In today’s post, the focus will be on hyaluronic acid (HA) fillers and what differentiates the different products from one another. You may have heard of many names thrown around for HA fillers including Juvederm, Juvederm ultra, Juvederm vollure, Restylane silk, Restylane refyne, Belotero, etc.
What is Hyaluronic Acid and How does it Work?
Hyaluronic acid (HA) is a type of sugar (polysaccharide) that is present in body tissues, such as the skin and cartilage. It is able to combine with water and swell (hydrophilic) when in a gel form, causing a smoothing/filling effect. Sources of hyaluronic acid used in dermal fillers are now mostly created from bacterial fermentation but were historically obtained from rooster combs (avian or bird source).
What Makes Different Hyaluronic Acid Fillers Different?
In some cases, the hyaluronic acid used in dermal fillers is chemically modified (crosslinked) to make it last longer in the body. The effects of this material last approximately 6 – 24 months. HA fillers have both natural and synthetic linkages between molecules. Hyaluronidase, a natural enzyme present in the body, breaks down the natural linkages quicker than the synthetic linkages which were formed as a result of chemical modification. These differences in cross-linking attribute to the quality, duration and characteristics of each product. Those with the least links breakdown faster but tend to be the smoothest hydrators. Those with the greatest number of links are stiffer, provide the most projection or lift and last the longest.
A second modification to hyaluronic acid fillers has to do with altering the chemical makeup of the specific molecule that is used. While most fillers are 100% High-molecular weight HA, some are formulated with 90% Low-molecular weight HA and only 10% High-molecular weight HA (“VYCROS” technology). This “VYCROS” technology was developed to created a smoother product that is easier to inject and is therefore less painful to the patient. Recently, however, an increased risk of delayed nodule formation with the use of these products has been noted thought to be due to modulation of immune tolerance (https://www.ncbi.nlm.nih.gov/pubmed/30789508).
Thirdly, different manufacturers process the hyaluronic acid molecules differently. Some are broken into smaller molecular clumps enzymatically, others are filtered through microscopic sieves to separate the molecule sizes.
XpresHAn vs NASHA Fillers
The newest forefront is a class of fillers with “XpresHAn” (pronounced “expression”) technology (Restylane refyne and Restylane defyne) which are characterized by more flexibility and intended to be used in areas of expression. These are in contrast to the more traditional “NASHA” (non-animal stabilized hyaluronic acid) products such as Restylane lyft, restylane-L, and restylane silk which are intended to be used to provide structure and contouring. In fact, the major difference between these “NASHA” products is simply the fact that they are filtered through different size sieves and therefore consist of different molecule sizes. This a great video which shows the different physical properties of these two classes of fillers.
With this post, I hope I was able to answer some of your questions regarding the different HA fillers. The underlying structure of hyaluronic acid fillers is what determines their clinical utility and I focus on this important topic above. We are truly fortunate to have many different products available in our armamentarium that allow us to achieve aesthetic goals across a wide variety of patients and anatomic areas.