Bakker, Dewi Pascal

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   University of GroningenBacterial adhesion to modified polyurethanesBakker, Dewi PascalIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2004Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Bakker, D. P. (2004). Bacterial adhesion to modified polyurethanes. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 08-06-2022     Chapter 8    General Discussion                Chapter 8 137 In general, there are two ways to solve the problem of a fouling surface, discriminated by the moment of intervention in the process of adhesion. First of all, it is possible to interfere with the actual adhesion process by discouraging the fouling organisms to adhere by offering unfavorable conditions for adhesion. The second solution is removal of adhered bacteria from a fouled surface after adhesion has occurred.   In the past years, many investigations in the medical field, food and marine industry have focussed on the development of non-stick surfaces within the limitations dictated by each application, resulting in different priorities. One can imagine that toxicity is not allowed in the medical field, whereas costs are more restrictive in the development of a marine coating. Resistance of bacteria against antibiotics and bacteriocides urges investigation of other ways to protect implanted biomaterials from infection. In food industry, addition of biocides to keep processing units clean is mostly excluded. Recently, the International Marine Organization tightened the rules for application of toxic compounds in the marine environment. As an alternative, cuprous oxides (also toxic) and non-stick coatings are applied on high-speed ferries or vessels that navigate a lot (i.e. of which the hull is subject to high shear). Summarizing, there is a need of non-emissive coatings discouraging bacterial adhesion and growth, which have a great variety of applications.     This thesis evaluates modified polyurethanes for use as non-fouling surfaces in the medical and marine environment. Experiments have been confined to initial adhesion, and are largely based on adhesion in a model system, i.e. a flow chamber. We will now subsequently discuss the methodology used, the selection of bacterial strains for evaluation, detrimental effects of bacterial biofilms, and future perspective for non-stick coatings.    METHODOLOGY  The flow chamber proved to be a valuable tool to measure affinity of a bacterium for a substratum (1), as an implanted biomaterial or ship hull does not allow real time and in situ observation. Many investigations showed that bacteria adhere to every possible surface, regardless of the physicochemical properties it possesses, when exposed to a bacterial suspension. In this thesis, as well, we did not find a great reduction in the final density of bacteria adhering on any of the polyurethane surfaces tested. Initial deposition rates are a   138 measure for the affinity and the results are therefor valuable both with regard to the prevention of adhesion as well as to an easier cleansing of the surfaces. This ‘cleansing event’ can be the blinking of the eye over a contact lens or a period of navigation for a ship at a high speed releasing the fouling that occasionally adhered. These cleaning forces have been analyzed for small particles and as a result of a laminar fluid flow, two forces work (14) on an adhered microorganism, viz. a lift force and a drag force. On the limit for laminar flow in the stagnation point and in the parallel plate flow chamber, the force exerted by the flow is not enough to detach an adhering bacterium. Turbulent flow or the passages of air bubbles over a coating will however, more efficiently clean the surface (7), so future research should also focus at detachment under above-mentioned conditions. For this purpose, it is necessary to adapt the flow chambers.   THE SELECTION OF BACTERIAL STRAINS FOR EVALUATION  For both the marine and the medical evaluation of the polyurethanes, the selected bacterial strains were considered representatives of fouling bacteria, covering a range of hydrophobicities. The real situation is, however, a complex and well-balanced system comprising a multitude of microbial species. Adding to the complexity of the system, are the human immune system in the medical environment and the great variety of strains colonizing a biomaterial.   