Development of Antifouling Hyperbranched Polyglycerol Layers on

Article Cite This: Langmuir 2017, 33, 14657−14662

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Development of Antifouling Hyperbranched Polyglycerol Layers on Hydroxyl Poly‑p‑xylylene Coatings Pei-Ru Chen, Ting-Ching Wang, Shih-Ting Chen, Hsien-Yeh Chen, and Wei-Bor Tsai* Department of Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 106, Taiwan ABSTRACT: Antifouling surfaces that are resistant to protein adsorption and cell adhesion are desirable for many biomedical devices, such as diagnostic devices, biosensors, and implants. In this study, we developed an antifouling hyperbranched polyglycerol (hPG) surface on hydroxyl poly-p-xylylene (PPX-OH). PPX-OH was deposited via chemical vapor deposition (CVD), and an hPG film was then developed via the ring-opening reaction of glycidol. The hPG film greatly reduced the adhesion of L929 cells and platelets as well as protein adsorption. The addition of alkenyl groups in the hPG layer allows the conjugation of biomolecules, such as peptides and biotin, and elicits specific biological interactions. Since the CVD deposition of PPX-OH could be applied to most types of materials, our approach makes it possible to decorate an antifouling hPG film on most types of materials. Our method could be applied to biosensors, diagnostics, and biomedical devices in the future.

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mers using the “graft-from” technique have been reported. The advantages of the “graft-from” technique over the “graft-to” technique include better control over the placement of hyperbranched polymers and the better chance to create thick hPG films.19 In the “graft-from” strategy, the growth of hPG could be initiated from substrates containing nucleophilic groups, such as oxidized silicon,19 aminopropylsiloxane,20 and oxidized metals,13,21 via exposed hydroxyl groups after activation through deprotonation.19,21 For example, Khan and Huck used the “graft-from” technique to develop hPG on Si/ SiO2 surfaces via anionic ring-opening polymerization of glycidol.19 However, the above “graft-from” examples are limited to specific types of substrates and could not be expanded to most types of materials, which restrains the wide application of hPG coatings. Therefore, a more versatile platform for the surface-initiated formation of hPG is needed for broadening the applications of hPG coatings. Chemical vapor deposition (CVD) of a thin film (20−100 nm) of poly-p-xylylene (PPX) via polymerization of [2.2]paracyclophanes could be applied to a wide variety of materials such as polymers, metals, and ceramics.22 PPX coatings are stable and biocompatible, so they have been successfully applied to several medical devices such as stents and cardiac pacemakers.22 A remarkable feature of the PPX coating is that PPX with a variety of functionalities could be formed for anchoring bioactive molecules for biomedical applications.23−25 Previously, hydroxyl-PPX (PPX-OH) has been synthesized and its biocompatibility has been demonstrated.26,27 We suggest that the PPX-OH surface could be used for the initiation of an hPG film for antifouling purpose.

INTRODUCTION Antifouling surfaces that are resistant to protein adsorption and cell adhesion are desirable for many biomedical devices, such as diagnostic devices, biosensors, and implants. A biomedical device with a suitable antifouling capacity can prevent detrimental clinical complications or device malfunctions that are initiated from nonspecific attachment of proteins/cells.1 An important character of antifouling surfaces is the ability to attract tightly bound water molecules. A common strategy to create antifouling surfaces is decoration of biomaterials with hydrophilic polymeric materials such as poly(ethylene glycol) (PEG), poly(HEMA), polyacrylamide, dextran, and zwitterionic polymers.2−8 Among the antifouling polymers, PEG’s antifouling ability has been the golden standard in the pharmaceutical and biomedical industry. As linear PEG has been grafted on biomaterials extensively as antifouling coatings, hyperbranched polyglycerol (hPG), structurally similar to PEG, has recently become popular as an alternative to PEG.9,10 hPG possesses better thermal and oxidative stability than PEG,11,12 making it favorable to implantable devices that often require thermal sterilization or resistance to oxidative degradation. hPG macromolecules can be easily synthesized by the ring-opening polymerization of 2hydroxymethyloxirane (glycidol) initiated by nucleophiles.13,14 The techniques for the surface conjugation of hPGs can be categorized into “graft-to” and “graft-from” methods. In the “graft-to” strategy, hPGs are synthesized prior to the physical or chemical attachment to substrates.15−18 Typically, hyperbranched polymers are synthesized with reactive groups and then grafted to surfaces via specific reactions with the reactive groups on the substrates. For example, disulfide-functionalized hPG covalently attaches on a gold surface and effectively prevents protein adsorption.11 On the other hand, relatively fewer studies regarding surface-initiated hyperbranched poly© 2017 American Chemical Society

