2.8. Inulin-FITC Leakage Assay

Paracellular permeability was quantified by inulin-FITC (0.1 mg.mL⁻¹ in PBS or medium) perfusion of bioengineered intestinal tubules. This was done as described before [11]. In short, bioengineered intestinal tubules were washed with PBS and perfused with inulin-FITC for 10 min at a speed rate of 0.1 mL/min. Samples were taken from the chamber to assess inulin-FITC leakage by absorbance at excitation wavelength of 480–492 nm and emission wavelength of 518–520 nm using a multimode plate reader (Promega, Leiden, The Netherlands). Results are shown relative to positive control, unexposed bioengineered intestinal tubules. Bioengineered intestinal tubules were extracted from the 3D-chamber and cut in pieces and used for cell viability and alkaline phosphatase activity.