Overview
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ABSTRACT
Synthesis of microcapsules capable of encapsulating water-soluble payloads is of interest for cosmetic and pharmacological applications, but also for the production of artificial cells. There are a lot of methods available to produce such capsules; however, the main problem is to encapsulate payloads within them. In this article, several methods for synthesizing such microcapsules and why it remains difficult to encapsulate materials within them are commented. Finally, an emerging method to fabricate microcapsules is discussed; it consists of using all-in-water emulsions that can spontaneously encapsulate payloads.
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Jean-Paul DOULIEZ: Research Director - INRA Bordeaux-Aquitaine, UMR 1332 Fruit Biology and Pathology, Mollicute team Villenave-d'Ornon, France
INTRODUCTION
In the fields of cosmetics and pharmacology, it is essential to protect water-soluble active ingredients from the outside environment by encapsulating them. The microcapsules used are generally micrometric spherical objects, composed of an aqueous core containing the active ingredients, covered by a more or less solid layer (or membrane) providing protection. Similarly, to synthesize an artificial cell, biological material (DNA, proteins, etc.) is encapsulated within microcapsules, mimicking a cell such as a bacterium. This approach represents a major challenge for understanding the origins of life, for determining the minimum conditions for life to exist, and for creating bioreactors capable of synthesizing molecules of interest on demand.
A classic example of microcapsules is liposomes (or vesicles), whose protective layer is composed of a lipid membrane. However, there are also microcapsules whose membrane is made of particles or polymers, forming a relatively solid structure around the aqueous core. The methods of preparing such microcapsules described below make it difficult to encapsulate water-soluble active ingredients or biological material within them.
One emerging method involves the use of water-in-water emulsions. These result from microscopic phase separation in aqueous mixtures of polymers, surfactants or even polyelectrolytes. Micrometric aqueous droplets, enriched with one or more of these compounds, are dispersed in the aqueous medium, hence the term water-in-water emulsion, by analogy with oil-in-water emulsions in which oil droplets are dispersed in the aqueous medium.
The major advantage of these water-in-water emulsions is that they are capable of spontaneously sequestering water-soluble compounds such as DNA or proteins, as well as particles and small molecules. However, these aqueous water-in-water droplets have no protective layer on their surface and can therefore coalesce, leading to macroscopic phase separation and the formation of two distinct phases one on top of the other.
This article shows how, by adding various compounds, it is possible to stabilize these water-in-water emulsions, forming a layer or membrane at the droplet interface. The result is microcapsules in which active ingredients or biological material initially sequestered spontaneously in water-in-water droplets can be encapsulated.
A glossary and table of acronyms are provided at the end of the article.
Field: Microencapsulation
Degree of technology diffusion: Emergence
Applications: Cosmetics, pharmacology, artificial cells
Main French players:...
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KEYWORDS
encapsulation | all in water emulsions
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Unit operations. Chemical reaction engineering
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Microcapsules: from encapsulation to artificial cells
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