Physicochemical and Interfacial Insights into Porphyrin-Loaded HPMC Hydrogels

Hydroxypropyl methylcellulose hydrogels were designed as polymeric matrices for porphyrinic photosensitizer samples (5-(2-hydroxy-5-methoxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl) porphyrin (P3.2) and 5,10,15,20-tetrakis-(4-carboxymethylphenyl) porphyrin (P3.1) to investigate their physicochemical behavior and structure–property relationships. Fourier transform infrared, UV–Vis, and fluorescence spectroscopy showed that both porphyrins remained monomerically dispersed in the polymeric matrix by establishing moderate interactions with HPMC by hydrogen bonding. X-ray diffraction and atomic force microscopy showed the uniform microstructural organization of the hydrogel matrix, while thermal analyses confirmed the stability of both studied systems. Rheological measurements demonstrated that the incorporation of porphyrins in the hydrogel network slightly modulates viscoelastic behavior. The swelling, density, and pH studies highlighted correlations between molecular interactions and macroscopic hydrogel properties. The swelling ratio determined after 6 h showed values of about 89% for the hydrogel of HPMC with P3.1. and about 92% for the hydrogel of HPMC with P3.2, respectively. The pH value was found to be 7.0 for both hydrogels. These results highlighted interfacial and physicochemical insights into polymer–porphyrin interactions in hydrogel matrices. All studies show that a controlled dispersion of chromophores preserves their monomeric state and controlled structure–property relationships.