Scientists from the University of Basel and the University Hospital of Basel have created a miniature model of the human bone marrow that faithfully mimics its actual structure and function. This three-dimensional model measures 8 mm in diameter and 4 mm in thickness and contains the complete mix of cells and signals needed to make blood. In the laboratory, it can sustain the production of human blood cells for several weeks. The model is made entirely of human cells and represents a significant step towards a better understanding of bone marrow biology compared to previous studies based on animal models. This system can serve as a complement to animal experiments in the study of health and blood diseases, and also in the testing of new drugs. In the future, it could allow the creation of personalised bone marrow models based on the cells of specific patients, which would help in selecting the most effective treatment. However, for the purposes of mass drug testing, the model would need to be scaled down. The research has been published in the journal Cell Stem Cell, and the researchers stress that this is an important step towards reducing the use of animal experiments[1][2][3].