Highly Hydrophilic Surfaces from Polyglycidol Grafts with Dual

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Highly Hydrophilic Surfaces from Polyglycidol Grafts with Dual Antifouling and Specific Protein Recognition Properties Sarra Gam-Derouich,† Monika Gosecka,‡ Sandrine Lepinay,§ Mireille Turmine,|| Benjamin Carbonnier,*,§ Teresa Basinska,*,‡ Stanislaw Slomkowski,‡ Marie-Claude Millot,§ Ali Othmane,# Dalila Ben Hassen-Chehimi,^ and Mohamed M. Chehimi*,† †

ITODYS, University Denis Diderot & CNRS (UMR 7086), 15 rue Jean de Baïf, 75013 Paris, France Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 y
od
z, Poland § Institut de Chimie et des Mat
eriaux Paris Est, CNRS UMR 7182, Facult
e des Sciences Universit
e Paris Est Cr
eteil, 2 rue Henri Dunant 94320, Thiais, France LISE, CNRS (UPR 15) and University Pierre & Marie Curie, Case 133, 4, Place Jussieu, 75005 Paris, France ^ Laboratoire d'Application de la Chimie aux Ressources et Substances Naturelles et a l'Environnement, D
epartement de Chimie, Facult
e des Sciences de Bizerte, Zarzouna, Bizerte 7021, Tunisia # Laboratoire de Biophysique, Facult
e de M
edecine de Monastir, 5000 Monastir, Tunisia

)

‡

ABSTRACT: Homopolymer grafts from R-tert-butoxy-ω-vinylbenzyl-polyglycidol (PGL) were prepared on gold and stainless steel (SS) substrates modified by 4-benzoyl-phenyl (BP) moieties derived from the electroreduction of the parent salt 4-benzoyl benzene diazonium tetrafluoroborate. The grafted BP aryl groups efficiently served to surface-initiate photopolymerization (SIPP) of PGL. In similar conditions, SIPP of hydroxyethyl methacrylate (HEMA) permitted the production of PHEMA grafts as model surfaces. Water contact angles were found to be 66, 15, and 0 for SS-BP, SSPHEMA, and SS-PPGL, respectively. The spontaneous spreading of water drops on SSPPGL was invariably observed with 1.5 μL water drops. PPGL thus appears as a superhydrophilic polymer. Resistance to nonspecific adsorption of proteins of PPGL and PHEMA grafts on gold was evaluated by surface plasmon resonance (SPR) using antibovine serum albumin (anti-BSA). The results conclusively show that PPGL-grafts exhibit enhanced resistance to anti-BSA adsorption compared to the well-known hydrophilic PHEMA. PPGL grafts were further modified with BSA through the carbonyldiimidazole activation of the OH groups providing immunosensing surfaces. The so-prepared PPGL-grafted BSA hybrids specifically interacted with anti-BSA in PBS as compared to antimyoglobin. It is clear that the superhydrophilic character of PPGL grafts opens new avenues for biomedical applications where surfaces with dual functionality, namely, specific protein grafting together with resistance to biofouling, are required.

1. INTRODUCTION In the biomedical and sanitary domains, there is a demand for hydrophilic and biocompatible polymer surface grafts which ensure resistance to nonspecific protein adsorption1 3 and/or pathogen bacterial adhesion.4 However, it is also desirable that the same type of polymers are modified so that they specifically attach antibodies or cells while retaining resistance to biofouling of the unmodified segments or regions, hence a dual functionality.5 In these applications, wetting remains an important issue as polymer surfaces must have a surface that preferably binds water molecules instead of being colonized (occupied) by undesirable (ballast) plasma proteins.1 In this regard, over several years PEG, PEGylated polymers, polyglycerols, polysaccharides, polyamides, polybetaines, and so on have proven efficient at resisting nonspecific attachment of proteins and regulating cell adhesion.1,6 8 Among these hydrophilic polymers, poly(2-hydroxyethyl methacrylate), PHEMA, r 2011 American Chemical Society

received much attention because it is the simplest hydroxylated polymethacrylate. It resembles poly(ethylene glycol methacrylate) except that it has a side chain containing only one ethylene oxide unit. PHEMA is very well-known to impart nonbiofouling character to surfaces provided it is densely packed4,9,10 with a thickness preferably in the 25 45 nm range.11 Aside from these well-known polymers, a few papers have also been published recently on synthesis and characteristics of polyglycidol12 and its derivatives13 with various morphologies. Particularly, R-tertbutoxy-ω-vinylbenzyl-polyglycidol-based (hereafter PGL) polymeric materials have interesting properties that make them suitable alternatives to the above-mentioned ones. Indeed, the main chain of polyglycidol (Figure 1) has a chemical structure Received: January 21, 2011 Revised: June 14, 2011 Published: June 16, 2011 9285

