Cracks in consolidants containing TiO2 as a habitat for biological colonization: A case of quaternary bioreceptivity

The recently proposed concept of quaternary bioreceptivity applies to substrates treated with coating materials and it is considered in the present study with the alga Bracteacoccus minor and the cyanobacterium Nostoc sp. onto granite specimens treated with ethyl silicate and nano-sized silica doped with different amounts of TiO2 (0, 0.5, 1 and 3 wt%). The findings showed a lack of correlation between the amount of TiO2 and the level of colonization (main bioreceptivity estimator) to the presence of cracks on the surface, which annul the biocidal power of TiO2. Crack formation, which depends on the mechanical properties, greatly influences the bioreceptivity of the material. Thus, the cracks provided anchor points where water is retained, in turn strongly influencing the early stages of colonization kinetics, to a greater extent than the biocidal power of TiO2, which will probably increase as the biofilm develops over the entire surface. In addition, although the cracks were more abundant and wider in the ethyl silicate-based consolidant, the nano-sized silica provided better anchoring points, making the material treated with the corresponding consolidant more bioreceptive.

Automated summary

The study found that the formation of cracks on granite specimens treated with TiO2 plays a crucial role in the level of colonization and bioreceptivity. Cracks act as anchor points for water retention, influencing the early stages of colonization kinetics more than the biocidal power of TiO2.