Katarina Edsman

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 (cmin). 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 cmin, 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.

Intra-articular Duration of Durolane™ after Single Injection into the Rabbit Knee:

Objective: The aim of the present study was to investigate the intra-articular duration of Durolane™ in a rabbit model to allow comparison between Durolane™ residence time and data reported for other hyaluronic acid products as well as native hyaluronic acid. Design: 14C-labeled Durolane™ was manufactured by labeling the cross-linker used for stabilization. A single injection of approximately 0.3 mL 14C-labeled Durolane™ was administered intra-articularly in both knee joints of male New Zealand White rabbits. At days 1, 2, 3, 7, 28, 60, 96, and 120 after injection, the knee joints of 4 animals were collected, and the radioactivity of the remaining gel was measured. The obtained data were fitted by exponential models to calculate the half-life of the gel. Two additional rabbits were used for histology of the joint 127 days after the injection. Results: The elimination of 14C-labeled Durolane™ followed first-order kinetics with an apparent half-life of approximately 32 days. Histology showed no morphological changes in the knee joints. Conclusions: This study shows that Durolane™ has a half-life of 32 days in the rabbit knee joint, which is much longer compared to literature data on hyaluronic acid and other modified hyaluronic acid products.

Is There a Method That Can Measure Cohesivity? Cohesion by Sensory Evaluation Compared With Other Test Methods.

BACKGROUND Cohesion is described as the force between particles of the same substance that acts to unite them. Contrary to rheology, there are currently no ready-made instruments designed to measure cohesion, or methods which could be easily adapted to gels. To study and compare the possible clinical effects from the cohesive properties of a gel, it is necessary to standardize the definition and measurement of cohesion. OBJECTIVE The purpose of this study was to develop and evaluate methods for measuring cohesion. METHODS AND MATERIALS Three different methods were evaluated and compared with measures of perceived cohesion; compression force, dispersion in water and drop weight. Two different families of fillers (Emervel and Restylane) were used for evaluating the different methods. RESULTS The compression force did not reflect the measures of perceived cohesion. The dispersion method showed variable results over time, had some practical issues, and is evaluated by subjective assessment. The best correlation to the perceived cohesion was found with the drop weight method. CONCLUSION The drop weight method which closely resembles the definition of cohesion (IUPAC) was considered to be the best method for measuring cohesion.