Articular cartilage regeneration with a microgel as a support biomaterial. A rabbit knee model

Articular cartilage has limited regenerative capacity, so focal lesions generate mechanical stress in the joint that induces an aggravation of the damage, which ultimately leads to osteoarthritis. We recently suggested the use of microgels at the site of the cartilage defect, as a support material, to generate a biomechanical environment where pluripotent cells differentiate towards the hyaline cartilage phenotype. Here we propose a chondral regeneration strategy based on subchondral bone injury, and filling the defect site with an agglomerate of two types of microspheres, some rigid made of a biodegradable polyester (40 μm mean diameter), and others with a gel consistency made of platelet-rich plasma obtained from circulating blood (70-110 μm diameter). A 3-mm diameter defect was made in the articular cartilage of the knee joint in rabbits, exposing the subchondral bone, in which incisions were made to produce bleeding. Microgels were implanted filling the defect, which was covered with a synthetic membrane of the same polyester. Three months later, cartilage regeneration was analyzed according to the International Cartilage Repair Society (ICRS) guidelines. The newly formed tissue showed histological characteristics of hyaline cartilage, being significantly closer to native cartilage than when only the membrane was implanted, mainly in parameters such as tissue (70.0 ± 20.9) and cell morphologies (100.0 ± 0.0), and surface architecture (90.0 ± 22.4) and assessment (70.0 ± 11.2), with native tissue having a value of 100. Polyester microspheres and membrane were not bioreabsorbed during the three months, but rather moved towards the subchondral bone, leaving space for the organization of the newly formed tissue.