Epithelial surfaces rely on a mucous layer at contact interfaces to protect against mechanical stresses. Disruption of mucous lubrication compromises its protective function, increasing the exposure and vulnerability of underlying tissues to frictional damage. This study uses a novel biofidelic epithelial model that incorporates living cells, to study the interface-level mechanisms of friction, stress-induced cell membrane rupture and cell detachment in the presence and absence of mucous lubrication. This comprehensive approach bridges the disciplines of cell biology and tribology, offering new insights into particle-mediated lubrication at biological interfaces. This is relevant to understanding the heightened ocular and oral sensations associated with mucous lubrication failure, as seen in dry eye and dry mouth conditions and during oral perception of alternative plant protein ingredients such as fava bean protein isolate (FBPI). Friction experiments and subsequent cell damage analysis revealed that FBPI particles reduced friction by mitigating adhesion forces, while mucous layers further diminish shear-induced damage. In the absence of a mucous layer, stronger adhesive interactions at the cell-probe interface led to increased friction and cellular damage. Cell membrane rupture occurred when mechanical stresses exceeded critical thresholds, whereas detachment resulted from the breaking of fibronectin bonds at cell-fibronectin junctions. These findings highlight interface level mechanisms that can be applied towards the development of alternative food proteins and the further design of biofidelic testbeds.

Consumption of plant-based food products having high composition of polyphenols leads to the sensation of astringency. For sliding oral surfaces, friction is an essential property during the oral perception of roughness and dryness which are attributes associated with astringency. Different factors including the chemical composition of interacting layers, structure and operation of interfaces have an effect on the astringency development process. The manner of interactions occurring at oral interfaces suggest there is a system dependence of astringency and highlights the importance of adopting a tribosystems approach. Available measurement techniques have shown an existing relationship between salivary protein-polyphenol interaction and an astringent mouthfeel. Nevertheless, the tribo-chemistry involved in this multifaceted sensation remains largely unexplored in a comprehensive manner. In this review the underlying tribo-chemical processes useful in understanding the mechanism of astringency are highlighted and discussed considering current techniques employed to investigate astringency perception. Loss of lubrication on oral surfaces owing to the tribo-chemical interactions involving saliva and astringent plant proteins requires subsequent deformations of oral tissues which are significant enough to induce strains at mechanoreceptor locations, leading to the sensation of astringency. It is proposed that micro-scale contact modelling on the interaction of food particles/aggregates, boundary layers and oral surfaces shows potential in addressing the knowledge gap between tribo-chemical measurement techniques and panel tests, making it possible to attain a predictor for astringency.