**7. New proposals for repairing articular cartilage**

In recent years they have sought new strategies for cartilage repair, with technological advances have currently been proposed the use of scaffolding or matrix on which cells can grow. Among the scaffolds used in the clinic (Table 2) are those that are based on collagen, hyaluronic acid and fibrin as these provide a substrate normally found in the structure of native articular cartilage. Collagen is a major extracellular matrix protein, exists to provide strength and stability to the connective tissues. At the clinic is used collagen I-III as scaffolds for growing chondrocytes in order to improve the structural and biological properties of the graft [116, 117] this is used as a sponge, foam, gel and membrane form, all these are subject to enzymatic degradation. Hyaluronic acid is another important component of articular cartilage matrix and is a glycosaminoglycan that is involved in homeostasis [118, 119] provides viscoelasticity to synovial fluid, is credited as a lubricant and shock absorbing properties, is essential for the correct structure of proteoglycans in articular cartilage. Between scaffolds containing hyalur‐ onic acid is the Hylaff-11, which is an esterified derivative of hyaluronic acid and is used for growing chondrocytes in three dimensions, has been shown that when using this type of scaffold maintaining the chondrocyte phenotype, so that chondrocytes are capable of produc‐ ing the proteins and molecules characteristic of a hyaline cartilage [120-122]. Fibrin is a protein involved in blood coagulation, is regarded as a biomaterial for cartilage repair, as can be found in gel form, having an adhesive function that is also biocompatible and biodegradable [123]. However in vivo studies in animals have shown to have low mechanical stability and can also trigger an immune response [124, 125], fibrin because this has only been used clinically to ensure healthy cartilage tissue-engineered the [126-128].

Based on the foregoing and which is being used in the clinic and according to results obtained in patients who have been treated with different biomaterials has been observed that although there is a suitable biomaterial that contributes to the production of extracellular matrix to provide the right conditions for chondrocyte cell differentiation. So it is necessary to propose new biomaterials that help produce extracellular matrix, capable of activating a cascade of signaling that can form a cartilage which has structural properties suitable for tissue repair, as well as having viscoelastic properties and to provide mechanical stability.
