH2-CO-NH-), 2.27 (t, 2H, CH2-CO-O), 2.62 (t, 2H, CH2-Ar), 3.32 (t, 2H, CH2-N3), 3.39 (q, 2H, CH2-NH-), 4.09 (t, 2H, CH2-O-CO), 6.05 (br, 1H, NH), 6.49 (d, 1H, ArH), 6.66 (s, 1H, ArH), 6.74 (dd, 1H, ArH). 13 C NMR (75 MHz, CDCl3): 173.4 (CdO); 144.2, 143.1, 130.6, 120.6, 115.7, 115.3 (CdC); 61.6 (CH2-O); 48.2 (CH2-N3); 41.0 (CH2-NH-); 35.4, 34.7, 33.1, 28.0, 20.9 (C-CH2-C). Preparation of 4. 4 was synthesized from hydroxyl-chainterminated surfactant Zonyl-FSO-100 (Mw ≈ 725 g/mol, (CF2)x, x ≈ 8 and (CH2CH2O)x, x ≈ 8 from 19F and 1H analysis). ZonylFSO-100 (2 g, 1 equiv, 2.76 mmol), 4-pentynoic acid (0.297 g, 1.1 equiv, 3.034 mmol), and DMAP (0.025 g, 0.075 equiv, 0.207 mmol) were dissolved in anhydrous CH2Cl2 (20 mL) and the solution was cooled to -5 C. DCC (0.85 g, 1.5 equiv, 4.14 mmol) in CH2Cl2 (10 mL) was added dropwise to the Zonyl solution, and the reaction was allowed to return to ambient temperature while stirring overnight. The solution was filtered and the solvent was evaporated. The residue was dissolved in CH2Cl2 (100 mL), and the organic phase was washed with water (10 mL), dried over anhydrous Na2SO4, and filtered. The solvent was evaporated under reduced pressure, affording Zonyl derivative 4 in 94% yield as a light-brown viscous oil. 1H NMR (300 MHz CDCl3): 2.01 (t, 1H, -CtCH ), 2.37-2.7 (m, 6H, CH2-CH2-CtCH þ CH2-CF2-), 3.57-3.85 (m, O-CH2-CH2-O), 4.27 (t, 2H, CH2-O-CO-). Langmuir 2010, 26(20), 15920–15924
Preparation of Clickable Titanium Surfaces. Titanium plates (Ø = 1.5 cm) were first treated with an acidic oxidizing solution of concentrated sulfuric acid and hydrogen peroxide (H2SO4/H2O2 1:1) for 2 min to generate the corresponding hydroxylated titanium dioxide surface. Titanium plates were thoroughly rinsed with water, acetone, and ethanol and dried under nitrogen before functionalization. The pretreated titanium surfaces were then soaked in a solution containing 1 mM anchor 3 in methanol overnight, affording, after washing with methanol, the functionalized titanium Ti-azide surface. In the typical Huisgen 1,3-dipolar cycloaddition (CuAAC) on titanium plates, 50 mg of an alkyne derivative were dissolved in acetone (2 mL). CuSO4. 5H2O (3.5 mg) and sodium L-ascorbate (20 mg) were dissolved in water (1 mL). The two solutions were degassed with N2 for 2 min and combined in a glass sample jar. The discs were immersed in the solution that was held at 40 C for 24 h. After reaction, the samples were thoroughly rinsed with water and methanol and then dried under nitrogen. 1 H and 13C NMR spectra were recorded at 25 C with a Bruker Avance 300 spectrometer. Electrochemical experiments were performed using an Autolab PGSTAT 30 workstation. The experiments were carried out in a phosphate buffer at pH 7. A threeelectrode configuration was used with a titanum disk (1.5 cm diameter) as the working electrode and a counter electrode. An Ag/AgCl electrode was used as reference. The solution was purged with nitrogen prior to recording the electrochemical data, and all measurements were recorded at 25 C under a nitrogen atmosphere. XPS analyses were performed on a VG Escalab 220 XL system (Thermo Fisher Scientific) using a nonmonochromatic Al KR X-ray source (hν = 1486.6 eV). The emission voltage and the current of this source were set to 15 kV and 20 mA, respectively. The pressure in the analyzing chamber was maintained at 10-7 Pa or lower during analysis, and the size of the analyzed area was 8 mm 8 mm. Survey (0-1100 eV) and high-resolution (C 1s) spectra were recorded at pass energies of 100 and 40 eV, respectively. XPS analyses were performed with a takeoff angle of 90 relative to the sample surface. The core-level spectra were referenced to the Ti 2p binding energy at 458.6 eV for TiO2 and Ti-azide plates and to the F 1s binding energy at 688.3 eV for the Ti Zonyl sample. Data treatment and peak-fitting procedures were performed using Casa XPS software. Contact angle measurements were evaluated with a Digidrop contact angle meter from GBX Scientific Instruments at room temperature. A water drop was used to measure the contact angle values (θ). The measurement was repeated five times to obtain an average value for the surface.
