A University of Washington research team is developing artificial cartilage that can change its properties during the manufacturing process. The scientists presented their results in the journal ACS Biomaterials Science and Engineering.
In recent years, researchers have used an approach based on growing cartilage tissue from patient cells on special collagen matrices. These matrices help cells better synthesize tissue and provide lubricating properties. But the result is still too soft – reminiscent of cartilage from the nose or ears – therefore it is suitable only for minimal surgical interventions. Natural cartilage in the knee or hip joints is a thin layer 2-4 mm thick, consisting of three zones. The lower layer, tightly connected to the bone, is very rigid and reinforced with vertical fibers. The middle layer serves as a shock absorber, and the top layer, smooth and elastic, ensures gliding and flexibility of the joints.
In their experiment, Washington State University researchers created a bioreactor that allowed bone marrow stem cells to form cartilage with gradient properties – that is, varying in different areas. To do this, they used surface mechanical forces to guide cell growth. In a cone-shaped bioreactor, the flow of liquid creates different levels of shear in different areas, which causes the cells to form cartilage, which becomes more elastic and elastic in one place, and stronger and tougher in another.
Scientists have shown that they are able to form cartilage tissue with different strengths and characteristics by changing the mechanical loads affecting the cells. The resulting tissue sections are close in their properties to the natural three-layer structure of cartilage. In addition, as part of the project, the team creates a special feedback system. One of the difficulties in growing cartilage is that stem cells can sometimes differentiate into bone cells rather than cartilage cells. To control this process, researchers introduce fluorescent proteins. If cells begin to form bone tissue, the protein turns red, and scientists can quickly adjust conditions to suppress unwanted gene activity. If everything goes correctly and cartilage is formed, another protein turns on – it glows green.