Foam-in-vein: rheological characterisation of liquid sclerosing foams using a pipe viscometer

Sclerotherapy is one of the most common and least-invasive treatment methods for varicose veins. While bench-top properties of sclerosing foams (e.g., bubble size distribution and foam half-life) have been studied previously, their flow behaviour and its relationship to therapeutic efficacy remain largely uncharacterised. To address this research gap, the present study reports on a novel approach for the rheological characterisation of sclerosing foams aimed at obtaining clinically-applicable data. A pipe viscometry apparatus was employed under conditions that mimic the end-point therapeutic application of foams. Polidocanol (1% v/v) foams of various liquid-to-gas volume ratios (1:3, 1:4 and 1:5) were formulated manually using the Tessari and DSS (double syringe system) methods across a clinically-relevant range of shear rates (≈ 7s−1 – 400s−1), in polytetrafluoroethylene pipes of different diameters (2.48 mm and 4.48 mm). Additionally, end-effect and wall-slip correction methods were utilised to model the nominal rheology of sclerosing foams. The rheological data were fitted into a power-law model to obtain fluid flow index (n) and fluid consistency index (K) of sclerosing foams, followed by an in-depth statistical analysis of the power-law indices. The observed rheological behaviour of sclerosing foams is shown to be dependent on vessel diameter and liquid-to-gas ratio, while the type of manual formulation technique used appears to be statistically insignificant towards foam rheology. Sclerosing foams behaved as shear-thinning fluids with observed flow indices ranging 0.238 < n K