- freely available
Micromachines 2019, 10(1), 61; https://doi.org/10.3390/mi10010061
2. Materials and Methods
2.1. Selection of Materials
2.2. Electrode Design and Fabrication
- The 4 inch silicon carrier wafers were thoroughly cleaned using piranha etchant (4 H2SO4:1 H2O2) to remove any organic contaminants. Afterwards, a HF-dip (2% HF) was performed followed by a rinsing cycle in DI water. The substrate was dried using purified nitrogen.
- A 400 nm thin layer of silicon oxide was grown on the substrate using a wet thermal oxidation process. The oxide served as a sacrificial layer which aids in the final release of the devices from the carrier wafer in a later step.
- A first insulation layer of Parylene-C was deposited, yielding a 7 µm thick layer.
- The 400 nm thick Pt conductors were deposited by sputter coating on a lithographically patterned photoresist bilayer (LOR10B/S1818). The lift-off process was completed by soaking the wafers in n-methyl-2-pyrrolidone (NMP) overnight at room temperature.
- A second layer of Parylene-C, with a thickness of 7 µm, was deposited using a similar process.
- The device shape was defined by reactive ion etching (RIE) of the Parylene-C using an aluminum hard mask. The device outline was lithographically patterned using a negative photoresist on top of which a 40 nm thick layer of aluminum was thermally evaporated. After a lift-off step in acetone, the wafers were ready for RIE. As platinum is not etched by the RIE plasma, it also functions as an etch stop, which opens up the electrode contacts and bond pads.
- The wafer was annealed at a temperature of 200 °C for 4 h (2 °C/min ramping rate) in a nitrogen atmosphere to relax any residual stress that was built up during the processing, as well as to prevent delamination .
- Finally, the wafer was soaked in a 1% HF solution that removed the Al hard mask and underetched the sacrificial silicon oxide layer. After 1 h of etching, the adhesion between the Parylene-C electrode and the carrier wafer was reduced to such a level that the electrodes could be peeled off the carrier wafer using tweezers.
2.3. Micromechanical Characterization
2.4. Dissolution Rate
2.5. In Vivo Experiment
2.5.1. Implantation Procedure
- Overnight soak in blocking buffer (1% BSA, 0.1% Triton X100 in PBS) to reduce non-specific background staining
- Application of primary antibodies (1:100 MAB377 mouse anti-NeuN; 1:500 polyclonal rabbit anti-GFAP Z0334 in blocking buffer)
- Rinse in PBS (three times)
- 2 h incubation in blocking buffer
- Application of secondary antibodies (ALEXA fluor 488 (Abcam, Cambridge, UK) donkey anti-mouse IgG (H + L) and Cy3 Donkey Anti Rabbit IgG (H + L), 1:1000 in blocking buffer).
- Rinse in PBS (three times)
3.1. Micromechanical Characterization
3.2. Dextran Dissolution Rate
3.3. Image Analysis
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