A bending fluctuation-based mechanism for particle detection by ciliated structures.

To mimic the mechanical response of passive biological cilia in complex fluids, we study the bending dynamics of an anchored elastic fiber submitted to a dilute granular suspension under shear. We show that the bending fluctuations of the fiber accurately encode minute variations of the granular suspension concentration. Indeed, besides the stationary bending induced by the continuous phase flow, the passage of each single particle induces an additional deflection. We demonstrate that the dominant particle/fiber interaction arises from contacts of the particles with the fiber, and we propose a simple elastohydrodynamics model to predict their amplitude. Our results provide a mechanistic and statistical framework to describe particle detection by biological ciliated systems.

Collective stiffening of soft hair assemblies.

Many living systems use assemblies of soft and slender structures whose deflections allow them to mechanically probe their immediate environment. In this work, we study the collective response of artificial soft hair assemblies to a shear flow by imaging their deflections. At all hair densities, the deflection is found to be proportional to the local shear stress with a proportionality factor that decreases with density. The measured collective stiffening of hairs is modeled both with a microscopic elastohydrodynamic model that takes into account long-range hydrodynamic hair-hair interactions and a phenomenological model that treats the hair assemblies as an effective porous medium. While the microscopic model is in reasonable agreement with the experiments at low hair density, the phenomenological model is found to be predictive across the entire density range.

Probing in-mouth texture perception with a biomimetic tongue.

An experimental biomimetic tongue-palate system has been developed to probe human in-mouth texture perception. Model tongues are made from soft elastomers patterned with fibrillar structures analogous to human filiform papillae. The palate is represented by a rigid flat plate parallel to the plane of the tongue. To probe the behaviour under physiological flow conditions, deflections of model papillae are measured using a novel fluorescent imaging technique enabling sub-micrometre resolution of the displacements. Using optically transparent Newtonian liquids under steady shear flow, we show that deformations of the papillae allow their viscosity to be determined from 1 Pa s down to the viscosity of water (1 mPa s), in full quantitative agreement with a previously proposed model (Lauga et al. 2016 Front. Phys.4, 35 (doi:10.3389/fphy.2016.00035)). The technique is further validated for a shear-thinning and optically opaque dairy system.

Differing structural properties of foods affect the development of mandibular control and muscle coordination in infants and young children.

The development of chewing is an essential motor skill that is continually refined throughout early childhood. From a motor control perspective, the advancement of textures is dependent upon the fit between a child's oral anatomic and motor system and food properties. The purpose of this exploratory study is to identify age-related changes in chewing motor coordination and control and to determine if these changes are associated with the differing structural properties of solid foods, as well as to explore the role of explanatory variables such as the emergence of teeth and bite force. The masticatory muscle coordination (i.e., coupling of synergistic and antagonistic muscle pairs) and control (i.e., speed, displacement, chewing rate, duration, and number of chews) of fifty children were assessed cross-sectionally at five ages: 9-, 12-, 18-, 24-, and 36-months using electromyography (EMG) and 3D optical motion capture while children ate three foods that had differing structural properties. The results of this study found that children made gains in their chewing motor control (decreased duration of chewing sequences and lateral jaw displacement) and coordination (improved jaw muscle coupling) throughout this period. The structural differences in foods also affected chewing performance at all ages. These preliminary findings suggest that some solid textures are better adapted for immature mandibular control than others and that the development of chewing is a protracted process that may be impacted by the emergence of teeth and changes to bite force.

Advancement in Texture in Early Complementary Feeding and the Relevance to Developmental Outcomes.

A child's transition to independent eating is a protracted process that progresses over the course of many years. Although major health agencies, such as the World Health Organization, now offer clear guidance when to begin introducing solids, advice about how to safely transition to progressively challenging foods is varied and comes from a staggering number of sources. The resulting conflicting views have promoted parental confusion and anxiety about what foods are appropriate and when to advance to new textures. Efforts to develop science-based recommendations for complementary feeding include research on the development of chewing motor skills. Chewing development is an essential aspect of feeding readiness that is often overlooked by agencies developing recommendations for complementary feeding, and little is known about the development of chewing motor skills and how children learn to accommodate foods with varying textures. Such information is essential for designing developmentally appropriate foods, minimizing food aversions, providing caregivers science-based guidance regarding the safety and appropriateness of new foods, and identifying children at risk for choking or feeding impairments.

Frequency-Amplitude Cross Interaction during Pulsatile Taste Delivery Using Gustometers.

In this article, we numerically resolve the flow profiles of tastant concentration in the pipe of a gustometer used to deliver alternative pulses in concentration, which is a typical case of Taylor dispersion. Using this model, we can define the cases where the experimenter will deliver to the assessors a concentration profile which is significantly different from that intended. This can be simply assessed a priori using a scaling argument which involves calculating a dimensionless frequency. This is a function of the pulses frequency, the dimensions of the pipe and the flow rate used. We show that unless this parameter is taken into account, modifying the pulse frequency will modify the pulse amplitude. This design criterion is absent from the literature but we suggest this is important for designing such experiments.

Adaptation of mastication mechanics and eating behaviour to small differences in food texture.

