Towards bone graft manufacturing via endochondral ossification

In tissue engineering field, conventional manufacturing processes for graft generation have been recently challenged by new insights in basic biology, technological tools and clinical demands.
In the context of long bone repair, we have described for the first time the capacity of expanded, adult human bone marrow derived mesenchymal stromal cells to generate frank bone through endochondral route, by engineering cartilaginous template in vitro. In fact, the process recapitulated the time course of events occurring during limb development, namely (i) cellular condensation and hypertrophic chondrogenesis, (ii) morphogen signaling activation, (iii) formation of bony collar through perichondral ossification, (iv) matrix remodeling and vascularization, and (v) formation of complete bone organ, including hematopoietic elements, in line with the so called “developmental engineering” approach.
With the perspective of clinical applications, we applied bioreactor technology to control, streamline and upscale the process. We focused on optimizing the first events of the endochondral route, developing a novel bioreactor based manufacturing paradigm for cartilaginous graft production, which could be applied for cartilage tissue engineering and used as platform for endochondral recapitulation.
Finally we wanted to achieve control over cell condensation, throughout 3D scaffold and under perfusion regime, as first step of bioreactor-based endochondral tissue engineering. Therefore we aimed at applying computational fluid dynamics model to predict cell behavior within specific milieu and, more precisely, we generated a model system where scaffold design and computed perfusion regime were optimized and validated experimentally by using controlled cell distribution upon perfusion seeding.
The recapitulation of biological and molecular events occurring during development in bone tissue engineering might provide biological and practical advantages and lead to a modern perspective of regenerative medicine. Moreover, the combination with bioreactor based cell culture might facilitate the understanding and optimization of in vitro processes, towards the development of simplified and streamlined regenerative approaches.