In the marine environment, ships navigate through water with greatly varying conditions and microbial populations.  Twelve well-defined zones were defined in the oceans of the world that vary in salinity, clarity, temperature and nutrients, and the type and numbers of native fouling organisms are different in each of these zones (4). The intention of the thesis was not to determine fouling rates in the natural environment, but the selected strains were used as model organisms in order to understand the effect of a change in physicochemical properties of the substrata offered.   Chapter 8 139 DETRIMENTAL EFFECTS OF BACTERIAL BIOFILMS  In the medical environment bacterial adhesion on a surface has in general a detrimental effect on its function, as these biofilms possess increased resistance against bacteriocides and the human immune system and are therefor related with increased risk to infections. Adhering bacteria are metabolically active and can easily adapt to altered conditions. Therefor they can present a surface with different physicochemical surface promoting specific or a-specific adhesion of other organisms. In the oral cavity, it was shown that some bacterial strains co-adhere and adhesion of one strain promotes adhesion of the co-adhering strain (9). In the marine environment, microbial biofilms promote corrosion due to penetration of a coating and thereby strongly reduce its protective effects. Furthermore metabolites excreted by adhering bacteria tend to accelerate the corrosive process. In Fig. 1 the end-stage of biofilm formation in the marine environment is presented. Submersed in seawater for prolonged periods of time, solid substrata are most likely to possess a biofilm comprising diatoms, protozoa and microalgae, seaweed and marine invertebrates of which the barnacles are causing most serious problems. Among the cues for settlement are also factors influenced by the conditioning film and the marine microbial biofilm (13).   Figure 1. A marine biofilm causing corrosion.   140 Investigations on the exact role of the biofilm, however, showed that bacteria may be a source of positive and negative cues for barnacles, because the cyprid stage of the barnacle is able to respond to both inhibitory and stimulatory compounds on the surface (10).   FUTURE PERSPECTIVE FOR NON-STICK COATINGS   Most non-stick materials based on physicochemical surface properties are either fluorinated or silicone coatings. In general, the fluorinated coatings are tough, highly hydrophobic and resist fouling, but in time a tight bond to the coating is formed possibly due to a conditioning film. Most non-stick coatings need a mild ‘cleansing event’ to remove the biofilm. For the fluorinated coatings, a high shear force can be applied without damage to the coating. This is in contrast to silicone coatings, which are relatively soft, weak and easily damaged. Silicone coatings are a bit less hydrophobic than fluoropolymers and foul therefor more rapidly and consequently tighter bonds are formed. A flexible coating like the silicone coating deforms when a hydrodynamic force acts on an adhered organism and is peeled away from the surface, which requires a smaller force than in case of the shear as with the fluorinated coatings, as shown schematically in Fig. 2.                 Figure 2. Hydrodynamic forces resulting in a peel and a shear force on an adhering bacterium on the elastic surface, whereas on the stiff surface shear force dominates. elastic surface stiff surface peel shearshearChapter 8 141 Different research now focuses on the application of polyurethanes, which combine various properties for optimization. They allow independent modification of hydrophobicity and elastic modulus and therefor a tough hydrophobic elastomeric coating can be made, which tolerates no more than a weak, easily failing joint (5). Some recent developments in marine anti-fouling coatings are based on mimicking natural phenomena like the skin of a whale and the surface of some red algae, which stay clean under continuous fouling pressure. It is of importance to learn from nature and for example, try to find functional biocides or enzymes for application in coatings (2) as a zymogel which keeps the skin of a pilot whale clean. Other strategies that are recently investigated are the application of nano- (3,8) or micro-structures (6), silicone oil or a layer of air covering the hull (which also lowers hydrodynamic resistance). Some of these strategies or combinations of strategies can also be used in or originate from medical applications and mutual exchange of ideas can be very fruitful.   