Ultrasound Imaging of Artificial Tongues During Compression and Shearing of Food Gels on a Biomimetic Testing Bench

Characterizing the deformations undergone by the tongue during food oral processing could help to better understand how texture sensations are perceived. In this article, we propose to study the potential of ultrasound (US) imaging to monitor the deformations undergone by artificial tongues during compression and shear of agar food gels. Four polyvinyl alcohol cryogels were used as artificial tongues (two levels of roughness and two levels of stiffness), while three agar gels of different concentrations were considered as model foods. Throughout the experiments, US images were acquired from a transducer array positioned underneath the artificial tongue, while force signals were obtained from a multi-axes sensor located above an artificial palate plate. Image analysis first consisted of tracing the contour of the dorsal surface of the artificial tongue. It was thus possible to observe how the deformations are distributed between the artificial tongues and the agar gels and to follow over time the heterogeneity of this distribution along the axis of the transducer array. Then, Particle Image Velocimetry (PIV) analysis was conducted to characterize the velocity fields related to deformations within the artificial tongue. In particular, the horizontal component of the velocity was studied during the shear movements and allowed one to distinguish static and dynamic friction phases, and to highlight the deformation gradients in the bulk of the artificial tongue. Such US method can provide a better understanding of the impact of the mechanical properties of food gels on the stimulation of mechanoreceptors responsible for translating mechanical stimuli into sensory perceptions.