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Figure 1. Chemical structure of PGL macromonomer.

similar to that of poly(ethylene oxide), PEO, and with respect to the presence of CH2OH groups in each monomeric unit, this polymer is expected to be highly hydrophilic. Actually, the relative free enthalpy of hydration (ΔGsol) of the most stable conformers for PEO and PGL (trimers) were found to be 16.05 and 26.14 kcal/mol, respectively. It follows that PGL is thermodynamically more favorably prone for hydration than PEO (see computation details in Appendix). As previously shown by Basinska et al.,14 polyglycidol tethered on poly(styrene-co-PGL) microspheres (P(S-PGL)) exhibited mobility comparable to that of macromonomer chains in solution. It was also found that the longer polyglycidol chains in the particle surface layers were more mobile compared to the shorter ones and provide better protection against nonspecific protein adsorption.15 Actually, these microspheres proved efficient in substantially resisting nonspecific adsorption of human serum albumin compared to PS microspheres surface, however, without completely suppressing protein adsorption. This is due to the interaction of proteins with the aromatic domains within the polystyrenecontaining polymer structures that unavoidably can be present at the PGL-rich surface. Recently, the hydrophilic character of core/shell P(S-PGL) colloidal crystals has been interrogated by contact angle measurements.16 At room temperature, the advancing and receding water contact angles were found to be 62.8 and 36.3, respectively. These characteristics reflect a hydrophilic character but to a lesser extent compared to PEGylated polymers. This somehow shows that styrene segments are probed by water drops, which parallels the minimized but not suppressed protein adsorption on P(S-PGL) colloids. In order to study the behavior of PGL vis-a-vis protein adsorption, it is thus imperative to investigate the hydrophilic character of homopolymer grafts of PGL and determine their propensity to act as an antifouling material. One way to prepare PPGL (ultra)thin brushes is via surfaceinitiated radical polymerization. Particularly, UV-assisted surface polymer grafting17 20 has emerged in recent years as a simple and versatile means of controlling the surface properties of a wide panel of substrates by polymer grafts. These methods of polymer grafting rely mainly on the attachment of initiators to surfaces via silane or thiol interface chemistry, but none has tackled the facile diazonium salt chemistry in this regard. In this work, we explore the simple and efficient tandem diazonium salt electrografting and surface-initiated photopolymerization (SIPP), recently described by Gam-Derouich et al.,21 to prepare homopolymer grafts of the R-tert-butoxy-ω-vinylbenzylpolyglycidol macromonomer (PGL). Toward this end, we modified gold and stainless steel (SS) substrates by 4-benzoylphenyl ( C6H4 CO C6H5, BP) moieties derived from the electroreduction of the parent diazonium salt BF4-,+N2 C6H4 CO C6H5 (DS). Gold substrates served as model surfaces, while SS was chosen because it is the base for medical-grade tools and devices such as stents. SIPP of PGL was conducted on BP-

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modified Au and SS in chloroform using dimethyl aniline as hydrogen donors. The SS- and gold-grafted PPGL hybrids (SS-PPGL and Au-PPGL in short) were characterized by X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection adsorption spectroscopy (PM-IRRAS), and water contact angles. Surface plasmon resonance (SPR) was implemented to demonstrate the ability of Au-PPGL hybrids to resist nonspecific protein adsorption in relation to the wetting behavior of the polymer grafts. To the best of our knowledge, SPR has actually never been utilized thus far to study protein repelling properties of polyglycidol-based surfaces. Moreover, the effectiveness of the activation reaction of PGL hydroxyl groups for nucleophilic coupling to proteins was applied to provide protein-functionalized sensing layers. Biospecific interaction potentiality of these Au-PPGL-antigen hybrids was evaluated through the real-time monitoring of antibody antigen interactions.

