Factors Affecting the Rheological Measurement of Hyaluronic Acid Gel Fillers.

BACKGROUND: With the number of available dermal fillers increasing, so is the demand for scientifically based comparisons, often with rheological properties in focus. Since analytical results are always influenced by instrument settings, consensus on settings is essential to make comparison of results from different investigators more useful.

OBJECTIVE: Preferred measurement settings for rheological analysis of hyaluronic acid (HA) fillers are suggested, and the reasoning behind the choices is presented by demonstrating the effect of different measurement settings on select commercial HA fillers.

MATERIALS AND METHODS: Rheological properties of 8 HA fillers were measured in a frequency sweep from 10 to 0.01 Hz at 0.1% strain, using an Anton Paar MCR 301, a PP-25 measuring system with a gap of 1 mm at 25°C. A 30-min period was used for relaxation of the sample between loading and measuring.

RESULTS: The data presented here, together with previously published data, demonstrate differences in G' from 1.6 to 7.4 times for the same product.

CONCLUSION: A large part of the differences were concluded to be due to differences in rheometry measurement settings. The confusion from the many parameters involved in rheometry can be avoided by simply using the elastic modulus (G') to differentiate products. <p><em>J Drugs Dermatol. 2017;16(9):876-882.</em></p>.