# Regeneration of Articular Cartilage Using Membranes of Polyester Scaffolds in a Rabbit Model
###### Abstract
The degradation products should be non-toxic, non-inflammatory, and mechanically neutral (with adequate softness, stiffness, and roughness). These materials should also be resistant to the conditions in the body, such as pH and body temperature for a certain period. Membranes should have an appropriate microstructure (porosity, pore size, pore shape) [28] and allow for the formation of functional gap junctions and interaction with other cells and the extracellular matrix. The asymmetry of the membrane structure is extremely important--one surface of the membrane should have numerous and large pores, while the opposite surface should have as few and as small pores as possible. This prevents the cells from escaping from the substrate. The size of the pore is properly defined in the purpose of the research, among other things, as is the kind of cells for which the membranes are intended. For example, working with chondrocytes requires smaller pores than working with stem cells for chondrogenesis or with osteoblasts. However, the most important parameters are: biodegradation time; non-toxic, soft metabolites; and a safe degradation process without inflammatory reactions [10; 13; 16; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39]. Materials for an implant are mainly made of synthetic or natural polymers or a combination of both (hybrid materials) Currently, commercial scaffolds for cartilage regeneration are made primarily of collagen. Due to defects in the natural polymers, these scaffolds do not meet the appropriate requirements (their rapid hydrolysis, low mechanical stability) that lead to the regenerated tissue being non-valuable fibrocartilage rather than hyaline cartilage [13; 16; 26; 27; 28; 37; 40]. Unlike natural materials, polyesters provide good mechanical properties and can be used to produce a variety of scaffold shapes using many techniques. They are biocompatible with good mechanical strength that hydrolyze into harmless components that are metabolized in the body and are easily removed from the organism [27; 37; 41; 42; 43]. Currently, research is focused on synthetic polymers, such as polycaprolactone (PCL) and poly (L-lactic acid) (PLLA). Various proportions and combinations of these biodegradable polymers can be used to achieve the desirable surface, mechanical, and structural properties [41; 44; 45; 46; 47]. Synthetic polyesters, such as poly(Llactide-\(\epsilon\)-caprolactone) copolymers, are biocompatible and completely bioresorbable. Their degradation products are non-toxic to cells and the major route of the first stage of degradation is hydrolysis. The degradation pathway is through monomers that are elastic and they do not damage the articular surface. The second stage of degradation is the conversion of the monomer to carbon dioxide and water. When polylactide membranes are broken down, lactic acid is formed, which induces inflammation. On the one hand, however, the use of a lactic acid copolymer reduces the concentration of lactic acid in the decomposition products; on the other, it allows the glass transition temperature of the copolymer to be lowered and, ultimately, by disturbing the regularity of the PLA structure, it accelerates the decomposition process [48; 49]. An important advantage of co-polyester PLCA structures is that they do not lose their strength in the aquatic environment, and their mechanical and biological durability is significantly greater than that of the collagen substrate. The fact that caprolactone, which is part of the copolymer, has been used for many years to coat absorbable surgical sutures, is an argument in favor of the selected membranes [50]. Individual polyesters differ in biodegradation time--the rule is that the longer the carbon chain, the longer the decomposition time. Due to this mechanism, we can roughly estimate the time it takes for the entire substrate to convert to water and carbon dioxide [51; 52; 53]. Such membranes can be used in medicine where scientists and doctors are still looking for new scaffolds for the treatment of articular cartilage.