Figure 1.

Fouling materials classified on the basis of modulus. Estimated values of modulus for: soft fouling materials such as bacterial biofilm on a catheter tube [30–32] (obtained from CDC Public Health Image Library under public domain) and marine algae adhered to a ship hull [33], along with hard fouling materials like barnacles [34] (image reproduced with permission from [35], licensed under https://creativecommons.org/licenses/by/4.0/), clathrates in petroleum pipelines [36] (image reproduced from www.usgs.gov under public domain), ice on a wind turbine blade [37] reproduced from [38] (with licence under https://creativecommons.org/licenses/by-nc-sa/3.0/) and inorganic scale deposited in a pipe carrying cooling water (licensed under https://creativecommons.org/licenses/by-sa/3.0/deed.en).