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Ionic Multicompartment Micelles from Triblock Terpolymers in Water

Von Christopher Synatschke (26.06.2013)

After reading this rather complicated title, the first thought might have been: “What the heck is he talking about?” Since you did not stop reading there, let me explain the topic of my PhD step-by-step. First of all, polymers are large molecules built up by connecting individual molecules (monomers) repeatedly with each other. Typically, polymers have a linear structure where the monomers are lined up like pearls on a necklace. 

Now, instead of only using one type of monomer, we use three different kinds (monomers A, B and C). A statistical arrangement of the monomers along the chain is called a random copolymer, while in my case the monomers are arranged in a strict order of only A-type monomers in the beginning of the chain, followed only by monomers B in the middle and finally only monomers C at the end of the chain. Such a block like arrangement of three different monomers along a polymer chain is called a triblock terpolymer (Scheme 1a). They can form many interesting structures, and the topic of my PhD was to study the mechanism of structure formation and how to make use of them, for example in medical applications. 

[Bildunterschrift / Subline]: Fig. 1: Illustration of the polymerization of a triblock terpolymer and its self-assembly to MCMs (a). cryogenic-Transmission electron microscopy images of various MCMs from a triblock terpolymer in water.

In order to understand why these structures form, you need to know that polymer blocks from different monomers are usually not miscible and will try to minimize the contact area (interface) between each other, while maximizing the interface with blocks of the same monomer type. For example, the A-block of an A-B-C triblock terpolymer chain will try to have only A-blocks of other A-B-C polymers close to it, while excluding B- and C-blocks as much as possible (phase separation). This separation of blocks can only happen on a small lengthscale in the range of several nanometers (nm), because of the physical connection of the blocks within their chain. Therefore, any larger assembly of such polymers will spontaneously form domains of the individual blocks with a size of several nanometers. The spatial arrangement of each domain within the superstructure must fulfill the principle of minimizing contact between different blocks and maximizing contact between similar blocks. 

If the self-assembly takes place in solution, for example with water as the solvent, a commonly obtained super-structure is a micelle. These micelles are built up from molecules – in my case polymers as building units - having both a water-soluble and a water-insoluble part. In most cases, spherical micelles are obtained, where the molecules arrange with their water-soluble part (corona, block C) pointing towards or even mixing with the water, while the water-insoluble part is buried in the micellar core minimizing its contact with water. Due to the use of triblock terpolymers in my case and the immiscibility of its two core-forming blocks A and B, the micelle has a further sub-structuring of the core, leading to a sphere-on-sphere arrangement (morphology) of the domains as shown in the last step of Scheme 1a. In micelles, such domains from chemically different blocks are also called compartments, and since here one micelle contains several domains it is called a multicompartment micelle (MCM). Finally, some of the blocks in my A-B-C polymer are built from charged monomer units. The charges are retained in the micellar superstructure in water, which are therefore called ionic micelles. Scheme 1b is a selection of different MCM structures we could obtain from my triblock terpolymer in water. 

Now you can understand the title of the work I spent the last few years on, but what did we actually find out? First, we were able to use the charged corona for the interaction with oppositely charged polyions. This led to additional compartments within the micelles and completely new micellar structures. Also, the corona could be changed by the same mechanism to different water-soluble polymers. Apart from these rather fundamental studies or “playing around” with the system, we could use them as a platform for the synthesis of metallic nanoparticles. Such nanoparticles are interesting as catalysts for chemical synthesis or in photonic applications. In a medical context, MCMs can be useful as carrier systems for poorly water soluble or highly toxic drugs, where several drugs can be transported simultaneously and be specifically released only at the target site. During a 6-months stay in Japan, we were able to incorporate a photoactivated anti-cancer drug inside of the micelles and deliver it to a model tumor in mice. 

With this I will leave you and hope to have shown you that even a rather abstract topic can lead to interesting and unexpected applications in real life, like going from polymer chemistry to anti-cancer research.

Wissenschaftlicher Werdegang
  • 2005 - 2009
  • Studium der Chemie auf Diplom an der Universität Bayreuth
  • seit Sep. 2009
  • Promotion in Chemie am Lehrstuhl für Makromolekulare Chemie II der Universität Bayreuth
  • Jan. – Juli 2012
  • Forschungsaufenthalt in der Gruppe von Prof. Kazunori Kataoka an der University of Tokyo, Tokyo, Japan

  • 2008 - 2010
  • Stipendiat bei E-Fellows.net
  • seit 2010
  • Promotionsstipendium nach dem Bayerischen Eliteförderungsgesetz
  • Apr. – Juli 2012
  • Forschungsstipendium des “Center for Medical Systems Innovation” (CMSI) der University of Tokyo, Tokyo, Japan

Publikationen (Auszug)
  • * C.V. Synatschke, F.H. Schacher, M. Förtsch, M. Drechsler, A.H.E. Müller, Soft Matter, 2011, 7(5), 1714-1725
  • * A. Schallon, C.V. Synatschke, V. Jérôme, A.H.E. Müller, R. Freitag, „Nano-particulate non-viral agent for the effective delivery of pDNA and siRNA to differentiated cells and primary human T lymphocytes“, Biomacromolecules, 2012, DOI: 10.1021/bm3012055
  • * C.V. Synatschke, T. Nomoto, A. Kishimura, A.H.E. Müller, K. Kataoka, Polymer Preprints, 2012, 53 (3), 398.