Swollen hydrogel pads were taken out of solution, excess solvent was carefully removed and the slide was sealed with a PDMS frame stuck to a quartz glass slide. The sealed slide was irradiated with the quartz glass slide pointing towards the light source. As UV source a UVA Cube 2000 (Dr. Hönle AG, Gilching, Germany) was used (11.45 mW cm -2 ). and with a regular frequence imaged by fluorescence microscopy on a Keyence BZ-X800 with a 2X magnification lense (Keyence Co., Ösaka, Japan) in the TRITC channel (Excitation 544 nm, Emission 570 nm) at 4 ms excitation time. The recorded images were segmented and analyzed to determine the fluorescence area and the integrated intensity of every single pad.