3D Bioprinting Skin Equivalents: A Methodological Perspective on Human Keratinocyte and Fibroblast Models for Wound Repair and Regeneration

Three-dimensional (3D) bioprinting is a promising approach to developing reliable tissue substitutes for translational research. The great interest in creating skin substitutes still faces challenges considering its structural and cellular complexity. Despite significant advancements, the lack of reproducible protocols and different translational barriers limit the clinical applicability of current methods. This review aims to provide guidance for future studies and improve methodological replication on wound repair and regeneration. Following the PRISMA 2020 guidelines, a search was conducted on MEDLINE/PubMed, EMBASE, and Web of Science. Inclusion criteria focused on 3D bioprinter constructs with human keratinocytes and fibroblasts for wound healing. Authors screened titles and abstracts, followed by full-text documents. Data extraction was conducted and cross-checked by two others using customised table sheets. Eighteen studies met the inclusion criteria, primarily focusing on skin substitutes, with no studies found on oral mucosal models. Geographic distribution was predominantly China (44.4%) and the United States (27.7%), with notable international collaborations. Most studies used extrusion-based bioprinting, with gelatin-based hydrogels as the most frequent components in the bioinks (61.6%). Other common materials included fibrinogen (38.8%) and alginate (33.3%), while some studies incorporated human serum and silk to enhance functionality. Constructed skin substitutes included epidermal layers with keratinocytes and dermal layers with fibroblasts, with some incorporating endothelial and follicle papilla cells for added complexity. Analyses included morphology, cell viability, histology, proliferation, protein and gene expression, and transepidermal electrical resistance. Many studies (61.1%) validated results through animal model implantation, primarily in mice. This review underscores the global interest and collaborative efforts in 3D bioprinting for skin wound healing and regeneration. However, we also emphasise the need for standardised protocols to improve replicability and enhance translational potential for clinical applications. Belike, future studies using computational modelling or machine learning should refine these technologies.