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Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates
Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Q1 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates Ruijie Guo b,n, Guangda Yin a,b, Xiaojuan Sha a,b, Liqiao Wei a,b, Qi Zhao c a Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024, China b College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China c Division of Mechanical Engineering and Mechatronics, University of Dundee, Dundee, DD1 4HN, UK
art ic l e i nf o
a b s t r a c t
Article history: Received 8 September 2013 Accepted 25 December 2014
Coupling agent 3-amino propyl triethoxy silane (γ-APTS) was facilely grafted onto silicon rubber through UV irradiation to form the self-assembly monolayer (SAM). N atoms with lone pairs of electrons in the coupling agent then anchored the silver atoms during electroless plating and produced antibacterial coatings with remarkably improved adhesion to substrates. The grafting of coupling agent was verified by X-ray photoelectron spectroscopy (XPS), the coatings adhesion was tested according to ASTM D 335902 and their antibacterial activity was characterized by inhibition halo test. The composition of the composite coatings was investigated by energy dispersive X-ray spectrometer (EDS). The surface morphology was revealed by Atom Force microscopy (AFM). The results showed that the adhesion of Ag-PTFE coatings with strong and stable antibacterial activity was tremendously improved to silicon rubber substrates. & 2015 Published by Elsevier B.V.
Keywords: Adhesion Biomaterials Thin films Surface
1. Introduction Indwelling devices such as urinary catheters are frequently used in clinical applications and an increased risk of infection is associated with the implantation. Bacterial adhesion and the formation of biofilm on implanted biomedical devices often lead to device-related infections, which are extremely resistant to antibiotics and host defences and are frequently persist until the implant are removed [1]. The hardly removable biofilm is a source and center of further infection [2]. For example, catheter-associated urinary tract infection (CAUTI) results in nosocomial infection with significant morbidity and mortality [3]. In addition to the significant human suffering, the medical complications caused by catheter-related infections are leading to substantial economic losses. So, even though catheters are prerequisite in many cases, their clinical applications are limited. To solve such a problem, one of the effective ways is to modify the catheter surface to endow it superior antibacterial activity. It has long been agreed that silver has inherent antibacterial property [4], and the Ag coatings deposited on catheter surface could serve as an antibacterial layer to minimize infection. As for the Ag coating technology, electroless deposition is a
n
Corresponding author. Tel: þ 86 13835189092. E-mail address: [email protected] (R. Guo).
cost-effective alternative since no special equipment is required compared with other possible routes. Catheters are mainly made of polymer, and silicon rubber is one of the most commonly used materials as it has superior biocompatibility and long-time durability even in the presence of aqueous solution. The silicon rubber has low surface energy and is lack of reactive groups, so it is difficult to bond with polar surface which is necessary in fields requiring high adhesion such as coatings. The inertness often connects the applications of silicon rubber to the risk of adhesion failure. That is, the Ag coatings electrolessly deposited on it are readily peeled off. However, it is well known that polymer surface can be modified to improve the adhesion between two materials [5]. The modification ways include mechanical roughening, wet chemical treatment, flame, corona, plasma and UV radiation treatment. UV treatments offer advantages over the other techniques since they have distinct superiority such as fast reaction rate, low cost of processing, simple equipment and easy industrialization. Our purpose is to introduce surface functionalities by UV irradiation onto the polymer to enhance adhesion strength. Pretreatment of polymer with UV irradiation can yield hydroxyl [7], peroxide and hydroperoxide groups on the substrates [6], providing the surface with more reactive sites. Then coupling agent 3-amino propyl triethoxy silane (γ-APTS, (CH3O)3SiCH2CH2CH2NH2) reacts with reactive function groups on the pretreated silicon rubber and form self-assembly
http://dx.doi.org/10.1016/j.matlet.2014.12.125 0167-577X/& 2015 Published by Elsevier B.V.
