Functional polymer foams

Potential applications

en

Fig. 1: Manufactured functional polymer foam.

Open-pored polymer foams are interesting materials for numerous applications, especially as adsorber materials for separation or accumulation, as carriers for chemo- or biocatalysis, as well as three-dimensional carriers for mammalian cells or microorganisms. Conductive foams, formed by suitable additives, are even suitable as materials for electrodes for biofuel cells. For the named applications the inner surface of the pores must generally be equipped with functional groups or molecules. Depending on the pore structure and type of the polymer used for the foam, this is currently impossible or extremely difficult.

New single-stage production

Fig. 2: Single-stage synthesis of the foam using an emulsion polymerization process.

We have developed a single-stage synthesis strategy for the simple production of macroporous polymer foams with functional groups that can easily be implemented using the so-called click reaction.

An emulsion polymerization process (high internal phase emulsion) was used to produce a crosslinked polymer foam with azide functions for this. The organic phase contains the monomer, the crosslinker and a surfactant. The aqueous phase, which is placed into a reaction vessel together with the organic phase, contains the initiator for the radical polymerization.

Foam with functional pores

en

Fig. 3: Scanning electron microscope image of the manufactured foam.

en

Bild 4: Click-Reaktion des funktionalen Schaums mit Propargyl-PMMA.

The end material shown as an example in Fig. 1 has a porosity of approx. 90 percent. The scanning electron microscope image in Fig. 2 shows the structure with open macropores in the range of approx. 5–10 µm and micropores below 1 µm.

Azide functions react with alkyne functions (click reaction) under very mild conditions, such as biomolecules require for example, and without side reactions. We were able to show the binding of small molecules and polymers at the inner surface of the synthesized foam using an azide-alkyne cycloaddition (Fig. 4) in the examples of propargyl alcohol (Fig. 4A) and propargyl-poly(methyl methacrylate) (Fig. 4B).

Biocompatibility/biofunctionality

In order for the material to be used as a cell carrier its biocompatibility is a necessary prerequisite. Initial tests with human skin cells on the PMMA-modified foams showed, after incubation for 24 hours, improved cell adhesion in comparison to unmodified foam. Live/dead staining of the human cells that had been cultured at the surface for 24 hours, showed a high number of living cells.

Outlook

In the technology developed here, in contrast to conventional polymer foams, not the finished polymer is foamed . The material therefore has all the advantages of a synthetically producible polymer. The material’s crosslinked structure makes it resistant to organic solvents. Furthermore, the freedom of choice of chemical components enables targeted setting of the desired properties, such as e.g.hydrophilic properties or elasticity.

Now that the production of easily modified polymer foams with ideal porosity in a single-stage synthesis has been shown, the macroporous material should continue to be developed so that it can be applied for colonization with microbial cells for material enrichment.

Funding

We would like to thank the Fraunhofer-Gesellschaft for funding the project “Bakterien hinter Gittern zur Rückgewinnung von Phosphor” within the Fraunhofer “Netzwert” symposium 2011.