Differentiation of NASHA and OBT Hyaluronic Acid Gels According to Strength, Flexibility, and Associated Clinical Significance.

BACKGROUND: With a wide range of hyaluronic acid (HA) filler products available, knowledge of gel characteristics is a key part of tailoring treatments to each patient's aesthetic goals. This paper presents 2 main gel characteristics - strength/firmness and flexibility - for HA fillers produced using NASHA® and OBT™ and their clinical significance for tissue performance. METHODS: Three NASHA gels (Restylane®; Restylane Silk; Restylane Lyft) and 4 OBT gels (Restylane Refyne; Restylane Kysse; Restylane Volyme; Restylane Defyne) were studied in dynamic mode using a PP25 rheometric measuring system at 25 degrees C. Gel strength/firmness was measured using frequency sweep, with G prime evaluated at 0.1 Hz. Flexibility assessments used amplitude sweep measurements between 0.1% and 10,000% strain at 1 Hz, with xStrain being the strain value at the crossover point where G prime and G double prime have the same value.  Results: Restylane, Restylane Silk, and Restylane Lyft had G primes of 701, 416, and 799 Pa, respectively. OBT G primes for Restylane Refyne, Restylane Kysse, Restylane Volyme, and Restylane Defyne were 70, 160, 171, and 271 Pa, respectively. The xStrain values were 1,442% (Restylane Refyne), 908% (Restylane Kysse), 930% (Restylane Volyme), 761% (Restylane Defyne), 7% (Restylane), 19% (Restylane Silk), and 17% (Restylane Lyft).  Conclusions: OBT products had high flexibility (tolerance to deformation) and low to intermediate strength/firmness, which make them appropriate for dynamic facial areas. NASHA products showed greater strength/firmness, with the potential to create lift and projection. Altogether, NASHA and OBT HA gels covered a wide range of strength and flexibility. J Drugs Dermatol. 2024;23(1):1332-1336.     doi:10.36849/JDD.7648.

A randomized, split-face, double-blind, comparative study of the safety and efficacy of small- and large-particle hyaluronic acid fillers for the treatment of nasolabial folds.

BACKGROUND: Injections of hyaluronic acid (HA) for tissue augmentation are one of the most common aesthetic treatments performed worldwide. However, few studies have compared the safety and efficacy of small- and large-particle HA (SP-HA; LP-HA). AIM: To assess and compare the safety and efficacy of SP-HA and LP-HA for the correction of nasolabial folds (NLFs). METHODS: A prospective, split-face, triple-blind study design was used. Ten female subjects were recruited. Patients underwent treatment at baseline, an optional touch up at Week 2, and a follow-up visit at Week 4. At weeks 2 and 4, a blinded reviewer assessed the patients using the Global Aesthetic Improvement Scale (GAIS) and Wrinkle Severity Rating Scale (WSRS); and subjects completed the Patient Satisfaction Questionnaire (PSQ). At all visits, 3-dimensional imagery and ultrasonography of patients' NLFs were captured. Adverse events (AEs) were evaluated by the Investigator and recorded by subjects in diaries. RESULTS: The GAIS response rate, defined as ≥ "improved" from baseline, was between 90 (2 weeks) and 100% (1 month) for SP-HA and was 100% for LP-HA, at both visits. Paired-samples t tests revealed significant differences in the change in WSRS scores between groups, at both visits (P < .01). Differences in the clinical effect and lifting capacity of both products were observed in 3-dimensional imagery and ultrasonography. Treatment volumes varied, with 61.32% more SP-HA being required than LP-HA for achieving a ≥ one-grade WSRS improvement. There were no severe AEs throughout the trial, nor AEs related to the investigational device. CONCLUSIONS: LP-HA demonstrates better efficacy for correcting bony resorption in the nasal pyriform region.

Relaxation and diffusion of water protons in BDDE cross-linked hyaluronic acid hydrogels investigated by NMR spectroscopy-Comparison with physicochemical properties.

Cross-linked hyaluronic acid (HA) hydrogels are used in many biomedical applications but their characterization in order to distinguish between physicochemical properties is challenging. Longitudinal (T1) and transverse (T2) relaxation times and diffusion coefficient (D) of water protons in diepoxide 1,4-butanediol diglycidyl ether (BDDE)-cross-linked HA hydrogels were analyzed by high-field NMR spectroscopy to distinguish between different physicochemical properties. Hydrogels of different degrees of modification and cross-linking, representing a range of gel content, swelling ability, elastic and viscous behavior were studied, as well as solutions of native HA of different molecular weights. T1, T2 and D were measured for several concentrations of HA and as a function of temperature. D and T1 showed a weak concentration dependence, but did not differ between the hydrogels. T2, dominated by chemical exchange between water protons and exchangeable protons of HA, varied significantly between the different hydrogels and the temperature profiles changed dramatically between different concentrations.

Cohesion of Hyaluronic Acid Fillers: Correlation Between Cohesion and Other Physicochemical Properties.

BACKGROUND: There are several published articles on characterization of fillers, describing methods for both chemical and physicochemical characterization. Recently a lot of focus has been on the development of methods for measuring cohesion of hyaluronic acid (HA) fillers. OBJECTIVE: The aim of this study is to investigate and compare the drop-weight method and the correlation between cohesion and other physicochemical properties using a variety of HA fillers. MATERIALS AND METHODS: HA fillers covering several product families and manufacturing techniques were used. The HA fillers also covered a range of HA concentrations from 12 to 24 mg/mL. Cohesion was determined using sensory evaluation and the drop-weight method. Other physicochemical properties evaluated were rheology and the swelling factor. RESULTS: In this study, it was verified that values obtained by the drop-weight method reflect the perceived cohesion very well. The correlation with rheology is affected by the HA concentration in the products. A remarkably good correlation between swelling factor and cohesion was found. CONCLUSION: Cohesion correlates with other physicochemical methods. It could be discussed whether there is a need for a separate cohesion method because other already established physicochemical methods such as rheology and swelling factor can describe the underlying properties that affect cohesion.

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.

J Drugs Dermatol. 2017;16(9):876-882.

Gel properties of hyaluronic acid dermal fillers.

BACKGROUND: Most of the hyaluronic acid (HA)-based dermal fillers currently on the market are chemically modified with cross-linkers to improve the mechanical properties and duration in vivo. OBJECTIVE: To investigate differences in the properties of dermal fillers that can be related to the respective cross-linking and manufacturing methods used. METHODS AND MATERIALS: Thirteen commercially available HA fillers were analyzed. Two different measures of gel strength were used: the elastic modulus (G') determined by rheology and a measure of the swelling capacity of the gel (c(min)). The degree of modification was determined using nuclear magnetic resonance spectroscopy, and the cross-linking ratio was determined using size exclusion chromatography coupled with mass spectrometry. RESULTS: There was a wide variation in gel strength, and the degree of modification varied between 1% and 8% for the HA fillers investigated. CONCLUSIONS: Both measures of gel strength, G* and c(min), can be used because the results from the two methods are well correlated. No differentiation in filler properties could be seen as a result of manufacturing process used, except that the nonanimal stabilized HA stabilization process resulted in products with high gel strength and a low degree of modification.