摘要：

Hyaluronic acid (HA) derivatives have been develop to try to enhance rheological properties of this molecule to make it suitable for various medical applications. The main dermatological application of HA derivatives is the augmentation of soft tissues, via injection into the dermis. HA derivatives are indicated for the correction of cutaneous contour deficiencies of the skin, particularly in cases of ageing or degenerative lesions or to increase lips. Two HA derivatives have been evaluated: Hylaform&reg Viscoelastic Gel (Hylan B), derived from rooster combs and subjected to cross-linking, and Restylane&reg, produced through bacterial fermentation (streptococci) and stabilized, as declared by the producer. In both cases the purpose is to improve HA rheological characateristics and slow down its degradation once it is in contact with biological structures. Distribution of particle dimenisions, pH,protein concentration and rheological characteristics properties have been investigated inorder to evalutate their reliability as fillers for soft tissue augmentation. The results of the analysis showed that there are differences between Restylane&reg and Hylaform&reg. Especially as far as rheological characterisitics are concerned, the results ouline different structures of the products: Hylaform&reg behaves as a strong hydrogel. Restylane&reg as a weak hydrogel: rheologically Hylaform&reg is clearly superior to Restylane&reg. Hylaform&reg contains a definitely minor quantity (about a quarter) of cross-linked hyaluronic acid than Restylane&reg. Furthermore, although not declared by the manufacturer, Restylane&reg contains protein, resulting from bacterial fermentation or added to enable cross-linking reaction; the quantity of proteins contained by Restylane&reg can be as much as four times the quantity contained by Hylaform&reg, for the same volume (1 ml). It is evident that Hylaform&reg offers higher safety margin than Restylane&reg. Furthermore, wide literature and 20 years of clinical experience on hyaluronan derived from rooster combs confirm the reliability of this derivative while we did not find evidence regarding about the safety of HA obtained from streptococcus. 1999 Elsevier Science B.V. All rights reserved.

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