Langmuir 2007, 23, 4719-4723
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Highly Effective Contact Antimicrobial Surfaces via Polymer Surface Modifiers Pinar Kurt,† Lynn Wood,‡,§ Dennis E. Ohman,‡,§ and Kenneth J. Wynne*,† Department of Chemical and Life Science Engineering and Department of Microbiology and Immunology, Virginia Commonwealth UniVersity, Richmond, Virginia 23284, and McGuire Veterans Affairs Medical Center, Richmond, Virginia 23249 ReceiVed December 22, 2006. In Final Form: February 14, 2007 Contact antimicrobial coatings with poly(alkylammonium) compositions have been a subject of increasing interest in part because of the contribution of biocide release coatings to antibiotic resistance. Herein, a concept for antimicrobial coatings is developed on the basis of the thermodynamically driven surface concentration of soft block side chains. The concept incorporates structural and compositional guidance from naturally occurring antimicrobial proteins and achieves compositional economy via a polymer-surface modifier (PSM). To implement this concept, polyurethanes were prepared having random copolymer 1,3-propylene oxide soft blocks with alkylammonium and either trifluoroethoxy or PEGlyted side chains. Six carbon (C6) and twelve carbon (C12) alkylammonium chain lengths were used. The PSMs were first tested as 100% coatings and were highly effective against aerosol challenges of Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli). To evaluate the surface concentration, solutions containing 2 wt % PSM with a conventional polyurethane were evaporatively coated onto glass slides. These 2% PSM coatings were tested against aerosol challenges of Gram-negative (Pseudomonas aeruginosa and Escherichia coli) and Grampositive (Staphylococcus aureus) bacteria (107 CFU/mL/30 min). A copolymer soft block containing trifluorethoxy (89 mol %) and C-12 alkylammonium (11 mol %) side chains gave the highest biocidal effectiveness in 30 min: 2 wt %, Gram(() bacteria, 100% kill, and 3.6-4.4 log reduction. A zone of inhibition test showed no biocide release for PSMs and PSM-modified compositions. Characteristics that contribute to concept validation include good hard block/soft block phase separation, a cation/co-repeat group ratio mimicking natural biocidal proteins, a semifluorinated “chaperone” aiding in alkylammonium surface concentration, and a low Tg for the alkylammonium soft block.
Introduction Almost 30 years ago, Isquith demonstrated contact kill for glass surfaces functionalized with alkylammonium groups and a concomitant absence of the zone of inhibition characteristic of biocide release.1 Subsequently, many approaches to alkylammonium-based biocidal surface modification have demonstrated contact kill on glass, paper, and other substrates.2-5 The mechanism by which surfaces interact with pathogenic organisms for contact kill has been discussed extensively.2,5-7 For contact kill, analogies have been drawn to the cell wall disruption proposed for solution kill by polycations.8-11 However, * Corresponding author. E-mail:
[email protected]. Tel: +1 804 828 9303. Fax: +1 804 828 3846. † Department of Chemical and Life Science Engineering, Virginia Commonwealth University. ‡ Department of Microbiology and Immunology, Virginia Commonwealth University. § McGuire Veterans Affairs Medical Center. (1) Isquith, A. J.; McCollum, C. J. Appl. EnViron. Microbiol. 1978, 36, 700704. (2) Tiller, J. C.; Liao, C. J.; Lewis, K.; Klibanov, A. M. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 5981-5985. (3) Tiller, J. C.; Lee, S. B.; Lewis, K.; Klibanov, A. M. Biotechnol. Bioeng. 2002, 79, 465-471. (4) Lin, J.; Qiu, S. Y.; Lewis, K.; Klibanov, A. M. Biotechnol. Bioeng. 2003, 83, 168-172. (5) Lee, S. B.; Koepsel, R. R.; Morley, S. W.; Matyjaszewski, K.; Sun, Y. J.; Russell, A. J. Biomacromolecules 2004, 5, 877-882. (6) Grapski, J. A.; Cooper, S. L. Biomaterials 2001, 22, 2239-2246. (7) Lin, J.; Qiu, S. Y.; Lewis, K.; Klibanov, A. M. Biotechnol. Prog. 2002, 18, 1082-1086. (8) Chen, C. Z. S.; Beck-Tan, N. C.; Dhurjati, P.; van Dyk, T. K.; LaRossa, R. A.; Cooper, S. L. Biomacromolecules 2000, 1, 473-480. (9) Tew, G. N.; Liu, D. H.; Chen, B.; Doerksen, R. J.; Kaplan, J.; Carroll, P. J.; Klein, M. L.; DeGrado, W. F. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 51105114. (10) Kuroda, K.; DeGrado, W. F. J. Am. Chem. Soc. 2005, 127, 4128-4129. (11) Ishitsuka, Y.; Arnt, L.; Majewski, J.; Frey, S.; Ratajczek, M.; Kjaer, K.; Tew, G. N.; Lee, K. Y. C. J. Am. Chem. Soc. 2006, 128, 13123-13129.
