Dip coating is a very common process in food manufacturing. Controlling the thickness of the coating is key to deliver the desired sensorial properties and to be compliant with the product?s nutritional claims. Whilst dip coating with Newtonian liquids is physically well understood, coating food products almost invariably involve liquids with more complex rheology. This makes the process more difficult to design and control and reduces the coating homogeneity. Developing novel food products with improved nutritional attributes often calls for reducing the coating thickness and non-homogeneity should be avoided to guarantee the quality of the final product. In this study, we focused on the coating of a flat surface using Carbopol solutions and a commercial ketchup, following a Herschel-Bulkley rheological model. The final average coating thickness was always significantly lower than the critical thickness that can be estimated from liquid density and yield stress. Liquids with a yield stress in the range 4-56 Pa were considered in this study and the steady withdrawal speed from the bath was varied in the range 0.1-20 mm/s. The resulting average coating thickness and its uniformity are discussed. The results are interpreted in the context of an existing theory for dip coating with liquids with a yield stress. This study paves the way toward an integrated design of the coating process and the liquid rheology of foods, such as chocolate or ketchup. This can enable the development of new food products allying improved nutrition, a consumer preferred sensory profile and cost.
Swallowing disorders are not uncommon among elderly and people affected by neurological diseases.
For these patients the ingestion of solid grains, such as pharmaceutical oral solid formulations, could
result in choking. This generally results in a low compliance in taking solid medications. The effect of the
solid medication size on the real or perceived ease of swallowing is still to be understood from the mechanistic
viewpoint. The interplay of the inclusion shape and the rheology of the liquid being swallowed together
with the medication is also not fully understood. In this study, a model experiment was developed to study
the oropharyngeal phase of swallowing, replicating the dynamics of the bolus flow induced by the tongue (by
means of a roller driven by an applied force). Experiments were performed using a wide set of solid inclusions,
dispersed in a thick Newtonian liquid. Predictions for a simple theory are compared with experiments. Results
show that an increase in the grain size results in a slower dynamics of the swallowing. Furthermore, the experiments
demonstrated the paramount role of shape, as flatter and more streamlined inclusions flow faster than
spherical. This approach can support the design of new oral solid formulations that can be ingested more easily
and effectively also by people with mild swallowing disorders.
Pumping suspensions and pastes has always been a significant technological challenge in a number
of industrial applications ranging from food processing to mining. Peristaltic pumps have become popular to
pump and/or dose complex fluids, due to their robustness. During the transport of suspensions with peristaltic
pumps, clogging issues may arise, particularly during transient operations. That is a matter of particular concern
whenever the pumping device is used intermittently to generate flow only on demand. Further understanding
of the transient dynamics of such systems and of the conditions that can lead to jamming would result in
more robust peristaltic pump design. To achieve these goals, an experimental setup that simplifies the statorrotor
assembly of a peristaltic hose pump was used. In this setup, a roller transfers momentum to a liquid
suspension, upon application of a constant load. The evolution of the velocity of the roller was recorded for
different concentrations of mono-dispersed spheres of different diameters. The flow is found not to be strongly
dependent on the dispersed particle volume fraction, if the size of the suspended phase is comparable with
the hose diameter. Conversely, the flow is strongly slowed down when their size is small and the particle
concentration is increased. These findings could help improving the design of peristaltic pumps by a more
appropriate sizing, given the diameter of the hose and that of the particles to be transported.
The compliance of patients to solid oral dosage forms is heavily conditioned
by the perceived ease of swallowing, especially in geriatric and pediatric populations.
This study proposes a method, based on an in vitro model of the
human oropharyngeal cavity, to quantitatively study the oral phase of human
swallowing in presence of single or multiple tablets. The dynamics of swallowing
was investigated varying the size and shape of model tablets and adjusting
the applied force to the mechanical setup to simulate tongue pressure variations
among individuals. The evolution of the velocity of the bolus, the oral transit
time, and the relative position of the solid oral dosage form within the liquid
bolus were measured quantitatively from high speed camera recordings. Whenever
the solid dosage forms were big enough to interact with the walls of the in
vitro oral cavity, a strong effect of the volume of the medication in respect of
its swallowing velocity was observed, with elongated tablets
owing faster than
spherical tablets. Conversely, the geometrical properties of the solid oral dosage
forms did not significantly affect the bolus dynamics when the cross section of
the tablet was lower than 40% of that of the bolus. The oral phase of swallowing
multiple tablets was also considered in the study by comparing different
sizes while maintaining a constant total mass. The predictive power of different
theories was also evaluated against the experimental results, providing a mechanistic
interpretation of the dynamics of the in vitro oral phase of swallowing.
These findings and this approach could pave the way for a better design of solid
oral medications to address the special needs of children or patients with swallowing
disorders and could help designing more successful sensory evaluations
and clinical studies.
