Gel Properties of Hyaluronic Acid Dermal Fillers

BACKGROUND: Most of the hyaluronic acid (HA)-based dermal fillers currently on the market are chemically modified with cross-linkers to improve the mechanical properties and duration in vivo. OBJECTIVE: To investigate differences in the properties of dermal fillers that can be related to the respective cross-linking and manufacturing methods used. METHODS AND MATERIALS: Thirteen commercially available HA fillers were analyzed. Two different measures of gel strength were used: the elastic modulus (G') determined by rheology and a measure of the swelling capacity of the gel (c(min)). The degree of modification was determined using nuclear magnetic resonance spectroscopy, and the cross-linking ratio was determined using size exclusion chromatography coupled with mass spectrometry. RESULTS: There was a wide variation in gel strength, and the degree of modification varied between 1% and 8% for the HA fillers investigated. CONCLUSIONS: Both measures of gel strength, G* and c(min), can be used because the results from the two methods are well correlated. No differentiation in filler properties could be seen as a result of manufacturing process used, except that the nonanimal stabilized HA stabilization process resulted in products with high gel strength and a low degree of modification.