elucidating a more detailed mechanism for rapid contact kill at the bacterium-solid surface interface remains an important research goal. To achieve this goal, continued development of methodology for surfaces with better defined properties such as charge density, wetting behavior, and adhesive properties is necessary. The need for advances in contact kill coatings is clear in that the buildup of resistance to antibiotics and even biocides is a growing problem.5,12,13 For example, the release of silver (Ag+) for controlling pathogens has been known for centuries.14 Continued interest in wound dressings containing silver arises from advances in formulations utilizing polymeric materials, the accessibility of silver compounds, and the increased prevalence of bacterial resistance to antibiotics.14-16 However, some bacterial strains are inherently resistant to silver17 and some develop resistance,14,15 but it is unclear whether this situation is as serious as the buildup of antibiotic resistance. Whereas surface modification has been an active area, developing easily utilized coatings that provide contact biocidal function has seen less attention. Alkylammonium modification of a polyurethane hard block was addressed by Cooper.6 Prior to testing, these hard-block-substituted polyurethanes were subjected to a hydration preconditioning step. The coatings were effective against Staphylococcus aureus but ineffective against Escherichia coli. Recently, Klibanov has reported alkylammo(12) Giamarellou, H. Expert ReV. Anti-Infect. Ther. 2006, 4, 601-618. (13) Spelman, D. W. Med. J. Aust. 2002, 176, 286-291. (14) Silver, S.; Phung, L. T.; Silver, G. J. Ind. Microbiol. Biotechnol. 2006, 33, 627-634. (15) Silver, S. FEMS Microbiol. ReV. 2003, 27, 341-53. (16) Grunlan, J. C.; Choi, J. K.; Lin, A. Biomacromolecules 2005, 6, 11491153. (17) Johnson, J. R.; Delavari, P.; Azar, M. Antimicrob. Agents Chemother. 1999, 43, 2990-2995.
10.1021/la063718m CCC: $37.00 © 2007 American Chemical Society Published on Web 03/28/2007
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Figure 1. Polymer surface modifier (PSM) concept where A and B are complementary side chains that generate an amphiphilic, biomimetic soft block.
nium coatings based on polyethylene imine (PEI).18 This commercially available water-soluble polymer has primary, secondary, and tertiary amines. PEI and a four-component PEI copolymer were alkylated and then dip coated onto substrates. Optimum compositions were highly effective against both Gram(+) and Gram(-) bacteria. Coatings of quarternized polystyrene-b-poly(4-vinylpyridine) copolymers were recently reported.19 Alkylammonium pyridinium groups were generated with 1-bromohexane and 6-perfluorooctyl-1-bromohexane, CF3(CF2)7(CH2)6-Br. The fluorinated block copolymers were found to be more effective in decreasing the viability of airborne S. aureus than N-hexylpyridinium counterparts. Unlike these block copolymers, the semifluorinated side chains employed in the PSMs reported below do not bear a charge. In this article, a new approach to polyalkylammonium contact kill is described that draws partly from past research on surface properties generated by novel copolymeric oxetane soft blocks.20,21 The antimicrobial coatings reported herein are based on polyurethane polymer surface modifiers (PSMs). Ideally, a PSM provides a surface property identical to that of the neat PSM film. PSM function has been limited mostly to the modification of wetting behavior.22-25 However, polydimethylsiloxane PSMs increase biodurability,22,26 and hydantoin PSMs display oxidative biocidal function27 as expected on the basis of the pioneering work of Worley.28 The alkylammonium antimicrobial PSM strategy (Figure 1) has the following features: (1) leverages the surface concentration of soft blocks in polyurethanes;29-32 (18) Milovic, N. M.; Wang, J.; Lewis, K.; Klibanov, A. M. Biotechnol. Bioeng. 