3D bioprinting of in vitro full-thickness skin model with a rete ridge structure

Rete ridges are undulating structures located between the epidermis and dermis that play a crucial role in maintaining the skin's barrier function, protecting the body from pollutants and ultraviolet (UV) radiation. This formation of rete ridges within in vitro skin models is essential for evaluating the efficacy and safety of pharmaceuticals or cosmetics, replacing the need for animal models. Micro-molding is a prominent technique for recreating the rete ridge structure in in vitro skin models. However, this method is characterized by high technical difficulty. Although 3D bioprinting technology has demonstrated potential for fabricating skin models with the rete ridge structure, it is also limited by the extended time required for structural implementation. In this study, we introduce a methodology for fabricating full-thickness skin equivalents with rete ridges using preset extrusion bioprinting. A polycaprolactone frame was 3D-printed, and the dermal layer was bioprinted in the frame. Subsequently, furrowing steps were undertaken to create a substrate for the stable anchoring of strands produced by the preset extrusion bioprinting, fabricating a dermis layer with a rete ridge structure. Keratinocytes were then seeded and differentiated, forming the stratum corneum. We observed that protein expression was preserved in the valleys of the rete ridge after UV irradiation of the rete ridge full-thickness skin equivalent, similar to that of human exvivo skin models. Therefore, the rete ridge full-thickness skin equivalent generated using our method exhibits potential as a promising model to replace animal experiments and human ex vivo skin models.