Please cite this article as: Guo R, et al. Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2014.12.125i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
R. Guo et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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120,000
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C/S
C1s N 1s
O 2s
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Binding Energy (e/V) Fig. 1. XPS survey spectra of (A) silicon rubber substrates and (B) substrates after grafting of coupling agent γ-APTS. The N1s peak in (B) was amplified and shown in (C).
Fig. 2. EDS analysis of Ag-PTFE composite coatings deposited on silicon rubber substrates (A), and EDS mapping for F (B) and N (C).
monolayer (SAM), producing an active surface with free –NH2 attached to substrates. During the subsequent electroless deposition process, the exposed –NH2 end group with nitrogen lone pairs of electrons would “anchor” Ag þ which has unoccupied molecular orbital, and thus Ag coatings are covalently bonded onto substrates with dramatically enhanced adhesion strength. In this contribution, we report the preparation of Ag-PTFE antibacterial composite coatings. The incorporation of PTFE nanoparticles into Ag coatings, as has been demonstrated before [8,9], could endow the as-resulted coatings with remarkable bacterial resistance. In order to improve the adhesion of Ag-PTFE coating to
silicon rubber substrates, we at first time attempted to modify the substrates before electroless plating Ag-PTFE.
2. Materials and methods 2.1. Materials: All the chemical reagents were analytically pure and used as received. γ-APTS (98.0%) and PTFE emulsion (60%) with particle size in the range of 0.05–0.5 μm were obtained from Aldrich. Silver nitrate (AgNO3, 99.8%), glucose (C6H12O6, 99%) and xylose (C4H6O6, 99%) were purchased from Tianjin Delan Fine
Please cite this article as: Guo R, et al. Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2014.12.125i
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Fig. 3. Photograph of coatings surface: (A) on un-modified silicon rubber, (B) on modified silicon rubber, (C) on modified silicon rubber after the immerging test, (D) after the tape test, (E) on un-modified silicon rubber after the immerging test, (F) on polyurethane and (G) on modified polypropylene.
Fig. 4. AFM images of sample: (A) untreated substrates and (B) UV-irradiated substrates.
Chemical Factory. Acetone (C3H6O, 99.5%), ammonia solution (NH3 H2O, 25%), KH2PO4, Na2HPO4, NaCl and KCl were supplied by Tianjin Chemical Reagent Co. Inc. Silicon rubber was provided by Jinan Chensheng Medical Silicone Rubber Product Co. Ltd. 2.2 Surface modification of silicon rubber: The silicon rubber sheets with dimension of 10 mm 10 mm 0.5 mm were chosen as substrates and cleaned before modification. UV irradiation was employed to activate the inert silicon rubber surface. The cleaned silicon rubber sheets were put in the UV irradiation chamber with UV wavelength of 272 nm and subjected to UV treatment from both sides for 20 min, followed by the immersion of the treated sheets into γ-APTS solution for 1 h. The γ-APTS solution was a mixture of 10 ml of γ-APTS and 100 ml of alcohol. Then the sheets were taken out of the solution and washed successively with
acetone, alcohol and deionized water to remove the adsorbed coupling agent molecules completely. The samples were at last dried in ambient conditions. 2.3 Electroless plating of Ag-PTFE antibacterial composite coatings: The detailed procedure for the electroless plating of Ag-PTFE coatings was described before [8]. 2.4 Characterization: X-ray photoelectron spectroscopy (XPS) was used to analyze the surface composition and chemical states by a PHI 1600 ESCA System. Spectra were produced with an Al anode at 250 W. The adhesion was evaluated by a tape test according to ASTM D 3359-02 standard [10]. Scanning electron microscopy (SEM) was carried out on a FEI-quanta-200 F equipped with energy dispersive X-ray spectrometer (EDS). The acceleration voltage was 30 kV. Antibacterial behavior was characterized by the
Please cite this article as: Guo R, et al. Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2014.12.125i
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R. Guo et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Fig. 5. Inhibition halo tests against (A) S. aureus and (B) E. Coli.
inhibition halo test toward two bacterial, Gram negative (Escherichia Coli) and Gram positive (Staphylococcus aureus) in accordance to standards of the National Committee for Clinical Laboratory (NCCLS) [11]. For the life time study, the samples were immersed in 0.01 M phosphate-buffered saline (PBS) and maintained at a constant temperature of 37 1C for 28 days.
