Inorganic Submicron Colloidosomes: A new type of drug carrier

Tiny holes between the nanoparticles of the shell are the reason for the special characteristics of the microcapsul.

Material scientists from Bremen (Germany) and Stanford (USA) have made a breakthrough in miniaturizing a new type of drug carrier / Article published in ACS „Chemistry of Materials“

They are 1000-times smaller than a grain of sand and 20-times thinner than a human hair. This is the size of a novel class of microcapsules aptly called Submicron Colloidosomes. Colloidosomes are of great interest because of their potential to be used as novel drug-carriers that can target specific cells with a precisely defined dose of medication. Materials scientist from the University of Bremen (Germany) and Stanford (USA) have now developed the next generation of nanoparticle based microcapsules with diameters in the range of 300 nanometers. In this respect it’s actually size that matters, being more than 10-times smaller than the smallest previously described colloidosomes, which were initially described by a research group based in Harvard, the new submicron colloidosomes now open novel paths for the treatment of various diseases, like, for example, cancer.

These microcapsules can be compared to a tiny ball that is filled with water and whose shell is build from individual nanoparticles. The shell is the part of the colloidosome that is responsible for the novel properties of this capsule. During the synthesis, tiny holes between the particles are created featuring diameters of 1 to 5 nanometers. These pores can selectively control the administration of drugs or other active agents that are encapsulated in the capsules’ water core. Consequently, the capsules are specifically suitable as novel drug carriers in the field of medicine. Tobias Bollhorst, who is working on the submicron colloidosomes for his dissertation at the Advanced Ceramics group at the University of Bremen, is certain that these capsules will eventually be used in the field of medicine: “It is our long-term goal to incorporate chemotherapeutics in the colloidosomes and then use the shell-forming particles for enhanced tumor treatment, like magnetic nanoparticles that are already used today for hyperthermia cancer treatment. By this we might be able to significantly increase the efficiency of certain cancer treatments.” Previously described colloidosomes were simply too big to be used effectively in the human organism. This is why the miniaturization of colloidosomes is the key breakthrough towards the application as drug carriers.

A recently published article in the journal “Chemistry of Materials” describes the synthesis process and the properties of the microcapsules in detail. The secret of the new colloidosomes is in the usage of so-called lipids (fatty acids) that stabilize the capsules. Fatty acids are part of many consumer products including margarine and are nontoxic for the human organism. The fatty acids self-assemble between the capsule-forming particles and in so doing stabilize the colloidosomes.

Michael Maas, a former postdoctoral fellow at Stanford University and now senior scientist at the Advanced Ceramics group, laid the foundations for the synthesis of the new microcapsules. During his two-year stay in California, he conducted extensive research on the formation of extremely thin layers or films that consist of nanoparticles and fatty acids. He found that only specific combinations of fatty acids and nanoparticles can be used for the synthesis of films with a specific thickness. This is the basis of the new submicron colloidosomes. Dr. Maas says: ”It’s great being able to use results from fundamental research to develop novel types of drug delivery systems. In theory, we can use all kinds of combinations of nanoparticles for the synthesis of colloidosomes. This way, we have a versatile tool box at hand that can be tailored and expanded at will.”

Professor Kurosch Rezwan, director of the advanced ceramics group at the University of Bremen sees great potential in the new microcapsules: “We achieved a real breakthrough by pushing colloidosomes below a diameter of 500 nanometer, though this is just the beginning. We are certain that these types of new microcapsules have great properties and will be used for many applications. Our primary goal is to optimize the system in the next years and bring the submicron colloidosomes from the lab to application.” Moreover Rezwan points out that the quality of the high resolution electron microscopy images would not have been possible without close collaboration with Prof. Rosenauer and Tim Grieb of the Institute of Solid State Physics at the University of Bremen.

Full citation of the scientific article: Tobias Bollhorst, Tim Grieb, Andreas Rosenauer, Gerald Fuller, Michael Maas, Kurosch Rezwan: Synthesis Route for the Self-Assembly of Submicrometer-Sized Colloidosomes with Tailorable Nanopores, Chemistry of Materials, 2013, in print


Further information:

University of Bremen
Faculty of Production Engineering
Advanced Ceramics

M.Sc. Tobias Bollhorst
Tel.: +49 421 218 64961

Dr. rer. nat. Michael Maas
Tel.: +49 421 218 64939

Prof. Dr.-Ing. Kurosch Rezwan
Tel.: +49 421 218 64930