Engineering of barrier properties of colloidosome interface to reduce oxidation and control the release of encapsulants

Yuan Zhao

doi:10.17918/etd-4260

Silica nanoparticles are extensively used to stabilize colloidosomes for encapsulation of bioactive compounds of food, pharmaceutical and cosmetic applications. However, due to electrostatic repulsion between similarly charged particles, colloidosome shells composed of single-type nanoparticles have limited interfacial coverage, resulting in sub-optimum barrier properties. Since barrier properties of interfacial layers have a significant role in controlling oxidative stability and release kinetics of colloidosomes, it is imperative to develop encapsulation systems with optimized barrier properties. In order to address this, the research project focused on improving the properties of colloidosome shell using-(1) silica aggregates synthesized by mixing oppositely charged silica nanoparticles and (2) silica-polymer hybrid aggregates synthesized by mixing negatively charged silica nanoparticles with positively charged polymer ([epsilon]-polylysine). The underlying hypothesis is that mixing of oppositely charged silica nanoparticles or polymers will - (a) increase the interfacial thickness, and (b) decrease the electrostatic repulsion between interfacial colloidal particles. Together, this can improve the barrier properties of colloidosome interface. Barrier properties of the colloidosomes interfaces were measured by quantifying the rate of permeation of peroxyl radicals across the colloidal shell. This was accomplished by incorporating peroxyl radical sensitive dye in the oil phase of colloidosomes. This dye changes its fluorescence intensity upon interaction with peroxyl radicals permeated from the aqueous phase to oil phase. The stability and release kinetics of a model bioactive compound (curcumin) were characterized based on spectrophotometric measurements to quantify the amount of encapsulated curcumin in colloidosomes as a function of time. The images of scanning electronic microscopy (SEM) and fluorescence imaging confirmed the formation of silica aggregates and colloidosomes, together with particle size and [zeta]-potential measurement. A significantly (p<0.05) lower rate of fluorescence decay for the peroxyl radical sensitive dye in colloidosomes stabilized by silica aggregates was observed. Combining with theoretical diffusion models, we found that colloidosomes whose shells contained colloidal silica aggregates displayed lower permeability to peroxyl radicals than ones stabilized by single type of silica nanoparticles. Furthermore, the permeability varied as a function of the ratio of oppositely charged silica nanoparticles in the shell. Curcumin encapsulated within theses colloidosomes showed higher stability and retarded release in the colloidosome stabilized by silica aggregates. In silica-polylysine aggregates approach, the formation of aggregates was confirmed by SEM images. The colloidosomes stabilized using these aggregates showed higher average particle diameter and positively charged [zeta]-potential as compared to colloidosomes stabilized by anionic silica nanoparticles alone, indicating localization of these aggregates at colloidosome interface. The enhanced barrier properties were confirmed by measuring the transport rate of free radicals using the fluorescence based method discussed above.

Engineering of barrier properties of colloidosome interface to reduce oxidation and control the release of encapsulants

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Engineering of barrier properties of colloidosome interface to reduce oxidation and control the release of encapsulants

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