Development of a three-layered keratin-based nanofibrous scaffold as an in vitro model of the human nail barrier

Nail infections, particularly onychomycosis, affect millions of people worldwide, reducing quality of life. Therapeutic efficacy remains limited by the nail plate's dense keratinised structure, which restricts topical drug permeation. Current in vitro models based on human nails or animal hooves face structural variability, ethical and availability constraints, while synthetic alternatives fail to replicate the nail's architecture and biochemical composition, limiting their predictive value.

This study reports the development of a multilayer biomimetic ungual model based on a nanofibrous scaffold produced by sequential electrospinning, combining synthetic polymers with keratin extracted from human hair to mimic the three layers that constitute the nail plate. A biomimetic lipid layer was subsequently deposited to reproduce the protein–lipid interface governing transungual transport.

Structural characterisation confirmed a stratified architecture with distinct fibre morphologies across layers, consistent with native nail organisation. Functional validation was performed by in vitro permeation assays in Franz diffusion cells, using caffeine (hydrophilic) and terbinafine (lipophilic) as model compounds. The multilayer model significantly reduced caffeine flux (J = 5.04 ± 0.23 μg/cm²/h), approximately 2.3-fold lower than simpler nanofibrous structures, confirming its barrier function. Conversely, terbinafine permeation increased ~2.7-fold, reflecting preferential affinity for the incorporated lipid domains.

These results indicate that the model reproduces key physiological features of the human nail, capturing compound-dependent selective permeation. This reproducible platform offers a promising alternative to current nail surrogates for transungual delivery research and provides a robust basis for ongoing work on developing an infected onychomycosis model for disease-state drug screening.