Formulation and Characterization of Carbopol-Based Porphyrin Gels for Targeted Dermato-Oncological Therapy: Physicochemical and Pharmacotechnical Insights

Abstract

Malignant skin conditions are classified as the most common forms of cancer, with an evolution of one million new cases reported every year. Research efforts in the medical field are focused on developing innovative strategies for the dissemination of measures for preventing cancer and providing new antitumor compounds. The present research examines the development and evaluation of 1% Carbopol-based hydrogels incorporating two porphyrin derivatives-5,10,15,20-tetrakis-(4-acetoxy-3-methoxyphenyl) porphyrin (P2.1) and 5-(4-hydroxy-3-methoxyphenyl)-10,15,20-tris-(4-acetoxy-3-methoxyphenyl) porphyrin (P2.2)-to create formulations suitable for topical photodynamic therapy (PDT) applications. The physicochemical properties of the obtained hydrogels were carefully evaluated, revealing the successful integration of the porphyrins into the 1% Carbopol hydrogel matrix. Rheological analysis demonstrated pseudoplastic behavior, with an increase in viscosity properties for P2.1 and P2.2, suggesting interactions with the Carbopol polymer structure. UV-visible and fluorescence spectroscopy confirmed the maintenance of the porphyrins' photodynamic properties, essential for therapeutic efficacy. Pharmacotechnical studies highlighted the hydrogels' suitability for topical applications. The formulations maintained an optimal pH range, ensuring skin compatibility and minimizing the potential for skin irritation. Their mechanical properties, including elasticity and rigidity, provided stability during handling and application. The high swelling capacity indicated effective moisture retention, enhancing skin hydration and drug release potential. Furthermore, the hydrogels demonstrated excellent spreadability, enabling uniform application and coverage, crucial for efficient light activation of the photosensitizers. The combination of robust physicochemical and pharmacotechnical properties highlights the potential of these porphyrin-loaded 1% Carbopol hydrogels as promising carriers for topical PDT. These results permit further biological and therapeutic investigations to optimize the formulation for clinical use, advancing the development of effective localized photodynamic therapies.

Keywords: Carbopol; biomedical applications; hydrogel; photodynamic therapy; unsymmetrical porphyrin.

Figure 1

The FTIR spectra of the studied hydrogels (a) between 4000 and 500 cm⁻¹ and (b) between 1500 and 770 cm⁻¹.

Figure 2

The X-ray diffractograms of (a) 1% Carbopol gel, (b) C-P2.1, and (c) C-P2.2.

Figure 3

The TG/DTG and DTA curves of (a) 1% Carbopol gel, (b) C-P2.1, and (c) C-P2.2.

Figure 4

Enhanced-color 2D AFM topographic images of the 1% Carbopol (a), C-P2.1 (b), and C-P2.2 (c) samples recorded at the scale of 8 µm × 8 µm. Below each AFM image, two characteristic surface profiles (red and green scan lines) are exemplified.

Figure 5

(a) Corrugation parameters: RMS roughness (Rq) and peak-to-valley parameter (Rpv); (b) mean fractal dimension (MFD) and textural direction index (Stdi) for the hydrogels based on Carbopol (1% Carbopol, C-P2.1, and C-P2.2) at the scale of 8 µm × 8 μm.

Figure 6

Enhanced-color 2D AFM topographic images of the 1% Carbopol (a), C-P2.1 (b), and C-P2.2 (c) samples at the scale of 2 µm × 2 µm; below each AFM image, the characteristic profiles (scan lines) are exemplified. Angular Fourier spectra of the mean fractal dimension (MFD) (d–f) and textural direction index (Stdi) (g–i) were plotted for the AFM images of the 1% Carbopol, C-P2.1, and C-P2.2 samples at the scale of 2 µm × 2 µm.

Figure 7

(a) Corrugation parameters: RMS roughness (Rq) and peak-to-valley index (Rpv); (b) mean fractal dimension (MFD) and textural direction index (Stdi) for the hydrogels based on Carbopol (1% Carbopol, C-P2.1, and C-P2.2) at the scale of 2 µm × 2 µm.

Figure 8

Absorption (a) and emission (b) spectra of P2.1 and P2.2 in the Carbopol matrix.

Figure 9

The hydrogels’ spreading properties.

Figure 10

Variation in dynamic viscosity and shear stress as a function of shear rates in (a) Carbopol, (b) C-P2.1, and (c) C-P2.2.

Figure 11

The swelling rate of the studied samples.