2. EXPERIMENTAL SECTION Materials. Gold-coated silicon wafers with a thickness of about 1000 Å were purchased from Aldrich and cut into slides of 1  2 cm2. Just before use, and in order to remove the organic residues on the surface, the slides were ultrasonically rinsed with acetone, water, and ethanol, then dried in a stream of argon, cleaned in a UV cleaner (Boekel, Inc., model 135500), and rinsed with acetonitrile (ACN). Stainless steel plates (Weber M
etaux, ∼1 mm thick) were carefully polished by 0.3 μm Al2O3 and rinsed under sonication in acetone, water, and ethanol. The polished surfaces were then UV-treated and finally rinsed with ACN. The composition in at % as we have determined by EDX is O = 15.37%, Si = 0.98%, Cr = 16.9%, Mn = 1.18%, Fe = 58.84%, Ni = 6.73%. Glycidol (Aldrich), chloromethylstyrene (Aldrich), 1-ethyl vinyl ether (Fluka), styrene (S, 105.15 g/mol, Fluka), 4-aminobenzophenone (Alfa Aesar), N,N-dimethylaniline (DMA, Fluka), carbonyldiimidazole (CDI), bovine serum albumin (BSA), antibovine serum albumin (antiBSA), and antimyoglobin were purchased from Aldrich and used as received. Chloroform (CHCl3), methanol (MeOH), toluene, and phosphate-buffered saline (PBS, 10 mM, pH 7.4) were all of analytical reagent grade from Acros Organics and were used as received. Water was deionized using a Millipore purification system. Synthesis of r-tert-Butoxy-ω-vinylbenzyl-polyglycidol Macromonomer (PGL). The exact procedure for preparation of

R-tert-butoxy-ω-vinylbenzyl-polyglycidol macromonomer (PGL) was described elsewhere.12,22 Briefly, 1-ethoxy ethyl glycidyl ether (EEGE) was synthesized from glycidol according the procedure developed by Fitton et al.23 Then, anionic polymerization of 1-ethoxy ethyl glycidyl ether and subsequent end-capping with chloromethylstyrene yielded R-tert-butoxy-ω-vinylbenzyl-polyglycidol ether. Finally, deprotection of hydroxyl groups from repeating units of macromonomer was carried out according to Halacheva at al.24 1H NMR spectrum (200 MHz, D2O) δ ppm: 1.12 (s, 9H), 3.45 3.64 (m, 5H), 4.60 (d, 2H), 5.23 (d, 1H), 5.78 (d, 1H), 6.71 (m, 1H), 7.38 (m, 4H aromatics). Number average molecular weight (Mn) and molecular weight polydispersity parameter (Mw/Mn) of R-tert-butoxy-ω-vinylbenzyl-polyglycidol macromonomer determined by GPC were equal to ∼1960 and 1.03, respectively.

Synthesis of the Diazonium Salt BF4 , +N2 C6H4 CO C6H5. Seventeen millimoles of 4-aminobenzophenone was dissolved in

11.5 mL of HBF4. The mixture was maintained under stirring. After cooling the solution at 0 C with ice, a solution of NaNO2 (34 mmol dissolved in a minimum of water) was added and the reaction was left to proceed for 30 min. The solution was then kept in the freezer at 5 C for 24 h in order to allow the DS to gently precipitate. The brown solid 9286

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Figure 2. Chronoamperometric grafting of 4-benzoyl phenyl groups to stainless steel plates. Conditions: 5 mM DS in ACN + 0.1 M NBu4BF4, 700 mV negative potential, t = 300s, v = 0.2 V.s 1. Reference SCE. Inset shows the determination of the reduction peak potential of the diazonium salt. was washed with cold diethyl ether. The powder was dried and stored at 5 C. 1H NMR (200 MHz, DMSO), δ ppm: 8.9 (d, 2H) and 8.3 (d, 2H); 7.5 (t, 2H) and 7.8 (m, 3H).

