Evaluation of porcine ear skin as a model for human skin: influence on the diffusion of different photosensitizers.

Porcine ear skin is widely employed as an ex vivo biological interface for investigating molecular interactions between bioactive compounds and skin tissue due to its structural and compositional similarity to human skin. In this study, we analyze how structural maturation of the cutaneous biointerface as a function of age influences the interaction and diffusion behavior of three bioactive photosensitizers, curcumin, erythrosine B, and methylene blue, within porcine ear skin. Skin samples were obtained from animals aged 40, 75, 115, and 150 days, corresponding approximately to body masses of 10, 40, 70, and 100 kg, in order to evaluate progressive tissue maturation effects. Photoacoustic spectroscopy (PAS) was employed as an optical and thermal technique sensitive to biointerface properties to probe molecular absorption profiles within superficial regions of the epidermis and dermis. Complementary characterization was performed using attenuated total reflectance Fourier transform infrared spectroscopy (FTIR-ATR) combined with principal component analysis (PCA) to identify age-related molecular and compositional changes in skin tissue. The spectroscopic analyses revealed that structural modifications associated with collagen reorganization are more pronounced in the dermis, whereas the epidermis remains comparatively less affected as tissue maturation progresses. Following topical application of the photosensitizers (PSs), PAS measurements demonstrated that molecular interaction and diffusion behavior within the dermal region depend on both the physicochemical properties of the compounds and the structural state of the tissue. Among the investigated photosensitizers, methylene blue exhibited the highest sensitivity to biointerface maturation, whereas curcumin and erythrosine B showed comparatively limited variation. These findings highlight the role of age-dependent structural features of the cutaneous biointerface in modulating molecular interactions within skin tissue. By integrating PAS and FTIR-ATR, this work provides insight into how biological interface maturation influences the optical and molecular response of skin to bioactive compounds, contributing to the broader understanding of biointerface science.