Results and Discussion We have first designed and synthesized a new anchor incorporating a catechol fragment at one terminus to serve as a bidentate ligand capable of strongly binding to a titanium surface and an azide moiety at the other extremity, providing functionality to mediate the CuAAC reaction (Scheme 1). Functionalization of the Ti surface using this sequence would offer numerous advantages. The new anchor is relatively easy to produce, without the need for protecting groups, from commercially available dopamine. The anchoring step proceeds under mild conditions using a simple dip-and-rise procedure and, interestingly, can be easily monitored using electrochemical techniques because of the electrochemical signature of the catechol unit. The effectiveness and the versatility of CuAAC might offer access to a wide range of titanium-functionalized surfaces from our platform. As a proof of concept, we have exploited the CuAAC to modify the titanium surface with different species, including an electroactive probe (ferrocene) and a fluorinated oligomer (Zonyl). Compound 1 was prepared by reacting glutaric anhydride with 3-azido-1-propanol.19 After the activation of 1 with DOI: 10.1021/la102688m
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Watson et al. Scheme 1. Schematic Illustration of the Titanium Surface Functionalization Using Click Chemistry
Scheme 2. Synthesis of Azide-Functionalized Dopamine Anchor 3
N-hydroxysuccinimide, ester 2 was coupled with dopamine to furnish azide-functionalized anchor 3 in good yield (Scheme 2). Prior to the immobilization of anchor 3, the titanium surface was treated with an acidic oxidizing solution of concentrated sulfuric acid and hydrogen peroxide (H2SO4/H2O2 1:1) to generate the corresponding hydroxylated titanium dioxide surface.3 (Caution! Be careful when using piranha solution because it is very dangerous.) The pretreated titanium surface was then soaked in a solution containing 1 mM anchor 3 in methanol overnight, affording, after washing with methanol, the functionalized titanium Ti-azide surface (Scheme 1). Proof of the presence of 3 on the titanium surface was provided by recording a cyclic voltamogram (CV) in phosphate buffer at pH 7 (Figure 1). Indeed, CV gives rise to an irreversible two-electron oxidation wave at 0.65 V (vs Ag/AgCl) corresponding to the two-step oxidation of the catechol unit.20 The surface coverage Γ of the redox species can be calculated by integrating the anodic peak area (charge Q) according to Γ = Q/nFA, where F is the Faraday constant, n is the number of electrons exchanged (n = 2), and A is the surface area (Ø = 1.5 cm). The electrochemical results show that the surface coverage is 1.5 1015 molecules per cm2, which is consistent with a densely packed monolayer.20 Further evidence of the surface functionalization was obtained from XPS measurements. Indeed, the XPS survey of the catecholmodified titanium surface shows an increase in the nitrogen signal (19) Badiang, J. G.; Aube, J. J. Org. Chem. 1996, 61, 2484–2487. (20) Liu, J.; Yang, W.; Zareie, H. M.; Gooding, J. J.; Davis, T. P. Macromolecules 2009, 42, 2931–2939.
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at around 400 eV with a decrease in the titanium ratio compared to the bare titanium substrate. The N 1s core-level spectrum of the azide-terminated titanium surface exhibits a broad peak centered at 400 eV that could be fitted to two components at 400.0 eV (fwhm = 2.0 eV) and 401.4 eV (fwhm = 2.0 eV) (Figure 1, right). These two contributions were attributed to the azide21-24 and the amide25 functions, respectively, and are consistent with the chemical composition of the monolayer. In addition, a second peak centered at 404.5 eV (fwhm = 1.59 eV) is also observed and is attributed to the central electron-deficient nitrogen in the azide group.21-23,26 The click reaction between the azide-terminated surface TiN3 and ethynylferrocene was carried out in MeOH and catalyzed by Cu(I) by the in situ reduction of CuSO4 by sodium ascorbate. Cyclic voltametry measurements were utilized to confirm the formation of a covalent bond between the Ti-azide surface and the ferrocene derivative. Despite the passivating native oxide film, the cyclic voltamogram (Figure 2, left) reveals the characteristic reversible peak of the ferrocene unit at E1 = 0.42 V (vs Ag/AgCl). Moreover, the linear increase in current with scan rate and the identical values for the redox wave for both the oxidation and (21) Spruell, J. M.; Sheriff, B. A.; Rozkiewicz, D. I.; Dichtel, W. R.; Rohde, R. D.; Reinhoudt, D. N.; Stoddart, J. F.; Heath, J. R. Angew. Chem., Int. Ed. 2008, 47, 9927–9932. (22) Collman, J. P.; Devaraj, N. K.; Eberspacher, T. P. A.; Chidsey, C. E. D. Langmuir 2006, 22, 2457–2464. (23) Devaraj, N. K.; Dinolfo, P. H.; Chidsey, C. E. D.; Collman, J. P. J. Am. Chem. Soc. 2006, 128, 1794–1795. (24) Das, M. R.; Wang, M.; Szunerits, S.; Gengembre, L.; Boukherroub, R. Chem. Commun. 2009, 2753–2755. (25) Lyskawa, J.; Grondein, A.; Belanger, D. Carbon 2010, 48, 1271–1278. (26) Lee, M. T.; Ferguson, G. Langmuir 2001, 17, 762–767.
