DISCUSSION
The data reported herein demonstrate a broad range in flexibility and strength/firmness for the HA fillers manufactured by the NASHA and OBT technologies. Among the variety of parameters used to differentiate HA fillers, both G prime and xStrain are based on accepted rheological measures, of which G prime may be the most widely used.2,6,11 G primes for the Restylane fillers have previously been reported by, for example, Fagien et al (2019), Ohrlund et al (2018), and Lorenc et al (2017), and with similar results to what is reported herein.6,11,29 However, G primes for two of the products produced by NASHA were slightly higher than previously reported.6 In this study, respective G primes for Restylane and R. Lyft were 701 Pa and 799 Pa, compared with 544 Pa (Restylane) and 545 Pa (R. Lyft) reported by Fagien et al (2019).6 A possible explanation may be slightly different instrumental settings as there is a lack of standard measurement guidance among different stakeholders.29
Access to a range of HA fillers with different physicochemical and rheological profiles provides the clinician with a toolbox of options that can be used to individualize and adapt aesthetic treatment according to personal requirements, facial structure, and desired outcome.18,30,31 It is commonly suggested that clinicians must also have a good understanding of these properties to obtain optimum aesthetic results.2,4,5,7-10,32,33 However, although there is a wide body of literature describing how physicochemical and rheological properties can be used to characterize different HA fillers, there are very few studies that correlate in vitro measurements with clinical performance.6
As reported in this study and previous studies, the NASHA technology typically produces strong/firm gels that are able to resist deformation.6,12,33 Hence, these products are considered optimal for facial anatomical locations requiring precise projection, lift, or contouring. In a clinical setting, Di Gregorio et al (2022) demonstrated optimal aesthetic results with R. Lyft in the midface for subjects with thick tissue coverage and where the primary need for treatment was lifting or contouring.18 Similarly, Jones et al (2020) showed improved aesthetic results for midface contouring with R. Lyft.34 The high and precise projection capability of R. Lyft was demonstrated in a randomized and controlled clinical investigation showing R. Lyft to be effective in shaping the nasal dorsum and radix with aesthetic improvement maintained for up to 12 months.35 Huang and Tsai (2020) also demonstrated long-term aesthetic improvement and subject satisfaction (maintained over 24 months including one re-treatment) with both Restylane and R. Lyft used in multiple facial locations, including for example the midface, nose, and chin.36
As opposed to HA fillers based on the NASHA technology, HA fillers produced by the OBT technology are less strong/firm (softer, lower G prime) but highly flexible (high xStrain).11 Softer gels may be less capable of resisting deformation compared with stronger/firmer gels, but greater flexibility allows them to tolerate deformation because they have the ability to return to their original shape once the strain is removed. Hence, a flexible gel is optimized for treating dynamic areas of the face (eg, nasolabial folds, marionette lines, and perioral regions including the lips) where an increased strain is applied during facial movements or expressions and removed when the face relaxes and returns to a static condition. Perceived naturalness of dynamic facial expression when the face was in motion was shown to be maintained or enhanced through 6 months following treatment of wrinkles and folds in the lower face, including nasolabial folds, marionette lines, and oral commissures, with R. Defyne or R. Refyne.31,37 Percec et al (2020) used 3D digital imaging to show that R. Defyne and R. Refyne reduced the strain in most active facial expressions, and the changes in stretch and compression achieved resembled those of a more youthful face.27 In addition, enhanced naturalness of the lower face when in motion was demonstrated after treatment with R. Defyne or R. Refyne in subjects with moderate to severe nasolabial folds and marionette lines.26 Studies examining the use of R. Kysse in combination with R. Defyne and R. Refyne in the lips and perioral enhancement reported improved fulness, reduced wrinkle severity, and enhanced surface stretch, while natural movement and dynamic expression were maintained.38-40
CONCLUSION
Restylane HA fillers manufactured with NASHA and OBT Technologies displayed a wide range in both strength/firmness and flexibility. OBT products were highly flexible and lower in strength/firmness (with low to intermediate G prime), and have been shown to provide optimal clinical results in dynamic areas of the face such as nasolabial folds or lip region. By comparison, NASHA products were stronger (with higher G prime) but comparatively low in flexibility, conferring advantageous properties for targeted treatment to provide lift and projection in areas such as the nose and chin. These results provide a greater understanding of gel properties and how these properties translate to tissue performance to help guide clinicians in their selection of products for an optimal aesthetic outcome.
DISCLOSURES
Ake Ohrlund, Per Winlof, Torun Bromee, and Inna Prygova are all employees at Galderma, Uppsala, Sweden.
Funding: The study was funded by Galderma.
Authorship Statement: All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship for this manuscript, take responsibility for the integrity of the work as a whole, and have given final approval for this version to be published.