Flexible dosing and ease of swallowing are key factors when designing oral drug delivery systems for paediatric and geriatric populations. Multi-particulate oral
dosage forms can offer significant benefits over conventional capsules and tablets. This study proposes the use of an in vitro model to quantitatively investigate
the swallowing dynamics in presence of multiparticulates. In vitro results were compared against sensory tests that considered the attributes of ease of swallowing and post-swallow residues. Water and hydrocolloids were considered as suspending vehicles, while the suspended phase consisted of cellulose pellets of two different average sizes. Both in vivo and in vitro tests reported easier
swallow for smaller multi-particulates. Besides, water thin liquids appeared not optimal for complete oral clearance of the solids. The sensory study did not
highlight significant differences between the levels of thickness of the hydrocolloids. Conversely, more discriminant results were obtained from in vitro tests,
suggesting that a minimum critical viscosity is necessary to enable a smooth swallow, but increasing too much the carrier concentration affects swallowing negatively. These results highlight the important interplay of particle size and suspending vehicle rheology and the meaningful contribution that in vitro methods can provide to pre-screening multi-particulate oral drug delivery systems before sensory evaluation.
Swallowing is a complex physiological process transporting food from the mouth into the esophagus. Understanding how food properties condition flow, ease of swallowing and amount of post-swallow residues can support the design and development of novel products with improved texture and swallow-ability. Diagnostics allowed visualizing directly the effect of bolus consistency on flow, but complementary approaches are needed to speed up the pace of product innovation.
Scope and approach
This review summarizes the state of the art with respect to the in vitro and in silico approaches to predict the ease of swallowing, with an overview of the oral, pharyngeal and esophageal swallowing. Physical and computational models are discussed and compared, highlighting capabilities and limitations.
Key findings and conclusions
In vitro and in silico experiments represent attractive complements to the in vivo investigations because they allow varying parameters independently, which is key to understand the effect of different food and drink properties and to adapting them to different needs. Two motor control strategies are commonly used, namely imposing displacements or stresses. These models have helped clarifying the role of bolus rheology in the oral phase of swallowing and the importance of salivary coating in the pharyngeal bolus flow. Few areas of improvements were identified: the use of more realistic geometries and mechanical properties representing the relevant tissues, of lubrication boundary conditions and of a wider variety of food boli. Further clinical studies should also focus on identifying the most realistic motor control strategy to mimic human swallowing.
Cerebrovascular and neurodegenerative diseases are clinical conditions increasingly observed in geriatric populations. A common symptom of these pathologies is represented
by the increased difficulty with food manipulation and intake. Developing food products,
dietary supplements and oral medications for this set of patients requires an improved understanding of the interplay between bolus rheology, tongue coordination and lubrication
of the oral cavity and their effect on the resulting ease of swallowing.
This study employs an in vitro model experiment to elucidate the role of bolus rheology
and to describe the oral swallowing dynamics in presence of suspended particles, to mimic
swallowing of solid oral dosage forms.
The model was first used to test viscoelastic liquids to validate the hypothesis that elasticity can contribute to a smoother bolus flow in the transition between the oral and the
pharyngeal phase of swallowing. In this respect, the experimental results confirmed the
effectiveness of thin viscoelastic liquids. These consistently led to a measurable reduction
in bolus fragmentation at the ejection from the in vitro oral cavity without however significantly delaying the overall oral transit time. Conversely, model thick elastic liquids
noticeably increased the measured oral transit times and led to an increased quantity of
post-swallow residues. These results suggests the existence of an optimum range of rheological properties in vitro to secure the best balance between bolus fragmentation and
bolus velocity. This finding, if confirmed in vivo could help designing novel products with
elastic properties for a better management of swallowing disorders.
Attention was then dedicated to the study of the alterations to the in vitro swallowing
dynamics resulting from the presence of suspended tablets and multiparticulates. This
topic was developed in relation to the peculiar needs of paediatric and geriatric populations
that require a high dose flexibility and often show a reduced acceptance towards large solid
oral dosage forms. Based on the theoretical results reported for simpler peristaltic flow, the
study aimed at quantifying the additional pumping effort required for swallowing single
and multiple tablets as a function of their physical attributes. in vitro tests confirmed
that model-tablets with a larger cross section in the direction of swallowing consistently
delayed the bolus flow. The viscosity of the suspending vehicle was also an important
factor: thicker liquid media were able to ensure a smoother flow in vitro, even for large
solid oral dosage forms. This finding confirms the effectiveness of thickened liquids as
suspending vehicles for the oral administration of tablets and capsules.
The importance of the suspending vehicle rheology was further highlighted with a combined in vitro and sensory study that considered the swallow-ability of placebo multiparticulates. The in vitro model provided a higher discrimination ability among the different
formulations. This helped to clarify the results obtained from the 30 untrained healthy
volunteers recruited for the sensory tests. Whilst confirming its utility, the study also
pointed out some of the limitations of the in vitro model that consistently over-predicted
the viscosity for smooth swallowing, compared to the in vivo data. This led to the development of a novel experimental setup, inspired by the functionality of the tongue, and
capable of tackling a significant number of the limitations observed for previous in vitro
studies of swallowing. This three dimensional model, can handle liquid boli spanning a
wide range of consistencies and the soft robotic actuation can also be tailored to provide
insights on the role of poor tongue coordination. The availability of this model allows to
greatly extend the kinematic and dynamic comparison with clinical data and can allow
for a more in-depth investigation of the role of oral lubrication in the bolus transport.