2005, 90, 715-722. (19) Krishnan, S.; Ward, R. J.; Hexemer, A.; Sohn, K. E.; Lee, K. L.; Angert, E. R.; Fischer, D. A.; Kramer, E. J.; Ober, C. K. Langmuir 2006, 22, 1125511266. (20) Fujiwara, T.; Makal, U.; Wynne, K. J. Macromolecules 2003, 36, 93839389. (21) Makal, U.; Uilk, J.; Kurt, P.; Cooke, R. S.; Wynne, K. J. Polymer 2005, 46, 2522-2530. (22) Ward, R. S.; White, K. A.; Hu, C. B. Prog. Biomed. Eng. 1984, 1, 181200. (23) Santerre, J. P. U.S. Patent 6,127,507, 1998. (24) Malik, A. A.; Carlson, R. P. U.S. Patent 5,637,772, 1997. (25) Thomas, R. R.; Ji, Q.; Kim, Y. S.; Lee, J. S.; McGrath, J. E. Polyurethane 2000 Polymer DiVision Abstracts, 2000. (26) Bernacca, G. M.; Gulbransen, M. J.; Wilkinson, R.; Wheatley, D. J. Biomaterials 1998, 19, 1151-1165. (27) Makal, U.; Wood, L.; Ohman, D. E.; Wynne, K. J. Biomaterials 2006, 27, 1316-1326. (28) Sun, G.; Allen, L. C.; Luckie, E. P.; Wheatley, W. B.; Worley, S. D. Ind. Eng. Chem. Res. 1995, 34, 4106-4109. (29) Garrett, J. T.; Runt, J.; Lin, J. S. Macromolecules 2000, 33, 6353-6359. (30) Garrett, J. T.; Siedlecki, C. A.; Runt, J. Macromolecules 2001, 34, 70667070. (31) Ratner, B. D.; Cooper, S. L.; Castner, D. G.; Grasel, T. G. J. Biomed. Mater. Res. 1990, 24, 605-620. (32) Tingey, K. G.; Andrade, J. D. Langmuir 1991, 7, 2471-2478.
Letters
Figure 2. Structure of co-telechelics, where R ) CF3CH2O-(3FOx), CH3O(CH2CH2O)2-(ME2Ox) and p ) 5 (C6) or 11 (C12); x and y are defined in Figure 3.
(2) focuses on copolymer soft blocks with A and B repeat units that generate a synergistic, functional pair (e.g., when the A repeat unit acts as a “chaperone” to surface-concentrate B groups27); (3) aims at achieving compositional economy by using the AB-soft block polyurethane as a minor PSM constituent in a blend such that PSM defines the surface properties and the matrix polymer defines the bulk mechanical properties and adhesion to the substrate; and (4) adopts a biomimetic, amphiphilic polycation approach that takes compositional guidance from the ratio of charged to uncharged groups in naturally occurring antimicrobials such as magainins and defensins.33,34 In some sense, the approach seeks to adapt successful research on water-soluble polycationic35 and polymer biomimetics9,10 to PSMs. The PSM strategy provides considerable flexibility in exploring compositional and processing options and, as will be seen, avoids difficulties such as complex surface modification procedures that cannot easily be scaled up, water-swelling for hard-blockmodified coatings,6 biocidal polymer dissolution,18 and limited scope of application for alkylammonium-modified silicones.36 To implement our approach, new alkylammonium polyoxetane telechelics with repeat units shown in Figure 2 were prepared. A brief description of the two-step process is provided in the next paragraph, and details are reported separately.37 The mole fraction of alkylammonium side chains was guided by the mole fractions of charged side chains for magainins (∼0.2) and defensins (∼0.3).33,34 A somewhat lower ratio of A/B side chains (∼0.13) was chosen for the initial work on co-polyoxetane soft blocks described herein. 3-Methyl-3-bromo-butoxy methyl oxetane (BBOx)38 provided a convenient alkyl halide side chain for quarternization. In the first step, BBOx-containing co-telechelics were prepared via cationic ring opening polymerization39 using known oxetane monomers 3FOx39 and ME2Ox.20 The two monomers are added to BF3/butane diol cocatalysts in methylene chloride at 0 °C. After 15 h, the reaction mixture is washed with water and the telechelic is precipitated as a viscous oil from water/methanol. The designation for the co-telechelic intermediates is typified by P[(3FOx)(BBOx)0.89:0.11], where P indicates polymerized, ringopened oxetane structures followed by the respective repeat unit mole fractions. By 1H NMR spectroscopy, the repeat-unit mole fractions for P[(3FOx)(BBOx)]x:y and P[(ME2Ox)(BBOx)]x:y intermediates closely match feed ratios. The trifluoroethoxy side (33) Gesell, J.; Zasloff, M.; Opella, S. J. J. Biomol. NMR 1997, 9, 127-35. (34) Wu, Z.; Ericksen, B.; Tucker, K.; Lubkowski, J.; Lu, W. J. Pept. Res. 2004, 64, 118-125. (35) Ikeda, T. High Perform. Biomater. 1991, 743-64. (36) Hazzizalaskar, J.; Helary, G.; Sauvet, G. J. Appl. Polym. Sci. 1995, 58, 77-84. (37) Kurt, P.; Duan, B.; Wynne, K. J. To be submitted for publication, 2007. (38) Kawakami, Y.; Takahashi, K.; Hibino, H. Macromolecules 1991, 24, 4531-4537. (39) Malik, A. A.; Archibald, T. G. U.S. Patent 5,703,194, 1995.
