Hyaluronic Acid

Hyaluronic acid is a polysaccharide, glycosaminoglycan, that is chemically identical across all species and tissue types [19]. Hyaluronic acid was first used commercially in 1942 when Endre Balazs applied for a patent to use it as a substitute for egg white in bakery products [20]. It plays an important role in giving volume to the skin, shape to the eyes, and elasticity to the joints. As humans age, cells lose their ability to produce hyaluronic acid, and the skin becomes drier, thinner, and looser, leading eventually to wrinkling, among other changes.

Two main sources of hyaluronic acid have been developed to create a filling agent able to correct moderate rhytids and folds and augment lips: (1) nonanimal hyaluronic acid derived from bacteria in a biofermentation process, and (2) hyaluronic acid from the combs of roosters. Its ability to bind large volumes of water makes hyaluronic acid attractive for dermal implantation [21]. Although the effect of hyaluronic acid is temporary, it is very long lasting [8]. Hyaluronic acid is cross-linked with ester and ether linkages to stabilize the molecule for dermal purposes. The amount of cross-linking of the molecule affects biocompatibility of hyaluronic acid: Less cross-linking of the molecule achieves greater biocompatibility.


Hyaluronic Acid Derived from Bacterial Biofermentation Process
Several preparations of nonanimal hyaluronic acid (example: Restylane) are derived from Streptococcus bacteria in a biofermentation process. Three forms differ in terms of concentration, volume, needle size, and recommended usage [9]. Restylane contains hyaluronic acid particle size of 200 µm and 1% cross-linking; 20 mg/ml hyaluronic acid is cross-linked with ester and ether linkages to stabilize the molecule. Some theorize that the less cross-linking of molecules, the more biocompatible the hyaluronic acid.

In a randomized, double-blind, multicenter comparison of the efficacy and tolerability of nonanimal hyaluronic acid versus bovine collagen cross-linked with glutaraldehyde for the correction of nasolabial folds, it was shown that less injection volume was required for “optimal cosmetic result” with hyaluronic acid gel than with bovine collagen. Moreover, both patients and investigators judged hyaluronic acid more effective in maintaining cosmetic correction [22].

Viscoelastic,Nonanimal Hyaluronic Acid Gel Derived from Bacterial Biofermentation
Another family of products containing a viscoelastic nonanimal hyaluronic acid gel (example: Juvederm) is available in three different concentrations (18 mg/ml, 24 mg/ml, and 30 mg/ ml) to address different correction needs.Hyaluronic acid gel is eventually absorbed into the body.

Viscoelastic Hyaluronic Acid Gel from Rooster Combs
Another hyaluronic viscoelastic gel contains hyaluronic acid derived from the combs of roosters (example: Hylaform). Hylaform contains 5.5 mg/ml hyaluronic acid with a particle size of 500 µm. It has 20% cross-linking as a result of using glutaraldehyde and vinyl sulfone for hyaluronic acid stabilization. According to the manufacturer, the product’s high molecular weight makes it more viscous and longer lasting than the hyaluronic acid produced from bacteria.