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Research Projects @ Polymer Synthesis Group

Synthesis

The foundation of all our projects is the synthesis of polymers with precisely defined molecular structure, and their accurate placement in defined polymer surface architectures and polymeric materials.

This includes:

  • precise control over the repeat unit chemistry and molecular mass;
  • well-defined homo- and copolymer architectures;
  • defined end-groups;
  • control over surface morphology using surface nanostructuring techniques;
  • control over polymer position in multi-layer architectures.

 

The control over these properties enables us to make materials with unique functionalities.

We have documented experience in the synthesis of new, demanding monomers, as well as their polymerization using ring-opening metathesis polymerization (ROMP), living anionic polymerization, controlled radical polymerization, ring-opening polymerization (ROP), emulsion polymerization and others.

 

Polymer Characterization in Solution, on Surfaces, and in Bulk

We put a high effort in the profound characterization or our polymer building blocks and more complex materials. Thus, we are highly proficient in polymer analytics, particularly polymer characterization in solution (GPC-RI-MALLS-Visco triple detection, light scattering) and surface characterization (ellipsometry, surface plasmon resonance spectroscopy, surface zeta potential analysis, and atomic force microscopy (AFM)). 

 

Physical Chemistry of Polymers and Polymer Systems

Using our polymer building blocks, we make materials and surfaces with defined functionalities, e.g. nano- and microstructured functional surfaces and polymer stacks with precise architectures. We carefully characterize the properties of the thus obtained materials and systems with physical-chemical methods.

We are also interested in the interaction of precision polymers with biological interfaces (lipid layers and cells).

Currently, our focus is on bioactive polymers and degradable polymers. We are always open for collaborations inside and outside these fields.

The following is a show-case of current and recent projects.

 

Polymer-Based Synthetic Mimics of Antimicrobial Peptides (SMAMPs)

  • SMAMPs are the current work horse in our group. These poly(oxanorbornenes) imitate natural antimicrobial peptides and are facially amphiphilic (Figure 1a). Their solution properties depend on their precise molecular architecture and molecular mass. [1-3] When their properties are well-controlled, these amazing molecules selectively kill bacteria, but not mammalian cells and are thus promising alternatives to antibiotics. [4]
  • We have also constructed surface-attached polymer networks made from these special polymers (Figure 1b). Here, the poly(oxanorbornene) SMAMP platform enabled us to have precise control over the network hydrophobicity and charge density. This results in a high antimicrobial activity and an excellent cell compatibility of these polymer surfaces. By correlating their biological data with their chemical structure (hydrophobicity and charge density) and physical properties, we found interesting relations, for example that the antimicrobial activity of these surfaces is proportional to their acid constant pK.

figure 1.png

Figure 1: a. Antimicrobial peptides (left) are the natural archetype for facially amphiphilic SMAMP homopolymers and copolymers (orange: backbone, green: hydrophobic groups, blue hydrophilic groups). b. Using thiol-ene reactions, SMAMPs can also be turned into surface-attached polymer networks with excellent antimicrobial activity and cell-selectivity. [from Reference 5, originally published by The Royal Society of Chemistry]

 

Bifunctional Polymer Surfaces:
Combining Antimicrobial Activity and Protein-Repellency

The great dilemma of antimicrobial polymer surfaces made from polycations is that these surfaces may be inactivated when they become polluted by adhered biomolecules and dead bacteria. We develop new approaches to overcome this problem by combining our antimicrobial poly(oxanorbornene)-based SMAMPs (Figure 2a) with protein-repellent polyzwitterions (Figure 2b).

