1. Good bugs, Bad bugs; Sol-gel Encapsulated Bacteria in Anti- Fouling and Anti-Corrosion Coatings Professor R. Akid & Dr H. Wang Centre for Corrosion Technology r.akid@shu.ac.uk Dr T. J. Smith Biomedical Research Centre t.j.smith@shu.ac.uk Sheffield Hallam University

2. What are the benefits of these coatings?

3. For industrialised countries the cost of Corrosion is currently around 3-4% GDP. This is estimated this at a cost of $140Bn Bridges, railroads Gas, Electricity distribution Road, air, sea Oil & gas, chemicals Defence Nuclear waste 1 Hurricane Katrina every year!

4. Costs of fouling 1994 – world shipping fleet burnt 184 Million tonnes of fuel oil. If no antifouling paints are used this fuel consumption is increased by 40% (= 72M tonnes of FO) Note in that year the North Sea oil platforms produced 100M tonnes of FO

5. Existing antifouling/corrosion strategies Use of inhibitors and biocides – Expensive – Often ineffective (location & concentration issues) – Can be damaging to the environment

6. Outline Sol-gel : Materials chemistry and anti-corrosion aspects (RA) Sol-gel : Microbiology and Antifouling aspects (TJS) Summary Acknowledgements

7. Gelation is the process of bond formation Evaporation Gelation GelSol Nanocomposite dense material Cure at T & t Formation of Sol-gel Materials What is sol-gel? A sol is a colloidal suspension of solid particles (1-1000nm size) in a liquid What is a gel? A gel is a substance that contains a continuous liquid phase What is gelation?

8. Sol gel chemistry Metal substrate Precursor Si (OC 2 H 5 ) 3 = Si-O-R ', where R ' = C 2 H 5 O R'-O-Si-O-R ' Si-O-R' Si O O Hydrolysis Condensation Tetraalkoxysilanes – (Methoxy or Ethoxy)

9. Bond Formation of the Sol-gel Coating Metal Sol-gel applied on Inner layer Outer layer -O-Si-O-R ' Si-O-R' Si O O O M O ─ Si O R M O O Sol gel Al interface Si particles

10. Opportunities for organic-inorganic hybrid sol-gel basic network structures 1. Modify the Si backbone 3. Modify silicon structure with functional organic groups (R) 2. Incorporate three- dimensional inorganic oxide network based on silicon or other metals ( M= Ti, Zr, or Al) 3. Encapsulated functional additives, e.g., bacteria, antibiotics, inhibitors M

11. Sol gel Application Methodology Cure at selected temperature Apply top coat directly to sol gel for anti-corrosion coating Use as functional/ barrier coating Colloid solution(s) Organic and Inorganic components Functional Additives e.g., corrosion inhibitors, bio-active molecules, etc. Mix and Age* *Ageing time dependant upon formulation chemistry Apply to metal; Dip, Spray..

12. Bioactive coating for anti-fouling and anti-microbial induced corrosion applications.

13. Background Fouling & Microbially-induced corrosion –Marine corrosion is exacerbated by the formation of destructive biofilms on metal surfaces –For example, sulfate-reducing bacteria (SRB) such as Desulfovibrio desulficurans forms H 2 S as a metabolic by product

14. Microbiologically Influenced Corrosion (MIC) (Bacteria & Biofilms) } Colonisation of Sulphate Reducing Bacteria (SRB) H 2 S formation Localised Corrosion (pitting) Microorganisms, especially bacteria, colonise surfaces to form Biofilms Biofilm formation; up to 48hrs depending upon temperature

15. Consequences of MIC

16. Current Approaches to mitigate Fouling & MIC Application of synthetic polymers/paints: some bacteria can use the coating as a hydrocarbon food source Controlled dosing with biocides: impacts upon the environment Changes in environmental conditions, e.g., remove water from fuels, oils etc. not often feasible Biocoat approach Bacteria can reduce corrosion Coating designed upon fundamental knowledge of corrosion and microbial ecology

17. Do protective bacteria exist and work? High Corrosion Rate Low Note: the bacterial strain(s) are added as planktonic bacteria (i.e., freely suspended)

18. Antifouling/MIC approach at SHU Combination of anti-corrosion sol-gel coating and protective bacteria. Uniform distribution of protective bacteria fixed on the surface Substrate 'Biocoat' Viable bacterial cells immobilised in coating

19. Paenibacillus polymyxa A bacterium that actually inhibits corrosion and biofouling often found in soil non-pathogenic Forms highly-resistant endospores in response to environmental stress Endospores remain inert until nutrients/germinants available Magnification x 1000 Paenibacillus polymyxa endospores

20. Viability of P. polymyxa endospores within sol-gel coating

21. Viability of P. polymyxa endospores within sol-gel coating on AA 2024 T3 Following immersion in artificial sea-water, germination occurs, forming microcolonies within the sol-gel microstructure Coating thickness ~10µm Akid R, Wang H, Smith T. J, Greenfield D, and Earthman, J. C, 2008, Advanced Functional Materials 18, 203-211 Magnification x 1000 Abiotic Biotic

22. Colonisation of cells within sol-gel coating Rods - Vegetative cells Solid discs - Endospores Immersion in nutrient broth for 1 hour

23. Immersion in nutrient broth for 8 hours

24. Spores in the coating remain viable There is an increase in the number of vegetative cells visible under fluorescence microscopy the longer the Al 2024 coupons are immersed in the nutrient broth This suggests a sustained ability of the spores to germinate under these conditions, and that enough nutrition is able to reach the spores in order to induce germination

25. Propagation of corrosion/biofouling bacteria from the coating It was possible to recover vegetative cells from the nutrient broth, following removal of the metal substrate This indicates the release of vegetative cells from the sol-gel coating that are the result of the germination of encapsulated spores

26. Bio-active coating - field trials