The development of microgels/nanogels for drug delivery applications

Nanoemulsions fabricated from food-grade ingredients are being increasingly utilized in the food industry to encapsulate, protect, and deliver lipophilic functional components, such as biologically-active lipids (e.g., ω-3 fatty acids, conjugated linoleic acid) and oil-soluble flavors, vitamins, preservatives, and nutraceuticals. The small size of the particles in nanoemulsions (r<100 nm) means that they have a number of potential advantages over conventional emulsions-higher stability to droplet aggregation and gravitational separation, high optical clarity, ability to modulate product texture, and, increased bioavailability of lipophilic components. On the other hand, there may also be some risks associated with the oral ingestion of nanoemulsions, such as their ability to change the biological fate of bioactive components within the gastrointestinal tract and the potential toxicity of some of the components used in their fabrication. This review article provides an overview of the current status of nanoemulsion formulation, fabrication, properties, applications, biological fate, and potential toxicity with emphasis on systems suitable for utilization within the food and beverage industry.

Food-grade nanoemulsions: formulation, fabrication, properties, performance, biological fate, and potential toxicity.

Micro- and macrorheology of mucus.

There is increasing interest within the food, beverage and pharmaceutical industries in utilizing edible nanoemulsions to encapsulate, protect and deliver lipophilic functional components, such as oil-soluble flavors, vitamins, preservatives, nutraceuticals, and drugs. There are a number of potential advantages of using nanoemulsions rather than conventional emulsions for this purpose: they can greatly increase the bioavailability of lipophilic substances; they scatter light weakly and so can be incorporated into optically transparent products; they can be used to modulate the product texture; and they have a high stability to particle aggregation and gravitational separation. On the other hand, there may also be some risks associated with the oral ingestion of nanoemulsions, such as their ability to change the biological fate of bioactive components within the gastrointestinal tract and the potential toxicity of some of the components used in their fabrication. This tutorial review provides an overview of the current status of nanoemulsion fabrication, properties, and applications with special emphasis on systems suitable for utilization within the food industry.

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Edible nanoemulsions: fabrication, properties, and functional performance

The efficient development and production of high quality emulsion-based products depends on knowledge of their physicochemical properties and stability. A wide variety of different analytical techniques and methodologies have been developed to characterize the properties of food emulsions. The purpose of this review article is to provide a critical overview of the most important properties of emulsions that are of interest to the food industry, the type of analytical techniques that are available to measure these properties, and the experimental protocols that have been developed to characterize the stability of food emulsions. Recommendations are made about the most suitable analytical techniques and experimental protocols needed to characterize the stability and properties of food emulsions.

Critical Review of Techniques and Methodologies for Characterization of Emulsion Stability

For concentrated disperse systems, exhibiting newtonian behaviour, a new viscosity-concentration relationship is deduced from the optimization of viscous energy dissipation. Comparison with several theoretical and experimental investigations gives satisfactory agreement up to packing concentrations.

Rheology of concentrated disperse systems and minimum energy dissipation principle. i. viscosity-concentration relationship.

Energy of interaction in colloids and its implications in rheological modeling.

A relative viscosity — volume concentration relationship,η

 r
 =η

 r
 
(φ) deduced from an energy principle, which operates in newtonian range, is phenomenologically extended to the description of non-newtonian behaviour. Such an extension is performed, using a structural intrinsic viscosity
 
$$\tilde k$$

 , which depends on volume concentrationφ and shear rate
 
$$\dot \gamma $$

 . At constant
 
$$\dot \gamma $$

 , some new results concerningk(φ) are given, leading to determination of the thickness of a surfactant layer onto particle surface, and allowing good agreement to the semi-empirical viscosity relation given byThomas. At constantφ, a rate equation governs the evolution of
 
$$\tilde k$$

 as a structural parameter. In steady conditions (
 
$$\dot \gamma $$

 = const.), an equilibrium value
 
$$\tilde k(\dot \gamma _r )$$

 is reached,
 
$$\dot \gamma _r $$

 being a relative shear rate, depending on the overall time relaxation of the structure. A non-newtonian shear viscosity for steady flows is then obtained, depending on
 
$$(\dot \gamma _r )^p $$

 . For systems of non-spherical particles, an empirical determination ofp givesp ≈ 0.5.

Rheology of concentrated disperse systems II. A model for non-newtonian shear viscosity in steady flows

A non-newtonian viscosity equation$\eta _r = (1 - \tfrac{1}{2} \cdot \tilde k\phi )^{ - 2} $ whereφ is the volume concentration and$\tilde k = (k_0 + k_\infty \dot \gamma _r^p )/(1 + \dot \gamma _r^p )$ is an intrinsic viscosity, function of a relative shear rate$\dot \gamma _r = \dot \gamma /\dot \gamma _c , k_0 , k_\infty $ and$\dot \gamma _c $ being structural parameters, has been proposed in a previous paper (1). From empirical grounds, the valuep = 1/2 holds for a large class of systems, like suspensions of rodand disc-shaped particles. In the high shear rate limit, aCasson law-type is recovered and discussed, especially the concentration dependence of the yield stress. However, the latter disappears in the low shear limit, and must be considered as a pseudo-yield stress. Good agreement is found in this low shear limit with some theoretical results ofBueche for polymers. More generally, the viscosity equation displays pseudo-plastic behaviour and fitting it on experimental data allows the determination of the structural parameters. Some examples (especially Red Blood Cell suspensions and Blood) are studied and support the model. Nevertheless, for spherical particle suspensions, the best fitting is reached forp = 1. Accurate values of particle diameters can be deduced from the structural parameter$\dot \gamma _c $, in this case.

Rheology of concentrated disperse systems III. General features of the proposed non-newtonian model. Comparison with experimental data

We describe a new method for characterizing the non-linear behavior of complex fluids at both small and large deformations. For creep measurements, we use the coupling between the instrumental inertia and the material‘s elasticity to follow the rheological behavior of a solution of iota carrageenan both above and below the yield stress. It is shown that this coupling selectively excites one particular frequency of the relaxation spectrum. An analytical calculation is used to quantify the non-linear behavior near the yield stress. The “free“ oscillations observed during the first few seconds allow us to choose the most appropriate mechanical model. Comparison with experiment shows that even above the yield stress, a linear model can still give independently reliable information about the changes in each element of the mechanical model. A comparison of free and forced oscillations in controlled stress rheometry shows both experimentally and theoretically the conditions under which the use of free oscillations is advantageous.

Daniel Quemada

Papers

Rheology of concentrated disperse systems and minimum energy dissipation principle. i. viscosity-concentration relationship.

Energy of interaction in colloids and its implications in rheological modeling.

Rheology of concentrated disperse systems II. A model for non-newtonian shear viscosity in steady flows

Rheology of concentrated disperse systems III. General features of the proposed non-newtonian model. Comparison with experimental data

Using instrumental inertia in controlled stress rheometry