# Regeneration of Articular Cartilage Using Membranes of Polyester Scaffolds in a Rabbit Model
## 4 Discussion  
In our work, we examined scaffolds that have potential use for cartilage tissue engineering. Our scaffolds are characterized by biocompatibility, degradability, and adequate structure. They have perforated top layers with pore diameters of more than 20 \(\upmu\)m that allow MSCs to penetrate inside the membrane. The interiors of both membranes (Figures 1 and 2) shows a network of interconnected macropores with an appropriate pore diameter larger than 300 \(\upmu\)m, necessary for the chondrogenesis of MSCs [16; 66; 67; 68]. Their structures provide an appropriate environment for the proliferation, migration, and adhesion of cells. The semipermeable structure assures nutritious, oxygen transport, and metabolic products. Furthermore, the bottom skin layers of the scaffolds are dense, preventing cells from getting out from scaffolds [28]. During the implantation phase, we noticed that membrane \"Z\" was more fragile and disintegrated easier compared to membrane \"PVP\". Because of this, it was easier to place  
Figure 9: Shows histological samples of the cartilage of the rabbit of the studied groups. The following observations were made by one histological. (**A**) PVP group after 8 weeks of observation—the defect is easily visible; (1) the surface has irregularities, (2) cells are disorganized, (3) increased remodeling of subchondral bone. (**B**) Z group after 8 weeks of observation—the defect is easily visible; (1) the surface has irregularities, (2) cartilage necrosis, (3) cells are distributed in clusters (4) chondral fracture reaching the subchondral bone. (**C**) Control group after 8 weeks of observation—the defect is easily visible; (1) the surface has irregularities, (2) massive loss of subchondral bone, (3) Bone fractures with the separation of necrotic fragments. (**D**) PVP group after 16 weeks of observation; (1) cells are distributed in clusters, (2) cartilage fracture, the surface has irregularities; (3) porous subchondral bone in some places, otherwise normal. (**E**) Z group after 16 weeks of observation—the defect is easily visible; (1) cells are distributed irregularly, (2) the surface is torn, (3) porous subchondral bone in some places, otherwise normal. (**F**) control group after 16 weeks of observation—the defect is easily visible; (1) the surface is torn, (2) chondral fractures reaching the subchondral bone, (3) cells are distributed irregularly. (**G**) PVP group after 24 weeks of observation; (1) the surface is torn/has irregularities, (2) cartilage fractures, cells are distributed irregularly, (3) increased remodeling of subchondral bone. (**H**) Z group after 24 weeks of observation; (1) the surface is torn, (2) necrosis, (3) cells are distributed in columns. (**I**) Control group after 24 weeks of observation; (1) the surface has irregularities; (2) full thickness chondral fracture; (3) cells are distributed irregularly. (**J**) Histological image of correct hyaline cartilage in rabbit model—(1) cartilage, (2) subchondral bone. and hold the \"PVP\" scaffold at the chosen localization (defect). This feature can be of great importance during implantation, not with glue but with threads, e.g., in the human knee. We created (according to the International Cartilage Repair Society (ICRS) recommended guidelines for histological endpoints for cartilage repair studies in animal models and clinical trials) relatively large (0.1 cm\({}^{2}\)) and deep (3 mm) defects (Figure 3), which, especially after the first observation period (8 weeks), could have resulted in the lack of statistical significance of the cartilage regeneration assessments between groups. However, the extended observation time showed that the scores of regenerates without the use of a membrane were worse with each subsequent observation period and the scores of regenerates with membranes improved over time (Figures 7 and 8). We believe that this is because the cartilage in the control group is mechanically weak, despite the fact that, in the histological picture, it was initially similar to the other groups.