González, Anthony

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    Rheological characterization of pharmaceutical gel formulations
    (2010) González, Anthony; Acevedo-Rullán, Aldo; College of Engineering; Velázquez, Carlos; Ortiz, Patricia; Department of Chemical Engineering; Pérez, Nestor
    The aim of this research work was to study the rheological properties of an industrially relevant gelatin-based pharmaceutical formulation, since the rheology of the product provides information regarding the structure of the fluid. Moreover, it is desired to have better control over its final viscosity to meet product specifications stipulated by regulatory agencies. Accordingly, the rheological behavior of the formulation was studied under steady and dynamic flow conditions, typical of manufacturing processes. The biovariability of the main structural material can produce significant changes on the rheology of the final formulation. Thus, molecular weight distribution (MWD), water content, and chemical structure of various gelatin drum cuts were determined. Although variations on the distributions were observed, these were found to correlate poorly with the steady-state viscosity and gelation transition. Additionally, the excipients influence on the steady-state rheology was determined by a sensitivity analysis. Gelatin and xanthan were identified as the most important components of the formulation. By solution viscosity and gel strength measurements, poor or no gelation was observed at a gelatin to xanthan ratio of 20, 13, and 12.5 for gelatin 1, 1.3, 2.5 wt% mixtures, respectively. These suggest that under these conditions the formation of complexes prevails, as shown by zeta potential measurements. Addition of salts produced a reduction or vanishing of the interactions between gelatin and xanthan, attributed to the stabilization of xanthan carboxilic group charges. Xanthan is a polyanion and gelatin is an ampholyte, hence, it is possible that the opposed charges have a detrimental effect on the viscosity.