Synthesis of calcium carbonate capsules in water-in-oil-in-water double emulsions
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Hollow capsules have been intensively investigated due to their high capacity of encapsulating large quantities of guest molecules, making them promising candidate materials for various encapsulation applications. In this work, CaCO3 hollow capsules were successfully synthesized via an emulsion route. The interior hollow structure of the capsules was confirmed by using scanning electron microscopy and transmission electron microscopy (TEM). The vaterite polymorph of the as-synthesized CaCO3 capsules was determined by using x-ray diffraction, high-resolution TEM, and Fourier transform infrared spectroscopy. A self-assembly model was proposed to explain the formation mechanism of the vaterite capsules. By adjusting experimental parameters such as the internal solution amount and the surfactant amount of the double-emulsion system, the average capsule size could be adjusted accordingly. However, the increase in capsule size was at a compensation of size-uniformity degradation. The capsule size uniformity was then further optimized by increasing the magnetic stirring rate. The resultant vaterite capsules demonstrated biodegradability behavior after immersion in phosphate-buffered saline solution, leading to their promising applications in the area of controlled drug delivery.
I. INTRODUCTION
The variety, functionality, and sheer beauty of biologically created mineral phases have long fascinated materials scientists. Over the past decades, immense efforts have been devoted to the design and controlled fabrication of ordered structured materials with the aim of discovering an array of biomimetic processes for the creation of a range of new products.1–3 One of the particular recent interests is microscale bioceramic hollow capsules. This is primarily due to their hollow core structure, which renders a high capacity for encapsulating large quantities of guest molecules with adjustable internal volume.4 The bioceramic capsule structure can also provide a physical shield for the inserted guest molecules. These features make the bioceramic hollow capsules promising candidates for application in holding sensitive contents until release into the external environment, and attract increasing attention for use in biomedical applications, such as biomolecule protection and storage, and as a controlled-release reservoir for drugs.5–7
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0017 140 J. Mater. Res., Vol. 23, No. 1, Jan 2008 http://journals.cambridge.org Downloaded: 13 Mar 2015
Over the past decade, various techniques have been developed to fabricate hollow capsules from a variety of ceramic,8,9 metallic,10 organic, or polymeric materials11 to address specific encapsulation requirements. Generally, these techniques are mainly based on a templating method. So far, there have been two basic templating methods, with either hard or soft templates. The hard templating method involves the deposition of desired materials or their precursors on rigid colloid particles to form core-sh
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