TEMPERATURE-INDEPENDENT ISOVISCOUS EFFECT IN TERNARY-SYSTEMS OF WATER, TETRONIC-1307, AND HEMA

The effect of HEMA (2-hydroxyethyl methacrylate) on the rheological behavior of Tetronic (Tetronic 1307 poloxamine polymer)/water mixtures was investigated at various temperatures. Unique viscosity profiles were observed with ternary systems of Tetronic/water/HEMA between 10 and 40°C. The individual viscosity isotherms showed maxima at low HEMA concentrations which declined with increasing HEMA levels as molecular association was progressively inhibited. An "isoviscous" region was observed where the viscosities of the various systems were independent of the temperature. The increase in viscosity at low HEMA concentrations was interpreted as an increase in the size of the various cylindrical and laminar Tetronic micelles due to adsorption of HEMA. Gelation of systems with low HEMA contents occurred as the temperature was increased; hydrophobic bonding resulting from the association of the Tetronic molecules to form more ordered micelles and liquid crystals was promoted. At high HEMA concentrations, the cosolvent action of HEMA promoted a phase change through destabilization of the associated Tetronic network by adsorbed HEMA molecules; the viscosity dropped with the phase change and was then determined primarily by the HEMA/water fluidity. pH effects on the systems were minimal. The rheological characteristics determine syringeability and injectability and become a critical variable in the design of these systems for use as pharmaceutical/medical implants for drug delivery/prosthetic applications. © 1990.