Adapalene-loaded poly(ε-caprolactone) microparticles: Physicochemical characterization and in vitro penetration by photoacoustic spectroscopy

Abstract

Adapalene (ADAP) is an important drug widely used in the topical treatment of acne. It is a third-generation retinoid and provides keratolytic, anti-inflammatory, and antiseborrhoic action. However, some topical adverse effects such as erythema, dryness, and scaling have been reported with its commercial formula. In this sense, the microencapsulation of this drug using polyesters can circumvent its topical side effects and can lead to the enhancement of drug delivery into sebaceous glands. The goal of this work was to obtain ADAP-loaded poly(ε-caprolactone) (PCL) microparticles prepared by a simple emulsion/solvent evaporation method. Formulations containing 10 and 20% of ADAP were successfully obtained and characterized by morphological, spectroscopic, and thermal studies. Microparticles presented encapsulation efficiency of ADAP above 98% and showed a smooth surface and spherical shape. Fourier transform infrared spectroscopy (FTIR) results presented no drug-polymer chemical bond, and a differential scanning calorimetry (DSC) technique showed a partial amorphization of the drug. ADAP permeation in the Strat-M membrane for transdermal diffusion testing was evaluated by photoacoustic spectroscopy (PAS) in the spectral region between 225 and 400 nm after 15 min and 3 h from the application of ADAP-loaded PCL formulations. PAS was successfully used for investigating the penetration of polymeric microparticles. In addition, microencapsulation decreased the in vitro transmembrane diffusion of ADAP.

Fig 1. Chemical structure of adapalene (ADAP).

Fig 2. Schematic setup of photoacoustic spectroscopy.

The radiation font, the mechanical modulator, monochromator, filters, lens, microphone as the detector, and a personal computer for data acquisition.

Fig 3

Scanning electron micrographs of PCL microparticles: F0 (a), F10 (b) and F20 (c). Magnifications of 2000X presenting a spherical shape and smooth, slightly flaky surface.

Fig 4. FTIR results of ADAP, PCL, PM, and PCL microparticles (F0, F10, and F20).

PM presented bands at 1140, 1300, 1477, 1688, 2847, and 2903 cm^-1 that are related to ADAP; bands at 961, 1728 and 2949 cm^-1 that are attributed to PCL. The F10 and F20 do not present any shifts on these bands. In this case, the encapsulation process does not induce chemical interaction between the drug and PCL.

Fig 5. DSC curves of ADAP, PCL, PM, and PCL microparticles (F0, F10, and F20).

The formulations F10 and F20 do not present the melting point of ADAP at 326°C, showing a complete drug amorphization.

Fig 6. Experimental data of frequency scan by OPC technique for the Strat-M membrane with a thickness of 310±10 μm.

The solid line represents the best data fit by Eq (2).

Fig 7

(a) PAS result for the Strat-M membrane. We can notice a redshift with decreasing depth, indicating the difference of the polymeric layers from the membrane. (b) FEG-SEM image of the membrane with 200x of magnification. The arrows illustrate the thermal diffusion length (μ_membrane) obtained for frequencies of 5, 23, 51, and 203 Hz, and the colors are the same as the respective spectrum from (a).

Fig 8. Photoacoustic spectra of formulations.

ADAP and ADAP-loaded PCL microparticles. The Gaussian curves are centered at 272, 336, and 369 nm. The bands at 336 and 369 nm decrease in intensity for F10 and F20, indicating the enclosure of the drug molecules into polymeric microparticles.

Fig 9. Photoacoustic spectra for the membranes after 15 min of application formulations (Formulation+Strat-M).

Excitation in the internal side of the membrane with a 203 Hz modulation frequency (33 μm depth). The figure indicates the position of the peaks attributed to ADAP (250–269, 336 and 370–380 nm) and Strat-M (280, 300–350 nm).

Fig 10

Evolution of ADAP permeation in the membrane as a function of thermal diffusion length after 15 min (a) and 3 h (b) of application obtained by the sum of the areas under the Gaussian curves related to ADAP (250–269, 336, and 370–380 nm). The hatched marks are approximately the positions where the formulations were applied. After 15 min, the highest drug concentration remains at approximately 210 μm for all formulations. After 3h, for ADAP and PM formulation, the drug permeates through all layers of the membrane until 33 μm. The F10 and F20 concentrate ADAP in 100 μm of penetration depth.