# Regeneration of Articular Cartilage Using Membranes of Polyester Scaffolds in a Rabbit Model
## 2 Materials and Methods  
### Materials  
#### 2.1.1 Membranes  
Scaffolds were obtained from the Institute of Biocybernetics and Biomedical Engineering (BBE) of Polish Academy of Sciences. Both scaffolds were made of PLCA by the wet inversion phase method. The difference was the use of various nonwovens as macroporous precursors. Membranes were obtained according to the method presented in previous work [25].  
In the first case, the macropore precursor was a nonwoven fabric made of polyvinylpyrrolidone 1.3 MDa (PVP). We named it \"PVP\" (Figure 1). It was received as follows: the PLCA and Pluronic polymers with 4:1 were dissolved in dioxane with constant stirring to obtain 10 wt.% concentration. Next, a polymer mixture was poured onto the glass base and then the PVP nonwoven layer was laid. Then another portion of polymers was poured on the nonwoven and again a second slice of nonwoven and third layer of membrane forming solution were added. All layers were pressed and the air was removed using a Teflon roller. The received membrane was gelled in a bath with deionized water with ice (about 4 \({}^{\circ}\)C). The prepared membranes were stored in 70% ethanol. It is important to protect the PVP nonwoven from water to prevent its dissolving.  
In the second case, the macropore precursor was a nonwoven fabric made of gelatin. We named it \"Z\" (Figure 2). It was obtained in a similar way to the previous membrane. The PLCA and PVP 10 kDa polymers with 4:1 ratio were dissolved in chloroform with constant stirring to obtain 10 wt.% concentration. The scaffold was made analogous to \"PVP\" preparation. The only difference was that the gelation bath contained cooled methanol at 4 \({}^{\circ}\)C and the obtained membrane was treated with warm water (50 \({}^{\circ}\)C) to removed gelatin nonwoven. Similarly to \"PVP\" membrane, scaffolds were stored in 70% ethanol. The gelatin nonwoven needs to be protected from water.  
The SEM micrographs of \"PVP (Figure 1) and \"Z\" (Figure 2) scaffolds present an irregular structure with macropores and a three-dimensional network of interconnected macropores from 20 to even 500 \(\upmu\)m in diameter. Both scaffolds have perforated skin layers that allow cells to enter them. Furthermore, the addition of extra pore precursors of polymers Pluronic (\"PVP\") and PVP 10 kDa (\"Z\") affects the microporous morphology of the membranes. It ensures access to oxygen, nutritious substances, or allows for the removal of metabolic products from the interior of scaffolds. The average thickness of both scaffolds is about 700-1200 \(\upmu\)m. According to biomedical applications, the porosity and pore size of scaffolds are critical factors. In the previous study, the degradation rate and  
Figure 1: The SEM photomicrographs of the “PVP” membrane.  
porosity of membranes (before and after hydrolysis) were measured [25]. To determine the degradation rate of scaffolds, PBS and Hank's balanced salt solution (HBSS) fluids were used. The hydrolysis time was 5 weeks for \"PVP\" and 4 weeks for \"Z\" due to their faster destructions at 37 \({}^{\circ}\)C. The loss of weight was observed for both membranes in the range from 17 to 72 of weight percentage. We have also observed that the decrease in pH was not rapid--that should not have a negative effect on the body, such as the occurrence of inflammation. Results showed that both membranes were characterized by high porosity, about 95%. After degradation, this value increased, especially for \"Z\" in HBSS.