Release Profiles of Encapsulated Actives from Colloidosomes Sintered for Various Durations

Abstract

This paper presents the formation of low temperature colloidosomes from colloidal poly(styrene-co-butyl acrylate) particles for both water-in-oil and oil-in-water systems. An investigation into the sintering conditions examines the ultimate shell morphology formed, with longer sintering times and higher sintering temperatures producing less porous microcapsules. This has been verified by the release of an encapsulated dye from the aqueous core microcapsules, in which slower release has been detected for longer sintering times. The results are subsequently fitted with a diffusion equation to give a diffusion coefficient of fluorescein through the polymeric shell of 10 -17 m 2 /s.

Colloidosomes: Synthesis, properties and applications

“…One solution to this technical problem is to replace polystyrene latex with a lower T g copolymer latex, thus allowing a reduction in the sintering temperature. Accordingly, Routh and co-workers 19,20 utilized a poly(styrene-co-nbutyl acrylate) latex to prepare 2-5 µm diameter w/o emulsions and, after heating to 35-65 o C, robust colloidosomes with aqueous cores (see Figure 3). In this particular example, the copolymer latex alone was not an efficient Pickering emulsifier, hence a suitable oil-soluble co-surfactant (Span 80) was required to optimize colloidosome formation.…”

“…thermal annealing of latex particles), but closing all of these individual holes is a challenge and may explain the poor encapsulation efficiency of the colloidosome systems discussed at the start of this section. 20,59 In principle, an alternative approach could be to use polydisperse spheres, but this is likely to lead to shells of non-uniform thickness. Alternatively, a bimodal distribution of small and large spheres could be utilized such that the former are selected to fit within the interstices formed by the latter.…”

“…Although colloidosomes appear to offer exciting new opportunities for microencapsulation, the long-term retention of small molecules still represents a formidable technical challenge. Currently, the encapsulation of small molecules is typically limited to time scales of just a few hours, 20 which is simply not practical for most commercial applications. Whenever small molecules have been successfully encapsulated, usually deposition of a second impermeable layer over the original colloidosomes is required.…”

Synthetic cellularity based on non-lipid micro-compartments and protocell models

“…For example, control over the pore size and release rate of encapsulated dye molecules can be achieved by using organic colloids in the form of temperature-dependent polymer microgel particles that exhibit swelling/deswelling behaviour upon changing temperature [26]. Alternatively, sintering the temperature responsive polymer particles [27], coupling a pH-responsive crosslinker to the membrane components [28], or varying the size and shape of the nanoparticles [29] can be used to tune the permeability of the colloidosomes. However, these methods are only successful in suppressing the transport of molecules larger than a crucial value; in contrast, the diffusion of small molecules through the colloidosome monolayer is difficult to regulate over a broad range of membrane particle diameters [30].…”

Patchy colloidosomes – an emerging class of structures

“…Colloidosomes are typically made of a monolayered shell, though fabricating a multilayered shell has also been demonstrated [21]. The colloidosome's shell has to be reinforced (usually done as the last step of the preparation), and this is achieved by the sintering of surface particles [22,23], gel trapping [24,25], covalent cross-linking of colloidal particles [26,27], or polymerization of a thin layer on the inner or outer side of the shell [28,29]. The supporting material often has an additional function: the mechanism of release or uptake is controlled via permeability changes in the material that fills up the pores between the colloidal particles.…”