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Volume 88 Issue 21 | p. 7 | News of The Week
Issue Date: May 24, 2010

Dendrimersomes Debut

Supramolecular Chemistry: Self-assembled dendrimer-based structures could deliver drugs, other substances
Department: Science & Technology
News Channels: Nano SCENE
Keywords: dendrimer, Janus dendrimer, dendrimersome, liposome, polymersome
[+]Enlarge
Nanostructure
Dendrimersome cross-section shows its cell-membrane-like bilayer.
Credit: Courtesy of Virgil Percec
8821notw1_SLICE
 
Nanostructure
Dendrimersome cross-section shows its cell-membrane-like bilayer.
Credit: Courtesy of Virgil Percec
[+]Enlarge
Dendrimersomes
Micrographs show polygonal, cubic, spherical, tubular, rodlike, helical, and disklike dendrimersomes. Colorized versions are shown in alternate rows.
Credit: Science © 2010
8821notw2_dendrimersomes_lg
 
Dendrimersomes
Micrographs show polygonal, cubic, spherical, tubular, rodlike, helical, and disklike dendrimersomes. Colorized versions are shown in alternate rows.
Credit: Science © 2010
Janus dendrimers are amphiphilic, with nonpolar (red) and polar (blue) ends.
8821notw1_duo
 
Janus dendrimers are amphiphilic, with nonpolar (red) and polar (blue) ends.

Tiny bubbles and other nanostructures that form spontaneously when highly branched bifunctional compounds are put in water have been discovered and characterized. The nanostructures may be more broadly useful for delivering drugs and other substances than similar nanostructures made from phospholipids or polymers.

The new nanostructures form from “Janus dendrimers”—dendrimers (repetitively branched molecules) that branch out from a point and are amphiphilic (polar on one side and nonpolar on the other). Chemistry professor Virgil Percec of the University of Pennsylvania and coworkers report in Science that a new family of vesicles, tubes, disks, and other shapes—which they call “dendrimersomes”—self-assemble from the Janus dendrimers in water (2010, 328, 1009).

Dendrimersomes can act as hosts for a variety of guest molecules and could therefore have widespread applications as delivery vehicles for drugs, genes, imaging compounds, diagnostic agents, cosmetics, and other substances.

“This is truly groundbreaking work,” says Donald A. Tomalia of Central Michigan University, who discovered dendrimers in 1979. “It’s the first step toward a huge family of dendrimersome structures. I can see an endless number of libraries that one can construct by varying the structures of Janus dendrimers, so this paper is just the tip of the iceberg.”

Liposomes and polymersomes—synthetic vesicles made from phospholipids and polymers, respectively—have similar uses as delivery vehicles but several drawbacks: Liposomes tend to be unstable and have short lifetimes; polymersome membranes are too thick to accommodate biological receptor and pore-forming proteins; and both liposomes and polymersomes adopt a wide range of sizes when they form and are difficult to derivatize.

Dendrimersomes are stable for longer periods of time, are highly uniform in size, have the proper dimensions to accommodate membrane-spanning proteins, and are easily functionalized.

Self-assembly of a dendrimersome, from a homogenoeous solution of Janus dendrimer in water into a vesicle.
Credit: Courtesy of Virgil Percec

Several groups have been studying Janus dendrimers for nearly two decades, although they were so named more recently. In the new study, Percec and coworkers synthesized more than 100 Janus dendrimers, screened them for supramolecular self-assembly in water, and found that all adopted useful shapes.

The technique is reminiscent of the versatility with which “globular proteins can assemble into viral capsids and other complex biological nanostructures,” says Karen L. Wooley, a polymer chemist and nanomedicine expert at Texas A&M University.

Jan C. M. van Hest, a specialist in bioinspired materials at Radboud University Nijmegen, in the Netherlands, says it’s noteworthy that “dendrimersomes can be tailor-made with a high level of size control. Creating monodisperse vesicles is always difficult, but seems to be easier with Janus dendrimers.”

Self-assembly of the bilayer part of a vesicle from an aqueous solution of Janus dendrimer.
Credit: Courtesy of Virgil Percec

Dendrimersomes “are truly unique and highly differentiated from traditional liposomes and polymersomes, which are very fragile and very polydisperse,” Tomalia says. “They are incredibly robust and very monodisperse, and they allow you to do chemistry on the surface.” Tomalia believes it will be possible to select Janus dendrimers with specific sizes, shapes, and surface chemistries and then use them as building blocks to create dendrimersomes with designed structural and functional characteristics.

 
Chemical & Engineering News
ISSN 0009-2347
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