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Figure 1. Cyclic voltamogram of the catechol-modified titanium surface in phosphate buffer at pH 7 (left) and N 1s XPS core-level spectra of titanium surfaces modified by anchor 3 (right).
Figure 2. Cyclic voltamograms at different scan rates of a ferrocene-grafted titanium surface (left). Peak current as a function of scan rate for anodic and cathodic peaks (right).
reduction of ferrocene reflect the covalent surface attachment of the ferrocene unit (Figure 2). Integration of the ferrocene signal (n = 1) reveals a surface coverage of Γ = 1.0 1014 molecules per cm2, which is similar to other reports on gold surfaces,11 indicating the high functional density of the materials. Control of hydrophilicity/hydrophobicity plays a central role in surface science.27 In this study, we envisioned rendering the titanium surface hydrophobic by clicking block copolymer derivative 4 (Scheme 3), including a perfluororinated alkyl chain and a poly(ethylene glycol) block.28,29 This compound was conveniently synthesized30 from commercially available hydroxy-functionalized Zonyl FSO-100 (Supporting Information) using carbodiimide-promoted esterification. Proof of surface functionalization with 4 was obtained by XPS. Figure 3 shows the survey spectra of the titanium plate before and after functionalization. The XPS spectra of Zonyl-functionalized TiO2 surfaces exhibit an intense peak at around 690 eV that is attributed to the presence (27) Xia, F.; Zhu, Y.; Feng, L.; Jiang, L. Soft Mater. 2009, 5, 275–281. (28) Perrier, S.; Jackson, S. G.; Haddleton, D. M.; Ameduri, B.; Boutevin, B. Tetrahedron 2002, 58, 4053–4059. (29) Perrier, S.; Jackson, S. G.; Haddleton, D. M.; Ameduri, B.; Boutevin, B. Macromolecules 2003, 36, 9042–9049. (30) Fournier, D.; Du Prez, F. Macromolecules 2008, 41, 4622–4630.
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of fluorine31 in the grafted film. Moreover, after clicking 4 onto the azide-terminated titanium surface, the peak at 404.5 eV disappears and a broad peak centered at 400.2 eV (fwhm = 2.7 eV) appears, which is in accordance with the complete conversion of the azide group into the 1,2,3-triazole21-23 unit bound to the terminal zonyl head in good yield. Furthermore, the XPS survey of the derivatized surface clearly shows the complete disappearance of the Ti 2p signal at 450.6 eV, indicating that the thickness of the grafted layer is greater than the escape depth of the photoelectrons (i.e. 10 nm). Finally, to evaluate the impact on the wettability of the grafting of 4 onto the titanium surface, the static water contact angle for each substrate was evaluated (Scheme 3). The unmodified titanium surface exhibits a low contact angle of 23 ( 3, which is in accordance with the presence of hydrophilic hydroxyl groups on the titanium surface. After modification of the titanium surface with 3, the surface became more hydrophobic (70 ( 2), indicating that the grafting process was effective. When Zonyl derivative 4 was grafted onto the azide-terminated titanium surface, the contact angle increased to 125 ( 2, in agreement with the functionalization of the surface (31) Lyskawa, J.; Belanger, D. Chem. Mater. 2006, 18, 4755–4763.
DOI: 10.1021/la102688m
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Watson et al. Scheme 3. Study of Chemically Modified Titanium Surface Wettability by Contact Angle Measurementsa
a
(a) Bare titanium surface, (b) the azide-terminated titanium surface, and (c) after functionalization with Zonyl 4 via click chemistry.
Figure 3. XPS survey spectra of (a) the bare titanium surface, (b) the azide-terminated titanium surface, and (c) after functionalization with 4 via click chemistry. (Inset) (a) N 1s XPS core-level spectra of titanium surfaces modified by anchor 3 and (b) after the click reaction with 4.
with a hydrophobic oligomer. It is noteworthy that no change in the contact angle value was observed without catalytic activation, thus indicating the key role played by Cu(I) and also that no significant physical adsorption of 4 occurs.
Conclusions We have demonstrated that titanium surfaces can be successfully functionalized via the CuAAC reaction by utilizing a catechol-azide clickable platform. Contact angle measurements and electrochemical and XPS investigations unambiguously demonstrate the efficiency of functionalizing the azide-terminated catechol layer via click chemistry. This strategy may open the door to the application of modified titanium surfaces and also, thanks to the versatility of the catechol ligand, to other kinds of 15924 DOI: 10.1021/la102688m
surfaces such as Fe2O3 nanoparticles. In particular, this work is relevant because the strategy developed in this work can be used as a platform for grafting biomolecules onto titanium to furnish biomaterial devices. The functionalization of titanium implants with therapeutic agents using this strategy is in progress. The results will be published in a forthcoming paper. Acknowledgment. We thank CNRS, the European Community, and the Nord Pas de Calais region for funding (FANSBAMEB project). Supporting Information Available: XPS quantification and characterization spectra of 3 and 4. This material is available free of charge via the Internet at http://pubs.acs.org. Langmuir 2010, 26(20), 15920–15924
