Recent innovation in the design and development of colloidal carriers has led to the growth of numerous areas including food industries, biotechnology, cosmetics among others. Generally, colloidal carriers can be categorized based on their chemical nature, morphology, and structure or by the mechanism of the cargo release. For example, by considering the chemical nature, they are grouped into organic, inorganic and hybrid. On the other hand, a passive release is a result of degradation or diffusion through the capsule while a controlled release depends on the changes in the pH, temperature magnetic field, light and redox potential.
Despite the remarkable improvements, a convenient criterion for selecting stabilization agents, materials and release methods is highly desirable to ensure continued improvement of the colloidal carriers. Recent studies show that through particle-stabilized Pickering emulsion, encapsulation of oily phase can be realized. Unfortunately, it is hard to realize the desired controlled release through the destruction of the Pickering emulsion due to their stability.
To this note, a group of Bulgarian researchers at the Sofia University: Dr. Gergana Radulova, BSc student Tatiana Slavova, Professor Peter Kralchevsky, Dr. Elka Basheva, Dr. Krastanka Marinova, and Professor Krassimir Danov investigated the formation of stable composite capsules by using polymers and particles without the need for step polymerization. They fabricated microcapsules with a shell from the provided colloidal particles in which the openings between the particles were blocked by mixing the layers produced by the polymer and surfactant. Their research work is currently published in the journal, Colloids and Surfaces A: Physicochemical and Engineering Aspects.
In brief, the Sofia University led research team commenced their work with a detailed cross-examination of the various classifications of the colloidal carriers such as the micelles, dendrimers, polymersomes, colloidosomes among others. Next, the most appropriate polymer material was selected from a given collection after conducting tests. Consequently, partially hydrophobized hydrophilic silica particles were utilized to allow for stabilization of the Pickering emulsions. Eventually, they investigated the possibility of encapsulating various types of oils and fragrances.
The authors observed that the obtained capsules were stable in aqueous solution for a pH value ranging from 3-6. However, exceeding the required pH value resulted in destabilization of the capsules and release of their cargo. Encapsulation of various oils and fragrances such as citronellol and limonene were realized even though they had limited solubility in water. Additionally, the authors noted that the irreversible adsorption at the interface of the oil and water was a key contributor for producing stable capsules. However, oils with either high solubility or zero solubility were not suitable for producing stable capsules.
The study demonstrated that the adsorbed polymer was not only used to block the dissolution of the encapsulated fragrance and oil but also to prevent the dissolution of the surfactants thus ensuring stabilization. Therefore, both of the polymer and surfactant played a significant role in the production of pH-responsiveness microcapsules. Therefore, the brick and mortar concept employed in the study will pave the way for the realization of more stable nano and microcapsules through the selection of appropriate polymers.
Radulova, G., Slavova, T., Kralchevsky, P., Basheva, E., Marinova, K., & Danov, K. (2018). Encapsulation of oils and fragrances by core-in-shell structures from silica particles, polymers and surfactants: The brick-and-mortar concept. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 559, 351-364.Go To Colloids and Surfaces A: Physicochemical and Engineering Aspects