Electrochemical etching of titanium alloy in a fluoride-containing electrolyte results in ordered nanotextured surfaces. The reproducibility of nanotextured surfaces depends on several process parameters, most notably the fluoride ion concentration in the electrolyte. In the present work, electrochemical etching of Ti6Al4V alloy foils in ethylene glycol containing 0.66 wt% NH 4 F and 2% deionized water was carried out at 60 V for 45 minutes. This paper describes the depletion of fluoride ion concentration and contamination of electrolyte upon reuse. Inductively coupled plasma-optical emission spectroscopy was used to measure the dissolution of metal oxides in the electrolyte during etching. We found increasing concentration of the alloy elements Ti, Al, V contaminated the electrolyte due to repeated reuse of the electrolyte. The results show an appreciable log-linear depletion of fluoride ion concentration resulting in a changed surface morphology, chemical composition and etched volume. This paper provides an important insight to changes in surface morphology and surface chemistry with extended reuse of the etching electrolyte, useful for regulatory approvals.
The design and fabrication of a novel 3D electrode microdevice using 50 µm thick graphene paper and 100 µm double sided tape is described. The protocol details the procedures to construct a versatile, reusable, multiple layer, laminated dielectrophoresis chamber. Specifically, six layers of 50 µm x 0.7 cm x 2 cm graphene paper and five layers of double sided tape were alternately stacked together, then clamped to a glass slide. Then a 700 μm diameter micro-well was drilled through the laminated structure using a computer-controlled micro drilling machine. Insulating properties of the tape layer between adjacent graphene layers were assured by resistance tests. Silver conductive epoxy connected alternate layers of graphene paper and formed stable connections between the graphene paper and external copper wire electrodes. The finished device was then clamped and sealed to a glass slide. The electric field gradient was modeled within the multi-layer device. Dielectrophoretic behaviors of 6 μm polystyrene beads were demonstrated in the 1 mm deep micro-well, with medium conductivities ranging from 0.0001 S/m to 1.3 S/m, and applied signal frequencies from 100 Hz to 10 MHz. Negative dielectrophoretic responses were observed in three dimensions over most of the conductivity-frequency space and cross-over frequency values are consistent with previously reported literature values. The device did not prevent AC electroosmosis and electrothermal flows, which occurred in the low and high frequency regions, respectively. The graphene paper utilized in this device is versatile and could subsequently function as a biosensor after dielectrophoretic characterizations are complete. Video LinkThe video component of this article can be found at
Externally attached stiffeners/actuators are required for providing structural rigidity to flexible parylene-based cochlear implants for maintaining a perimodiolar shape in the post-implantation phase. Such backing devices being bulky add dead volume to the implant making the fluid-filled scala tympani chamber more congested during insertion resulting in shallow insertion depth. A thin film parylene array with integrated stiffener will provide a smaller implant cross-section potentially allowing a deeper implantation. A novel fabrication method for embedded cochlear implant stiffener structures by hot embossing of poly(lactic acid) (PLA) films is reported. PLA packaging film has been hot embossed on parylene coated silicon substrates using a custom fixture. Embossing results show good pattern transfer fidelity. Rigidity of the embossed stiffeners has been compared with the structural rigidity of poly (ethylene terephthalate) actuators.
Cochlear implants continue to be used in the treatment of profound deafness. Because of the tonotopic nature of the cochlea, more controlled insertion is perhaps the most important factor affecting device performance. The implant stiffness, and therefore the scala tympani (ST) wall contact force, contributes to insertion difficulties. Attempts to correlate the implant carrier structural properties and the intracochlear contact forces during insertion are limited. Researchers in the Michigan Center for Wireless Integrated Microsystems are developing perimodiolar-shaped silicon and parylene-based thin film cochlear electrode arrays and backing devices for a more controllable implantation. We report a method developed for measuring the thin film actuated electrode array rigidity to quantify the ST and modiolus wall contact forces during and after insertion. The method used a pneumatically actuated polyethylene terephthalate (PET) monolithic electrode actuator using pressurized air (0–200 kPa) for actuation. The prototype actuators consisted of PET tubes with an ID of 365 μm and a wall thickness of 58 μm. Force calculations using cantilever beam bending theory were performed to estimate the tube bending forces as a function of internal pressure and therefore variable structural stiffness. Based on estimations, a method was developed to measure such small forces avoiding the use of commercially available, relatively insensitive load cells. A fixture was fabricated incorporating two brass microcantilevers (reference and deflection arms) sensitive to sub-mN forces applied by the actuator on the deflection arm of the cantilevers. Microcantilver deflection data, captured by an interferometric microscope, was used to calculate the actuator force and eventually the reaction force acting on the actuator. The implant actuation forces ranged from 0–0.76 mN over an actuation pressure range of 0–140 kPa, from nearly straight to the relaxed perimodiolar post-implantation shape. For estimating the implant rigidity (EI), the actuator stiffness and the actuation pressure was correlated. The actuator stiffness at different actuation pressures was obtained both theoretically (using beam bending theory and PET tube structural properties) and experimentally (using the derived unconstrained actuator deflections at measured actuator forces). The theoretical and experimental stiffness values ranged from 3.6E-08 to 5.34E-07 N/μm and 2.5E-08 to 7.8E-06 N/μm respectively over the working pressure range. The calculated rigidity constant (EI) of the best prototype insertion tool from the experimental stiffness measurement was 6.71E06 Nμm2. The insertion tool-ST wall contact forces were calculated, using the estimated rigidity, in a hypothetical insertion situation. Force calculations assumed that the implant is equipped with actuator deflection feedback sensors and the actuator's stiffness remains constant over its entire length for a given operating pressure. A contact force of 1.19 mN was found acting on the cochlear ST wall when the insertion tool hits the wall and deflects by 200 μm at an actuation pressure of 140 kPa.
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