Viscoelasticity of hyaluronan and nonhyaluronan based vocal fold injectables: implications for mucosal versus muscle use

OBJECTIVES: The purpose of this study was to measure and compare biomechanical properties of commonly used vocal fold injectates Cymetra, Radiesse, Restylane, Hylaform, and one investigational injectate, Carbylan-GSX 5%, to determine suitability for mucosal injection. STUDY DESIGN: Rheologic investigation. METHODS: Oscillatory shear stress was applied to five samples of each injectate using a parallel plate controlled stress rheometer. Shear stress, shear strain, and strain rate associated with the oscillatory shear deformation were computed from the prescribed torque and measured angular velocity; viscoelastic data were obtained on the basis of these functions. Values calculated included elastic shear moduli, viscous moduli, and dynamic viscosity as a function of oscillatory frequency (0.01-150 Hz). RESULTS: Elastic moduli for all samples increased as the frequency increased. Hyaluronan based materials were all comparable with each other and at least an order of magnitude lower than the stiffer and more viscous Cymetra and Radiesse. Carbylan-GSX 5% was found to have almost identical values to Hylaform with the exception of its mean viscosity, which was noticeably lower. CONCLUSIONS: Hyaluronan based biomaterials offer less resistance to flow and stiffness and may be better suited for injections into the mucosa, whereas Cymetra and Radiesse appear to be appropriate for injections into muscle. Viscoelastic properties of Hylaform and Carbylan-GSX 5% were found to most resemble that of the human vocal fold mucosa.