Received: August 10, 2017 Revised: November 9, 2017 Published: December 1, 2017 14657

DOI: 10.1021/acs.langmuir.7b02826 Langmuir 2017, 33, 14657−14662

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Langmuir Scheme 1. Synthetic Route for Surface Deposition of hPGa

a The substrate was first deposited with hydroxyl-PPX. The nucleophilic hydroxyl groups initiate the ring-opening polymerization of glycidol to create an hPG layer.

of alkenyl hPG coatings, 1,2-epoxy-5-hexene (cat. #260347, SigmaAldrich) was added in the glycidol solution in a 1/100 molar ratio of glycidol. The samples for 1- or 3-day reaction are referred to as hPG1−ene and hPG3−ene, respectively. Surface Characterization. Surface wettability was investigated by dynamic water contact angle (WCA) measurement (FTA-125, First Ten Angstroms, USA) using 5 μL of deionized water. At least four locations on each sample were measured. The film thickness of hPG coating was determined based on light reflection (model F20, Filmetrics, USA). The surface chemical composition of each sample was characterized by electron spectroscopy for chemical analysis (ESCA). The samples for ESCA were prepared on tissue culture polystyrene. ESCA spectra were recorded on a VG ESCA Scientific Theta Probe (UK) with an Al Kα X-ray source radiation (1486 eV) at a take-off angle of 53°. The atomic compositions of the surfaces were calculated from the highresolution spectrum of each element. L929 Cell Adhesion to hPG Surfaces. The hPG-modified substrates were sterilized in 70% ethanol, followed by rinsing with sterilized water and PBS prior to cell experiments. L929 fibroblasts were inoculated on each substrate at a density of 2 × 104 cells/cm2 for 6 h. The unattached cells were rinsed away with PBS, and the attached cells were then fixed and stained with 4′,6-diamidino-2-phenylindole (DAPI). Fluorescent images were taken using a fluorescence microscope (100-fold magnification). The DAPI-stained nuclei were counted from the fluorescent photos using ImageJ software (NIH) for the determination of cell densities (three images/substrate). Platelet Adhesion to hPG Surfaces. Washed platelets were isolated from the fresh blood of healthy human donors according to a previous procedure,28 which was approved and maintained by the Research Ethics Committee at the National Taiwan University Hospital under the guidelines of Human Subject Research Acts of Taiwan. Informed consents from the donors were obtained. Briefly, the blood was collected into a syringe containing ACD anticoagulant.

In this study, an hPG film was formed on PPX-OH and was evaluated in its antifouling ability against cell adhesion and protein adsorption. Alkenyl groups were also incorporated in the hPG coating and then used for the conjugation of biomolecules to elicit specific biologic interactions.