  • Nanostructuring approach: We fabricate surfaces with a chemical contrast using colloidal lithography, on which we could precisely attach the two different types of functional polymers with orthogonal chemical reactions (Figure 2c). This enables us to correlate the bioactivity of these materials with the spatial distribution of these polymers. AFM is a key tool to characterize these materials. [6]
  • Grafting-onto approach: By grafting polyzwitterions onto surface-attached polymer networks (Figure 2d), we obtain bifunctional polymer architectures with precise spatial control over the distribution of their components normal to the surface. The result is a material with excellent protein-resistivity. [7]

 

figure 2.png

Figure 2: Antimicrobial SMAMPs (a.)  were combined with protein-repellent polyzwitterions (b.). From these components, materials with two different surface architectures were obtained: nanostructured polymer surfaces with a precise distribution of the two polymers on a chemical surface contrast (c.) patches, and a bifunctional material with a grafting-onto architecture (d.) [from: Reference 6, originally published by Wiley-VCh].

 

Self-regenerating Antimicrobial Polymer Surfaces

As described above, the contamination of antimicrobial polymer surfaces made from polycations is an intrinsic problem that limits their use. Other functional surfaces also suffer from biofilm formation. So if we cannot make the perfectly biofilm resistant surface, why not make surfaces that can regenerate by erosion or degradation? However, when a surface is just erodible, craters form and we have no control over the surface properties. To solve this problem, we create multilayer architectures with precise layer positioning (Figure 3). These consist of alternating functional layers and degradable interlayers. By this, we dial in the properties of the emerging layers during build-up. We then degrade the interlayers and recover the properties of the functional layers. We demonstrated this concept by successfully shedding an antimicrobial layer from a three layer stack. The functionality of the emerging antimicrobial bottom layer was fully retained after shedding.

 figure 3.png

Figure 3: Inspired by nature: like a reptile shedding its skin, our multilayer systems can shed their exhausted top layer and thereby uncover a new functional layer. The degradation of the interlayer (blue) between the two functional layers (red) enables this process. [Reprinted with permission from Reference 7. Copyright 2015 American Chemical Society]

 

References

  1. Lienkamp, K.; Madkour, A. E.; Musante, A.; Nelson, C. F.; Nusslein, K.; Tew, G. N., Antimicrobial Polymers Prepared by ROMP with Unprecedented Selectivity: A Molecular Construction Kit Approach. J. Am. Chem. Soc. 2008, 130 (30), 9836-9843.
  2. Lienkamp, K.; Tew, G. N., Synthetic Mimics of Antimicrobial Peptides-A Versatile Ring-Opening Metathesis Polymerization Based Platform for the Synthesis of Selective Antibacterial and Cell-Penetrating Polymers. Chemistry--A European Journal 2009, 15 (44), 11784-11800.
  3. Al-Ahmad, A.; Laird, D.; Zou, P.; Tomakidi, P.; Steinberg, T.; Lienkamp, K., Nature-Inspired Antimicrobial Polymers – Assessment of Their Potential for Biomedical Applications. PLoS One 2013, 8 (9), e73812.
  4. Dorner, F.; Boschert, D.; Schneider, A.; Hartleb, W.; Al-Ahmad, A.; Lienkamp, K., Toward Self-Regenerating Antimicrobial Polymer Surfaces. ACS Macro Lett. 2015, 1337-1340.
  5. Zou, P.; Laird, D.; Riga, E. K.; Deng, Z.; Perez-Hernandez, H.-R.; Guevara-Solarte, D. L.; Steinberg, T.; Al-Ahmad, A.; Lienkamp, K., Antimicrobial and Cell-Compatible Surface-attached Polymer Networks – How the Correlation of Chemical Structure to Physical And Biological Data Leads to a Modified Mechanism of Action. Journal of Materials Chemistry B 2015, 3, 6224-6238.
  6. Hartleb, W.; Saar, J. S.; Zou, P.; Lienkamp, K., Just Antimicrobial is not Enough: Toward Bifunctional Polymer Surfaces with Dual Antimicrobial and Protein-Repellent Functionality. Macromolecular Chemistry and Physics 2016, 217 (2), 225-231.

  7. Zou, P.; Hartleb, W.; Lienkamp, K., It takes walls and knights to defend a castle - synthesis of surface coatings from antimicrobial and antibiofouling polymers. J. Mater. Chem. 2012, 22 (37), 19579-19589. 

 

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