Hyaluronic acid (HA) was first discovered by Meyer and Palmer in 1934. HA is a long, linear polysaccharide composed of repeating disaccharide units of N-acetylglucosamine and D-glucuronic acid. HA has potential use in skin rejuvenation, is rapidly metabolized by hyaluronidase and free radicals, and is highly soluble. By using cross-linking agents, the in vivo residence of HA can be increased. Currently various HAs are being used to rejuvenate facial skin. Animal-source single-cross-linked HA was developed in 1990; its concentration is 5.5 mg/mL, and its duration is relatively short. Non-animal-source single-cross-linked HA was developed in 1994, with a concentration of 20–24 mg/mL and a duration that is relatively longer than the animal-source HA. More recently, a non-animal-source double-cross-linked HA, Puragen, which was recently renamed Prevelle (Mentor Corp.), was developed.

WHAT IS PURAGEN?

Restylane and Puragen have the same concentration of HA (20 mg/mL); however, Puragen has different constituent properties from Restylane. First, the HA chains of Puragen are chemically cross-linked, giving in vivo stability to the product. Hylaform, Restylane, and Juvéderm are single cross-linked with ether bonds. Puragen is double cross-linked with ether bonds and ester bonds. Ester bond linkages confer increased stability and protect ether bonds during sterilization, and are hydrophobic. The novel process can be tailored to yield water-insoluble gels and films with a broad range of physical and chemical characteristics, and greater resistance to degradation by hyaluronidase and free radicals. Second, Restylane has a larger particle size (about 250–300 μm) than Puragen (about 200 μm).