3. Results and discussions 3.1 Coating characterization: The surface analysis before and after grafting of coupling agent was carried out by XPS (Fig. 1). The silicon rubber substrate exhibited intense peaks of O 1 s, C 1 s and Si 2p (Fig. 1A). Nitrogen peak at around 400 eV was also detected, as shown in Fig. 1B and C. This peak was attributed to coupling agent γ-APTS and provided evidence of γ-APTS grafting onto the modified silicon rubber surface (Fig. 1B, C). The EDS analysis of the Ag-PTFE coatings confirmed the presence of Ag, F, Si, C and O (Fig. 2) which revealed the coexistence of both PTFE and Ag. Due to the EDS volume resolution, N attributed to coupling agent γ-APTS was also detected and presented further testimony of the grafting of γ-APTS onto substrates surface. The EDS mapping showed that F element was distributed uniformly, indicating the uniform distribution of PTFE nanoparticles within the coatings (Fig. 2B). The presence of N element in the mapping coincided with the EDS elemental analysis result and was also distributed uniformly (Fig. 2C). 3.2 Adhesion characterization: It could be concluded from Fig. 3 that coatings on modified substrates (Fig. 3B) presented well adhesion to the polymer. For silicon rubber without modification, the coatings had flaked along the edges and on parts of the squares, and the adhesion was rated 2B (Fig. 3A). After modified, the coating displayed remarkably improved adhesion. Small flakes of the coating were detached at intersection, which less than 5% of the area was affected and the adhesion could be rated 4B (Fig. 3B). It seemed that the UV irradiation and the followed coupling agent γ-APTS grafting could dramatically improve the adhesion of the coatings to polymer substrates. The life time of coatings were also studied. Catheterization time for urinary catheter is usually for a period of 1–28 days. We have evaluated the durability of the coatings by immerging tests and standard tape test. The coatings were put into PBS for 28 days and then dried. No obvious damage on the coatings on modified substrates was observed (Fig. 3C), and the tape test results indicated that coatings on modified substrates presented well adhesion to the polymer substrate (Fig. 3D). Coatings on unmodified substrates exhibited flakes (Fig. 3E). The effect of surface morphology of substrate on coating adhesion was investigated. It is believed that the surface roughness help
strengthen adhesion. Fig. 4 reveals the roughness of silicon rubber surface before (Fig. 4A) and after (Fig. 4B) UV irradiation, and an increased roughness value (RMS) from 734 nm to 843 nm for the scan size utilized (25 25 μm2) is observed, which is attributed to the UV ablation. The rougher surface provides an increasing contact area, which benefits the adhesion improvement. The same effect of UV irradiation and coupling agent graft on adhesion strength is also obtained on substrates polyurethane and polypropylene (Fig. 3F and G). It shows that this modification strategy works well on other polymer substrates besides silicon rubber. Both the surface morphology changes and the increased surface activity contributed to adhesion strengthen. 3.3 Antibacterial activity: Inhibition halo test results towards Staphylococcus aureus and Escherichia Coli were shown in Fig. 4 and clear inhibition zones were observed around the as-resulted composite Ag-PTFE coatings. The coatings showed a 2 mm width halo towards S. aureus and 3 mm width halo towards E. Coli, respectively. These results verified that the coatings possessed satisfied antibacterial activity Fig. 5.
