The Father of Dendrimers Speaks...

At the NanoCommerce conference in Chicago, I was able to get an interview with Don Tomalia, in the brief period between his appearance on a Homeland Security panel and his quick departure back to Michigan. You can listen to the full 20 minute interview by visiting Nanotechnology.com’s multimedia page.

Back in the 1980s at Dow Chemical, Don Tomalia invented dendrimers, branching polymers that grow onion-like into molecularly precise spherical structures. They are, in effect, a kind of radial plastic, and like plastic have myriad uses, or they would have, if they weren’t so expensive. But, as Tomalia points out, when nylon was first invented, it was the most expensive material in the world. Tomalia believes that with a new process Dendritic Nanotechnologies has solved the price problem, reducing the cost from $100s of dollars per gram for conventional PAMAM dendrimers to eventually $10-$25 per pound, for the company’s new Priostar family of dendrimers.

Already, dendrimers have found some commercial applications. Qiagen sells dendrimers for the “transfection” of DNA into cells for genetic engineering purposes. Dade Behring markets a rapid dendrimer-based kit for diagnosing heart attacks that is used in emergency rooms. An Australian firm, Starpharma, has begun clinical trials of a dendrimer that prevents HIV infection and may be used eventually as an AIDS therapeutic. Starpharma’s Tom McCarthy refers to dendrimers as “molecular Velcro”—multiple binding sites on the surface of the dendrimer surround the virus and prevent it from functioning. The company has patented the use of dendrimers as anti-microbials against a wide variety of pathogens.

Cambridge Display Technology is working on dendrimers conjugated to phosphorescent groups in the hope of making white light organic LEDS. Dendritic Nanotechnologies is working with unnamed partners to “passivate” quantum dots—essentially wrapping the dot in a dendrimer. This prevents unwanted chemical interactions; commercial quantum dots are usually composed of highly toxic cadmium selenide.

Tomalia’s group worked for three years with James Baker, from the University of Michigan Medical School, to develop dendrimers as drug delivery agents for the treatment of cancer. The ideal cancer drug, in Baker’s view, would have a module that would target a particular cancer type, a module that would contain a contrast agent for MRI detection, a module that would contain the chemotherapeutic agent, and perhaps a module that would allow for fluorescent detection. Such a “smart drug” could be composed of dendrimers that could be mixed and matched as needed. Baker has been funded by the National Cancer Institute to make these smart drugs a reality.

Tomalia is a visionary; when he talks about his favorite subject, his eyes tend to roll up in his head and his voice grows rapturous. Dendrimers, he says, have a core and shell structure, analogous to atoms. Each generation of the branched polymer adds to the shell and changes the weight and properties of the dendrimer. There could be, he says, a whole new chemistry--periodic tables of dendrimers, each table involving different chemical structures. There are over 100 described compositional families of dendrimers and each new dendrimer is essentially an atomically precise nanodevice. Add to that about 1000 different chemistries used to modify the surface and you can generate a literally infinite number of possible combinations of dendrimers with selected chemical properties. Time, money and imagination seem to be the only limiting factors.