<p>The evaluation of biomaterial compatibility often relies on viability assays using tetrazolium salts, such as WST-8, to assess cytotoxicity. However, potential interference by bacterial nanocellulose (BNC) with these assays may compromise the accuracy of biocompatibility assessments. In this study, we examined the interference of BNC with tetrazolium salt-based viability assays by evaluating mesenchymal stem cells derived from adipose tissue (ASC) and dermal fibroblasts in contact with BNC. Our findings revealed significant interference of BNC with the hydrophilic tetrazolium salts WST-8 and WST-1, in contrast to the lipophilic MTT salt, which showed no such interference. Notably, the absorbance signal decreased by more than 50% when the BNC membrane was incubated with the supernatants of the blank solution compared with the conditions without BNC incubation. Critically, when BNC remained present during the reaction, absorbance-based viability values decreased by 78.71% (WST-8), 59.61% (WST-1), and 7.05% (MTT) compared to control wells where BNC was removed prior to the tetrazolium salt reaction. This study underscores the critical importance of accounting for possible interference in cytotoxicity assessments to ensure accurate biomaterial compatibility evaluations, thereby supporting the safe and effective application of these materials in biomedical contexts. </p> Graphical abstract <p></p>