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Gavard Molliard et al. Plast Aesthet Res 2018;5:17 I http://dx.doi.org/10.20517/2347-9264.2018.10 Page 7 of 8

Table 3. Key rheological properties of HA fillers all along their clinical lifetime. Influence of viscosity η, normal force F N ,
elastic modulus G’, elastic modulus E’ and cohesivity at each step of the HA fillers’ clinical lifetime
Viscosity Normal force of Elastic modulus in Elastic modulus in Cohesivity
η compression shear-stress compression
G’ E’
F N
Step 1: injection & integration Major Major
Step 2: projection Major
Step 3: dynamic facial expression Major Major
Step 4: degradation Major Major Major

Illustration of the key rheological properties with a novel range of HA fillers
The novel range of HA fillers obtained according to the OXIFREE™ technology was designed with the
aim to offer optimized cohesivity and rheological properties for clinical indications covered by each
product. Two of these HA fillers (A and B), designed for dermal injection, i.e., superficial administration,
have lower viscosities to obtain optimal injection and HA distribution/integration in this skin layer. The
normal forces of compression have been selected to deliver an efficient intradermal projection to treat
superficial to medium indications of the face, e.g., to treat fine lines or medium to deep-sized depressions
of the skin. The 2 other HA fillers of this range (C and D), were designed for subcutaneous injection and
to that end, they have high viscosities and high normal forces of compression to procure an optimal
capacity of tissues projection in the treatment of the facial contours. Especially, it is notable to observe
that product D, intended for the restoration of the volume of the face, has a very strong ability to project
the skin tissues thanks to its very high normal force of compression and its high viscosity, even in front of
Juvéderm Voluma™, the worldwide market leader in the segment of the volumizing HA products. Finally,
it is important to outline that all HA fillers of this range have both high elastic moduli G’ and E’, which
give a powerful capacity to all the gel implants of this range for withstanding to the mechanical stress in
shearing and compression, with the essential purpose to move as one with the skin tissues and therefore
to provide natural clinical outcomes, particularly throughout the dynamic expression of the face.

Conclusion
HA fillers play an increasingly important role in minimally invasive aesthetic procedures and a broad palette
of products is now available to the physicians. Science-based evaluation of the HA fillers and especially the
analysis of their rheological characteristics was emphasized to be a very useful tool for the physicians to
guide them in the selection and usage of the most relevant products, administration techniques and depths
of injection for the intended treatments.

The present article highlights the importance of the 4 key rheological properties viscosity η, elasticy
G’, normal force F and elasticity E’ for better understanding and predicting the behavior of HA fillers
N
during their whole lifetime in the skin tissues, i.e., from their injection in dermal layer or subcutaneous
tissues, to their in vivo degradation and therefore, their loss of clinical effects. The purpose of this article
is to provide valuable scientific rationale for better explaining the products’ behavior during their tissue
integration after injection, their capacity to project the skin tissues, their ability to respond to the dynamic
facial expression for generating a treatment natural effect, and the gradual disappearance of the clinical
benefits.

On the other hand, this article provides a scientific evaluation of a novel range of HA fillers with advanced
rheological features with the aim to better predict its clinical behavior. The highlighted findings illustrate
how the study of key rheological properties can help the physicians to select the most appropriate product
to be administered for the intended use, the volume of product to be injected and the most relevant
injection technique to be applied for optimizing aesthetic outcomes, safety and patient satisfaction.