3D Bioprinting a Novel Skin Co-Culture Model Using Human Keratinocytes and Fibroblasts.

3D bioprinting can generate the organized structures found in human skin for a variety of biological, medical, and pharmaceutical applications. Challenges in bioprinting skin include printing different types of cells in the same construct while maintaining their viability, which depends on the type of bioprinter and bioinks used. This study evaluated a novel 3D bioprinted skin model containing human keratinocytes (HEKa) and human dermal fibroblasts (HDF) in co-culture (CC) using a high-viscosity fibrin-based bioink produced using the BioX extrusion-based bioprinter. The constructs containing HEKa or HDF cells alone (control groups) and in CC were evaluated at 1, 10, and 20 days after bioprinting for viability, immunocytochemistry for specific markers (K5 and K10 for keratinocytes; vimentin and fibroblast specific protein [FSP] for fibroblasts). The storage, loss modulus, and viscosity properties of the constructs were also assessed to compare the effects of keratinocytes and fibroblasts individually and combined, providing important insights when bioprinting skin. Our findings revealed significantly higher cell viability in the CC group compared to individual keratinocyte and fibroblast groups, suggesting the combined cell presence enhanced survival rates. Additionally, proliferation rates of both cell types remained consistent over time, indicating non-competitive growth within the construct. Interestingly, keratinocytes exhibited a greater impact on the viscoelastic properties of the construct compared to fibroblasts, likely due to their larger size and arrangement. These insights contribute to optimizing bioprinting strategies for skin tissue engineering and emphasize the important role of different cell types in 3D skin models.