This thesis shows that there are many complicating environmental factors in the development of a non-stick surface, which starts with the formation of a conditioning film. It is concluded that physicochemical interactions do play an important role in adhesion and may be used to weaken the bond between a bacterium and the surface. Considering the variety and multitude of mechanisms that bacterial species utilize to adhere, it is realistic that there will always be an exceptional strain that is able to adhere. Therefore we have to conclude that synthetic non-stick surfaces most probably do not exist and the ultimate goal of a non-stick surface that can be achieved will therefor be to facilitate cleansing. The coatings can be of help in the different methods that have been suggested to remove fouling, which range from ordinary brush cleaning to removal of bacteria by application of electric fields (12), passage of air bubbles (7) and ultrasound (11). A more appropriate term for antifouling coatings based on physicochemical properties would therefore be ‘easy-to-clean surface’.      142 REFERENCES   1.  Bakker, D. P., A. van der Plaats, G. J. Verkerke, H. J. Busscher, and H. C. van der Mei. 2003. A comparison of velocity profiles in different flow chamber designs used in studies of microbial adhesion to surfaces. Appl. Environ. Microbiol. 69:6280-6287.  2.  Baum, C., W. Meyer, D. Roessner, D. Siebers, and L.-G. Fleischer. 2001. A zymogel enhances the self-cleaning abilities of the skin of a pilot whale (Globicephala melas). Comp. Biochem. Physiol. A. 130:835-847.  3.  Baum, C., W. Meyer, R. Stelzer, and L.-G. Fleischer. 2002. Average nanorough skin surface of the pilot whale (Globicephal melas, Deplhinidae): considerations on the self-cleaning abilities based on nanoroughness. Marine Biol. 140:653-657.  4.  Brady Jr., R. F., and I. L. Singer. 2000. Mechanical factors favoring release from fouling release coatings. Biofouling 15:73-81.  5.  Brady, R. F., and C. L. Aronson. 2003. Elastomeric fluorinated polyurethane coatings for nontoxic fouling control. Biofouling 19:59-62.  6.  George, R. P., P. Muraleedharan, K. R. Sreekumari, and H. S. Khatak. 2003. Influence of surface characteristics and microstructure on adhesion of bacterial cells onto a type 304 stainless steel. Biofouling 19:1-8.  7.  Gomez-Suarez, C., H. J. Busscher, and H. C. van der Mei. 2001. Analysis of bacterial detachment from substratum surfaces by the passage of air liquid interfaces. Appl. Environ. Microbiol. 67:2531-2537.  8.  Kaper, H., H. J. Busscher, and W. Norde. 2002. Characterization of poly(ethylene oxide) brushes on glass surface and adhesion of Staphylococcus epidermidis. Biomater. Sci. Polymer Edn. 14:313-324.  9.  Kolenbrander, P. E. 2000. Oral microbial communities: biofilms, interactions, and genetic systems. Annu. Rev. Microbiol. 54:413-437.  10.  Maki, J. S., D. Rittschof, M.-O. Samuelsson, U. Szewzyk, A. B. Yule, S. Kjelleberg, J. D. Costlow, and R. Mitchell. 1990. Effect of marine bacteria and their exopolymers on the attachment of barnacle cypris larvae. Bull. Mar. Sci. 46:499-511.  11.  Oulahal-Lagsir, N., A. Martial-Gros, E. Boistier, L. J. Blum, and M. Bonneau. 2000. The development of an ultrasonic apparatus for the noninvasive and repeatable removal of fouling in food processing equipment. Lett. Appl. Microbiol. 30:47-52. Chapter 8 143  12.  Poortinga, A. T., J. Smit, H. C. van der Mei, and H. J. Busscher. 2001. Electric field induced desorption of bacteria from a conditioning film covered substratum. Biotechnol. Bioeng. 76:395-399.  13.  Rodriguez, S. R., C. Riquelme, E. O. Campos, P. Chavez, E. Brandan, and N. C. Inestrosa. 1995. Behavioral responses of Choncholepas conchelepas (Bruguière, 1789) larvae to natural and artificial settlement cues and microbial films. Biol. Bull. 189:272-279.  14.  Ryan, J. N., and M. Elimelech. 1996. Colloid mobilization and transport in groundwater. Coll. Surf. A 107:1-56.       

Bacterial adhesion to modified polyurethanes

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Bacterial adhesion to modified polyurethanes

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