Complex viscosity and cohesive energy density of mixtures of sodium hyaluronate and hypromellose for medical devices

In the present study binary formulations of sodium hyaluronate ([Formula presented]) and hypromellose ([Formula presented]) were proposed as medical devices in the field of eye surgeries. Viscoelasticity is tested directly on binary solutions while the rheological behavior in the human eye is mimicked by monitoring the viscoelasticity of ternary mixtures [Formula presented]/[Formula presented]/[Formula presented]. Both binary and ternary formulations were rheologically characterized at 25 ∘C and 37 ∘C by means of measurements in the oscillatory regime. Amplitude sweep tests revealed that the range of linear viscoelasticity is strongly dependent on the concentration of [Formula presented]. For the proposed formulations, it was ascertained that the cohesive energy density at 37 ∘C decreases as [Formula presented] concentration surges; in contrast, at 25 ∘C we detected an increase of cohesive energy were detected. At [Formula presented] mass fraction of α1, the two obtained values were comparable. Frequency sweep tests revealed the pseudoplastic character of the binary formulations. In order to fit the complex viscosity modules, the Carreau-Yasuda model was modified. Numerical analysis of the results indicates that the best-fit to the model is obtained when the characteristic parameters take constant values, i.e. n=0 and m=1, regardless of the composition of the formulation. This implies that the modulus of complex viscosity decays hyperbolically. Frequency sweep tests on the ternary formulations were analyzed in terms of both the modulus of complex viscosity to confirm the previous scientific evidence together with an investigation of the phase shift angle between the viscous and elastic components. The results indicate that the addition of water has a different impact on the structure and the cohesion of the mixture at different temperatures. These results suggest that the ternary mixture structure can be sensitively modulated by temperature and the content of water.