4. Conclusion Being modified by UV irradiation and grafting of coupling agent containing N atom, the silicon rubber substrates provided reactive surface for the chemical bond formation between Ag þ in the electroless plating solution and nitrogen with lone pairs of electrons bonded in substrates, leading to the remarkably improved adhesion of Ag-PTFE coatings to substrates. With superior adhesion to substrates and satisfied antibacterial activity, the composite Ag-PTFE coatings will undoubtedly find great applications in the field of health care. The modification and preparation methods are simple, facile and cost-efficient, having cheerful prospect for industrialization accordingly.
Acknowledgments The authors acknowledge the financial support of the Program of International Science and Technology cooperation (2011DFA90830) and the National Natural Science Foundation of China (No. 21306124).
References [1] Schierholz JM, Beuth J. Implat infections: a haven for opportunistic bacteria. J Hosp Infect 2001;49:87–93. [2] Leone M, Garnier F, Avidan M, Martin C. Catheter-associated urinary tract infections in intensive care unites. Microbes Infect 2004;6:1026–32.
Please cite this article as: Guo R, et al. Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2014.12.125i
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[3] Balagna C, Perero S, Ferraris S, Miola M, Fucale G, Manfredotti C, et al. Antibacterial coating on polymer for space application. Mater Chem Phys 2012;135:714–22. [4] Sawada I, Fachrul R, Ito T, Ohmukai Y, Maruyama T, Matsuyama H. Development of a hydrophilic polymer membrane containing silver nanoparticles with both organic antifouling and antibacterial properties. J Membr Sci 2012;387388:1–6. [5] Gray JE, Norton PR, Griffiths K. Mechanism of adhesion of electrolessdeposited silver on poly(ether urethane). Thin Solid Films 2005;484:196–207. [6] Deng J, Wang L, Liu L, Yang W. Developments and new applications of UVinduced surface graft polymerizations. Prog Polym Sci 2009;34:156–93.
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[7] Wu Z, Tong W, Jiang W, Liu X, Wang Y, Chen H. Poly(N-ninylpyrrolidone) -modified poly(dimethylsiloxane) elastomers as anti-biofouling materials. Colloid Surf B: Biointerfaces 2012;96:37–43. [8] Zhao Q, Liu Y, Wang C. Development and evaluation of electroless Ag-PTFE composite coatings with anti-microbial and anti-corrosion properties. Appl Surf Sci 2005;252:1620–7. [9] Zhao Q. Effect of surface free energy of graded Ni-P-PTFE coatings on bacterial adhesion. Surf Coat Technol 2004;185:199–204. [10] ASTM D3359-02. Standard test methods for measuring adhesion by tape test. [11] NCCLS M2-A9. Performance standard for antimicrobial disk susceptibility tests. Approved Standard, 9th ed., 2006.
Please cite this article as: Guo R, et al. Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2014.12.125i
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Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates Ruijie Guo b,n, Guangda Yin a,b, Xiaojuan Sha a,b, Liqiao Wei a,b, Qi Zhao c a Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024, China b College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China c Division of Mechanical Engineering and Mechatronics, University of Dundee, Dundee, DD1 4HN, UK
art ic l e i nf o
a b s t r a c t
Article history: Received 8 September 2013 Accepted 25 December 2014
Coupling agent 3-amino propyl triethoxy silane (γ-APTS) was facilely grafted onto silicon rubber through UV irradiation to form the self-assembly monolayer (SAM). N atoms with lone pairs of electrons in the coupling agent then anchored the silver atoms during electroless plating and produced antibacterial coatings with remarkably improved adhesion to substrates. The grafting of coupling agent was verified by X-ray photoelectron spectroscopy (XPS), the coatings adhesion was tested according to ASTM D 335902 and their antibacterial activity was characterized by inhibition halo test. The composition of the composite coatings was investigated by energy dispersive X-ray spectrometer (EDS). The surface morphology was revealed by Atom Force microscopy (AFM). The results showed that the adhesion of Ag-PTFE coatings with strong and stable antibacterial activity was tremendously improved to silicon rubber substrates. & 2015 Published by Elsevier B.V.
