Fiveeasy

Four amino acids (glycine, alanine, serine, and lysine) and three common reducing sugars (glucose, xylose, and galactose) were selected to construct the model TTIs. Solutions of amino acid and reducing sugar (both at 0.25 M) were combined and then mixed in a water bath (HH-4, Changzhou Aohua Instrument Co., Ltd., China) at 80 °C for 60 min. The absorbance of the solution at a wavelength of 420 nm,^{34,35 (link)} which reflects the major colored products of the Maillard reaction, was measured with a multimode reader (Infinite M200 Pro, Tecan, Switzerland) at 10 min intervals.
To determine the optimal concentration of materials for the model TTI, different concentrations of amino acids and reducing sugars were investigated. Then, quantitative amounts of the amino acid and reducing sugar were dissolved in a series of 0.2 M PBS with pH values of 6.0, 6.5, 7.0, 7.5 and 8.0 (FiveEasy, Mettler Toledo, America) to determine the optimal pH of the reaction solution. All the mixed solutions were placed in a water bath at 80 °C for 30 min, and the UV absorbance was measured at 6 min intervals.

The level of media acidification reached by the U2OS-GFP and U2OS-GFP-HK2 cell lines were monitored using a FiveEasy™ pH meter (Mettler Toledo). One million cells were seeded in regular media and allowed to attach for 6 h to the plate. Then, the cell culture media were replaced with fresh media and the pH of the cells’ supernatant measured 4 h later (n = 6).

The
viscosity was measured with a viscometer (DV2T, Brookfield, Middleboro,
MA, USA), surface tension was measured with a tensiometer (AquaPi,
Kibron, Helsinki, Finland), and electrical conductivity was measured
with a conductivity meter (FiveEasy, Mettler Toledo, Columbus, OH,
USA).