TJP1 and neoplasm: Consistent with decreased ZO‐1 expression in conditions with co‐culture of tumor spheroids, our ODSEI chips showed that co‐culture of tumor spheroids exhibited an average permeability of 7.5 (± 2.2) × 10−5 cm s−1, which is 7.5‐fold higher than that of the mono‐culture endothelium at 1.0 (± 0.4) × 10−5 cm s−1 (Figure S7, Supporting Information).