Electrochemical Reduction of the Diazonium Salt on Gold and SS Surfaces. Grafting aryl layers on gold from electroreduction of DS was conducted by chronoamperometry by setting the potential at 700 mV, a potential more negative than the reduction peak found at 380 mV (see details in ref 21). In the case of SS, the reduction peak of DS was found to be centered at 385 mV (inset in Figure 2). The mechanism of electrografting was described in detail elsewhere.25 Cyclic voltammetry served for the determination of reduction potential of the diazonium salt. The current decreases dramatically after the first wave, indicating the onset of the electrode passivation. After the second and third cycles, the current gets very low. The chronoamperometry plot shows that a very steep decrease of the current with time is characteristic of the formation of the organic layer, which hampers the electron transfer from the electrode. Benzoyl phenyl (BP)-modified gold and stainless steel (SS) plates (Au-BP and SS-BP, respectively) served as photoinitiators for SIPP of PGL and HEMA. UV Light Source. UV irradiation was carried out in the commercial ultraviolet processor Spectrolinker XL 1500 UV (Spectronics Corp). This processor was equipped with 6 tubes (8 W) having a wavelength of 365 nm and intensity of 17.6 mW/cm2 at 365 nm. Surface-Initiated Photopolymerization. The growth of polymer grafts on Au-BP and SS-BP was performed as follows: a homogeneous mixture solution of monomer (4 mmol) and 4 wt % of DMA in chloroform (4 mL) was prepared. The glassy vessel containing the SSBP and Au-BP plates dipped in polymerization mixture was degassed by bubbling with argon for 5 min. The slides were then exposed to UV light at 365 nm at room temperature for a period of 2 h in the case of PGL, while for the SIPP of HEMA, 800 s were sufficient for grafting a densely packed PHEMA chains as reported in ref 21. After SIPP, the slides were thoroughly sonicated in chloroform for 4 min to remove the unreacted monomer, then washed with ethanol and dichloromethane to remove organic species. The polymer-coated slides were dried and stored under argon. Immobilization of BSA on Au-PPGL. Imidazolyl carbamate moieties were first introduced on the surface of Au-PPGL hybrids by carbonyldiimidazole reaction (30 mg/L in DMF) with the hydroxyl groups of PPGL. The reaction was carried out at room temperature

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during 6 h. The Au-PPGL was next thoroughly rinsed with DMF and PBS, successively. The so-activated Au-PPGM was immersed in a BSA solution (4 mg/mL, 16 h) for covalent immobilization under bidirectional stirring. GPC. GPC plots were recorded using a system composed of a 1100 Agilent isocratic pump, a multiangle laser light scattering (MALLS) DAWN EOS photometer (Wyatt Technology Corporation, Santa Barbara, CA), and differential refractometer K-2300 (Knauer). ASTRA 4.90.07 software (Wyatt Technology Corporation) was used for data collecting and processing. Two TSK Gel columns (G 2000 H and G 6400 H) were used and samples were injected as a solution in methylene chloride. The volume of the injection loop was 100 μL. Methylene chloride was used as a mobile phase at a flow rate of 0.8 mL/min. It is to note that, in the present work, the MALLS photometer permits the determination of absolute molecular weight directly from the angular dependence of the scattered light intensity.26 XPS. The spectra were recorded using a Thermo VG Scientific ESCALAB 250 system fitted with a microfocused, monochromatic Al KR X-ray beam (1486.6 eV, 500 μm spot size). The samples were stuck on sample holders using conductive double-sided adhesive tape and outgassed in the fast entry lock for at least 1 h at 5  10 7 mbar or better. The Avantage software, version 3.51, was used for digital acquisition and data processing. The spectra were calibrated against the C1s main peak component C C/C H set at 285 eV. The thickness of the polymer grafts was determined by QUASES software developed by Tougaard.27 The algorithm based on peak shape analysis permits estimatation of the thickness and coverage from the structure of the background. In this method, the user relies on a visual inspection of the agreement between the spectrum and a calculated background that extends to ∼100 eV below the kinetic energy position of the peak. By iterating between the model and experimental data in this spectral region, the fitted background shape permits us to highlight lateral and in-depth differences in composition. It is noteworthy that, contrary to traditional peak-fitting procedures to determine the various components of a given elastic peak, Tougaard’s algorithm instead permits fitting the spectral background in order to assess the elemental distribution in the sample. However, this approach cannot provide distributions of chemical species, but only elements. PM-IRRAS. PM-IRRAS spectra were recorded with a Nicolet 860 FTIR (Thermo-Electron) spectrometer with a resolution of 8 cm 1 by adding 2000 scans with an optical mirror velocity of 0.474 cm 1/s. Contact Angle Measurements. Water contact angles were determined with a Kr€uss DSA 100 instrument (Hamburg, Germany), fitted with a drop shape analyzer. Typical wetting experiments were described elsewhere.21 Surface Plasmon Resonance (SPR). The SPR system employed (GenOptics, Orsay, France) has been described in detail previously.28 Briefly, it uses a monochromatic laser light source operating at a wavelength of 660 nm focused onto a glass slide coated with a 50 nm gold film index matched to the top of a glass prism using index-matching oil (Cargille Laboratories, USA). This system was further modified to introduce an injection loop (20 μL) for sample loading, thus providing continuous flow between each stage of the experiment. The protein adsorption was monitored in real time as the change in the SPR response measured at fixed angle.

