LIPOPHILIC SEMISOLID EMULSION SYSTEMS - VISCOELASTIC BEHAVIOR AND PREDICTION OF PHYSICAL STABILITY BY NEURAL-NETWORK MODELING

The influence of different ratios of individual components (silicone s urfactant, hydrophilic and lipophilic phase) on the viscoelastic behav iour of semisolid lipophilic emulsion systems was studied. The creams were prepared according to a preliminary experimental design (mixture design). The content of all three phases was varied: surfactant (1-5%) , purified water (from 40 to 90%) and white petrolatum (5-59%). Oscill atory rheometry was used as the most appropriate experimental method f or the evaluation of the emulsions. The rheological properties were in fluenced by the ratio of the components. For highly concentrated syste ms the predominant elastic response in the whole frequency range was m easured. The cross-over point is characteristic for the concentrated s ystems. For the low concentrated systems, viscous behaviour is predomi nant. Rheometry has also been employed to follow and evaluate physical stability as one of the critical factors of emulsion systems. The dyn amic rheological parameter, tan delta, has been chosen as the basis fo r developing mathematical models (linear, polynomial, neural) to forec ast stability related to the content of the separate components in emu lsion systems. After testing the linear models their non agreement to statistical criteria for a good model F-reg, F-lof, CC, DC, and RMS wa s found. The two-level neural network has been proven to be a statisti cally acceptable model, as were the polynomials of the second order. T he two-level neural network model was also evaluated and the results h ave shown a great degree of reliability. The prediction of tan delta u sing a neural network model was found to be of-great interest for the contemporary pharmaceutical formulation design because a lot of additi onal testing can be omitted. (C) 1998 Elsevier Science B.V. All rights reserved.