Giga-size development in nanocapsules

2009-08-24 957

A research achievement first published in the world’s foremost chemistry journal Angewandte Chemie by a prominent Korean chemist and his coworkers has gained spotlight with additional coverage in Nature Nanotechnology, Chemistry World and other world’s leading chemistry and medical related journals.

Prof. Kimoon Kim and his team at the Dept. of Chemistry have developed a novel approach to the production of polymeric nanocapsules, which has revolutionized our understanding of manufacturing nanocapsules. Furthermore, the research has generated much interest not only from chemists in the area of nanotechnology but also from the medical profession because of its potential medicinal applications.

The result was highlighted in Nature Nanotechnology, an affiliate of Nature, under the title of “Nanocapsule: A hollow victory” on January 26th and was also covered by the Royal Society of Chemistry’s Chemistry World on February 12th entitled, “Nano-pumpkins fitted for drug delivery.”

In addition, ScienceDaily, FirstScience, Chemie and other science news media, as well as world’s largest independent health and medical news website Medical News Today, has covered the result in its headline news and Nano Today, published by Elsevier, will also introduce the research in its coming April issue.

Nature Nanotechnology described that “although polymer nanocapsules have potential for many applications ranging from drug delivery to imaging, it is made using multistep procedures that can be time-consuming and often require the use of templates to form the shell structure,” and that Kim and his team have made nanocapsules in a “one-pot template-free reaction.”

Chemistry World reported in detail of the achievement quoting Achim Muller from the University of Bielefeld, Germany stating, “Although many types of nanocapsules are known, nearly nothing is known about those which can interact specifically with their environment.” Muller had previously created similar shapes based on inorganic chemistry.

To date, all methods for the production of tiny polymer capsules require preorganized structures or “molds” to shape hollow spheres and most methods require a lengthy, tedious synthetic or purification procedure. Now, Kim and co-workers have now overcome these problems by developing a new method that allows polymer nanocapsules to be made directly. Their method directly produced polymer nanocapsules with a highly stable structure and relatively narrow size distribution without the need for any pre-organized structure, emulsifier or template.

Kim and co-workers made their nanocapsules from rigid, disk shaped monomers. The monomers have special molecular “hooks” on their rim, which, when activated by ultraviolet light, grab onto each other to form small 2D “patches” that, in turn, hook onto other patches. Once they reach a certain size, the patches bend around and close off to form hollow spheres with many tiny cavities on their surface. The size of the spheres is very uniform and depends largely on the solvent in which the linking reaction takes place. The researchers used this method to produce capsules with diameters ranging from 50 to 600 nm.

As described in the journal Angewandte Chemie, this method is generally applicable to any monomers as long as they have a flat core and multiple polymerizable groups at the periphery. “Normally, one would expect a 3-dimensionally cross-linked polymer when a monomer with multiple polymerizable groups is polymerized,” says Kim. “In this case, however, we observed the spontaneous formation of nanocapsules with a thin and robust shell, which makes the discovery extraordinary.”

The little disks used in this process deserve special consideration: Kim and his colleagues chose to use curcurbiturils. These disk-shaped molecules have a cavity at their center. As their shape resembles a hollowed-out pumpkin, this class of compounds was named after the plant genus of pumpkins, the cucurbitaceae. When the mini-pumpkins are linked together, they form an empty sphere with many tiny cavities on its surface. These “pockets” can be filled with certain nitrogen-containing biomolecules, such as spermine, in a very stable fashion.

To demonstrate that their nanocapsules could be used in medical applications, the researchers demonstrated that the cavities on the surface of the spheres can be filled with biomolecules, such as “spermine” coupled to the vitamin folic acid. This could be important for delivering drugs to tumours so that they can be destroyed. Tumours have significantly increased numbers of folic acid receptors on the surface of their cells. The folic acid on the nanocapsule docks into these sites and is brought into the interior of the cell where the content of the capsule, such as a drug or contrast agent, can then be released to selectively attack the tumour or make an unambiguous diagnosis.

The research was funded by the Creative Research initiatives Program provided by the Korean Ministry of Science and Technology.