In vitro skin culture media influence the viability and inflammatory response of primary macrophages.

The replacement of animal models for investigation of inflammation and wound healing has been advancing by means of in vitro skin equivalents with increasing levels of complexity. However, the current in vitro skin models still have a limited pre-clinical relevance due to their lack of immune cells. So far, few steps have been made towards the incorporation of immune cells into in vitro skin and the requirements for immunocompetent co-cultures remain unexplored. To establish suitable conditions for incorporating macrophages into skin models, we evaluated the effects of different media on primary keratinocytes, fibroblasts and macrophages. Skin maturation was affected by culture in macrophage medium, while macrophages showed reduced viability, altered cell morphology and decreased response to pro- and anti-inflammatory stimuli in skin differentiation media, both in 2D and 3D. The results indicate that immunocompetent skin models have specific, complex requirements for supporting an accurate detection of immune responses, which point at the identification of a suitable culture medium as a crucial pre-requisite for the development of physiologically relevant models.

Toward Immunocompetent 3D Skin Models.

3D human skin models provide a platform for toxicity testing, biomaterials evaluation, and investigation of fundamental biological processes. However, the majority of current in vitro models lack an inflammatory system, vasculature, and other characteristics of native skin, indicating scope for more physiologically complex models. Looking at the immune system, there are a variety of cells that could be integrated to create novel skin models, but to do this effectively it is also necessary to understand the interface between skin biology and tissue engineering as well as the different roles the immune system plays in specific health and disease states. Here, a progress report on skin immunity and current immunocompetent skin models with a focus on construction methods is presented; scaffold and cell choice as well as the requirements of physiologically relevant models are elaborated. The wide range of technological and fundamental challenges that need to be addressed to successfully generate immunocompetent skin models and the steps currently being made globally by researchers as they develop new models are explored. Induced pluripotent stem cells, microfluidic platforms to control the model environment, and new real-time monitoring techniques capable of probing biochemical processes within the models are discussed.