Max Schwade

Optimized in vitro procedure for assessing the cytocompatibility of magnesium-based biomaterials.

Magnesium (Mg) is a promising biomaterial for degradable implant applications that has been extensively studied in vitro and in vivo in recent years. In this study, we developed a procedure that allows an optimized and uniform in vitro assessment of the cytocompatibility of Mg-based materials while respecting the standard protocol DIN EN ISO 10993-5:2009. The mouse fibroblast line L-929 was chosen as the preferred assay cell line and MEM supplemented with 10% FCS, penicillin/streptomycin and 4mM l-glutamine as the favored assay medium. The procedure consists of (1) an indirect assessment of effects of soluble Mg corrosion products in material extracts and (2) a direct assessment of the surface compatibility in terms of cell attachment and cytotoxicity originating from active corrosion processes. The indirect assessment allows the quantification of cell-proliferation (BrdU-assay), viability (XTT-assay) as well as cytotoxicity (LDH-assay) of the mouse fibroblasts incubated with material extracts. Direct assessment visualizes cells attached to the test materials by means of live-dead staining. The colorimetric assays and the visual evaluation complement each other and the combination of both provides an optimized and simple procedure for assessing the cytocompatibility of Mg-based biomaterials in vitro.

Multi-scale directed surface topography machined by electro discharge machining in combination with plasma electrolytic conversion for improved osseointegration

Major deficits concerning biodegradable and non-biodegradable orthopaedic implants are a result of insufficient osseointegration and an accelerated corrosion rate. These in turn are significantly influenced by the surface tissue-interface. Cells belonging to different steps of the osteoblast differentiation cascade respond differently to the same surface structure. Therefore, a combination of particular micro and macro structures resulting in a multi-scale directed surface topography may significantly improve the cell response throughout the whole osseointegration process. This paper proposes the possibility to adapt the structural properties of a surface independently throughout different magnitudes of topography by a combination of electro discharge machining and a plasma electrolytic conversion process. Examples of such structures are demonstrated in samples made of the magnesium alloy WE43 as well as the most commonly used titanium alloy for orthopaedic implants Ti6Al4V.

Development of a Process Evaluation System for Wire-EDM Applications Using an Intelligent Process Monitoring Tool

In this paper a first approach is presented to investigate the electrical parameters of the EDM process using an intelligent process monitoring tool to evaluate different technologies and generators. Goal is to characterize every single discharge by extracting relevant data from recorded current and voltage signals using an adequate algorithm. For demonstration purposes a steel material is machined using a corresponding technology recommended by the machine tool supplier as well as a recommended technology for hard metal. In a first step the machining quality is evaluated by the cutting rate and surface roughness which is common practice for EDM. These results are then compared to the data extracted by the process monitoring tool. In the future this tool may be able to accelerate the parameter development for a specific task or material significantly. The effectiveness of the process could be determined directly during the process and no longer indirectly by a quality inspection of the machined part. By investigating the course of each discharge the process parameters can be linked to the actual physical parameters and a direct influence could be identified.

Fundamental Analysis of the Process Conditions during Electro Discharge Machining of Biodegradable Magnesium

Magnesium is one of the most promising materials for the application as degradable biomaterial for load bearing implants due to the initial stability and extraordinary biocompatibility. But up until now magnesium degrades too fast before the ingrowing bone can support itself. One possible approach is the application of an interconnecting channel structure. This design increases the surface area to promote bone regeneration and gives the bone the possibility to build a supporting structure throughout the implant. In combination with a surface modification which increases the corrosion resistance the bone can regain enough stability to support itself before the implant has dissolved noticeably. Due to the low process forces EDM is very suited for the machining of the necessary filigree structures. But up until now there are no standard technologies for the machining of this material available. Therefore a fundamental analysis of the material specific influence of magnesium on the EDM process is necessary. In this paper the machining of three different magnesium alloys are compared to the machining of a tool steel. Due to the numerous influencing factors and their interdependencies it is normally not possible to analyze the impact of each input parameter of a typical EDM technology on the continuous process separately making the correlation of input and output parameters very difficult. Therefore the electrical signals are recorded during the machining process to identify and monitor the resulting discharge conditions and frequency. These results are compared to the fundamental influence of the material derived from single discharge experiments in which the boundary conditions are constant to a large extent. By this method the material removal rate as well as the resulting surface roughness of the continuous process can be linked to the material dependent process conditions. As a result technologies for the machining of new materials can be developed and optimized based on fundamental knowledge.

Novel Processes for the Machining of Tool Inserts for Precision Glass Molding

In this chapter, two new process chains are introduced using novel processes for the machining of complex molds by diamond grinding and diamond profile grinding in combination with a machine-based abrasive profile polishing. Finest grained diamond grinding wheels with a metal bond provide superior grinding results. But the combination of a metal bond and very fine grains causes great difficulties for the trueing and dressing operation using conventional methods. For the machining of rotational symmetric mold inserts the novel process of electrochemical in-process dressing can be applied to achieve optical surface qualities without a subsequent polishing process.