Fungal growth setup
TPM has a special home built biological growth setup available, as shown in figure 3. This setup contains 100 samples which can be monitored simultaneously. The setup consists of an air flow over a water bath which saturates the air, and is subsequently cooled to a temperature to condense a certain amount of air to obtain the required relative humidity at the testing temperature. The fungal growth is monitored by a camera positioned above the glass plate covering the gypsum sample. The setup can switch between a high humidity range of 80%-100% and low air humidity range of 0-30%. By comparing the pictures with the initial picture at the start of the experiment for each color of the RGB palette the growth can be characterized. Additionally, from this RGB palette the average value (the grey value) was calculated. The results, indicating the amount of fungal growth, were evaluated by fitting the color change (y) using a reparameterized logistic model as recommended by Adan[1],[2]:
in which a is the upper asymptotic value of y, d the time coordinate of the inflection point and e the first derivative with respect to time in the inflection point. a represents the estimated final coverage area; e can be considered a measure for the growth rate in the exponential stage.
Using this setup it is possible to obtain a deeper analysis of the growth of organisms on materials and allows different humidity and drying conditions to be simulated. As a results of this a deeper understanding of the influence of wetting and drying cycles on growth of organisms can be investigated. Furthermore, in principle by visualizing the early growth on materials, faster testing is to be expected. Additionally the effect of biocides can be visualized. [3]
[1] O.C.G. Adan, “On the fungal defacement of interior finishes”, PhD thesis, Eindhoven University of Technology, the Netherlands (1994).
[2] O.C.G. Adan, R.A. Samson (Eds.), “Fundamentals of mold growth in indoor environments and strategies for healthy living”, Wageningen Academic Publishers (2011).
[3] J. Eversdijk, S.J.F. Erich, et al., “Development and evaluation of a biocide release system for prolonged antifungal activity in finishing materials”, progress in organic coatings (2011)