Advances in the use of microgels as emulsion stabilisers and as a strategy for cellulose functionalisation

Abstract

Microgel particles have recently emerged as an alternative route to emulsion stabilisation. Classed as soft colloidal particles, their ability to swell to differing degrees in certain solvents and to rearrange once attached to an interface makes them highly suitable for systems requiring long-term stabilization, such as formulations in the food, agricultural, cosmetic and pharmaceutical industries. Microgels made with biocompatible polymers such as proteins and polysaccharides in particular offer an environmental advantage and currently form a very active area of research. Cellulose, being a natural, biodegradable polymer, is an attractive ingredient for gels and microgels. However, its use as a functional material is often somewhat hindered by its insolubility in water and most other organic solvents. Furthermore, the surface activity of cellulose has proven difficult to harness and therefore its ability to act as an emulsion stabiliser has been almost exclusively applied to oil-in-water (O/W) emulsions, with very few reports on its water in oil (W/O) activity. This review aims to summarise some of the recent progress made in the microgel field including their ability to act as emulsion stabilisers, with a focus on cellulose microgels (CMGs). A brief overview of cellulose processing is also given, describing the dissolution and reprecipitation routes used to functionalise cellulose without covalent modification and the potential for cellulose particles and CMGs to act as O/W and W/O emulsion stabilisers. Graphic abstract

Current Advances of Polysaccharide-Based Nanogels and Microgels in Food and Biomedical Sciences

“… Ellulose microgel at the oil-water surface and oil droplets in water protected by microgel particles. Reprinted from [ 32 ]. …”

Cellulose as a Natural Emulsifier: From Nanocelluloses to Macromolecules

“…Another type of stabilization is provided by insoluble particles, often called Pickering stabilization; rigid particles, Janus particles and microgels, have been described as Pickering emulsifiers [13][14][15]. The amphiphilicity of a typical Pickering emulsifier (rigid particles) is usually described in terms of surface wettability, which is measured by the three-phase contact angle of a particle adsorbed at an oil-water interface.…”

“…They have the potential to effectively stabilize water-inwater emulsions, which are mixed solutions of thermodynamically incompatible polymers, producing two immiscible aqueous phases, and where the effective thickness of the interface is defined on a length scale considerably greater than the molecular dimensions of a conventional emulsifier [22,27]. However, microgels based on physical cross-linking of biopolymers are rather novel and much of their behavior at interfaces remains unclear [15]. Two examples of natural ingredients that exhibit microgel-like characteristics are casein micelles (in their native form) and whey proteins and gelatinized starch granules (upon heat treatment).…”

“…Overall, the emulsions produced by both methods display very good stability against droplet coalescence which can be referred to the irreversible adsorption of cellulose onto the droplet surfaces [34,78,79,85]. Soft cellulose microgels also impart an outstanding stability against flocculation because of the thick viscoelastic layers formed at the interface [15]. The mechanism behind droplet stabilization in emulsions prepared with cellulose particles is similar to that operating for nanocelluloses as described above, i.e., a combination of Pickering adsorption and network stabilization, often showing gel-like characteristics upon a concentration increase of cellulose [79,[82][83][84].…”

Co-delivery of EGCG and lycopene via a pickering double emulsion induced synergistic hypolipidemic effect

“…24 Research practices had proved that PDE were more stable than the traditional double emulsions that were stabilizing by inorganic small molecular weight surfactants. 25 In our previous study, we replaced the emulsifier (Tween 80, whey protein, etc.) that stabilized the external interface layer with colloidal particles (kafirin nanoparticles or bacterial cellulose), and the formed PDE showed an enhanced physical stability.…”