Effect of hydrogels on cell viability.
During the study of new drug formulations, polymeric scaffolds, or devices for biomedical applications, safety profiles are essential before their use in living cells and organisms (Rawal, 2019; Sudarsan, 2016). Using biocompatible materials is relevant for safe systems design, but it does not guarantee the absence of toxicity. Factors such as the presence of toxic reagents, even in small quantities, could induce some level of cytotoxicity (Ali, 2018). That is why, an in vitro viability assay is mandatory in this kind of studies.
HEp-2 cells viability in the presence of the four hydrogels was evaluated by MTT (Figure 6 ). The viability of the control cells (CC), incubated without hydrogels, was set as the 100% value. Incubation with Triton X-100 (1% v/v), a non-ionic surfactant that induces cell lysis, was used as cytotoxicity control (CT).
Starch hydrogel resulted the safest material; while starch-chitosan, regardless of the method of synthesis, showed good viability percentages (higher than 80%). In contrast, cells incubated with starch-PVA hydrogel were the most affected, presenting significantly lower values of cell viability. Considering that both polymers, starch and PVA, are biocompatible per se (Mansur, 2009; Perez, 2018), other factors related to hydrogel structure may be contributing to this result. The rigid starch-PVA structure and the lower water absorption, may influence the flow of substances through the hydrogel, originating areas of less access to nutrients in the plate. Particularly, by having less swelling, starch-PVA hydrogel remains drier and introduces a structural barrier to cell growth, leading to smaller values of cell viability.
The formation of rigid networks in PVA hydrogels indicates the existence of inter- and intra- polymer chain bonds; this decreases the number of exposed hydrophilic groups and reduces the swelling (Mansur, 2009; Tang, 2011). Starch-PVA hydrogels have been studied before, showing increased swelling with higher starch quantities (Hsie, 2013), and major (negative) effect on cell viability when PVA is a primary component of the hydrogel (Bernal-Ballen, 2019). According to these results, a possible way to decrease the negative effect on cell viability and to improve the swelling of our starch-PVA hydrogel could be an increase of starch quantity and/or a reduction of PVA content.