3. RESULTS AND DISCUSSION Preparation and Characterization of Polymer Grafts. The overall preparation process of the metal polymer hybrids by SIPP using electrografted 4-benzoylphenyl groups (BP) is schematically illustrated in Figure 3. XPS characterization of Au-BP was thoroughly discussed in ref 21. Concerning SS-BP, Figure 4 provides XPS evidence for the 9287

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Figure 3. Strategy of tandem diazonium salt electrografting and SIPP for the preparation of vinylic polymer grafts (monomers: 2-hydroxyl ethyl methacrylate and PGL; grafted initiator: 4-benzoyl phenyl groups; co-initiator (H donor): dimethylaniline; solvent: chloroform; temperature: RT; substrates (S): Au and SS.)

Figure 4. (a) Survey spectra of SS and SS-BP; and (b) high-resolution C1s region from SS-BP.

modification of SS by the BP aryl layers (Figure 4a). Cr2p3/2 (∼574 eV) is drastically attenuated at the expenses of C1s (285 eV) and O1s (∼532 eV) from the 4-benzoyl phenyl groups. The presence of zinc at the surface of bare SS could be due to surface contamination that occurred during the polishing step; it was not eliminated despite careful cleaning and rinsing. The high-resolution C1s peak from SS-BP (Figure 4b) exhibits a prominent feature due to C C/C H bonds at 285 eV, a peak at 288 eV due to CdO from the grafted BP species and finally a low intensity peak at 291.2 eV, assigned to a πfπ* shake-up satellite transition which is a fingerprint of the attached aryl groups. Figure 5 shows the XPS survey and high-resolution C1s regions for polymer-modified Au and SS plates. The organic coating thickness was determined by Tougaard’s QUASES method27 (Figure 6). Table 1 summarizes the quantitative XPS surface analysis of metal polymer hybrids. In Figures 5a and b, the main peaks Au4f7/2, C1s, O1s, and Fe2p3/2 are centered at 84, 285, 533, and 710 eV, respectively. Au-PPGL (Figure 5a) shows a prominent background due to the attenuation of gold core electrons levels but without completely screening these metallic characteristic peaks. The O/C ratio is 0.51, which is about 14% lower than the expected value for the actual PPGL. Probably, this is due to the detection of the aryl layer through PPGL. In the case of Au-PHEMA, Au features are not detected as we have previously reported.21 The O/C ratio is 0.42 slightly lower than the expected 0.5 value for pure PHEMA. In the case of SS-PPGL and SS-PHEMA the metal features have vanished and the inelastic background due to SS is absent (Figure 5b). Indeed, the background line is horizontal meaning that the metallic plates are completely screened by the polymer

grafts, hence the effective tandem diazonium salt electroreduction and SIPP to generate thick and dense organic coatings on SS. The O/C ratio is 0.53, very close to the theoretical one expected for PPGL with the average degree of polymerization of 24 for the hydrophilic chains borne by PGL macromonomers. An even better situation is reached with PHEMA, since the O/C ratio of 0.47 is only 6% lower than the theoretical value calculated for PHEMA. For all these surfaces, a lower than expected O/C ratio could be due to a slight adventitious hydrocarbon contamination. The peak-fitted high-resolution C1s peaks are displayed in Figure 5c f for metal polymer hybrids. In the case of PHEMA grafts, and as we have discussed in detail elsewhere,21 the spectra displayed in Figure 5c,d exhibit three components centered at 285, 286.5, and 289 eV assigned to C C/C H, C O, and O CdO, respectively. The components are in the 3.8:2.4:1 and 3.1:2.1:1 ratios for Au-PHEMA and SS-PHEMA, respectively. Therefore, both surfaces have compositions that match that of PHEMA. In Figure 5e, and despite the detection of Au4f and Au4d from gold, the C1s region of Au-PPGL exhibits two C1s maxima assigned to C C/C H (285 eV) and C O C/C OH bonds (286.5 eV) from PGL hydrophilic pendant chains. This is also the same situation for SS-PPGL (Figure 5f) which implies that both Au and SS have PGL-rich surfaces. Although styrenic fragments are present at the surface, there is no clear sign for a πfπ* shake-up satellite transition as in the case of pure polystyrene grafts21 or P(S/PGL) microspheres.29 The concentration of glycidol repeat units is indeed 24 times higher than that of the pendant phenyl groups. The sharp C O C/C OH component 9288

