Fig. 23
![Fig. 23](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40494-021-00599-w/MediaObjects/40494_2021_599_Fig23_HTML.jpg)
Micrographs (×5 objective lens) of a M2-G mock-up before (BC) and after (AC) cleaning with PU sponge indicate moderate soiling removal in some areas, but an overall satisfactory rating of 4 on soiling removal efficiency
Micrographs (×5 objective lens) of a M2-G mock-up before (BC) and after (AC) cleaning with PU sponge indicate moderate soiling removal in some areas, but an overall satisfactory rating of 4 on soiling removal efficiency