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EXPERIMENTAL SECTION

Materials. Most of the chemicals were purchased from SigmaAldrich (St. Louis, USA) and used as received, unless specified otherwise. L929 mouse fibroblast-like cells were received from Food Industry Research and Development Institute (Hsinchu, Taiwan). L929 cell culture medium contained alpha minimum essential medium (αMEM; HyClone, USA), supplemented with 10% fetal bovine serum (Biological Industry, Israel), 2 mg/mL NaHCO3, 0.5% of fungizone (Gibco, USA), 0.25% gentamycin (Gibco), and 0.679% β-mercaptoethanol. Phosphate-buffered saline (PBS) was composed of 137 mM NaCl, 2.7 mM KCl, 10 mM Na2HPO4, and 1.8 mM KH2PO4 at pH 7.4, and citrate PBS (CPBS) contained 10 mM Na2HPO4, 10 mM citric acid, and 120 mM NaCl at pH 7.4. A peptide [arginine−glycine− aspartic acid−cysteine (RGDC)] was purchased from Kelowna Inc. (Taipei, Taiwan). Preparation of hPG Adlayer on PPX-OH. The synthetic route for surface deposition of hPG is illustrated in Scheme 1. PPX-OH was deposited on glass coverslips (5 mm in diameter) via CVD polymerization of 4-hydroxymethyl[2.2]paracyclophane, according to a previous protocol.26,27 The procedure for the formation of hPG films is based on a previous protocol19 with modifications. Briefly, the PPXOH substrates were immersed in liquid glycidol (cat. #G5809, SigmaAldrich), which had been purged with nitrogen for 1 h, and then incubated at 120 °C under constant stirring for 1 or 3 days, hereafter referred to as hPG1 and hPG3, respectively. The substrates with shorter reaction times, such as 3, 6, and 12 h, were also prepared. The substrates were then rinsed with deionized water. For the preparation 14658

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Langmuir The platelet-rich plasma was obtained after centrifugation of the blood at 187g for 20 min, and then washed platelets were isolated using sizeexclusion chromatography in a Sepharose 2B column. The samples were immersed in 1% plasma in CPBS at 37 °C for 1 h, rinsed with PBS, and then blocked with 2 wt % bovine serum albumin in PBS at 37 °C for 1 h. Prior to the platelet adhesion experiments, the platelet solution was implemented with 1 mM Ca2+ and 1 mM Mg2+. The platelets were inoculated on the samples at a density of 1.6 × 106 platelets/cm2 for 1 h at 37 °C. The unadhered platelets were rinsed away using PBS. The density of the platelets adhered was quantified by a lactate dehydrogenase (LDH) activity assay.29 Briefly, adherent platelets were lysed by 1% Triton X-100, and the LDH activity was determined using a Cytotoxicity Detection Kit (Boehringer Mannheim, Germany). The number of adherent platelets was determined from a calibration curve generated by plotting optical density versus platelet concentration for a series of suspensions of known platelet concentration. Modification of Functional hPG Surfaces. Two molecules containing thiol, RGDC and biotin−PEG−SH, were conjugated to the hPG−ene substrates via the thiol−ene reaction. RGDC (0.1 mg/mL in PBS) or biotin−PEG−SH (0.52 mg/mL in PBS) was incubated with the substrates in the presence of 2,2′-azoisobutyronitrile (10−2 mmol) at 80 °C for 4 h and then rinsed with deionized water. The cell affinity of the RGD-conjugated surface and the adsorption of avidin−FITC to the biotin-conjugated surface were then determined. For the avidin adsorption, avidin−FITC solution (0.1 mg/mL in PBS) was placed on the biotinylated hPG surface at 37 °C for 2 h. After rinsing with PBS, the substrates were incubated with 300 μL Dbiotin solution (100 mg/mL in PBS containing 1% sodium dodecyl sulfate) at 37 °C for 3 h to elute the attached avidin−FITC. The fluorescence in the eluates was determined by a fluorophotometer to determine the amount of adsorbed avidin−FITC. Statistical Analysis. The data were reported as means ± standard deviation. The statistical analyses between different groups were determined using Student’s t-test. Probabilities of p ≤ 0.05 were considered as the significant difference. All statistical analyses were performed using a GraphPad InStat 3.0 program (GraphPad Software, USA).