Eating behaviour is significantly modified with the consumption of soft or hard textures. However, it is of interest to describe how adaptive is mastication to a narrow range of texture. ElectroMyoGraphy (EMG) and Kinematics of Jaw Movements (KJM) techniques were used simultaneously to follow mastication muscle activity and jaw motion during mastication of seven cereal products. We show that parameters such as the time of chewing activity, the number of chewing cycles, the chewing muscle EMG activity and the volume occupied for each chewing cycle are amongst others significantly different depending on products tested, even though the textural product space investigated is quite narrow (cereal finger foods). In addition, through a time/chewing cycle dependent analysis of the chewing patterns, we demonstrate that different foods follow different breakdown pathways during oral processing, depending on their initial structural properties, as dictated by their formulation and manufacturing process. In particular, we show that mastication behaviour of cereal foods can be partly classified based on the process that is used to generate product internal structure (e.g. baking vs extrusion). To the best of our knowledge, such time dependent analyses have not yet been reported. Those results suggest that it is possible to influence the chewing behaviour by modifying food textures within the same "food family". This opens new possibilities to design foods for specific populations that cannot accomplish specific oral processing tasks.

An alternative theory to explain the effects of coalescing oil drops on mouthfeel.

In this letter, we demonstrate that through non-trivial rheological effects occurring in narrow gaps, it is possible to explain how coalescent oil drops contribute to the specific mouthfeel of such unstable emulsions. This theoretical framework allows us to get away from the commonly referred to lubrication argumentation and offers the advantage of being simple enough in terms of computation to be tested both numerically and sensorially using oils of different viscosities. We show that this interpretation allows us to account for around two orders of magnitude of apparent viscosity increase in such emulsions, when the coalescence is catastrophic (total). Such phenomena are predicted to have profound effects on the damping of the mechanical signal perceived by mechanoreceptors in the oral cavity and thus on mouthfeel perception.

Numerical modeling of human mastication, a simplistic view to design foods adapted to mastication abilities.

The human diet contains a large variety of aromas, tastes and textures. The latter is particularly important since it determines whether foods are difficult to process orally and thus can be one source of food avoidance. It has also been reported in recent literature that food texture was a main driver for satiation processes and thus it is of interest for the food manufacturing industry to be able to control textural properties of food within the limits of acceptability for the consumer. For solid foods, fracture force is an important aspect of texture and we were interested in understanding the physiological drivers of this variable.We present a third order lever model of human bite force and the space between teeth based on data from the literature on human oral anatomy. The results from the model are compared with experimental data available in the literature. The model compares well with the experimental data (r2 = 0.95, p = 0.0010, MPE = 0.18), and can thus be used to derive a diagram of how food properties such as piece size or fracture force can be used to define whether foods are close to the limits of what the human jaw is capable of breaking. Such modeling tools can be used to define texture rules for tailor-made nutrition for specific populations based on their mastication abilities. The limitations of this modeling approach are also discussed, particularly the fact that tooth shape should also be considered, as this will ultimately define fracture stress, which is the deterministic factor of food fracture.

Anatomical, functional, physiological and behavioural aspects of the development of mastication in early childhood.

Mastication efficiency is defined as the efficiency of crushing food between the teeth and manipulating the resulting particles to form a swallowable food bolus. It is dependent on the orofacial anatomical features of the subject, the coordination of these anatomical features and the consistency of the food used during testing. Different measures have been used to indirectly quantify mastication efficiency as a function of children's age such as observations, food bolus characterisation, muscle activity measurement and jaw movement tracking. In the present review, we aim to describe the changes in the oral physiology (e.g. bone and muscle structure, teeth and soft tissues) of children and how these changes are associated with mastication abilities. We also review previous work on the effect of food consistency on children's mastication abilities and on their level of texture acceptance. The lack of reference foods and differences in testing methodologies across different studies do not allow us to draw conclusions about (1) the age at which mastication efficiency reaches maturity and (2) the effect of food consistency on the establishment of mature mastication efficiency. The effect of food consistency on the development of children's mastication efficiency has not been tested widely. However, both human and animal studies have reported the effect of food consistency on orofacial development, suggesting that a diet with harder textures enhances bone and muscle growth, which could indirectly lead to better mastication efficiency. Finally, it was also reported that (1) children are more likely to accept textures that they are able to manipulate and (2) early exposure to a range of textures facilitates the acceptance of foods of various textures later on. Recommending products well adapted to children's mastication during weaning could facilitate their acceptance of new textures and support the development of healthy eating habits.

Modelling the human response to saltiness.

Eating is a complex process with a range of phenomena occurring simultaneously, including fracture, temperature changes, mixing with saliva, flavour and aroma release. Sensory perception as experienced in the oral cavity has a strong effect on the overall acceptability of the food. Thus in an engineering sense one would want to be able to understand and predict phenomena for different food matrices in order to design more palatable foods through understanding food oral processing without the health concerns of adding salt, fat and sugar. In this work we seek to obtain such an understanding for salt release from food matrices and perception viewing the oral processing as a physical/chemical reactor. A set of equations was developed to account for mass balance and transfer. Data required for the model such as effective diffusivity and mixing times were obtained from the chemical engineering literature. The model predictions compared favourably with published TI data, managing to capture key phenomena including response to pulsed salt release. The model was used to predict response to a range of food matrices and indicated that for solids and thickened liquid food products there is the potential to modulate consumer response by pulsing the release of sodium.