Native hyaluronic acid

The method was developed by Robertson, Ropes, and Bauer (163) who used the native hyaluronic acid-protein complex from synovial fluid as the substrate. It was purified and concentrated by a series of precipitations and by dialysis. The final product contiuned 12.5% nitrogen and 7% amino sugar. 

Thus, ionizing radiation provides an excellent tool to reduce the molecular weight of a carbohydrate polymer whenever required for medicinal application, e.g. in the case of chitosan [83-85]. On the other hand, an increased stability against free-radical induced depolymerization might be required. This may be achieved by chemically crosslinking the native linear polymer the radiolytic behaviour of cross-linked hyaluronic acid, called hylan, has been studied [86]. 

As stated above, hyaluronic acid (Figure 1.1), also called hyaluronan and sometimes presented as a hyaluronate (poly)anion from the chemical/structural viewpoint, is a non-sulfated GAG, while all other glycosaminoglycans are sulfated polysaccharides (cf. Table 1.1). Another fundamental and remarkable difference between HA and the other GAGs is the mean molar mass of the native biopolymeric chains. While the value of several MDa is the most common one for HA synthesized by hyaluronan synthases (HASl, HAS2, and HASS), the molar mass of further glycosaminoglycans, on average, does not exceed the value of 50 kDa [8]. 

Erickson, I.E., Kestle, S.R., Zellars, K.H., Farrell, M.J., Kim, M., Burdick, J.A., Mauck, R.L., 2012. High mesenchymal stem cell seeding densities in hyaluronic acid hydrogels produce engineered cartilage with native tissue properties. Acta Biomater. 8, 3027—3034. 

Currently, an ester derivative of hyaluronic acid has been used as a tissue engineering scaffold [8,23,24]. Adipose precursor cells proliferated and differentiated in HA sponges [ 23,24]. Additionally, HA has been used for osteochondral repair by incorporating mesenchymal progenitor cells, which differentiate into osteoblasts and chondrocytes [8]. Furthermore, the interaction of chondrocytes embedded in HA has resulted in the expression of collagen type II, forming a tissue similar to native cartilage [23]. 

---