**4. Conclusions**

Fibroblast biocompatibility and wound healing efficacy of inorganic hydrogels formulated with two nanoclays in two natural spring waters have been studied. Both spring waters were fully biocompatible and favored wound healing, inducing faster gap closure with respect to control. The studied nanoclays did not interfere with cell viability to a great extent (≥80% of cell viability), thus not being cytotoxic at the studied concentrations. Nonetheless, they interfered with the in vitro wound healing processes, slightly delaying gap closure when used as powders. This effect could be ascribed to the presence of non-flocculated nanoclay particles in the culture medium. Hydrogels formulated with the aforementioned ingredients did not hindered gap closure and reported a higher percentage of wound closure after 24 h with respect to the control.

In conclusion, this study has demonstrated the usefulness and potential of PS9 and G30 clay minerals as excipients in the preparation of hydrogels intended for wound healing and other therapeutic uses. Maximum in vitro wound healing effects were achieved by using PS9 in the formulation of the hydrogels. These promising results encourage the use of clay minerals as wound healing ingredients. Thermal center treatments are mostly focused on the physical effects of thermal muds, which are very effective against musculoskeletal disorders. Nonetheless, the findings of this study have opened new perspectives, since the addressed nanoclay/spring water hydrogels could also be used to treat chronic wounds.

**Author Contributions:** Data curation, F.G.-V.; Funding acquisition, C.V. and G.S.; Methodology, F.G.-V., A.F., D.M. and M.R.; Project administration, C.V. and G.S.; Supervision, A.F. and D.M.; Writing—original draft, F.G.-V.; Writing—review & editing, R.S.-E., A.B.-S., P.C., S.R., C.V. and G.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Ministerio de Ciencia e Innovación, CGL2016–80833-R; Consejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía, P18-RT-3786 and Ministerio de Educación, Cultura y Deporte, FPU15/01577.

**Acknowledgments:** This project was supported by an FPU grant (MECD), the Spanish research group CTS-946 and the program for international mobility of PhD students (University of Granada). Special thanks to the Department of Drug Sciences of the University of Pavia (Italy).

**Conflicts of Interest:** The authors declare no conflict of interest.
