**Acknowledgements**

*Applications of Nanobiotechnology*

hydration [140].

**5. Conclusions**

7.5 ml/h) at its basal side. Histological examination confirmed the formation of a significantly thicker *stratum corneum* compared to the control constructs cultivated under static conditions. Moreover, the keratinocyte differentiation markers involucrin and filaggrin, as well as the tight junction proteins claudin 1 and occludin, showed increased expression in the dynamically cultured skin models. However, the skin barrier function of the dynamically cultivated skin models was not enhanced compared with the skin models cultivated under static conditions [36]. Similar results were obtained in a study by Kalyanaraman et al. [140], performed on engineered skin substitutes based on collagen-glycosaminoglycan sponges, containing fibroblasts in their inside and keratinocytes on their surface, which were exposed to the air-liquid interface. Perfusion of these construct with the medium at the flow rate of 5 ml/min increased the metabolic activity of fibroblasts and maintained the epidermal barrier created by keratinocytes similarly as in static controls, while higher flow rates of 15 ml/min, and particularly 50 ml/ min, decreased the cell metabolic activity, increased the degradation of the scaffolds and decreased the epidermal barrier function, manifested by its increased

Nanofibrous scaffolds made of synthetic polymers have been widely investigated

for their potential use in skin regenerative therapies. Non-degradable polymers used for preparation of nanofibrous scaffolds included polyurethane (which can also be prepared in degradable form), polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polyethersulfone (PES), and even polystyrene (PS). These scaffolds were mainly intended for wound dressing applications, and in case of PS, also for cultivation of skin cells in dynamic bioreactor and at the air/liquid interface. For creation of nanofibrous meshes, the non-degradable polymers have been often used in combinations with nature-derived polymers (dextran, chitosan, gelatin, and keratin), and loaded with various wound healing, angiogenic, antioxidant, anti-inflammatory, photoprotective, and antimicrobial substances. Non-degradable

synthetic polymers also include hydrogels, such as poly(acrylic acid) (PAA), poly(methyl methacrylate) (PMMA) and particularly poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA), which is thermoresponsive and suitable for controlled drug delivery and cell delivery into wounds. Degradable synthetic polymers have been also applied in wound healing, but also as direct scaffolds for skin tissue engineering, i.e., as carriers for keratinocytes, fibroblasts, and stem cells. The most widely used degradable polymers for these applications include polycaprolactone (PCL) and its copolymers with polylactides (PLCL), and also polylactides (PLLA and PDLLA) and their copolymers with polyglycolides (PLGA). Similarly as non-degradable polymers, also degradable polymers are almost exclusively used in combination with nature-derived polymers (collagen, gelatin, keratin, fibrin, and glycosaminoglycans) in order to increase their attractiveness for cell colonization, and also with some synthetic polymers, such as poly(ethylene glycol) (PEG), poly(ethylene oxide) (PEO), poly (vinyl alcohol) (PVA), and poly(vinyl pyrrolidone) (PVP). These synthetic polymers act as auxiliary, i.e., improving electrospinnability, mechanical properties, and wettability of other polymers. Similarly as non-degradable polymers, also degradable polymers have been loaded with a wide range of growth and angiogenic factors and other biologically active substances. The cell performance on non-degradable and degradable nanofibrous scaffolds can be further markedly improved by cultivation in dynamic bioreactors and/or at air/

**48**

liquid interface.

This review article was supported by the Grant Agency of the Czech Republic (grant No. 17-02448S) and the Ministry of Health of the Czech Republic (grant No. NV18-01-00332).