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Figure 3. New polyurethanes with alkylammonium-functionalized soft blocks.
chain was chosen to avoid environmental concerns about higher perfluorinated moieties, particularly perfluorooctanoate or “PFOA” derivatives that bioaccumulate.40,41 In the second step, alkylammonium co-telechelics were generated by nucleophilic substitution (overnight, 70 °C, acetonitrile, 100% substitution) using either C6 or C12 dimethylamines. End-group analysis20 for both BBOx and alkylammonium co-telechelics gave number-average molecular weights in the range of 6-8 kg/mol, a convenient range for soft blocks. Co-telechelic polyurethanes shown in Figure 3 were prepared conventionally by a soft-block-first method.42 4,4′-(Methylene bis(p-cyclohexyl isocyanate), H12MDI, and 1,4-butanediol, BD, were used for the hard block. Details of the synthesis procedures and 1H NMR spectroscopic analysis are reported separately.37 Interestingly, modulated differential scanning calorimetry (MDSC) showed that the low Tg for P[(3FOx)(BBOx)]0.89:0.11 (-48 °C) is retained in the alkylammonium co-telechelic P[(3FOx)(C12)]0.89:0.11 (-47 °C) and the soft block (-44 °C) in P(3FOx)(C12)0.89:0.11-PU. A similar result was found for the C6 telechelic and polyurethane. Whereas both P[(ME2Ox)(C6)]0.86:0.14 (-50 °C) and P[(ME2Ox)(C12)]0.86:0.14 (-59 °C) have low Tg values, the corresponding soft-block Tg values are about 30 °C higher, indicating some phase mixing of hard and soft blocks. Two sets of coatings were prepared by spreading THF/IPA solutions on microscope slides followed by solvent removal at ambient temperature and then at 50 °C in a vacuum oven. Set 1 was 100% alkylammonium polyurethanes. This set mimics a postprocessing spray of undiluted alkylammonium soft-block polyurethanes. Set 2 was generated by spread-coating as above from a solution of alkylammonium polyurethane (2 wt %) and 98 wt % conventional or base polyurethane. The latter is a 50 wt % hard block/poly(tetramethylene oxide) soft block (1000 (40) Martin, J. W.; Whittle, D. M.; Muir, D. C. G.; Mabury, S. A. EnViron. Sci. Technol. 2004, 38, 5379-5385. (41) Harada, K.; Koizumi, A.; Saito, N.; Inoue, K.; Yoshinaga, T.; Date, C.; Fujii, S.; Hachiya, N.; Hirosawa, I.; Koda, S.; Kusaka, Y.; Murata, K.; Omae, K.; Shimbo, S.; Takenaka, K.; Takeshita, T.; Todoriki, H.; Wada, Y.; Watanabe, T.; Ikeda, M. Chemosphere 2007, 66, 293-301. (42) Grasel, T. G.; Cooper, S. L. Biomaterials 1986, 7, 315-328.
