Microcapsules can be found in a range of commercial applications, including cosmetics, healthcare, agriculture, and food. The capsules serve as a storage vessel for an active ingredient, for example a nutrient or fragrance. They can have a variety of designs, the simplest form being a single internal liquid-based core surrounded by a solid shell. The chemical and physical characteristics of this shell influence the colloidal stability of capsules in formulations, dictate the permeability and mechanical robustness of the capsules, and can potentially regulate substrate adhesion. Beside storage, these features of the microcapsules are there to regulate and control release and delivery of the active compound.
A considerable part of the technologies used to produce microcapsule relies on the use of synthetic polymers that do not break down, with terrible consequences for environmental build up. One way is to make use of biocompatible and degradable plastics.
We provide an alternative solution, in that we fabricate the capsule from small molecular compounds, instead of polymers, that can crystallize.
Artist impression of textured microcapsules made through crystallization.
In our work, published in the scientific journal ACS Applied Materials & Interfaces we focus on the fabrication of microcapsules of which the capsule wall is composed of an inter-locked mesh of needle-like crystals, which besides capsule rigidity and semi-permeability, provides a roughened surface texture.
In this proof-of-concept study crystals of the small organic compound decane-1,10-bis(cyclohexyl carbamate) are formed within the geometric confinement of emulsion droplets, through precipitation from a binary-solvent dispersed phase. This binary mixture consists of a volatile solvent and non-volatile carrier oil. Crystallization is facilitated upon supersaturation due to evaporation of the volatile solvent. We show that the microcapsule diameter can be easily tuned using microfluidics.
The technology is shown to be scalable using conventional mixers, yielding spikey microcapsules with diameters in the range of 10-50 μm. We highlight that the capsule shape can be molded and arrested by jamming using recrystallization in geometric confinement.
With an eye on commercial applications we show that these textured microcapsules show enhanced deposition onto a range of fabric fibers. They outperform their traditional polymeric analogues by sticking better on fibrous substrates.
Prof. dr. ir. Stefan Bon says: “I am delighted with this work, a coordinated effort which was led by first author dr. Sam Wilson-Whitford. A while back we decided in BonLab that our science needed to be greener, and more sustainable. We think our way of making textured microcapsules meets these criteria. We hope that it inspires industry, and that the concept will prove to be useful across a variety of application areas.”
The paper can be accessed here:
https://pubs.acs.org/doi/10.1021/acsami.0c22378
A talk on the topic can be accessed here:
https://www.formulation.org.uk/pc20programme/250-past/2021/pc20/860-pc20-bon.html