Standardised Reconstructed Skin Models in Toxicology and Pharmacology: State of the Art and Future Development.

Three-dimensional (3D) reconstructed human skin (RhS) models featuring fully-differentiated characteristics of in vivo human epidermis have been known for almost 40 years. In this chapter, the topic of commercial in vitro tissue models is described, taking RhS models as an example. The need for highly standardised models is evident for regulatory testing purposes, e.g. the classification and labelling of chemicals and formulations, as well as for pharmacology-oriented research and drug development. Following the standardisation of RhS model production by commercial developers, international validation studies and regulatory acceptance, 3D RhS models are now used globally in both industrial and academic research laboratories. Industrial production of standardised 3D RhS models involves GMP-compliant processes together with ISO 9001 documentation in order to control and ensure reproducibility and quality. Key biological, functional, and performance features that are addressed in industrial production include barrier properties, histological and immunohistochemical characterisation, lipid profile characterisation, and tissue viability before and after transport. An up-to-date survey of commercial RhS tissue producers and the regulatory acceptance status of major safety, hazard, and efficacy assays currently available to chemical and pharmaceutical industries is presented in this chapter. Safety and ethical concerns related to the use of human tissue in the industrial production of RhS models are discussed. Finally, innovative approaches to the production of standardised 3D RhS models including automated production, development of more representative 3D RhS models using advanced additive manufacturing tools, microfluidics technologies, and bioprinting are presented. The future outlook for 3D RhS models includes a prevalence of high-quality models which will be fabricated by end-users rather than commercial producers. These will overcome problems with shipments and customs clearance that many users still face when buying RhS from overseas commercial suppliers. Open-source technologies and commercial components for "do-it-yourself" RhS will significantly change the skin model market as well as regulatory acceptance of open-source models during the next decade. All of these developments and improvements will together allow more widespread use of in vitro RhS models for broader application as animal replacements in areas ranging from industrial and regulatory toxicology and pharmacology, to drug development and personalised medicine.