become much more hydrophilic after hPG deposition. The ESCA data also demonstrate the deposition of hPG (Table 1). The oxygen concentration on PPX-OH was around 2.65%, whereas the oxygen concentrations were increased to ∼12% on both hPG1 and hPG3. The results indicate that the formation of hPG could be initiated on PPX-OH. The data of surface characterization indicate that hPG has been successfully formed on PPX-OH. The ring-opening polymerization of glycidol usually takes place at a high temperature (>100 °C) under an alkaline condition. It is important to confirm that the PPX coating is robust enough to resist the harsh reaction condition. The results also indicate that the PPX coating survives from the harsh reaction, and hPG was successfully deposited on the PPX-OH substrates. In the literature, the temperature and time for the formation of hPG layers depend on the substrate types. For example, hPG was deposited slowly but steadily on silicon at 100 °C, and the deposition rate was increased at 140 °C.13 By contrast, the growth of the hPG layer on stainless steel was even faster at 100 °C than that on silicon, but at 140 °C, no hPG layer was formed on stainless steel because the steel surface corroded at the high temperature in the polar reaction mixture. In this study, we chose 120 °C as the reaction temperature. The surface properties between hPG1 and hPG3 are similar, suggesting that hPG formation reached a plateau after 1 day reaction on the PPX substrate. Inhibition in Cell Adhesion to hPG. The resistance of hPG coating to cell adhesion was tested on L929 cells and platelets. The 6 h adhesion of L929 cells to PPX-OH was 2.47 ± 0.31 × 104 cells/cm2, whereas that to hPG1 and hPG3 was dropped to ∼500 cells/cm2, ∼97% decrease (Figure 1A). The

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RESULTS AND DISCUSSION Characterization of the hPG Surfaces. hPG surfaces were created on PPX-OH via the nucleophilic ring-opening reaction for 1 or 3 days. The film thicknesses of hPG1 and hPG3 were determined as 25.5 ± 8.3 and 21.4 ± 4.6 nm, respectively (Table 1). The surface wettability of hPG was Table 1. Surface Characterization of PPX-OH, hPG1, and hPG3 contact angle (deg) PPX-OH hPG1 hPG3

atomic concentration (%)c

a

advancing

receding

thickness (nm)b

C

O

80.5 ± 0.7 32.6 ± 3.0 28.1 ± 3.3

49.5 ± 1.4 7.4 ± 1.8 8.3 ± 2.0

326.1 ± 17.6 25.5 ± 8.3 21.4 ± 4.6

96.6 87.9 87.4

3.4 12.1 12.6

Average of four measurements. bAverage of 10 measurements. c Atomic percentage was determined by ESCA. The value is an average of two measurements.

Figure 1. Adhesion of (A) L929 cells and (B) platelets to PPX-OH, hPG1, and hPG3. The samples for 1- or 3-day ring-opening reaction are referred to as hPG1 and hPG3, respectively. *p < 0.001 vs PPXOH. n = 4.

determined by the dynamic WCA measurement. After the formation of the hPG layer, the advancing WCA was decreased from 80° on PPX-OH to ∼30°, whereas the receding WCA was reduced to less than 10° on both hPG1 and hPG3 (Table 1). No significant difference was found between the WCA of hPG1 and hPG3. The significant decrease in WCA on the hPG surfaces in comparison with PPX-OH indicates that the surfaces

results show that the hPG films almost totally inhibit the adhesion of L929 cells. Similarly, the 1 h platelet adhesion to hPG1 and hPG3 was significantly decreased to ∼1.54 × 104 platelets/cm2 in comparison with 2.35 × 105 platelets/cm2 on PPX-OH (Figure 1B). The hPG surfaces show a great resistance to cell and platelet adhesion. However, the difference in the inhibitive efficacy of hPG1 and hPG3 was not significant,

a

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Langmuir

The adhesion of L929 cells was almost inhibited on hPG1, hPG3, hPG1−ene, and hPG3−ene (Figure 3), indicating that

suggesting that the 1 day ring-opening reaction is sufficient to reach a maximal anticell adhesion efficacy. We further studied the cell resistance of hPG coatings with shorter reaction times (3, 6, 12, and 24 h) to investigate the film growth and the correlation between film thickness and cell adhesion. The thickness of the hPG film was increased with increasing reaction time, from 4.40, 7.78, 11.2, and 12.1 nm for 3, 6, 12, and 24 h of incubation, respectively (Figure 2A).

