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David Fisher
For more than 20 years, it has been possible to grow and stretch tissue cells outside of the human body using dynamic bioreactors; systems that control the conditions necessary for maintaining and stimulating living cells and tissues, while involving external mechanical stresses. However, it has still not been possible to produce tendon tissues of high enough quality to work successfully in human grafts.
An important limitation is in the method of mechanically stimulating the cells as Pierre-Alexis Mouthuy, lead author of the study explained. "We're far away from fully functional tendon tissue grafts, and this is partially because we're not providing the complexity of mechanical stresses that cells would experience in a human shoulder," he said. "Existing evidence suggests that delivering advanced physiologically-relevant mechanical cues, or realistic movement of the shoulder up, down, back and forward, with the cells being pushed, pulled, compressed and stretched, is important to mature the tissue properly."
Most current bioreactor systems are only able to deliver unidirectional stretching to the cells, so Pierre and the team from NDORMS looked to real-size musculoskeletal (MSK) humanoid robots as a possible solution to provide physiological stresses, i.e. multidirectional ones. MSK humanoid robots aim to replicate the human musculoskeletal system by mimicking the structure and mechanics of muscles, tendons and bones.
The flexible bioreactor chamber is subjected to repeated abduction-adduction exercises.
Their paper, published in Communications Engineering, explains how they firstly designed a flexible bioreactor chamber. Inside the chamber, cells were grown on stretchy synthetic scaffolds while being perfused with culture medium (providing them with oxygen and nutrients). On a daily basis, the chambers were positioned on the robotic arm and were subjected to repeated abduction-adduction exercises to replicate some of the forces and movements that they would undergo in a real tendon.
Pierre and his team hope that, in the future, lab grown tendon grafts can be used to improve repair outcomes in patients. "Now that we've demonstrated the feasibility of a humanoid bioreactor approach, we can explore the possibilities of this new platform and see if providing these more physiologically relevant mechanical stresses can really help to improve the quality of engineered tendon grafts."
See the robotic bioreactor in action in this Nature video.