MZT - Mikromedizintechnik
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Parylene-C is used for various biomedical devices because of its high conformity and biocompatibility. However, delamination could occur because of low adhesion between Parylene-C and other materials. For this experiment 4-inch Si-wafers are used. Parylene is deposited by chemical vapour deposition (CVD). Silane A-174 as adhesion promoter is added between Parylene-Parylene layers. The samples are soaked at different duration 1 h, 24 h and 120 h in PBS solution at 37 °C. A peel test is further performed to investigate the adhesion properties of the samples.
This work gives the theoretical background which is needed to understand what self-assembling monolayers are, how they work, how and for what they can be used. A closer look is taken on the possibility to create an area selective atomic layer deposition process. In a practical experiment the foundation for this process is laid. Therefor a silicon wafer is coated with gold using a evaporation process. The gold samples are exposed to the SAMs solution to grow them. Contact angle measurements as well as Fourier transform Infrared spectroscopy are used to check the existence of SAMs on the gold samples. Also there is investigated if different exposure times make any differences.
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.
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.
Optogenetics and optogenetic systems cover a wide range of applications in the research of neurological pathways. In this overview, relevant aspects regarding the development of optogenetic systems should be shown. These are the optogenetic systems – opsins and optical switches – as well as optoprobes, materials, application areas and limitations of these applications. Additionally, a short outlook should be given. No detailed analysis for specific optogenetic systems or their partial aspects were carried out.
In the present work, polyetheretherketone (PEEK) was pretreated with oxygen plasma to investigate the influence on the contact angle and surface energy. For this purpose, PEEK samples were fabricated over several manufacturing steps, which were used as substrates for later investigations. A series of measurements was performed at a power of 300 W for different treatment durations and the contact angle of H2O on the PEEK surface was determined. The results show that plasma pretreatment significantly affects the surface modification of PEEK disks. The best hydrophilic properties of the PEEK surfaces were measured at a treatment time of 540 s and a power of 300 W. A much longer treatment time caused the correlated values of contact angle and surface energy to increase and in this case an excessive treatment time did not contribute to a further increase in hydrophilicity.
The paper shows the influence of low-pressure plasma on polyethylene terephthalate (PET) to achieve improved layer adhesion between PET and ALD multilayers. The literature describes a relationship between functional groups that are incorporated into the polymer surface and better layer adhesion. In this work, the relative number of functional groups after treatment on the surface of PET was measured by the surface energy.
The PET film Hostaphan® RNK was exposed to oxygen and argon plasma with varying treatment times. Subsequently, the surface energy was determined via the contact angle measurement.
The investigations have shown that with increasing treatment time in the oxygen plasma, an increasing surface energy is associated, which is due to the increased incorporation of functional groups, such as hydroxy groups. Furthermore, the results have confirmed the thesis that if the plasma treatment is too long, oxidation takes place on the polymer surface and thus the surface energy decreases. Another aspect that has emerged in the results of the study is the subordinate role of the power of the plasma.
Since the study has not proven the connection between a good layer adhesion, of ALD multilayers on PET, and a high surface energy, this work should serve as an indication for the investigation of this thesis.
A major problem in the automotive sector is dealing with used hydraulic oil. Since this oil loses its purity over time, it must be changed. In most cases, the condition of the oil is not really checked, but is changed after a certain number of kilometers. It is possible that intact hydraulic oil is wasted in the process. Until now, there is no cost-effective method to check the purity on hydraulic oils, so there is nothing left but to remove all of the oil. The purpose of this work is to develop a measuring station for a MEMS-based oil quality sensor. With the help of the oil quality sensor, deviations of aged hydraulic oils shall be investigated. An infrared light source and a Fabri-Perot spectrum sensor will be used for more accurate detection of deviations in aged hydraulic oil. The goal is to clarify whether it is possible to use wavelength spectra to detect differences in aged hydraulic oil. To do this, a suitable Fabri-Perot spectrum sensor and a light source with the appropriate wavelength range were carefully selected. Furthermore, a measurement setup for static measurements was worked out. Subsequently, measurements were carried out with and without hydraulic oil and the measured data was compared with reference data. Finally, differences in the aged hydraulic oil could be determined by means of light wave measurements.