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Course of studies
Atomic Layer Deposition of Bioactive TiO2 Thin Films on Polyetheretherketone for Orthopedic Implants
(2021)
In this work, the comparability of the cooling effect of two Peltier elements from different manufacturers is investigated for cooling the reagent module of a chemiluminescence analyzer. The temperature inside the reagent module is measured and evaluated at several positions. In this study, two different types of verification tests are performed under extreme climatic conditions. On the one hand, in a specific functional “cold start test”, the temperature in the reagent module is measured and evaluated to determine whether the measured temperatures are within the specified temperature range after the specified time. In addition, the performance of the Peltier elements is also evaluated. On the other hand, as an unspecific regression stress test, a “smoke test” is performed that is mainly designed to allow identifying unpredictable events. While processing a long and
complex work list, any deviant system behavior can be detected. Again, the temperature inside the reagent module should not exceed the specified temperature range.
Parylene-C is a multifunctional polymer coating in the coating industry. In medical technology, it is approved for implants due to its biocompatibility. For example, it is used as a coating for electronic components and parts. The problem is that Parylene-C alone is too permeable to body water and the ions that are dissolved in it. Application as a coating material for long-term implants is therefore not possible. The infiltrating water not only corrodes the electronic components, but also reduces the adhesion between the Parylene-C and the coated surface. Therefore, layer systems of metal oxides and polymers are used for encapsulation. The aim of this work is to find out how different layer systems behave in relation to their water vapour transmission. Thicker systems should allow less water vapour to pass through than thinner ones. The task is to find this out using the test method for water vapour transmission barriers and to determine the water vapour transmission rate. It has been proven that in some cases the thicker layers performed worse than the thinner layer systems by a factor of ten. It has been shown that there is a relationship between the base substrate thickness, the thickness of the layer system and their flexibility.
In the course of researching a bellows to encapsulation the mechanical unit of a moving active implant, two photopolymer resins were calibrated for further investigation as part of this research. This has been done using a masked stereolithography (MSLA) printer, cleaning steps followed by curing. The resins were one biocompatible and the other with special flexibility. The evaluation of the printing was carried out using a validation matrix for SLA printing processes. The time required for the process steps had been observed as well. Both resins were calibrated with respect to their exposure time and the process chain was evaluated. The results are meaningful, but additional factors had been identified that need to be considered too.
Feasibility of Parylene C for encapsulating piezoelectric actuators in active medical implants
(2023)
Parylene C is well-known as an encapsulation material for medical implants. Within the approach of miniaturization and automatization of a bone distractor, piezoelectric actuators were encapsulated with Parylene C. The stretchability of the polymer was investigated with respect to the encapsulation functionality of piezoelectric chips. We determined a linear yield strain of 1% of approximately 12-μm-thick Parylene C foil. Parylene C encapsulation withstands the mechanical stress of a minimum of 5×105 duty cycles by continuous actuation. The experiments demonstrate that elongation of the encapsulation on piezoelectric actuators and thus the elongation of Parylene C up to 0.8 mm are feasible.
High voltage insulation properties of DLC-Parylene multilayer films for microsurgery instruments
(2016)
Investigation of Long-Term Stability of Hybrid Systems-in-Foil (HySiF) for Biomedical Applications
(2020)
ALD can be used in medical technology to produce thin and stable protective coatings. For example, such coatings can be used as tarnish and oxidation protection for silver electrodes used in high-frequency surgery. For the investigation of the pretreatment method, platelets of sterling silver were used instead of silver electrodes. Three methods were used to pretreat the silver substrates. The first pretreatment method is cleaning with acetone and isopropanol. In the other two, the samples are additionally cleaned with a phosphoric acid etching mixture or citric acid. The pretreated substrates were coated using the atomic layer deposition method. 45 nm of aluminum oxide was deposited on the silver samples, followed by another 45 nm of titanium oxide. Subsequently, the samples were autoclaved in order to check the clinical routine and the reusability. The results show a significantly improved adhesion in contrast to samples that were not cleaned. The layer no longer flakes off the silver substrate. Nevertheless, small blisters appear on the protective layer after autoclaving. These indicate that the layer is weakened by the stress.
Investigation on adhesion strength of Parylene-C coatings with different adhesion promotion methods
(2021)
Delamination of encapsulation materials (here the polymer Parylene-C) is one of the biggest failure mechanisms for active medical implants. This problem is addressed by the application of different pre-treatment and adhesion promotion methods. The methods applied in this research are oxygen and Silane A-174 solution pre-treatment and Silane A-174, titanium oxide and Trimethylsilane as adhesion promoters. The adhesion forces of these methods are quantified after different soaking times in phosphate buffered saline (PBS) solution to mimic environment of the human body.
Langzeitstabile Verkapselungsschichten mit integriertem Feuchtesensor für aktive Mikroimplantate
(2012)