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Encapsulation of Pickering oil microdroplets into alginate microgels by microfluidics for lipophilic compound delivery

Alginate microgels are widely used as delivery systems in food, cosmetics and the pharmaceutical industries for the encapsulation and sustained release of hydrophilic compounds and cells.

However, the encapsulation of several lipophilic molecules within a unique microgel remains a major challenge. Indeed, to date, only the encapsulation of one oil droplet in a hydrogel capsule has been demonstrated and uses surfactants that are globally undesired in formulations. Our objective is therefore to propose new biosourced and surfactant-free microgels of micrometric size containing highly stable oil microdroplets for the encapsulation and the controlled release of lipophilic active compounds. Our study describes an original two-step approach in which microfluidics allows the encapsulation of lipophilic multicores in a perfectly controlled size and composition. The first step consists in forming a stock of oil microdroplets via an oil-in-water (O/W) Pickering emulsion stabilised by hybrid particles made of cellulose nanocrystals and calcium carbonate (CaCO3). Pickering emulsions that use biosourced particles irreversibly adsorbed at the interface are an alternative solution to surfactants for stabilising oil microdroplets. In the second step, the resulting oil microdroplets are encapsulated using microfluidics into alginate-based microgels. By diffusion of acetic acid into the microdroplets of alginate, the CaCO3 adsorbed on the CNCs is solubilised, inducing the alginate gelation. This demonstrates the double action of the hybrid as an interface stabiliser and gelling agent for the encapsulation of the oil microdroplets in hydrogels. This innovative approach shows the possibility of generating monodisperse alginate microgels (85 μm in diameter) containing about 12 oil microdroplets (15 μm in diameter). For the first time, the microfluidic control associated with the stability of Pickering emulsions has led to new oil multicores in microgels. Moreover, the potential of this multicore lipophilic approach was confirmed by the efficient encapsulation of a model lipophilic compound (Red Nile). Our microgels remain stable for several months, suggesting excellent storage characteristics. In addition, controlled release results confirmed, on the one hand, the stability of the CNC shell at the O-W interface of independent oil droplets after the alginate degradation and, on the other hand, the lipophilic compound release in the medium using suitable solvents. These microgels have high potential for compartmentalised and simultaneous encapsulation of lipophilic and/or hydrophilic compounds such as vitamins, aromatics or anti-cancer drugs in a single microgel.

Publications :

M. Marquis, V. Alix, I. Capron, S. Cuenot, A. Zykwinska. Microfluidic encapsulation of Pickering oil microdroplets into alginate microgels for lipophilic compound delivery. ACS Biomaterials Science & Engineering (2016), 2, 535-543, 2016.