Development of natural salivary substitutes and evaluation of their rheological properties using an in vitro model
Résumé
Saliva is involved in complex and still partially understood processes during bolus formation: mixing, coating, dissolution, and breakdown of food particles. For these reasons, some studies are focused on mimicking its chemical or physical characteristics. This study aimed to create artificial saliva mimicking the rheological characteristics of human saliva and to evaluate its performance in an in vitro swallowing setup.
A fluid imitating saliva rheology was produced from a flaxseed extract and diluted at 0.7% and 0.25% w/w. Shear viscosity was measured with a couette-geometry in a range of shear rates between 0.5 and 1000 s-1. The extensional properties that are characteristic of saliva were measured by capillary break-up extensional rheometry. The performance of this artificial saliva was also evaluated using a soft-robotic in vitro setup that simulates the interaction between the tongue and the palate when the bolus is transported during the oral phase of swallowing [1]. Apple puree was used as a model food to create boluses of 5 g. Two types of conditions were assessed; (i) in the presence (PAS) and (ii) absence (AAS) of artificial saliva. Timings of bolus out, residues remaining after swallowing, and image analysis were assessed in triplicate. Flow curves showed shear-thinning behavior between 0.5 and 1000 s-1, with a decrease of shear viscosity (Pa·s) ranging from 0.314 to 0.023 Pa.s. Similar values ranging from 0.326 to 0.0018 Pa.s are reported in human saliva flow curves [2]. Moreover, when lubricating, residues decreased by 43% after the first swallow and by 26% after the second swallow. The flaxseed extract proposed in this study to imitate saliva rheology can help improve the performance of in vitro devices and could also be evaluated in clinical studies as a salivary substitute.
[1] Ramaioli, M., & Marconati, M. (2019). 9th ESSD Congress, 2019; Poster Session P1G. Dysphagia, 35(1), 133–205.
[2] Wagner, C. E., & McKinley, G. H. (2017). Age-dependent capillary thinning dynamics of physically-associated salivary mucin networks. Journal of Rheology, 61(6), 1309–1326.
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