C2: Laser-generated micofunctionalised implants

Project manager:
Dr. Nat. Sci. [rer. nat.] Dr. Dietmar Kracht
Dr. Eng. Dipl. Chem. Stephan Barcikowski
Dr. Med. Rüdiger Blindt

The goal of this subprojects is to provide a method for the implementation of partially nanostructured microsystems based on function-specific, customised implants for medical technology from NiTi shape-memory alloys (FGL) using the laser sintering process as well as absorbable stents of polylactide.
An application example of the FGL structures is the guided growth of cells in the area of reconstructive surgery. Here three-dimensional “growth splints” are generated which are to reach the respectively large target volume of the cultivated tissue (e.g. for the cultivation of biological implants with body contour defects or tumour operations). The plan is to investigate the generation of vascularised bone tissue on a model basis. To this purpose, hierarchical structures will be set up using microlaser sintering from actoric and biocompatible FG alloys.

The first central goal is this subproject was thus the process development of the micro laser sintering for the nickel-titanium shape-memory alloy (FGL) with the possibility of receiving material-specific, functional properties. These properties of NiTi-FGL are largely determined by the set alloy ratio of nickel to titanium. With melting processes there is, due to the large reactivity of titanium, the risk of oxygen consumption out of the processing atmosphere. For this reason, a high vacuum compatible processing chamber was constructed where the NiTi powder can be sintered to microstructures in the vacuum or in a highly pure protective gas atmosphere. Using the process technology developed and the analytic models, NiTi structures (Figure 1 right) could be constructed in micro laser sintering processing with a minimal individual bridge width of approx. 50 µm.

A further goal was the production of NiTi nanoparticles in liquid and organic solvents using ultrashort pulse laser beam ablation as well as evidence of stoichiometric preservation of the nanoparticles in order to achieve an improvement in the cell adhesion through coating the NiTi structures with NiTi nanoparticles. Using a coating process such as, for example, dip-coating, NiTi nanoparticles were applied to the NiTi surfaces and a coating implemented which shows the specified nanoscopic surfaces topographies. These surfaces could be implemented even on the sintered NiTi structures. In the investigation of biocompatibility of the nanoparticle coating and its influence on the cell growth and cell proliferation, good cell adhesion could be established both in immunocytochemical investigations and based on REM and ESEM recordings/photographs. It was discovered that the growth of the cells was not only flat on the test sample but rather experienced an increased extension in the third spatial direction on coated material (Figure 1 left). A chemically and mechanically-induced osteogenic differentiability of the adipogenic stem cells could be determined on all structured used (Figure 1 centre).