CAM Model: Intriguing Natural Bioreactor for Sustainable Research and Reliable/Versatile Testing

SIMPLE SUMMARY: The chicken embryo chorioallantoic membrane (CAM) is an in ovo model that has been known for years. It has mostly been used to test the characteristics of molecules and cell pellets and their potential interactions with vessels, particularly in cancer studies. Recently, we repurposed such a model by highlighting its ethical features, because, to a large extent, it can reduce the use of animal experimentation and produce rapid results. Its applications have multiplied in recent years, allowing for the development of more in-depth and comprehensive analyses and, thus, reducing the gap between in vitro and in vivo experimentation. Since the CAM model allows for the replacement, reduction, and refinement of preclinical experimentation (rules of the “3Rs”), it makes experimental research more sustainable and in line with animal welfare. The objective of this review is to illustrate the potential of the CAM assay, with a particular focus on the setup of organotypic cultures. This type of assay may be used as a preclinical model to assay recovery strategies for critically-sized bone injuries, i.e., severe fractures that do not spontaneously heal due to disruption of the vascular network and a large gap between the two bone stumps. ABSTRACT: We are witnessing the revival of the CAM model, which has already used been in the past by several researchers studying angiogenesis and anti-cancer drugs and now offers a refined model to fill, in the translational meaning, the gap between in vitro and in vivo studies. It can be used for a wide range of purposes, from testing cytotoxicity, pharmacokinetics, tumorigenesis, and invasion to the action mechanisms of molecules and validation of new materials from tissue engineering research. The CAM model is easy to use, with a fast outcome, and makes experimental research more sustainable since it allows us to replace, reduce, and refine pre-clinical experimentation (“3Rs” rules). This review aims to highlight some unique potential that the CAM-assay presents; in particular, the authors intend to use the CAM model in the future to verify, in a microenvironment comparable to in vivo conditions, albeit simplified, the angiogenic ability of functionalized 3D constructs to be used in regenerative medicine strategies in the recovery of skeletal injuries of critical size (CSD) that do not repair spontaneously. For this purpose, organotypic cultures will be planned on several CAMs set up in temporal sequences, and a sort of organ model for assessing CSD will be utilized in the CAM bioreactor rather than in vivo.