The treatment of facial lines and wrinkles has been battled with injectable collagen fillers for several decades. Despite its widespread use, it was never as popular or extensely used as injectable fillers today because the collagen was made from animal proteins that did not last that long.For six weeks of results, most patients were not overwhelmed to take it by needles for that short time of benefit. In the past few years, those concerns have been replaced by a new material, hyaluronic acid or hyaluron, that improves on all the problems associated with collagen.
Hyaluron (HA) is produced today by fermentation in cultures of equine streptococci. The fermented substance is then stabilized via epoxidic cross-links of the glycosaminoglycan chains. As a result of this processing method, the HA material does not cause immunologic sensitization and actually no risk of allergic reactions. The polysaccharide, hyaluron, is an integral component of the glue between the cells in which all human tissues differiate. In certain tissues, such as the vitreous cavity of the eye and synovial joint fluid, it is the major constituent. Unlike collagen, it is identical across all animal species and microbes. The largest amount of hyaluronan resides in skin, where it is present in both dermis and epidermis. Hyaluronan's high capacity for holding water and high viscoelasticity give it some unique properties that are useful in various medical and pharmaceutical applications.
Because it retains moisture, hyaluronan is used in some cosmetics to keep skin young and fresh-looking. The water-holding property of our skin decrees as we age due to hyaluron depolymerization. Hyaluron injected into or under the skin, therefore, helps in wrinkle reduction. HA can be rather rapidly degraded and is extremely metabolized in the liver. REcently, more stable forms of HA have been made that have even longer duration in humans. As degradation occurs over time, water is attracted to the material at the site of implantation. Water attaches to the HA molecules as it degrades thus accounting for its volume persistence. It is this feature which explains why it lasts longer than cow collagen. (isovolemic degradation)
A variety of varying grades of transparent gels are available, based on the same type gel from highly concentrated (20mg / ml) stabilized HA, which varies in particle size and subsequent indication. Restylane has a particulate size of 100,000 gel particles / ml, flows through a 27 gauge needle, and is indicated for mid-dermal applications such as deaf wrinkle reduction, as well as lip augmentation, nasolabial folds, and glabellar creases. Restylane Fine Lines has the highest concentration at 200,000 gel particles / ml. It is indicated for superior wrinkles and can be injected through a small 30 gauge needle. The lowest concentration gel is Perlane at 8,000 gel particles / ml which is injected through a 27 gauge needle and is intended for shaping facial contours, correcting deep folds, and for lip augmentation. Restylane was FDA-approved in December 2003, Perlane received its approval in 2007. There are numerous manufacturers of HA injectable fillers which, in addition to Restylane, includes Captique and Juvaderm.
The universal HA composition makes the need for pre-injection skin testing unnecessary as the risk for hypersensitivity reactions is minimal. Through a small-gauge needle, it flows smoothly and is easily injected. While not permanent, its persistence is reported to exceeded bovine collagen with estimates of between 4 and 6 months post-injection.Rare side effects, that I have not yet seen, include injection site inflammation at an incidence of 0.02% and local hypersensitivity reactions ( swelling, erythema, and induration) at an incidence of 0.02% lasting a mean of 15 days.
As of today in 2008, HA injectable soft tissue fillers are the gold standard by which all future injectable filler materials will be compared.