Number of sam to be on SCFA, BCFA, ammonia The procedure described in Example 8 results in 3 x 3 (experiments in triplicate) x 5 (sample time points) x 2 (types of samples - lumen and dialysate) (90) samples in total (lumen and dialysate), analyzed on SCFA, BCFA, and ammonia. Metabolites The dialysate and lumen fractions of TIM-2 were analyzed with gas chromatography for SCFA, (butyrate, acetate, and propionate) and BCFA (iso-butyric acid and iso-valeric acid). In addition, the samples were analyzed enzymatically for ammonia. The SCFA, BCFA and ammonia values from t=0h were used to set the values of these metabolites in the TIM-2 system artificially to zero. Results are expressed as cumulative production over time. For SCFA/BCFA, samples were prepared and analysed. Briefly, samples were centrifuged (12,000 rpm at 4 ° C for 10 min). A mixture of formic acid (20%), methanol, and 2-ethyl butyric acid (internal standard, 2 mg/ml in methanol) was added to the supernatant. Samples were measured by gas-chromatography. A 3 pi sample with a split ratio of 75.0 was injected on a GC-column (ZB-5FIT inferno, ID 0.52 mm, film thickness 0.1 0 urn; Zebron; phenomenex, USA) in a Shimadzu GC-2014 gas chromatograph. Standard curves were obtained by injecting calibrated quantities of a blend of volatile fatty acids (the measured SCFA and BCFA) and amounts were calculated from the graph obtained correlating peak height and time measured (all reagents from Sigma-Aldrich with the exception of formic acid which was from Merck). Samples for ammonia analysis were centrifuged as described above. Ammonia was determined based on the Berthelot reaction in which ammonia first reacts with alkaline phenol and then with sodium hypochlorite to form indophenol blue. In the currently used method phenol was replaced by salicylic acid. The absorbance of the indophenol blue is directly proportional to the original ammonia concentration and is measured at 660 nm. The measurement is automated on a Cobas Mira plus auto analyzer (Roche, Almere, The Netherlands). Concentrations in the samples was determined via comparison with a series of standard solutions with known concentrations.