ABSTRACT
Hyaluronic acid (HA) fillers used in aesthetic indications typically consist of chemically crosslinked HA molecules, resulting in a hydrogel that is less susceptible to enzymatic degradation and has improved rheologic properties compared with uncrosslinked HA. Understanding the range of HA filler products from the standpoint of their rheologic and physicochemical characteristics, can provide an initial framework for predicting treatment outcomes and assist clinicians in selecting the appropriate attributes for each treated facial area. Once injected, HA fillers encounter various forces, such as relative movement between tissue layers, gravity, and/or compression. The lips are treated with HA with medium elasticity. To enhance the lips, fillers are usually described as soft, that is, having low to medium elasticity and low to medium cohesivity, since the challenge in this area is to avoid edges and bumps. Also, a low swelling factor is usually recommended to avoid unnatural-looking results.
