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Feb 23, 2021 8:00:00 AM

How to Interpret Rheological Properties When Choosing a Dermal Filler

Selecting the right dermal filler for your patient can be difficult as each patient is unique in their concerns, skin type, and desired result. You can find our dermal filler Rheology report here. Read below on how to interpret this information so you can make the best choice for you, your clinic, and your patients.

 

WHY IS RHEOLOGY IMPORTANT WHEN CHOOSING A DERMAL FILLER?

The rheology of Hyaluronic Acid is crucial to its performance in its many applications. Properties such as viscosity, visco-elasticity, and phase angle all contribute to the handling, injection, and volumizing of the dermal filler. When you are looking at a rheology report of a dermal filler there isn’t necessarily a good or bad number in any of the properties, it simply means the dermal filler will be best suited for a specific application.

WHAT IS VISCOSITY?

Viscosity is the resistance of a fluid or gel to flow. The higher the number the “thicker” or more viscous a product is for injecting. A fluid that is highly viscous has a high resistance (like having more friction) and flows slower than a low-viscosity fluid. To think of viscosity in everyday terms, the easier a fluid moves, the lower the viscosity. For example, honey is more viscous than water. A dermal filler with a higher level of viscosity will be better suited to injecting at a deeper level like the subcutaneous layer of the skin. A dermal filler with a lower level of viscosity will be more likely to spread and is therefore be suited for more superficial applications.

WHY IS VISCO-ELASTICITY PERHAPS THE KEY PROPERTY TO LOOK AT IN A RHEOLOGY REPORT?

Visco-elasticity is defined as the measure of a gel’s rigidity or ability to maintain its shape after injection; or the measure of a gel’s resistance to deformation. The higher the number in visco-elasticity the higher the amount of force needed to change the shape or cause deformation of the gel. An example of this would be jelly compared to a lip balm. A higher amount of force is needed to cause deformation to jelly vs a lip balm. Jelly therefore has a higher visco-elasticity level. Why is visco-elasticity important? Visco-elasticity demonstrates how well formed the gel is. However, depending on what application you need a dermal filler for you may choose a gel with a higher or lower number. A dermal filler with a higher level of visco-elasticity will be better suited for facial contouring as the gel will be more resistant to change it's shape. A dermal filler with a lower visco-elasticity would be better suited for more superficial applications such as tear troughs or peri-oral lines where you would like the gel to be more easily molded.

WHAT IS PHASE ANGLE? 

Phase angle is the measure of the relative dominance of the elastic or viscous response of a sample. The lower the number the more elastic the gel is versus viscous. Conversely, the higher the number the more viscous the gel is versus elastic. If you think of whipped cream versus milk, whipped cream will hold its shape and give a higher level of projection, meaning it has more elastic properties rather than viscous and therefore has a lower phase angle. Whereas milk will easily spread and have a very low projection level which demonstrates that it’s more viscous and therefore has a higher phase angle. Why does this matter? A dermal filler with a lower phase angle gives more projection to the area of injection and is better suited to facial contouring or high definition in the lips. Whereas a dermal filler with a high phase angle will give less projection and will be desirable in applications where more spread is wanted.

Applying these definitions of viscosity, visco-elasticity, and phase angle to our Rheology Report allows us to summarize the following on our new M Series Line of Dermal Fillers:

  • M2 Plus is best suited for superficial application due to its lower viscosity, lower visco-elasticity, and the highest phase angle.
  • M3 Plus falls in between for all three categories. M3 Plus has a lower viscosity, lower visco-elasticity, and higher phase angle than M4 Plus but not nearly as close in numbers to M2 Plus. This shows that it will have more spread once injected and less projection than M4 Plus but still give very desirable results, especially in the lips.
  • M4 Plus has the highest viscosity, the highest visco-elasticity, and the lowest phase angle which very clearly shows it’s best suited to facial contouring in areas like the cheeks, chin, jawline, and nose.
As you can see the different viscous versus elastic properties of the gel are not better or worse, however they do strongly indicate how and where the gel should be injected.

TO DOWNLOAD YOUR OWN COPY OF THE RHEOLOGY REPORT CLICK HERE