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Video Transcript for Rheological Methods for Spreadability:
Spreadability is a key quality attribute for many topical semi-solids and can be investigated using a variety of rheological and tribological techniques.
Rheological data is so important that it is often included as a prerequisite to pass regulatory requirements. In this draft guidance from the EMA, specific metrics are requested including viscosity across a range of shear rates yield stress and viscoelastic moduli within the cosmetics industry. New and enjoyable textures are constantly being developed and have traditionally been characterized using human sensory panels, however the time cost and expertise needed to organize effective studies has driven the development of innovative alternatives.
In vitro analyses offer a rapid objective alternative to large-scale sensory panel studies, providing quantitative information to formulators enabling them to reduce the time spent on the development process. Breaking down spreadability into three distinct time points helps us think about the physical processes at play that we can objectively quantify using combinations of rheological and tribological techniques.
During the early stages of the spreading process the yield stress of the product is a useful quantity to describe the transition of the material as it becomes more susceptible to flow. Viscosity then helps describe the material while it is inflow i.e. being sheared but for old non-Newtonian products such as colloids gels and polymers viscosity is best described as a plot rather than a dot. For the late stage of the spreading process particularly where tactile sensory properties are concerned in topical creams, gels or ointments tribology can provide useful insight into the friction and lubrication characteristics of the process. However spreading is a dynamic process and the contributions of these metrics should be considered as a whole on the experience.
If you would like to discuss how we approach the topic of spreadability relevant for your product or industry then please feel welcome to contact us at lab rheologylab.com.