Scanning electron microscopy
Three inserts were, after treatment according to the instillation protocol described above, fixed using glutaraldehyde 2.5% (EM Grade 1.06 Polysciences). This was followed by incubation with increasing concentrations of ethanol. After incubation in 100% ethanol, critical point drying (CPD) was performed. The dry inserts where then sputtered with gold particles as final preparation for scanning electron microscopy. The same protocol was followed as Janssen et al. [9]