A Modular Bio-Hybrid Skin Model for Optical Testing Applications

Synthetic optical skin models offer reproducible, tunable optical properties but lack biological responsiveness, while tissue engineered skin models provide cellular authenticity but suffer from optical variability and limited controllability. The growing demand for alternatives to animal models in the development and validation of optical biomedical technologies highlights the need for a new class of test system that combines the strengths of both approaches while addressing their respective limitations. Here, we introduce the concept of a modular biohybrid skin model, a new testing concept that integrates an optically defined artificial epidermal layer, incorporating polydopamine nanoparticles for changes in skin tone, with living human keratinocytes in two and three-dimensional configurations. In the Optical Protection Model, UV-B-induced apoptosis in primary keratinocytes is quantitatively modulated by model pigmentation level, demonstrating a relationship between optical attenuation and caspase 3/7 activity across three artificial skin tone conditions. In a Structured Dermal Model, keratinocytes seeded onto a hydrogel scaffold localize within follicle-like microcavities, as confirmed by live/dead staining and confocal z-stack imaging. Together, these experiments lead to a new category of test system in the space between inert optical models and variable tissue models that may contribute to reducing the reliance on animal models in biomedical optics.