Viscosimetric properties of sodium hyaluronate and hypromellose solutions for medical devices

Sodium hyaluronate and hydroxypropyl methylcellulose (hypromellose) have proven to be highly useful, finding application in ophthalmic areas as viscosity enhancer agent in eye drops, gelling agent in injections and polymeric matrix in film, filaments and inserts. In this study, the viscosities of binary mixtures to be used as medical devices in microsurgery are analyzed and their pseudoplastic behavior under varying mixing conditions is monitored. All the way such polymers are used to solve extreme surgical situations leaving intermediate situations uncovered because viscosity data of their different combinations are lacking. In this paper, the viscosities of binary mixtures of medical devices used in microsurgery are analyzed and their pseudoplastic behavior under varying mixing conditions is monitored. The zero-shear viscosities, i.e., the maximum viscosity acquired by the system, are described in terms of two “hypothetical” fluids and the experimental results are in agreement with R2=0.98. This provides a useful and immediately used tool for predicting the viscosity of different binary mixtures between medical devices. An extrapolative technique is used to determine the viscosity at infinity γ˙. Non-Newtonian behavior is well-described by the Carreau-Yasuda model whose parameters were calculated. The model provides a useful analytical basis for predicting the behavior of different possible mixtures. The effect that prepared gels undergo in the human eye is mimicked by following the viscosimetric behavior along a dilution line where the mass(hypromellose)/mass(hyaluronate) ratio is constant. A complex rheological behavior emerges from the results due to the interaction of water molecules that make the 3D structure of hyaluronate brittle and reduce viscosity. At high dilutions, however, there is evidence of structure strengthening due to hydrophobic interactions between the polymer chains and an inversion of the viscosimetric curves at 25 ∘C and 37 ∘C is recorded.