## 3 Results and Discussion  
For efficient drug delivery and psoriasis treatment, sustained drug release for a prolonged time is important. Recently, a new medication concept called \"dose-dense chemotherapy\" has been introduced and successfully used, especially in cancer therapy, based on the technique of increasing dosage for a short time [26]. The smart nanofiber patch presented here has the potential to be used for temporal drug release triggered by external stimuli. For these purposes, we used nanofibers with embedded magnetic nanoparticles [27]. These nanoparticles are extensively heated when exposed to an alternating magnetic field [28; 29; 30; 31; 32; 33]. The second key physical principle we used was the low melting temperature of PCL polymer (45-52 \({}^{\circ}\)C) [25] attainable by alternating magnetic-field-mediated hyperthermia. It is analogous to gel-liquid crystal phase transition in liposomes, exploited in liposomal temperature-sensitive drug delivery systems [32]. A key factor in the successful use of nanofibers for the controlled release of a drug is the need for its effective incorporation. We used taxarotene, whose water solubility is 0.75 mg/L, so it is a hydrophobic drug. Nevertheless, the solubility of another drug from the retinoid class--tretinoin--is only 0.025 mg/L. This was also a reason why we used the hydrophobic polymer, PCL, which is in contrast to our previous study [21], where we incorporated methotrexate--a drug well soluble in water--into polyvinyl alcohol, a hydrophilic polymer. By using PCL, we managed to achieve an incorporation efficiency of 96.7%. This makes it possible to use a smaller patch that can be applied for a longer time. Scanning electron microscopy (Figure 7) was used to characterize the structure of the nanofibers. The fabricated nanofibers had diameters from 220 to 640 nm and a uniform smooth structure of their surface. Figure 7: Scanning electron microscopy of nanofibrous patch: (**a**) higher magnification; (**b**) lower magnification. To effectively embed them, we used magnetic nanoparticles stabilized in PCL, which allowed us not only to incorporate them effectively into the structure of a nanofiber from the same polymer, but also to achieve their homogeneous distribution in nanofiber patches, as shown in Figure 8, using colorimetric Prussian blue staining. For successful transdermal therapy, it is necessary for the drug to be concentrated rapidly on the skin surface in a therapeutically effective dose. To evaluate the ability of this formulation to cross the skin, we used human abdominal skin (obtained as frozen discs from Xenometrics) as a sample to measure tazarotene permeation using a vertical Franz cell (Figure 9). An analysis of the experimental data was carried out using the sigmoidal function proposed by [PERSON] in 1879 [34], which is based on the logistic sigmoidal equation, an appropriate starting point for the description of phase transition phenomena. As shown in Figure 9, the release of tazarotene is excellently described by this sigmoidal release pattern, which is therapeutically beneficial for timed release [35]. In addition to the phase transition of polycaprolactone, the release of tazarotene slightly increased, probably via the Arrhenius mechanism, in contrast to tazarotene permeation without heating with alternating magnetic field, where after 24 h, release of 70% tazarotene was observed. The sigmoidal curve reflects the experimental fact [33; 36] that the phase transition temperature for polycaprolactone is 52.1 \(\pm\) 2 \({}^{\circ}\)C, with an initial phase transition temperature of 45.4 \(\pm\) 2 \({}^{\circ}\)C, which means that the melting point of the polycaprolactone nanofiber and the subsequent drug release can be easily achieved by means of hyperthermia induced by an alternating magnetic field (Figure 4b). Figure 8: Colorimetric assay of magnetic nanoparticles in nanofiber patch: (**a**) optical microscopy image of patch without Prussian blue; (**b**) patch immediately after staining when Prussian blue crystals are formed.