As with carbon nanotubes, their industrial impact is not at the stage originally anticipated. However, dendrimers will have a major impact on the medical and sensors market and niche application in a raft of other sectors.
Dendrimers market
Dendrimers are synthetically produced monodisperse polymeric nanostructures with a tree-like, highly-branched architecture. They are typically 2 nm to 20 nm in diameter and are composed of combinations of core types such as:
• ethylene diamine (EDA)
• diaminobutyl (DAB)
• polyamidoamine (PAMAM)
• polypropylimine (PPI) .
They also have different surface residues such as amine, carboxyl, and alcoholic groups. Increasing the number of primary amine groups attached to the core will increase the size of the dendrimer, which is referred to as the ‘generation’ of the dendrimer. Dendrimers can be divided in three distinct regions: the core, the interior (or branches) and the periphery (surface groups).
Figure 1: Dendrimer schematic (Source: Wolfson Materials and Catalysis Center, University of East Anglia).
Dendrimers have found application or are being developed in a number of industries. Current and potential applications for dendrimers include:
Coatings
PAMAM dendrimer networks can be processed into self-supporting elastomeric or plastomeric films, sheets or coatings on a variety of substrates including glass, plastics, metals, paper, wood, ceramics, etc. Desirable properties for use in coatings include optical clarity, enhanced dispersion, increased solubilisation, reduced viscosity, transparency and lack of visible coloration and mechanical properties ranging from relatively soft and flexible rubbers to very hard and scratch-resistant glasses. They can also be applied to medical device coatings.
Sexual health
Starpharma produces VivaGel®, which contains a dendrimer based antimicrobial agent which is being applied to a range of sexual health products such as condoms, prevention of bacterial vaginosis (BV) and prevention of sexually transmitted infections (STIs). The active ingredient of VivaGel® is the proprietary dendrimer, SPL7013, which inhibits infection with viruses, including HIV and the genital herpes virus, and the growth of bacteria.
Sensors
Supramolecular dendritic architectures have demonstrated great potential in designing and developing sensor platforms. Due to their structure, ease of modification, and strong adsorption behaviour to a variety of substrates, PAMAM dendrimers can be used to produce monolayers or stacked film layers, which can be used as sensors to detect hazardous chemical vapours. Their structural uniformity, globular shape, monodispersity, the existence of dendritic crevices, high functional group density, hydrophilicity, versatility to design dendrimer of different composition and their nm size are also being exploited for developing high sensitivity biosensors.
Composites
Dendrimers and hyperbranched polymers have been developed for use as fillers in composites to improve viscosity or cross-linking and stiffness. They are also utilized in high performance plastics with dendrimers acting as compatibilisers and bonding agents and hyperbranched polymers used as tougheners in epoxy resins.
Bioimaging
Dendrimers have been developed as imaging agents for magnetic resonance imaging, X-ray computed tomography, optical imaging and nuclear medicine, and as contrast agents in medical imaging. The exterior primary amine groups can be functionalized, allowing attachment of contrast agents for Computed Tomography (CT), nuclear medicine, optical imaging and Magnetic Resonance Imaging (MRI). Targeting ligands, such as antibodies can also be attached.
Cancer treatment
Dendrimers have been developed for therapeutic and diagnostic purposes for cancer therapy, including enhancing delivery of antineoplastic and contrast agents, neutron capture therapy, photodynamic therapy, and photothermal therapy. Dendrimers can also be being applied to a variety of cancer therapies to improve their safety and efficacy.
Catalysts
Dendrimers have been investigated for application in catalysis for over two decades. Dendrimer-encapsulated bimetallic nanoparticles have been developed for heterogeneous colloid catalysis and hyperbranched polymers are increasingly being used as catalyst platforms. Desirable properties for dendrimer in catalysts include: persistent and controllable nanoscale dimensions, chemically reactive surface, favourable configurations in which all the active sites would always be exposed towards the reaction mixture so that they are easily accessible to migrating reactants, and soluble but can be easily recovered by filtration.
Inkjet inks and toners
Dendrimers have been developed for improving water resistance and adhesion of inks to a variety of substrates (e.g.. paper, glass, metal or plastic). In toners, they impart excellent mix and flow characteristics, stable properties, and high image quality.
Medical diagnostics
Due to the their size and shape and their low poly-dispersity index, dendrimers have impressive pharmacokinetic and pharmacodynamic properties which make them suitable for diagnostics. Dendrimer antibody conjugates have been developed for immunoassay for rapid and sensitive detection of markers indicative of heart attacks.
Drug-delivery systems
Dendrimers have also been developed for drug delivery vehicles or nanocapsules, whereby therapeutic payloads are encapsulated within the shell, or incorporated onto their multivalent surface, and targeted to tumour cells using ligands that specifically bind to cancer cells or in normal cells altered by nearby cancer cells. These vehicles can be tracked with imaging methods such as radionuclides or fluorophores. This ability to both deliver the drug and monitor the delivery is a very desirable property for dendrimers in medical applications.
Wound care
In collaboration with the US Army, Dendritech have developed dendrimers as substitute oxygen carriers for battlefield resuscitation applications.
Cosmetics
Dendrimers are used in cosmetics for increased solubility, dispersion and stability of active ingredients in water-based cosmetics formulations. Dendrimers allow for improved encapsulation, solubilization and controlled release.
Separation agents
PAMAM dendrimers have been used as chelating agents to remove certain metal ions from waste water and from contaminated soil. A program funded by the US Department of Defense has demonstrated the capabilities of Starpharma’s Priostar® dendrimers to remove perchlorate from groundwater.
Dendrimer suppliers
– Dendritech: Dendritech sells over 60 different products from two major dendrimer families (PAMAM and PAMAMOS), in up to 11 generations and 3 different grades, including technical, diagnostic and biomedical. www.dendritech.com
– Starpharma: Starpharma develops and commercialises dendrimer nanotechnology across a wide range of applications. www.starpharma.com
– Sigma-Aldrich: One of the world’s larget nanomaterials suppliers, they offer a wide selection of dendritic macromolecules, including dendrimers, dendrons, and hyperbranched polymers. www.sigmaaldrich.com/materials-science/nanomaterials/dendrimers.html
– Center for Molecular Design and Recognition, University of Akron:
Pilot plant production of dendrimers. www.dendrimers.com
– Polymer Factory: The company develops well defined dendrimers and dendron based on 2,2-bis(methylol)propionic acid where the company has the exclusive right to the production, marketing, and sales of such materials. www.polymerfactory.com/dendrimers
– NanoSynthons LLC. Founded in 2010 by Dr. DonaldTomalia, the pioneering scientist and inventor of dendrimers. www.nanosynthons.com
