  Molecular Communications (MC) research is increasingly focused on
applications within the human body, such as health monitoring and drug
delivery. These applications require testing in realistic and living
environments. Thus, advancing experimental MC research to the next level
requires the development of in vivo experimental testbeds. In this paper, we
introduce the Chorioallantoic Membrane ( CAM ) model as a versatile 3D in vivo
MC testbed. The CAM is a highly vascularized membrane formed in fertilized
chicken eggs and has gained significance in various research fields, including
bioengineering, cancer research, and drug development. Its versatility,
reproducibility, and realistic biological properties make the CAM model
perfectly suited for next-generation MC testbeds, facilitating the transition
from proof-of-concept systems to practical applications. We provide a
comprehensive introduction to the CAM model, its properties, and its
applications in practical research. Additionally, we present a characterization
of the CAM model as an MC system. As a preliminary experimental study, we
investigate the distribution of fluorescent molecules in the closed-loop
vascular system of the CAM model. We also derive an approximate analytical
model for the propagation of molecules in closed-loop systems, and show that
the proposed model is able to approximate molecule propagation in the CAM
model.
