Extensional rheology of human saliva

We have developed an oscillatory cross-slot extensional rheometer capable of performing measurements with unprecedentedly small volumes of test fluids (∼10–100 μL). This provides the possibility of studying exotic and precious or scarce bio-fluids, such as synovial fluid. To test our system, we have looked at a relatively abundant and accessible biological fluid, namely human saliva; a complex aqueous mixture of high molecular weight mucin molecules and other components. The results represent our first attempts to by this technique and as yet we have only sampled a small dataset. However, we believe we have produced the first successful quantitative measurements of extensional viscosity, Trouton ratio, and flow-induced birefringence made on saliva samples. The results significantly add to the scant literature on saliva rheology, especially in extension, and demonstrate the important role of saliva extensibility in relation to function.