Nanotechnology
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Man-made molecule:
Dendrimers come of age
A new cost-saving process is causing
industry to take a second look at dendrimers
Catherine Watkins
When Donald Tomalia created the first three-dimensional man-made molecule in the late 1970s, he was
working for Dow Chemical Co. in Midland, Michigan,
USA. Called a “dendrimer” because of its tree-like
structure, the new molecule had tremendous potential to serve as a nanoscale building block in the medical, food and agriculture, personal, household, chemical, and manufacturing markets.
COURTESY DNT
There was only one problem: The lengthy production process
for the original STARBURST™ PAMAM dendrimers took numerous steps and many months of processing time, leading to a
per-pound price of several hundreds of thousands
of dollars for a precisely engineered product.
Now known as “Daddy Dendrimer,” Tomalia
is the founder, president and chief technology officer of Dendritic Nanotechnologies Inc. (DNT)
on the campus of Central Michigan University
in Mount Pleasant, Michigan, USA. Founded in
2003, DNT recently introduced its new Priostar™ dendrimers at the National Plastics Exhibition in Chicago. The company’s new producTomalia
tion process and new compositions are expected
to bring the cost of dendrimers down into specialty chemical
range. And at that price, industry is taking a second look at using
dendrimers in their products.
Properties and applications
The size and shape of a dendrimer are determined by shells—
known as generations—grown around a core structure, while the
reactivity of the dendrimer is determined by its surface chemical
functionality, together with size and shape. Likewise, the properties of a dendrimer are controlled by the functional groups on the
molecular surface. For instance, a dendrimer can be water-soluble
when its end-group is a hydrophilic group, such as a carboxyl
group.
FIG. 1. Polymer types: At far left, polyethylenes (1930s) were
linear strands, much like spaghetti, used in plastic bags and
bottles. At second to left, epoxy resins (1940s) had strands
that were cross-linked; epoxy resins are used in paints and
hard coatings. Dendrimers (1979–now) are highly branched
spherical balls that can be precisely engineered to carry molecules inside or out.
By altering the chemical properties of the core, the shells,
and the surface layer, dendrimers can be tailored to fit the needs
of specific industries and applications. The new Priostar dendrimers may be engineered in more than 50,000 variations of
size, composition, surface function, and interior nanocontainer
space, according to DNT. Priostar dendrimers also have greater
thermal and hydrolytic stability than the original PAMAM molecules.
Lower-cost dendrimer nanostructures
are of interest to the cosmetic
industry because the highly
branched nanostructures could
encapsulate fragrances, vitamins,
or other active ingredients.
“What is so exciting?” Tomalia asks rhetorically. “Dendrimers have completely new properties compared to any of the
earlier polymeric architectural types such as polyethylenes and
epoxy resins.”
Many potential applications also exist in the personal-care
and detergents industries, according to DNT Director of Business
Development Ryan Hayes.
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information
It is no accident that “dendrimer” is based on the
Greek word “dendron,” which means “tree,” because inventor Donald Tomalia conceived of this new class of manmade molecules while out gathering tree cuttings. He noticed that whenever he made a cutting, the tree would
sprout two branches that would then create two more
branches. The process continued until a new tree had
grown in three dimensions. Thus, Tomalia wondered if it
would be possible to grow molecules in a similar way.
The National Dendrimer and Nanotechnology Center at Central Michigan University in Mount Pleasant works
to develop dendrimers-based research initiatives.
More information is available at netlink: www.dendrimercenter.org. In addition, further information about
DNT is available at its website at netlink: www.dnanotech.
com.
“With traditional linear, spaghetti-like polymers, larger molecular weights increase the viscosity. It is just the opposite with
a dendrimer. As they increase in size, they can decrease the viscosity,” he notes.
September 2006, Vol. 17 (9)
Many companies that initially were interested in dendrimers,
but could not afford the price, are now taking a second look,
Hayes and Tomalia report. In particular, lower-cost dendrimer
nanostructures are of interest to the cosmetic industry because the
highly branched nanostructures could encapsulate fragrances, vitamins, or other active ingredients.
The detergent industry is reassessing dendrimers because of
the inherent functionality of the dendritic structure. “The use of
dendrimers bypasses the whole issue of having to reach the critical micelle concentration in order for a surfactant solution to be
effective,” says Hayes. The dendrimer itself is like a preformed
micelle but has greater stability, thus allowing detergency “at levels you may not have seen before,” he says.
DNT holds a patent on a self-building surfactant that combines a dendrimer with a traditional surfactant, Hayes notes.
“Dendrimers are amazing chelating agents,” he says, “allowing for detergency in hard water without adding builder. We
would love to explore this application with corporate partners,”
he says.
“We tend to get swamped with ideas. We are looking to partner with companies who understand the applications so we can
put our heads together for a successful commercial development.”
Catherine Watkins is a freelance writer based in Urbana, Illinois,
USA.