Figure 3. Surfaces were conjugated with hPG layer in different coating conditions. After 1 day of culture, the cell numbers were quantified. The samples for 1- or 3-day ring-opening reaction are referred to as hPG1 and hPG3, respectively. −ene indicates that the surfaces contain alkenyl groups. *p < 0.001 vs PPX-OH and hPG-RGD surfaces. n = 5.

the addition of 1,2-epoxy-5-hexene does not affect the anticell adhesion property of the hPG layer. RGD peptide, an adhesion peptide, exists in several extracellular matrix adhesive proteins such as fibronectin and laminin for binding to cell membrane integrins to initiate cell adhesion.31,32 The peptide has been frequently conjugated to biomaterials for improving cell adhesion.33−35 In this study, RGDC peptides were immobilized onto hPG−ene substrates via the thiol−ene reaction between the surface alkenyl group and the cysteine residues of the peptide. After the conjugation of RGDC to hPG1 or hPG3, the cell adhesion was enhanced to ∼1.4 × 104 cells/cm2, indicating that RGDC is immobilized on the hPG−ene and supported cell adhesion. The hPG coating is known for its ability to reduce protein adsorption. In this study, avidin was used as a model protein to test the hPG’s ability in resisting the protein adsorption. Furthermore, avidin is known for its high noncovalent affinity with biotin with extremely large free association energy (Ka = 1013 M−1).36 One advantage of avidin−biotin complex is that avidin, a highly stable protein, can maintain its functional structure even under a variety of harsh conditions, such as high temperatures.37 Therefore, the avidin−biotin complex has been an important tool in many bioassays, biosensors, and purifications. In many applications, avidin is immobilized on a solid surface and then used for efficient immobilization or capture of biotinylated molecules via avidin’s extremely high biotin-binding affinity.37−39 Our hPG substrates provide a lowfouling platform and could be further conjugated with biotin molecules for the specific avidin binding. The adsorption of avidin−FITC on PPX-OH (324 ± 10 ng/ cm2) was decreased to ∼22 ng/cm2 on hPG1 and hPG3 (Figure 4), indicating that more than 90% of the protein adsorption is inhibited. When biotin molecules were conjugated onto the hPG−ene surfaces, the adsorption of avidin−FITC was increased to ∼55 ng/cm2 for hPG1−biotin and hPG3− biotin. The results show that surface biotin increases the immobilization of avidin−FITC via specific binding. We expect that the avidin binding could be further increased with increasing surface biotin concentrations. CVD deposition of PPX-OH provides a tool for the surface deposition of hPG for antifouling applications. In comparison with the previous studies that develop hPG layers on substrates containing nucleophilic groups, such as oxidized silicon,19

Figure 2. (A) Adhesion of L929 cells to PPX-OH, the PPX-OH subject to ring-opening reaction for 3, 6, 12, and 24 h, and the corresponding film thickness. *p < 0.001 vs PPX-OH. n = 4. (B) Percentage of inhibition of cell adhesion vs film thickness.