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Figure 5. XPS surface analysis of gold and SS-grafted polymer hybrids: Survey scans (a and b); high-resolution C1s narrow regions for metal-PHEMA hybrids (c and d); high-resolution C1s peaks from metal-PPGL hybrids (e and f).

at 286.5 eV is thus a clear indication that polyglycidol chains are oriented to the free surface of the plates. For both Au-PPGL and SS-PPGL, the atomic ratio computed from C286.5/C285 is 4.1 which indicates a large excess of C O/C OH carbon atom types at surfaces over those in C C/C H environments, hence the excess of functional groups that impart a hydrophilic character

over the carbon atoms that provide a rather hydrophobic effect (C C/C H at 285 eV). The organic coating thickness was determined by QUASES fitting the background in the O1s regions of the survey scans recorded for SS-PHEMA and SS-PPGL (Figure 6). In this regard, we assumed a uniform polymer coating and an attenuation length 9289

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Figure 6. Background fitting of the O1s regions by QUASES for SS-PPGL and SS-PHEMA hybrids. The red box indicates the start and the end of the polymer coating depths.

Table 1. Surface Chemical Composition of Metal Polymer Hybrids as Determined by XPS contributions to C1s (%)a

surface elemental analysis (at %) materials

a

C

O

O/C

C285

C286.5

C289

thickness (nm)

Au-PPGL

64.1

32.7

0.51

19.7

80.3

-

Au-PHEMA

70.6

29.4

0.42

53.0

33.1

13.9

SS-PPGL

65.2

34.8

0.53

19.8

80.2

-

40

SS-PHEMA

67.9

32.1

0.47

50.1

33.9

16.0

47

18.5 nm >100

C285, C286.5, and C289 are C1s components centered at ∼285 (C C/C H), 286.5 (C O C/C OH), and 289 (O CdO), respectively.

of 3.1 nm for O1s. The “buried layer” model was adopted for fitting the background. It is to note that the total organic thickness (polymer + aryl layer) was estimated to be 40 and 47 nm for SS-PPGL and SS-PHEMA, respectively. In the case of AuPHEMA (not shown), the organic coating thickness exceeds 100 nm.21 Thick polymer grafts prepared by photopolymerization have actually been reported elsewhere by Steenackers et al.19 and Dyer et al.30 In contrast, the Au-PPGL has an organic thickness of 18.5 nm. Detection of Au4f and Au4d through the organic could perhaps be due to elastic scattering. PM-IRRAS measurements (Figure 7) were carried out to characterize the grafted aryl and polymer layers on SS substrates. For comparison, the ATR spectrum of pure PGL is displayed. The PMIRRAS spectrum of SS-BP lacks the band at 2294 cm 1 characteristic of the NtN+- in DS21 which indicates that the reduction of the diazonium group has indeed occurred. The absorption band centered at 1657 cm 1 is assigned to the carbonyl stretch of the 4-benzoyl phenyl group, whereas the bands centered at 1600 and 3060 cm 1 correspond to CdC and C H, respectively, in phenyl group. The results reported for the actual SS-BP confirm the findings of Adenier et al. for the electrografting of BP to iron.31 The PM-IRRAS spectrum of SS-PHEMA shows absorption bands centered at 1735 and 1271 1167 cm 1 assigned to CdO and C O, respectively, of the methacrylate. Grafting PHEMA is further confirmed by the band around 3400 cm 1 characteristic of OH stretching vibration. The SS-PPGL and pure PGL spectra are to be compared. The two bands centered at 1100 and 1037 cm 1 correspond to stretching vibration of the ether group (C O C) in two different environments. The broad bands around 3400 3500 cm 1 are assigned the OH stretching vibration of PGL. The inset of the SS-PPGL spectrum shows clearly the successful photopolymerization of PGL by the disappearance of the peaks located to 1635 cm 1 and attributed (CdC) to the pure PGL. As far PPGL

grafts are concerned, the absence of vinylic CdC bond in the spectrum of SS-PGL indicates an efficient SIPP of PGL, therefore confirming XPS studies. Similar IR results were obtained for the polymers grafted to Au plates. Figure 8 shows θw vs time plots for the Au-BP, SS-BP, and the corresponding metal polymer hybrids. SS-BP and Au-BP are distinctively hydrophobic compared to their corresponding metal polymer hybrids. While Au-PHEMA exhibits a final contact angle of ∼36, SS-PHEMA is even more hydrophilic with a final contact angle of 15. For both SS-PPGL and AuPPGL, we repeatedly observed spreading of water drops indicating that PPGL grafts are highly hydrophilic (contact angle