Research Projects

Plasma Polymerization

Plasma polymerization also known as plasma enhanced physical vapor deposition is a process in which a monomer is evapoated into a reaktor. By means of an external electrical field excited species are being created from the monomer which can undergo disexcitation while forming oligomers and polymers which deposit on surfaces within the reactor thus forming polymer films. Since the process also involves plasma activation of the sample surfaces plasma polymers can be easily grafted on top of virtually any substrate.

The picture shows parts of a plasma reactor. The light comes from emitting species created be an electrical field.

Cell Adhesive Implant Surfaces

Medical implants often trigger so called foreign body reactions. The soft tissue surrounding the implant becomes irritated causing severe problems for the patient. It is of major interest to graft implant surfaces that provide a cell friendly environment and that exhibit a fast cell attachement and thus healing of the surrounding tissue.
There are several approaches one being the immobilization of fibronectin onto the surface. Fibronectin is an extracellular matrix protein which triggers cell adhesion thus naturally causing growth of tissue in our body. Also RGD, a small amino acid sequence within fibronectin, is thought to be the origin of that mechanism. Since it is cheaper and packing densities can be higher it can be utilized the same way as fibronectin.
Immobilization is performed by an diepoxy linker that easily undergoes reactions with nitrogen contained in the protein and peptide respectively. Nitrogen containing plasma polymer films can readily react with the other end of the linker and therefore cause a strong bond between implant and tissue.

The figure shows the layer system on a titanium implant surface. ppHMDSO (black) is used to bind a ppAA film (blue). Free amino groups can then be used to immobilize cell adhesion promoting proteins or peptides (orange) via an diepoxy linker (red arrow).

Cell Repelling Implant Surfaces

Medical implants not always are supposed to stay within the tissue. Especially in trauma surgery implants are used that will be removed from the patient. Some implants cause problems here due to uncontrolled incorporation within the soft tissue and invasive techniques have to be used. A cell repelling implant surface could cause wanted encapsulation of the implant which then can be easily removed since the encapsuling tissue has no strong connection to the material.
Hydrophobic plasma polymers like ppHMDSO can be easily grafted on the surface of implants. The films are known to be non toxic and do not cause irritation of the soft tissue. Due to their hydrophobic nature however they seem to prevent cell adhesion over several days at least.

The figure shows the layer system on a titanium implant surface. ppHMDSO (black) is used as a hydrophobic, cell repelling coating.

Antimicrobial Surfaces

Bacterial infections cause severe health problems to patients throughout the world. Hospitals are forced to invest large sums of money to prevent spreading of multi resistant strains of bacteria. Early stage prevention of bacterial attachement to surfaces of medical equipement and subsequent prevention of biofilm formation is the ultimate goal of this research.
Certain metals exhibit antimicrobial properties among them silver and zinc. Both can be utilized on their own as a single coating, but due to the porous structure of the plasma polymers they can be combined in a layered system to get enhanced effects on bacteria while minimizing cytotoxic effects. Additionally, any of the above mentioned coatings can be applied on top of the antimicrobial coatings to further enhance adhesive or non-adhesive efficacy on mammalian cells.

The SEM picture shows a layered film on top of a polished silicon wafer consisting of a plasma polymerized zinc-organic compound and a cell adhesive functional top layer.

Bacterial Adhesion Forces through Multi Cantilever Arrays

To evaluate adhesion forces between bacteria and surfaces one can use nano scale silicon cantilevers. Their bending gives an estimate of surface free energies on either side of the cantilever thus enableing us to evaluate forces that bacteria apply to the tested surfaces. This will give information about the anti microbial properties of films deposited on top of the cantilever and furthermore this could lead to set up a detection device for bacteria given that the surface is coated with an appropriate antigen.