Laser-Based Scaffold Creation & Surface Functionalisation
Laser engineering is used to provide structure to chemical, biochemical and solid materials, in accordance with the requirements of the patients and of the model systems.
The objectives include the following:
- Improving the integration of the implant into the tissue by generating specific surface topographies;
- Producing three dimensional supportive structures, known as “scaffolds” and “microporous implants”;
- Producing and incorporating nanoparticles, which can then be used for additional functionalisation.
Material surfaces can be structured in a controlled and reproducible manner, with ultrashort pulse laser ablation or with the micro replication technique in the nanometre or micrometre range. It was shown that these topographies can selectively control cell behaviour and demonstrate antibacterial activity. These microstructured surfaces can also be coated with various nanoparticles and thus extend or improve their desired effect on cells.
Microreplication can also be used for the production of scaffolds, although 3D structure is mostly produced by the 2 photon polymerisation (2PP) technique, a new technique which permits the CAD-based production of any 3D object in a single step. 2PP is triggered by the simultaneous absorption of two (or more) photons and therefore requires high intensities. The laser is set and focussed so that these intensities are only reached at the focus of the laser. As a consequence, the interactions between light and material are restricted to the focus volume, while the rest of the material remains unchanged. Two photon absorption initiates the polymerisation process and can, for example, transfer material from the liquid into the solid phase. The laser focus is directed through the volume of the material, leaving behind a thin trace of polymerised material. This makes it possible to reproduce any computer-generated 3D structure through a direct laser trace in the volume of the photosensitive polymer. As a consequence of the threshold property and the non-linear nature of the 2PP process, it is possible to achieve resolution beyond the diffraction limit by controlling the energy of the laser pulse and the number of laser pulses. In this way, three dimensional structures can be formed in both synthetic and natural materials, including fibrin, hyaluronic acid and gelatine. The cell biological activity of the structures produced is validated in collaboration with the module “Biocompatibility / Cell Test Systems” and the BIO modules. This can include studies on stem cell differentiation and vascularisation.
Nanoparticles can be generated in fluids by laser beam ablation in fluids and can be embedded in any medical plastic. One very promising approach is to use nanocomposites made of plastics with embedded metallic nanoparticles. These may be used to produce medical devices with antibacterial properties that protect against infection. In an aqueous environment, metallic nanoparticles of silver or copper release ions that can kill bacteria on contact, thus affording antibacterial protection.
If the whole component volume is functionalised with nanoparticles, this provides better long-term protection than with coating alone. Another major advantage of this procedure is that the resulting nanomaterials are of high purity, as chemical educts and stabilising reagents are unnecessary, The process-related particle loading gives high colloidal stability and permits additional functionalisation of the particles with biologically active additives, e.g. antibiotics, DNA molecules or other ligands.