Figure 4. ATR-IR spectra of base PU (A), 100% P[(3FOx)(C12) 0.89:0.11]-PU (B), and 2% P[(3FOx)(C12) 0.89:0.11]-PU/ 98% base PU (C) films. C-F stretching bands on PSM and 2% PSM modified PU are shown.
kg/mol) composition prepared in-house and designated HMDIBD(50)/PTMO-1000. Designations such as 2%P(3FOx)(C12)0.89: 0.11-PU are used for the second set. Set 2 tests PSM surface concentration effectiveness as per Figure 1. A control coating was prepared from the base polyurethane alone. Set 1. An investigation of surface morphology (TM-AFM) and wetting behavior is underway for the alkylammonium polyurethane coatings, all of which are optically transparent. Herein contact angles are equilibrium sessile drop measurements. Average values are reported (two samples, four drop sites each). The two ME2Ox polyurethanes are determined to be hydrophilic by Rame´-Hart sessile drop contact angle analysis (C6, θ ≈ 70°; C12, θ ≈ 57°), an unexpected order that needs further investigation but provides evidence for soft block surface concentration. Interestingly, the two 3FOx alkylammonium polyurethanes are also modestly hydrophilic (C6, θ ≈ 80°; C12, θ ≈ 87°). Hydrophobic wetting behavior for polyurethanes containing only a P(3FOx) soft block (advancing contact angle >100°) was
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Table 1. Results from Aerosol Spray Testing for Coatings Prepared from 2% PSMs (Column 1) and 98% HMDI/BD(50)-PTMO(1000) Escherichia coli (G-)
Pseudomonas aeruginosa (G-)
Staphylococcus aureus (G+)
2 wt % PSM designation
kill (%)
log red.
kill (%)
log red.
kill (%)
log red.
P[(ME2Ox)(C6)]0.86:0.14-PU P[(ME2Ox)(C12)]0.86:0.14-PU P[(3FOx)(C6)]0.89:0.11-PU P[(3FOx)(C12)]0.89:0.11-PU
61.1 100.0 97.7 100.0
0.41 4.30 1.65 4.38
59.0 100.0 98.5 100.0
0.39 4.28 1.83 4.33
65.0 98.7 98.7 100.0
0.46 1.90 1.88 3.57
previously reported.43 Physical surface studies including XPS are underway. A biocidal test was devised to simulate aerosol deposition (cough, sneeze) of pathogenic bacteria. With a sprayer designed to deliver a controlled volume, a challenge of Pseudomonas aeruginosa (107 CFU/mL) was delivered to the surface of 100% alkylammonium polyurethanes coatings, and the slides were placed in a constant humidity (85-95%) environment, a step that differentiates this procedure from a previously used protocol.18 Constant humidity is important because control experiments in ambient air showed irreproducible fractions of dead bacteria as a function of time. This step anticipates future studies estimating kill kinetics. After 30 min, the slides were placed in saline solution and vortex stirred for 2 min. One hundred microliter aliquots and (×10) dilutions were removed and spread onto agar plates that were incubated at 37 °C for 18 h. Live bacteria (cfu’s) on plates were counted to obtain the percent kill and log reduction. We chose a 30 min residence time because unless complete kill was achieved in this time our biomimetic/soft block approach would be neither interesting nor practical. Strikingly, all alkylammonium polyurethanes (set 1, Figure 3) showed very effective biocidal activity against P. aeruginosa with no surviving colony forming units (cfu) and 100% kill (4.6 log reduction) with the exception of P[(ME2Ox)(C6)]-PU which gave 1 cfu out of four plates resulting in 99.8% kill (2.62 log reduction). After this initial test, the same coatings were challenged again after rinsing with DI water. The biocidal activity was duplicated in this second challenge (up to 4.6 log reduction). Set 1 coatings showed high biocidal activity against E. coli as well, resulting in 100% kill (4.6 log reduction) with the exception of 1 cfu on one of four P[(ME2Ox)(C6)]-PU coatings. These results indicate a successful design strategy for contact biocidal activity. Compared to polyurethanes with alkyl ammonium groups incorporated into the hard block,6 the alkylammonium-soft block polyurethane compositions shown in Figure 3 did not require any pretreatment, absorbed little moisture, and were highly effective against Gram(-) E. coli. The coatings were also highly effective against Gram(-) P. aeruginosa. The enhanced biocidal activity is ascribed to surface-concentrated PSM soft blocks that are surface concentrated by a combination of differing hard block/ soft block solubility parameters and entropic effects resulting from a multiplicity of side chains that act as pseudochain ends.44 Set 2. Coatings containing 2 wt % PSMs were investigated by ATR-IR spectroscopy (Figure 4). The 1270 cm-1 C-F absorption for P(3FOx)(C12)0.89:0.11-PU occurs in a window for the base polyurethane. The ATR-IR spectrum of 2%P(3FOx)(C12)0.89:0.11-PU shows C-F stretching at 1270 cm-1, providing evidence for PSM surface enrichment. A C-F absorption at 1180 cm-1 is also present in the 2%P(3FOx)(C12)0.89:0.11-PU. 2%ME2Ox alkylammonium PSMs did not have a distinguishing (43) Makal, U.; Fujiwara, T.; Cooke, R. S.; Wynne, K. J. Langmuir 2005, 21, 10749-10755. (44) Jalbert, C.; Koberstein, J. T.; Hariharan, A.; Kumar, S. K. Macromolecules 1997, 30, 4481-4490.
