**4. Conclusions**

Within this study, we were able to fabricate a hierarchically structured composite consisting of PS microfibers and PA6 nanofibers using a two-nozzle electrospinning set-up in the single-step manufacturing method. We showed that controlling the surface morphology, chemistry, and roughness of composite meshes guided fibroblasts behavior and development. The filopodia formation and their further proliferation were affected by the size of fibers. The micronized PS fibers allowed deeper penetration of cells, allowing enhanced material integration with the living systems. Moreover, nanosized PA6 fibers with hydrophilic wetting behavior by itself promoted cell development and spreading, despite the fact that the obtained composites were, in general, hydrophobic. Manipulating the rate of PA6 nanofibers in the PS network of fibers allows us to tailor mechanical properties [37] and roughness of meshes [38], thus designing the environment for desired cell types [30,39]. The proposed combination of polymers and its structure is leading to multiple application strategies of nondegradable meshes supporting tissue in regenerative medicine.

In summary, we introduced a novel way to produce PS-PA6 composite meshes in a single-step manufacturing method to enhance cell proliferation and development. These nondegradable polymer composite meshes are able to create a favorable environment for cells reminding ECM with a perspective use in regenerative medicine and for in vitro studies of disease models as 3D constructs.

**Author Contributions:** Conceptualization, U.S.; methodology, J.K.-K., Z.J.K and U.S.; validation, U.S. and Z.J.K.; formal analysis, Z.J.K. and M.Z.G.; investigation, Z.J.K., J.K.-K., M.Z.G. and Ł.K.; resources, U.S.; data curation, Z.J.K., M.Z.G. and U.S.; writing—original draft preparation, Z.J.K. and U.S.; writing—review and editing, Z.J.K. and U.S.; visualization, Z.J.K., M.Z.G. and U.S.; supervision, U.S.; project administration, U.S.; funding acquisition, U.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was part of the "Nanofiber-based sponges for atopic skin treatment" project carried out within the First TEAM program of the Foundation for Polish Science co-financed by the European Union under the European Regional Development Fund, project no POIR.04.04.00-00- 4571/18-00 and supported by the infrastructure at International Centre of Electron Microscopy for Materials Science (IC-EM) at AGH University of Science and Technology. Joanna Knapczyk-Korczak thanks Sonata Bis 5 project, No 2015/18/E/ST5/00230 for PhD scholarship.

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

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