br The release behavior of CSs from the

The release behavior of CSs from the CDEAC hydrogel upon adding the ClO− (10 nM) was further studied. MCF-7 Cisplatin did not show ob-vious toxicity when cultured with ClO−/SCN−(Supplementary Fig. S21). As shown in Fig. 6A, the morphology of the released CSs were identical to that of the prerelease. Also, the average CS diameters prior to and following their release from the hydrogels on 7-day growth were 73 ± 10 and 76 ± 13 μm, respectively (Supplementary Fig. S22). In addition, the released CSs showed good cell viability (Fig. 6B). Fluor-escence images showed that the released CSs were formed by multiple cells (Fig. 6C) and existed the cell-cell interactions characterized by E-Cadherin expression (Fig. 6D). The CMC hydrogel dissociated from the CSs due to quenched red fluorescence (Fig. 6E). The spatial distribution of cell nuclei and Dio was illustrated by the merged fluorescence image of the CS (Fig. 6F). In addition, we used the corresponding IgG for anti-E-cadherin as a negative control (Supplementary Fig. S23).
To ensure that the released CSs existed the tumorigenic properties, the CSs released from the CMC hydrogel upon adding the ClO− was transferred into a fibrin gel that is one of the components of the tumor stroma [50]. Fig. 7A and B show that the dimensions of CSs released from the CMC hydrogel increased from 65 ± 5 to 140 ± 12 μm after 10-day re-culture in the fibrin gel (Fig. 7C and Supplementary S24). The cells in the CSs showed good cell viability. Moreover, the CSs in the fibrin gels exhibited strong cell-cell interactions, cellular cytoskeletal organization and 3D organization of the nuclei, which were demon-strated by immunostaining (Fig. 7D-G).  Biomaterials 194 (2019) 161–170
4. Conclusion
In summary, for the first time, we demonstrate using ClO−/SCN− reversibly responsive luminous nanocellulose hydrogels for realizing the growth and subsequent release of CSs. Such anion-regulated gel assembly system is developed using cellulose-based hydrogels functio-nalized with Eu(III) complex (guest) or DPY (host) moieties. Formation of a fluorescence hydrogel matrix by simple mixing of the two hydro-gelators at low concentrations under physiological conditions was de-monstrated. Reversible adhesion and dissociation transition of the hy-drogel may be controlled by ClO−/SCN−. Breast cancer cells seeded in the resulting hydrogel led to the formation of homogeneous spheroids of controllable size, and ClO− releases CSs entrapped in the hydrogel into aqueous solution in a noncontact mode. In addition, the additional fluorescent on-off response of the hydrogel help to spatially defined modulation on cellular microenvironments. This study opens up a novel approach to develop multifunctional and stimuli-responsive materials for biomedical applications.
Acknowledgments
The work was supported by the National Natural Science Foundation of China (21671088, 21431002, and 21501080), and Fundamental Research Funds for the Central Universities (lzujbky-2017-105 and 2018-it03). We wish to thank the Electron Microscopy Centre of Lanzhou University for the microscopy and microanalysis of our specimens.
Appendix A. Supplementary data
References
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