Dextran sodium sulfate dss

Dextran sulfate sodium (DSS; 40–50 kDa) was purchased from Affymetrix (Cleveland, OH). Occult bleeding was analyzed using the Hemoccult kit (Beckman Coulter, Mexico City, Mexico) according to the manufacturer's instructions. The following antibodies were used: anti-ZO-1, Alexa-labeled secondary antibodies (Thermo Fisher, Mexico City), and anti-E-cadherin (Santa Cruz Biotechnologies, Santa Cruz, CA).

All animal experiments were approved by the Animal Ethics Committee of the University of Tasmania (Ethics approval number: A13576) and conducted in accordance with the Australian Code of Practice for Care and Use of Animals for Scientific Purposes (8^th Edition 2013). Male C57BL/6 mice, (aged 8–10 weeks; 21–30 g, average ≈ 25 g), were obtained from the University of Tasmania animal breeding facility and housed in a temperature-controlled environment with a 12-hour day/night light cycle. Individual body weights were assessed daily over an initial acclimation period of 7 days. All mice were non-fasting and had access to food and autoclaved tap water for drinking ad libitum during experiment. Colitis was induced by feeding mice with 3% w/v dextran sulfate sodium (DSS, MW = 40000–50000, USB, Affymetrix Inc, Ohio, USA) dissolved in drinking water from day 1 to day 8. Control mice received water without DSS from day 1 to day 8.

Sprague Dawley (SD) rats (female, 8–12 weeks) weighing around 250 g were housed in groups of three rats per cage. SD rats were allowed unrestricted access to water and a standard laboratory diet before and after oral gavage. SD rats weighing around 250 g received 4.5% Dextran sodium sulfate (DSS, 40 kDa, Alfa Aesar) supplemented in the drinking water for 7 days to induce colitis, followed by normal water during the treatment. Healthy SD rats or DSS-induced colitic rats received a single oral gavage of 1.0 ml NPA₂ or NPA₃ coacervate (modified with a Cy7 tag, a near-infrared fluorescent dye). Briefly, an amine-NCO reaction between Cyanine 7 amine (0.2 mg, Lumiprobe) and polymerized PEG with terminated NCO groups (1 at Supplementary Method 1) was used to modify the hydrophilic PEG shell of NP nanoparticles with a Cy7 tag. Then SD rats were sacrificed after 0, 6, 24, or 48 h, and GI tracts were harvested to evaluate the fluorescence retention by an in vivo live imaging system IVIS200 (Xenogen) with an ICG filter channel to measure the fluorescent signal intensity.