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- Atomic layer deposition (ALD) (2)
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Course of studies
Atomic Layer Deposition of Bioactive TiO2 Thin Films on Polyetheretherketone for Orthopedic Implants
(2021)
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.
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.
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.