Keywords: Adhesion Biomaterials Thin films Surface
1. Introduction Indwelling devices such as urinary catheters are frequently used in clinical applications and an increased risk of infection is associated with the implantation. Bacterial adhesion and the formation of biofilm on implanted biomedical devices often lead to device-related infections, which are extremely resistant to antibiotics and host defences and are frequently persist until the implant are removed [1]. The hardly removable biofilm is a source and center of further infection [2]. For example, catheter-associated urinary tract infection (CAUTI) results in nosocomial infection with significant morbidity and mortality [3]. In addition to the significant human suffering, the medical complications caused by catheter-related infections are leading to substantial economic losses. So, even though catheters are prerequisite in many cases, their clinical applications are limited. To solve such a problem, one of the effective ways is to modify the catheter surface to endow it superior antibacterial activity. It has long been agreed that silver has inherent antibacterial property [4], and the Ag coatings deposited on catheter surface could serve as an antibacterial layer to minimize infection. As for the Ag coating technology, electroless deposition is a
n
Corresponding author. Tel: þ 86 13835189092. E-mail address: [email protected] (R. Guo).
cost-effective alternative since no special equipment is required compared with other possible routes. Catheters are mainly made of polymer, and silicon rubber is one of the most commonly used materials as it has superior biocompatibility and long-time durability even in the presence of aqueous solution. The silicon rubber has low surface energy and is lack of reactive groups, so it is difficult to bond with polar surface which is necessary in fields requiring high adhesion such as coatings. The inertness often connects the applications of silicon rubber to the risk of adhesion failure. That is, the Ag coatings electrolessly deposited on it are readily peeled off. However, it is well known that polymer surface can be modified to improve the adhesion between two materials [5]. The modification ways include mechanical roughening, wet chemical treatment, flame, corona, plasma and UV radiation treatment. UV treatments offer advantages over the other techniques since they have distinct superiority such as fast reaction rate, low cost of processing, simple equipment and easy industrialization. Our purpose is to introduce surface functionalities by UV irradiation onto the polymer to enhance adhesion strength. Pretreatment of polymer with UV irradiation can yield hydroxyl [7], peroxide and hydroperoxide groups on the substrates [6], providing the surface with more reactive sites. Then coupling agent 3-amino propyl triethoxy silane (γ-APTS, (CH3O)3SiCH2CH2CH2NH2) reacts with reactive function groups on the pretreated silicon rubber and form self-assembly
http://dx.doi.org/10.1016/j.matlet.2014.12.125 0167-577X/& 2015 Published by Elsevier B.V.
Please cite this article as: Guo R, et al. Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2014.12.125i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
R. Guo et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
120,000
Si 2s Si 2p
C/S
C1s N 1s
O 2s
20,000
60,000 40,000
O 2s
40,000
O KLL
C 1s
80,000
Si 2s Si 2p
60,000
100,000
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80,000
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O 1s
120,000
100,000
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Binding Energy (e/V) Fig. 1. XPS survey spectra of (A) silicon rubber substrates and (B) substrates after grafting of coupling agent γ-APTS. The N1s peak in (B) was amplified and shown in (C).
Fig. 2. EDS analysis of Ag-PTFE composite coatings deposited on silicon rubber substrates (A), and EDS mapping for F (B) and N (C).
monolayer (SAM), producing an active surface with free –NH2 attached to substrates. During the subsequent electroless deposition process, the exposed –NH2 end group with nitrogen lone pairs of electrons would “anchor” Ag þ which has unoccupied molecular orbital, and thus Ag coatings are covalently bonded onto substrates with dramatically enhanced adhesion strength. In this contribution, we report the preparation of Ag-PTFE antibacterial composite coatings. The incorporation of PTFE nanoparticles into Ag coatings, as has been demonstrated before [8,9], could endow the as-resulted coatings with remarkable bacterial resistance. In order to improve the adhesion of Ag-PTFE coating to
silicon rubber substrates, we at first time attempted to modify the substrates before electroless plating Ag-PTFE.
