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.

A radiofrequency air plasma has been used to incorporate new functionalities at the surface of cycloolefin polymers (Zeonex and Topas), polymethyl methacrylate (PMMA), styrene-acrylonitrile copolymer (SAN), and polystyrene (PS). The main goals with the plasma treatment of the different plastics were to hydrophilize the surfaces and to provide good cell culture properties. Surfaces treated at high RF power/gas flow ratios (50 to 100 W/sccm) became highly hydrophilic (water contact angles of about 5 degrees) and stable towards washing in 70% (v/v) ethanol. Those treated at lower power/gas flow ratios (3 to 10 W/sccm) were less hydrophilic and not wash-stable. Cell growth properties of HeLa cervix carcinoma cells as good as on commercial tissue-culture polystyrene could be obtained for Zeonex, SAN, and PS, treated at relatively low RF power/ gas flow ratios. However, no untreated plastics were suitable for culturing these cells. XPS spectra features show that ester, ether/alcohol, and ester/carboxyl groups are formed during the plasma treatments of the different plastics. Measurable amounts of carboxylic acid carbon after plasma treatment were only observed for PS and Topas. Furthermore, at high RF power/gas flow ratios fluorine, aluminium and silicon were incorporated in all investigated plastics surfaces due to ablation-deposition processes in the reaction chamber.

BACKGROUNDThere 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.OBJECTIVEThe 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 METHODSHA 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.RESULTSIn 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.CONCLUSIONCohesion 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.

Background: The majority of studies published on rheology of hyaluronic acid (HA) fillers have focused on results from frequency sweeps within the linear viscoelastic region (LVR), i.e. at nearly static conditions. To study the properties and behavior of HA fillers at more dynamic conditions, it is necessary to go outside the LVR. Objective: Evaluation of the G'/G'' cross-over point from the amplitude sweep is suggested as a manner to estimate the flexibility of HA fillers. Materials and methods: Rheological properties of 7 HA fillers were measured in an amplitude sweep from 0.1% to 10000% strain at 1 Hz, using an Anton Paar MCR 301, a PP-25 measuring system with a gap of 1 mm at 25˚C and a 30-min relaxation time. The cross-over point was evaluated for stress, strain and G (G' and G'' identical), the values denoted xStrain, xStress and xG. Results: The xStrain values spanned from below 1000% to above 2000% for the products based on the Optimal Balance Technology (OBT)™ (in the US, XpresHAn Technology™), compared to below 100% for the products based on the NASHA® technology. Conclusions: Measurement of the flexibility provides a more complete picture of the rheological properties of HA fillers as a complement to firmness measured as G'. The test results show that the Restylane family of products covers a large range in flexibility, and that the flexibility can be estimated using xStrain derived from the amplitude sweep.