Subject Number :S-16-2010, 2026
Support Type : Common use (including technical support necessary for the training),
Proposal Title (English) : Drug Release and Probing of Thermoresponsive Nanogels in Human Skin by Soft X-Ray Spectromicroscopy
Username (English) : K. Yamamoto1, A. Klossek1, T. Ohigashi2, F. Rancan3, R. Flesch1, M. Giulbudagian1, A. Vogt3, U. Blume-Peytavi3, P. Schrade4, S. Bachmann4, M. Calderón1, M. Schäfer-Korting5, N. Kosugi2, and E. Rühl1
Affiliation (English) : 1Institute for Chemistry and Biochemistry, Freie Universität Berlin, , 2UVSOR Synchrotron Facility, Institute for Molecular Science, 3Charité Universitätsmedizin, 4Abteilung für Elektronenmikroskopie at CVK, 6Institut für Pharmazie, Freie Universität Berlin,
The transport of drugs into human skin facilitated by triggered drug release from polymeric nanocarriers is reported. Label-free detection by X-ray microscopy is used to probe both, the drug and the drug nanocarriers. Dexamethasone (DXM) is used as a drug and the thermoresponsive gel was Poly(N- isopropylacrylamide) (nanogel). The stratum corneum (SC) is the top skin layer. It is the main barrier, which hinders drugs to penetrate into the viable epidermis. We recently published first results using X-ray microscopy for selectively probing DXM [1, 2] and core-multishell nanocarriers penetrating human skin [3]. It was shown that nanocarriers release the drug in the SC without penetrating into deeper skin layers. This yields higher local drug concentrations in the viable epidermis than for conventional drug formulations [3].
The experiments made use of excised human skin, which was exposed to DXM-loaded nanogels for penetration times of 100 and 1000 min. The nanogels were dissolved in water with a concentration of 33.5 mg/mL and had a drug load of 10%. Excised human skin was tape-stripped 30 times prior to topical drug application. In total 120 µL of this nanogel suspension containing 400 µg of DXM was applied per cm² of skin. Triggered drug release was initiated after 10 min by exposure of the skin samples to infrared radiation for 30 s, leading to a contraction of the nanogel and drug release.
Spectromicroscopy studies were performed at the BL4U beamline at UVSOR III using a scanning X-ray microscope. The chemical selectivity for probing either the thermoresponsive nanogel or DXM in fixed skin was achieved by exciting the samples selectively at the oxygen K-edge in the pre-edge regime (cf. [1-3]). Differential absorption maps were derived, similar to our previous work (see Fig. 1).
Fig. 1 shows a compilation of the results, where only the top skin layers are shown (SC and top part of the viable epidermis). Fig. 1(a)-(d) show results for the nanogel distribution, whereas Fig. 1(e)-(h) show the drug distribution. Triggered and non-triggered conditions result in distinct differences for both, the drug and the drug nanocarrier distributions. The nanogel appears to penetrate only efficiently the SC, if triggered by IR radiation (Fig. 1(b), (d)), but cannot reach the viable epidermis. Moreover, significant drug release and penetration into deeper layers only occurs, if the release is thermally triggered (Fig. 1(f), (h)). The nanogel also provides in the SC access for the drug into the corneocytes, which has not been observed before using other vehicles, then DXM remained in the lipid regions between the corneocytes [1-2]. This nanogel-induced effect goes along with swelling of the corneocytes, which has been recently observed by electron microscopy [4]. Stimulated Raman studies provide additional evidence that this is related to changes the organization of proteins and lipids [4]. These results underscore that label-free detection at high spatial resolution provides novel insights that are required for the optimization of topical drug delivery strategies facilitated by polymeric drug nanocarriers.

Fig. 1: The differential absorption of dexamethasone loaded nanogels penetrating the top skin layers for 100 and 1000 min, respectively: (a)-(d) selective probing of the nanogel; (e)-(h) selective probing of dexamethasone. Triggered ((b), (d), (f), (h)) and non- triggered ((a), (c), (e), (g)) drug release conditions show different distributions of the selected species.

[1] K. Yamamoto et al., Anal. Chem. 87, 6173 (2015).
[2] K. Yamamoto et al., Eur. J. Pharm. Biopharm., in press (2017). DOI: 10.1016/j.ejpb.2016.12.005
[3] K. Yamamoto et al., J. Control. Release 242, 64 (2016).
[4] M. Giulbudagian et al., J. Control. Release 243, 323 (2016).