Tiny chemical carriers form themselves
Results: Chemical engineers have developed a simple “mix and shake” technique for producing microcapsules – tiny shells that can hold substances such as drugs and medical imaging dyes. The technique, developed by a team at Rice University led by Michael Wong, resulted in microcapsules measuring less than a micrometer across.
Why It Matters: With microcapsules, researchers can more precisely control where, when, and in what quantities a substance is delivered and released. One current production method, which relies on meticulously depositing a coating onto a core that is then dissolved away, has produced stable microcapsules a few micrometers across. But this method is expensive to use because it requires carefully controlled conditions, such as very low pressures and high temperatures, and harsh chemicals. The Rice method works at room temperature and atmospheric pressure, and uses water as a solvent. It’s also simpler than other methods and potentially cheaper to use on a large scale.
Methods: The Rice recipe for microcapsules begins with a mixture of water and the chemical to be contained in the shells, such as a small-molecule drug. The researchers then add a salt and an organic polymer that, when mixed, form water-permeable globules. Next, the researchers pour in silicon dioxide nanoparticles about 100 times smaller than the globules. The particles stick into the walls of the globules, forming capsules that trap the chemical and water mixture inside. By adjusting the mixing intensity and the quantities and types of salts, polymers, and nanoparticles used, the researchers varied the thickness of the capsule walls and the size of the capsules, changing the timing and rate of the release of the contents.
Next Step: This method produces only grams of the shells at a time, and they are of nonuniform size. The team is now working on ways to produce the capsules by mixing the components in the form of individual streams of liquid. This would enable the continuous production of more consistently sized capsules.
Source: Rana, R., et al. 2005. Nanoparticle self-assembly of hierarchically ordered microcapsule structures. Advanced Materials 17:1145-1150.