Our research currently focuses on the following projects:

Polymer based carrier material for improved application of bone substitutes

Polymer based carrier material for improved application of bone substitutes

NanoBone S39 (NBS) granules are difficult to handle, contour into desired shapes, and remain in the defects. Inert polymers such as poloxamer are suitable for binding the granules and hence improving their handling characteristics. Poloxamer 407 (P407) is a nonionic triblock copolymer with many pharmaceutical applications, as it is nontoxic and biocompatible with cells and body fluid. Poloxamer 407 consists of a central hydrophobic block of polypropylene glycol flanked by two hydrophilic blocks of polyethylene glycol. The stability of the Poloxamer at various temperatures can be detected by Differential Scanning Calorimetry (DSC).

Nanostructured coating on PEEK surfaces

Nanostructured coating on PEEK surfaces

Fig. 1 Transmission electron micrograph of the interface between layer and implant (A PEEK; B silica hydroxyapatite).
Fig. 2. Electron diffraction curve of the PEEK surface after short melting and fast cooling (blue), the silica- hydroxyapatite layer (red) and the interface (black).

PEEK as a semi crystalline biomaterial is characterized by its very good mechanical and thermal properties. It has a bio-inert character due to its chemical stability. As a result, a bad bone-implant contact occurs in orthopedic implants, which prevents a permanent bone integration. For this reason the aim of this work was a bioactive coating on PEEK implants. The spin-spray technique produces a nanoporous SiO2 layer in which hydroxyapatite crystallites are embedded. It is now essential to create an interface between the layer and the PEEK surface. The polymer must penetrate the nanopores and thus form a composite of PEEK, SiO2 and hydroxyapatite. The development of this interface is documented with transmission electron microscopy and electron di ffraction. Fig. 1 shows that the PEEK penetrates into the nanopores of the material. The electron diffraction (Fig. 2) documents that the PEEK surface is a pure glass. Bragg reflexes are not detectable. The curve shows an amorphous maximum at 12 nm-1. The electron di ffraction curve of the interface is not a superposition of the PEEK curve and the curve of the layer. The di raction peak at 12 nm-1 is no
longer detectable. Obviously the mobility of the polymer chains in the nanopores is restricted, so that the relaxation is not possible.

Polymer-silica nanocomposites for wound dressing

Polymer-silica nanocomposites for wound dressing

Fig. 1 Differential scanning calorimetry of differently composed polymer-silica composites with the glass transition temperature (X).
Fig. 2 Blood vessel density in dermal wounds of mice on different days and with different wound dressing materials.

Nanostructured silica is essential for tissue growth and regeneration. We developed a nano-composite from PVP (polyvinylpyrrolidone) and silica nanoparticles for soft tissue regeneration. The silica nanoparticles are derived from sodium silicate solution and are 1.3 - 1.6nm in size. Fig. 1 shows the specific heat capacity over temperature of the composite with different silica content. The rise of the glass transition temperature with higher silica content points to a cross-linking between the polymer chains by the silica nanoparticles. The decreasing step in specific heat capacity is not only due to decreasing PVP content, but also by a formation of a rigid amorphous fraction of the PVP around the silica nanoparticles. Two wound dressings made from the polymer-silica nanocomposite were tested in a skin defect model on mice. Fig. 2 shows the blood vessel density in dermal wounds on different days. The growth of the blood vessels at early wound healing stages is accelerated in wounds, which were treated with wet composite wound dressings. Also the size of the remaining scar was significantly smaller.

Our research is financially supported by the European Regional Development Fund.