2. Materials and methods 2.1. Materials: All the chemical reagents were analytically pure and used as received. γ-APTS (98.0%) and PTFE emulsion (60%) with particle size in the range of 0.05–0.5 μm were obtained from Aldrich. Silver nitrate (AgNO3, 99.8%), glucose (C6H12O6, 99%) and xylose (C4H6O6, 99%) were purchased from Tianjin Delan Fine
Please cite this article as: Guo R, et al. Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2014.12.125i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
R. Guo et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Fig. 3. Photograph of coatings surface: (A) on un-modified silicon rubber, (B) on modified silicon rubber, (C) on modified silicon rubber after the immerging test, (D) after the tape test, (E) on un-modified silicon rubber after the immerging test, (F) on polyurethane and (G) on modified polypropylene.
Fig. 4. AFM images of sample: (A) untreated substrates and (B) UV-irradiated substrates.
Chemical Factory. Acetone (C3H6O, 99.5%), ammonia solution (NH3 H2O, 25%), KH2PO4, Na2HPO4, NaCl and KCl were supplied by Tianjin Chemical Reagent Co. Inc. Silicon rubber was provided by Jinan Chensheng Medical Silicone Rubber Product Co. Ltd. 2.2 Surface modification of silicon rubber: The silicon rubber sheets with dimension of 10 mm 10 mm 0.5 mm were chosen as substrates and cleaned before modification. UV irradiation was employed to activate the inert silicon rubber surface. The cleaned silicon rubber sheets were put in the UV irradiation chamber with UV wavelength of 272 nm and subjected to UV treatment from both sides for 20 min, followed by the immersion of the treated sheets into γ-APTS solution for 1 h. The γ-APTS solution was a mixture of 10 ml of γ-APTS and 100 ml of alcohol. Then the sheets were taken out of the solution and washed successively with
acetone, alcohol and deionized water to remove the adsorbed coupling agent molecules completely. The samples were at last dried in ambient conditions. 2.3 Electroless plating of Ag-PTFE antibacterial composite coatings: The detailed procedure for the electroless plating of Ag-PTFE coatings was described before [8]. 2.4 Characterization: X-ray photoelectron spectroscopy (XPS) was used to analyze the surface composition and chemical states by a PHI 1600 ESCA System. Spectra were produced with an Al anode at 250 W. The adhesion was evaluated by a tape test according to ASTM D 3359-02 standard [10]. Scanning electron microscopy (SEM) was carried out on a FEI-quanta-200 F equipped with energy dispersive X-ray spectrometer (EDS). The acceleration voltage was 30 kV. Antibacterial behavior was characterized by the
Please cite this article as: Guo R, et al. Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2014.12.125i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
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Fig. 5. Inhibition halo tests against (A) S. aureus and (B) E. Coli.
inhibition halo test toward two bacterial, Gram negative (Escherichia Coli) and Gram positive (Staphylococcus aureus) in accordance to standards of the National Committee for Clinical Laboratory (NCCLS) [11]. For the life time study, the samples were immersed in 0.01 M phosphate-buffered saline (PBS) and maintained at a constant temperature of 37 1C for 28 days.