However, the film growth in this batch was not as good as the results in Table 1. Similarly, although the cell adhesion was decreased with the increasing incubation time, the extent of inhibition on cell adhesion (∼86%) on the 24 h sample (Figure 2A) was not as good as that shown in Figure 1A (97.5% for hPG1). We plotted the inhibition percentage versus the film thickness (Figure 2B) and found out that the inhibition percentage reaches a plateau after the film thickness reaches ∼20 nm (Figure 2B). A previous study showed that hPG layers with >5 nm in thickness completely reduced the adsorption of albumin, fibrinogen, and globulin.13 Another study shows that the hPG layers with 17 nm thickness inhibited at least 90% adhesion on silicon for two bacterial strains, Escherichia coli and Acinetobacter baylyi.13 In comparison with our results, an hPG film thicker than 20 nm has an excellent antifouling ability. Functionalization of the hPG Substrates for Specific Cell Adhesion and Protein Immobilization. In this study, the hPG film was further designed to incorporate functional groups for later conjugation of biomolecules. The hPG layer was developed with the addition of 1,2-epoxy-5-hexene, providing alkenyl groups for the thiol−ene reaction with thiols.30 RGDC or biotin−PEG−SH was conjugated on the hPG−ene surfaces to support specific cell adhesion or protein binding. 14660

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REFERENCES

(1) Ratner, B. D. The blood compatibility catastrophe. J. Biomed. Mater. Res. 1993, 27, 283−287. (2) Banerjee, I.; Pangule, R. C.; Kane, R. S. Antifouling Coatings: Recent Developments in the Design of Surfaces That Prevent Fouling by Proteins, Bacteria, and Marine Organisms. Adv. Mater. 2011, 23, 690−718. (3) Zhao, C.; Li, L.; Wang, Q.; Yu, Q.; Zheng, J. Effect of Film Thickness on the Antifouling Performance of Poly(hydroxy-functional methacrylates) Grafted Surfaces. Langmuir 2011, 27, 4906−4913. (4) Liu, Q.; Singh, A.; Lalani, R.; Liu, L. Ultralow Fouling Polyacrylamide on Gold Surfaces via Surface-Initiated Atom Transfer Radical Polymerization. Biomacromolecules 2012, 13, 1086−1092. (5) McArthur, S. L.; McLean, K. M.; Kingshott, P.; St John, H. A. W.; Chatelier, R. C.; Griesser, H. J. Effect of polysaccharide structure on protein adsorption. Colloids Surf., B 2000, 17, 37−48. (6) Kuo, W.-H.; Wang, M.-J.; Chang, C.-W.; Wei, T.-C.; Lai, J.-Y.; Tsai, W.-B.; Lee, C. Improvement of hemocompatibility on materials by photoimmobilization of poly(ethylene glycol). J. Mater. Chem. 2012, 22, 9991−9999. (7) Kuo, W.-H.; Wang, M.-J.; Chien, H.-W.; Wei, T.-C.; Lee, C.; Tsai, W.-B. Surface modification with poly(sulfobetaine methacrylate-coacrylic acid) to reduce fibrinogen adsorption, platelet adhesion, and plasma coagulation. Biomacromolecules 2011, 12, 4348−4356. (8) Jiang, S.; Cao, Z. Ultralow-fouling, functionalizable, and hydrolyzable zwitterionic materials and their derivatives for biological applications. Adv. Mater. 2010, 22, 920−932. (9) Moore, E.; Thissen, H.; Voelcker, N. H. Hyperbranched polyglycerols at the biointerface. Prog. Surf. Sci. 2013, 88, 213−236. (10) Kainthan, R. K.; Janzen, J.; Levin, E.; Devine, D. V.; Brooks, D. E. Biocompatibility testing of branched and linear polyglycidol. Biomacromolecules 2006, 7, 703−709. (11) Siegers, C.; Biesalski, M.; Haag, R. Self-assembled monolayers of dendritic polyglycerol derivatives on gold that resist the adsorption of proteins. Chem.Eur. J. 2004, 10, 2831−2838. (12) Sunder, A.; Mülhaupt, R.; Haag, R.; Frey, H. Hyperbranched polyether polyols: A modular approach to complex polymer architectures. Adv. Mater. 2000, 12, 235−239. (13) Weber, T.; Bechthold, M.; Winkler, T.; Dauselt, J.; Terfort, A. Direct grafting of anti-fouling polyglycerol layers to steel and other technically relevant materials. Colloids Surf., B 2013, 111, 360−366. (14) Vandenberg, E. J. Polymerization of glycidol and its derivatives: a new rearrangement polymerization. J. Polym. Sci., Polym. Chem. Ed. 1985, 23, 915−949. (15) Weinhart, M.; Becherer, T.; Schnurbusch, N.; Schwibbert, K.; Kunte, H.-J.; Haag, R. Linear and hyperbranched polyglycerol derivatives as excellent bioinert glass coating materials. Adv. Eng. Mater. 2011, 13, B501−B510. (16) Zill, A.; Rutz, A. L.; Kohman, R. E.; Alkilany, A. M.; Murphy, C. J.; Kong, H.; Zimmerman, S. C. Clickable polyglycerol hyperbranched polymers and their application to gold nanoparticles and acid-labile nanocarriers. Chem. Commun. 2011, 47, 1279−1281. (17) Lukowiak, M. C.; Wettmarshausen, S.; Hidde, G.; Landsberger, P.; Boenke, V.; Rodenacker, K.; Braun, U.; Friedrich, J. F.; Gorbushina, A. A.; Haag, R. Polyglycerol coated polypropylene surfaces for protein and bacteria resistance. Polym. Chem. 2015, 6, 1350−1359. (18) Pranantyo, D.; Xu, L. Q.; Neoh, K. G.; Kang, E.-T.; Teo, S. L.M. Antifouling coatings via tethering of hyperbranched polyglycerols on biomimetic anchors. Ind. Eng. Chem. Res. 2016, 55, 1890−1901. (19) Khan, M.; Huck, W. T. S. Hyperbranched polyglycidol on Si/ SiO2 surfaces via surface-initiated polymerization. Macromolecules 2003, 36, 5088−5093. (20) Weber, T.; Gies, Y.; Terfort, A. Bacteria-repulsive polyglycerol surfaces by grafting polymerization onto aminopropylated surfaces. Langmuir 2012, 28, 15916−15921. (21) Zhou, L.; Gao, C.; Xu, W. Robust Fe3O4/SiO2-Pt/Au/Pd magnetic nanocatalysts with multifunctional hyperbranched polyglycerol amplifiers. Langmuir 2010, 26, 11217−11225.

