Understanding Rheology in Hyaluronic Acid Fillers: An Essential Guide for Medical Aesthetics

Dr Michelle Westcott 

Dermal Filler Training Ireland
In the realm of medical aesthetics, the term "rheology" refers to the study of the flow and deformation of matter, specifically how substances respond to applied forces. When it comes to hyaluronic acid (HA) fillers, rheology is pivotal in determining how the filler behaves under the skin, affecting everything from its ease of injection to its longevity and aesthetic outcome. This article explores the concept of rheology in HA fillers, outlines the key rheological properties, and discusses differences among leading brands in the market.

What is Rheology?

Rheology in the context of HA fillers involves studying the properties that dictate how the filler integrates and interacts with the body’s tissue. This field examines properties like viscosity (resistance to flow), elasticity (ability to return to original shape after deformation), and cohesivity (ability to stick together and not disperse under pressure).

Rheological Properties of HA Fillers

  1. Viscosity: This is a measure of a filler’s resistance to flow when a force is applied. High viscosity fillers are thicker and flow less easily, which helps them maintain their shape once injected.

  2. Elasticity (G’): Also known as the modulus of elasticity, this parameter measures the gel’s firmness and ability to resist deformation. Higher elasticity is preferred in areas requiring support and volume, like the cheeks and jawline.

  3. Cohesivity: This property determines how well the particles of the HA gel stick to each other. Fillers with high cohesivity are less likely to migrate from the injection site and often provide a more natural, uniform look.

  4. Thixotropy: Some fillers exhibit thixotropic behaviors, meaning their viscosity decreases under shear stress (e.g., during injection) and then increases once the stress is removed. This property allows for easier injection while maintaining form stability post-injection.

Comparing Rheological Properties Across Brands

Different brands of HA fillers are designed to target specific needs by varying their rheological properties. Here’s a look at how some of the leading brands compare:

  • Juvederm®: This line of fillers, produced by Allergan, is known for its Vycross technology, which offers a high degree of cross-linking. This results in fillers that are highly cohesive and elastic, suitable for both deep volume restoration and superficial fine lines. Juvederm fillers generally exhibit high viscosity and elasticity, making them effective in achieving long-lasting results.

  • Restylane®: Galderma’s Restylane products use NASHA technology, which stabilizes non-animal sourced hyaluronic acid. These fillers are designed to have a balance between elasticity and cohesivity, making them versatile for a variety of applications from lip enhancement to deep cheek volumization. They tend to have a slightly lower viscosity than Juvederm, which can make them easier to mold once injected.

  • Teosyal®: Teoxane’s Teosyal fillers are highly cohesive, which helps reduce the risk of migration. They are known for their resilience and ability to integrate smoothly with the existing tissues, supporting subtle enhancements that feel natural to the touch. Their rheological properties often emphasize high elasticity, particularly in products designed for resilient areas like the cheeks and jawline.

Importance of Rheology in Practice

Understanding the rheological properties of HA fillers is crucial for practitioners to choose the right product for the desired outcome. High viscosity and elasticity are typically sought for lifting and volumizing effects, while lower viscosity may be preferable for superficial injections or areas requiring finer touch-ups. The cohesivity of the filler impacts not only the outcome but also the longevity of the treatment, influencing how the product will age with the skin.

In conclusion, the rheology of hyaluronic acid fillers is a fundamental concept in medical aesthetics that influences everything from product selection to injection techniques and final results. By mastering the understanding of these properties, practitioners can enhance their ability to tailor treatments to individual patient needs, ensuring both safety and satisfaction in aesthetic outcomes. Dr Michelle Westcott Aesthetic Academy will train you on the various rheological properties of different dermal fillers.