Seide, Klaus

Diseases and injuries of the musculoskeletal system are of enormous social and economic importance. They are the main cause of chronic pain and mobility limitations worldwide. Fragility fractures are a main contributor to mortality, morbidity, and diminished quality of life in elderly people. Occurring costs and the burden will continue to rise in the future due to demographic and epidemiological shifts. The purpose of this dissertation is to develop an osteosynthesis implant that is able to track the healing progress after a fracture. This will aim for individualized healing tracking and the detection of early signs of complications. To achieve this objective, three tasks are defined: the design and development of a prototype, the verification of its function and a regulatory strategy to make the developed technology accessible. To be able to verify the results of the healing progress during the treatment, two different sensor technologies are used: mechanical strain sensors and electrical impedance measurements. Besides the continuous verification, both sensors combined lead to unique advantages through synergetic effects which eradicates and compensates specific weaknesses in stand-alone configuration, e. g., limitation at tracking of the healing directly after the operation (strain gauge) and detecting the load capacity (impedance). Based on requirements derived from literature, a prototype design was iteratively developed which is fabricated out of two materials – PEEK and titanium – that are both used widely in medical applications. The electronic components including electrodes and an area for the microchip described within the outlook were embedded in a medical epoxy. Generated computer aided design (CAD) data sets were used to investigate the impact of the design and material changes in comparison to a standard osteosynthesis plate among four different load cases (bending, torsion, axial load and a combined load). It was shown that bending has the most powerful impact on the osteosynthesis plate, followed by torsion and combined load, respectively. The yield strength of the titanium osteosynthesis plate is not exceeded in any of the load cases while it is exceeded for all load cases of the PEEK osteosynthesis plate expect the axial load. The in-vitro testing for verification was performed on a pig femur. Three different tissue types were used inside the fracture gap for simulation of fracture healing: blood (haematoma), cartilage (granulation tissue) and bone (healed status). Using a four-terminal approach allows the presentation of valid experimental results for low-frequency domains (0.1-10 kHz) additionally to typically used higher frequency domains. It was shown that all investigated types of tissue are distinguishable. A beta- and, based on the four-terminal approach, an alpha-dispersion is detected. Thus, in-vivo monitoring of the healing progress as well as distinction of changes of ionic concentrations seems possible with the developed prototype. Furthermore, equivalent electrical circuits were designed and simulated with LTSpice for investigation of influencing factors and verification of the results. Based on the experimental results, it can be shown that the diameter of the measured area is a major factor for influencing the output and assumedly varies based on the tissue composition. Moreover, the experimental results show that the sensors of the prototype work together synergistically and that the mechanical load has a minor impact on the measured impedance. Finally, regulatory pathways for commercialisation of innovative medical products are explored and described in relation to the different stakeholders, e. g. hospitals, research institutions or medical device manufacturers. A regulatory strategy was derived from an analysis of the European legal framework and different required documents were created based on the developed prototype and stakeholder.

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