Figure 4. Adsorption of avidin−FITC to hPG substrates with or without the conjugation of biotin molecules. The samples for 1- or 3day ring-opening reaction are referred to as hPG1 and hPG3, respectively. −ene indicates that the surfaces contain alkenyl groups. *p < 0.01 vs the other surfaces, n = 4.

aminopropylsiloxane,20 and oxidized metals,13,21 our platform could be applied to other materials that do not possess surface nucleophilic functionality. Furthermore, PPX-OH does not need preactivation through deprotonation for the initiation of ring-opening reaction of glycidol. Our strategy could expand the substrate applicability of hPG coatings.

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CONCLUSIONS We demonstrated that hPG could be fabricated from PPX-OH substrates via the ring-opening reaction of glycidol. Because the CVD deposition of PPX-OH could be applied to most of the materials, our approach made it possible to decorate an antifouling hPG layer on most types of materials. The antifouling property of the hPG layer could reduce protein adsorption and cell adhesion. The addition of alkenyl groups in the hPG film allows the conjugation of biomolecules. In summary, the combination of CVD deposition and the growth of hPG provide a simple tool to fabricate a low-fouling surface on a wide range of substrates and could be applied to biosensor, diagnostics, and biomedical devices in the future.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +886-2-3366-3996. Fax: +886-2-2362-3040. ORCID

Hsien-Yeh Chen: 0000-0001-5956-6680 Wei-Bor Tsai: 0000-0002-2316-5751 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Ministry of Science and Technology of Taiwan for the financial support (grant number: 104-2221-E002-123). 14661

DOI: 10.1021/acs.langmuir.7b02826 Langmuir 2017, 33, 14657−14662

Article

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DOI: 10.1021/acs.langmuir.7b02826 Langmuir 2017, 33, 14657−14662