3. Results and discussions 3.1 Coating characterization: The surface analysis before and after grafting of coupling agent was carried out by XPS (Fig. 1). The silicon rubber substrate exhibited intense peaks of O 1 s, C 1 s and Si 2p (Fig. 1A). Nitrogen peak at around 400 eV was also detected, as shown in Fig. 1B and C. This peak was attributed to coupling agent γ-APTS and provided evidence of γ-APTS grafting onto the modified silicon rubber surface (Fig. 1B, C). The EDS analysis of the Ag-PTFE coatings confirmed the presence of Ag, F, Si, C and O (Fig. 2) which revealed the coexistence of both PTFE and Ag. Due to the EDS volume resolution, N attributed to coupling agent γ-APTS was also detected and presented further testimony of the grafting of γ-APTS onto substrates surface. The EDS mapping showed that F element was distributed uniformly, indicating the uniform distribution of PTFE nanoparticles within the coatings (Fig. 2B). The presence of N element in the mapping coincided with the EDS elemental analysis result and was also distributed uniformly (Fig. 2C). 3.2 Adhesion characterization: It could be concluded from Fig. 3 that coatings on modified substrates (Fig. 3B) presented well adhesion to the polymer. For silicon rubber without modification, the coatings had flaked along the edges and on parts of the squares, and the adhesion was rated 2B (Fig. 3A). After modified, the coating displayed remarkably improved adhesion. Small flakes of the coating were detached at intersection, which less than 5% of the area was affected and the adhesion could be rated 4B (Fig. 3B). It seemed that the UV irradiation and the followed coupling agent γ-APTS grafting could dramatically improve the adhesion of the coatings to polymer substrates. The life time of coatings were also studied. Catheterization time for urinary catheter is usually for a period of 1–28 days. We have evaluated the durability of the coatings by immerging tests and standard tape test. The coatings were put into PBS for 28 days and then dried. No obvious damage on the coatings on modified substrates was observed (Fig. 3C), and the tape test results indicated that coatings on modified substrates presented well adhesion to the polymer substrate (Fig. 3D). Coatings on unmodified substrates exhibited flakes (Fig. 3E). The effect of surface morphology of substrate on coating adhesion was investigated. It is believed that the surface roughness help
strengthen adhesion. Fig. 4 reveals the roughness of silicon rubber surface before (Fig. 4A) and after (Fig. 4B) UV irradiation, and an increased roughness value (RMS) from 734 nm to 843 nm for the scan size utilized (25 25 μm2) is observed, which is attributed to the UV ablation. The rougher surface provides an increasing contact area, which benefits the adhesion improvement. The same effect of UV irradiation and coupling agent graft on adhesion strength is also obtained on substrates polyurethane and polypropylene (Fig. 3F and G). It shows that this modification strategy works well on other polymer substrates besides silicon rubber. Both the surface morphology changes and the increased surface activity contributed to adhesion strengthen. 3.3 Antibacterial activity: Inhibition halo test results towards Staphylococcus aureus and Escherichia Coli were shown in Fig. 4 and clear inhibition zones were observed around the as-resulted composite Ag-PTFE coatings. The coatings showed a 2 mm width halo towards S. aureus and 3 mm width halo towards E. Coli, respectively. These results verified that the coatings possessed satisfied antibacterial activity Fig. 5.
4. Conclusion Being modified by UV irradiation and grafting of coupling agent containing N atom, the silicon rubber substrates provided reactive surface for the chemical bond formation between Ag þ in the electroless plating solution and nitrogen with lone pairs of electrons bonded in substrates, leading to the remarkably improved adhesion of Ag-PTFE coatings to substrates. With superior adhesion to substrates and satisfied antibacterial activity, the composite Ag-PTFE coatings will undoubtedly find great applications in the field of health care. The modification and preparation methods are simple, facile and cost-efficient, having cheerful prospect for industrialization accordingly.
Acknowledgments The authors acknowledge the financial support of the Program of International Science and Technology cooperation (2011DFA90830) and the National Natural Science Foundation of China (No. 21306124).
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Please cite this article as: Guo R, et al. Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2014.12.125i
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Please cite this article as: Guo R, et al. Effect of surface modification on the adhesion enhancement of electrolessly deposited Ag-PTFE antibacterial composite coatings to polymer substrates. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2014.12.125i
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