Comparative chemical evaluation of two commercially available derivatives of hyaluronic acid (Hylaform((R)) from rooster combs and Restylane((R)) from streptococcus) used for soft tissue augmentation

Hyaluronic acid (HA) derivatives have been developed to try to enhance rheo logical 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 derivative s are indicated for the correction of cutaneous contour deficiencies of the skin, particularly in cases of ageing or degenerative lesions or to increa se lips. Two HA derivatives have been evaluated: Hylaform(R) Viscoelastic G el (Hylan B), derived from rooster combs and subjected to cross-linking, an d Restylane(R), produced through bacterial fermentation (streptococci) and stabilized, as declared by the producer. In both cases the purpose is to im prove HA rheological characteristics and slow down its degradation once it is in contact with biological structures. Distribution of particle dimensio ns, pH, protein concentration and rheological properties have been investig ated in order to evaluate their reliability as fillers for soft tissue augm entation. The results of the analyses showed that there are differences bet ween Rest ylane(R) and Hylaform(R). Especially as far as rheological charac teristics are concerned, the results outline different structures of the pr oducts: Hylaform(R) behaves as a strong hydrogel, Restylane(R) as a weak hy drogel; theologically Hylaform(R) is clearly superior to Restylane(R). Hyla form(R) contains a definitely minor quantity (about a quarter) of cross-lin ked hyaluronic acid than Restylane(R). Furthermore, although not declared b y the manufacturer, Restylane(R) contains protein, resulting from bacterial fermentation or added to enable cross-linking reaction; the quantity of pr oteins contained by Restylane(R) can be as much as four times the quantity contained by Hylaform(R), for the same volume (1 ml). It is evident that Hy laform(R) offers higher safety margin than Restylane(R). Furthermore, wide literature and 20 years of clinical experience on hyaluronan derived from r ooster combs confirm the reliability of this derivative while we did not fi nd evidence regarding about the safety of HA obtained from streptococcus. ( C) 1999 Elsevier Science B.V. All rights reserved.