band to assess surface concentration compared to that of bulk HMDI-BD(50)/PTMO-1000. Thus far, sessile drop wetting behavior has not provided evidence of surface concentration for 2 wt % PSM compositions. Contact angles for the base polyurethane (∼83°) are similar to those for 2%3FOx alkylammonium polyurethanes, whereas the wetting behavior of 2%ME2Ox alkylammonium compositions is complex and requires more study. The biocidal activity of the 2%PU-PSM coatings was tested against aerosol sprays of Gram(-) P. aeruginosa and E. coli and Gram(+) S. aureus (107 CFU/mL/30 min) as described above. The results in Table 1 show that (unlike the “pure” PSMs) biocidal effectiveness varies considerably. The trends are similar for Gram(+) and Gram(-) bacteria strains. P[(3FOx)(C6)]0.89:0.11-PU (2%) is the most effective antimicrobial PSM, yielding a 3.64.4 log reduction in Gram(+)/Gram(-) bacteria in 30 min. A representative set of plates for control polyurethane and 2%P[(3FOx)(C6)]0.89:0.11-PU is shown in Figure 5. Comparing the C6 and C12 series (Table 1), longer alkyl chains (C12) showed better biocidal activity than shorter chains (C6), which parallels solution studies.45,46 The significant difference between 2%P(ME2Ox)(C6)0.86:0.14-PU and 2%P[(3FOx)(C6)]0.89:0.11-PU indicates that with the processing conditions employed, PEG-like side chains are less effective than P(3FOx) in PSM surface concentration. The trifluoroethoxymethyl side chain is clearly a chaperone that surface concentrates the shorter alkylammonium C6 chain. The difference between C6 and C12 PSMs with PEG-like methoxyethoxyethoxy side chains is interesting and indicates some combination of the longer C12 alkylammonium self-chaperoning/self-concentrating along with the higher biocidal activity of C12. All coatings were tested for the zone of inhibition (ZOI) by two different modified ASTM methods. ZOI tests gave no evidence of any biocidal leaching from the coatings, indicating that bacterial kill occurred only via surface contact.
Conclusions The four-component PSM strategy delineated above provided the highly effective antimicrobial polyurethanes shown in Figure
Figure 5. Images of agar plates for control PU (left) and 2%P[(3FOx)(C12) 0.89:0.11]-PU (right) samples after the aerosol challenge with E. coli.
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3. Paralleling naturally occurring biocides,33,34 the ratio of charged to uncharged groups was set at 0.11-0.14. The alkylammonium polyurethanes had almost indistinguishable 100% effectiveness against aerosol challenges of Gram(-) bacteria with a residence time of 30 min. However, 2%PSM antimicrobial performance was differentiated, with 2%P[(3FOx)(C12)]0.89:0.11-PU showing excellent biocidal activity against Gram(-) P. aeruginosa and E. coli and Gram(+) S. aureus. These results set the stage for systematic studies of structure-property relationships. In
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this preliminary study, several variables were fixed that can be easily altered, including exposure time, weight percent of PSM, and mole fraction charged groups. Changing the mole fraction of alkylammonium groups will give control over surface charge density, an important factor in antimicrobial contact kill.47 Acknowledgment. We are grateful for support from the National Science Foundation Division of Materials Research (P.K. and K.J.W., DMR 0207560). LA063718M
(45) Kanazawa, A.; Ikeda, T.; Endo, T. Kobunshi 1994, 43, 237. (46) Kim, C. H.; Choi, K. S. J. Ind. Eng. Chem. (Seoul, Repub. Korea) 2002, 8, 71-76.
(47) Kuegler, R.; Bouloussa, O.; Rondelez, F. Microbiology (Reading, UK) 2005, 151, 1341-1348.
