Wilfried Mokwa

Sputtered Iridium Oxide Films as Charge Injection Material for Functional Electrostimulation

The paper reports on the deposition of iridium oxide thin films by dc reactive magnetron sputtering and their characterization by surface analysis methods (X-ray diffraction, scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy) and electrochemical techniques (cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic square waves). The sputtering process was investigated by applying the method of generic curves. An optimal combination of sputtering parameters has been established [40 standard cubic centimeters per minute (sccm) argon/8-12 sccm oxygen/40% effective pump power/100 W dc power/cold sputtering] that yields stable microporous amorphous films with a highly extended surface. These films have shown an excellent electrochemical reversibility in physiological saline solution with a safe potential range of -1.2 to 1.3 V vs. Ag/AgCl reference electrode, a charge delivery capacity of 90-95 mC/cm 2 , a constant impedance of 70-80 Ω in the frequency range of 100 kHz down to 0.5-1.0 Hz, and a quick response to bipolar current pulses with a safe charge per phase of 2 mC/cm 2 /ph. The demonstrated remarkable electrochemical characteristics combined with their established long-term mechanical stability and corrosion resistance allow one to recommend the use of sputtered iridium oxide films as an ideal electrode material for neural stimulation.

Implantation and Explantation of a Wireless Epiretinal Retina Implant Device: Observations during the EPIRET3 Prospective Clinical Trial

PURPOSE Visual sensations in patients with blindness and retinal degenerations may be restored by electrical stimulation of retinal neurons with implantable microelectrode arrays. A prospective trial was initiated to evaluate the safety and efficacy of a wireless intraocular retinal implant (EPIRET3) in six volunteers with blindness and RP. METHODS The implant is a remotely controlled, fully intraocular wireless device consisting of a receiver and a stimulator module. The stimulator is placed on the retinal surface. Data and energy are transmitted via an inductive link from outside the eye to the implant. Surgery included removal of the lens, vitrectomy, and implantation of the EPIRET3 device through a corneal incision. The clinical outcome after implantation and explantation of the device was determined. The implant was removed after 4 weeks, according to the study protocol. RESULTS Implantation was successful in all six patients. While the anterior part was fixed with transscleral sutures, the stimulating foil was placed onto the posterior pole and fixed with retinal tacks. The implant was well tolerated, causing temporary moderate postoperative inflammation, whereas the position of the implant remained stable until surgical removal. In all cases explantation of the device was performed successfully. Adverse events were a sterile hypopyon effectively treated with steroids and antibiotics in one case and a retinal break in a second case during explantation requiring silicone oil surgery. CONCLUSIONS The EPIRET3 system can be successfully implanted and explanted in patients with blindness and RP. The surgical steps are feasible, and the postoperative follow-up disclosed an acceptable range of adverse events.

Micro-transponder systems for medical applications

The low power consumption of CMOS electronics with on-chip cointegrated sensors or actuators make it ideal for use in implanted systems that need a very low power consumption. Three examples are presented here, which are powered by the energy of an external RF-field. The first microsystem described is a system for measuring the intraocular pressure (IOP). Second, a system for measuring blood pressure will be introduced The third system is used for stimulating the nerve cells of the retina of patients suffering from retinitis pigmentosa. Typical microsystem chip dimensions are about 2.5 mm /spl times/ 2.5 mm and typical power consumption is about 240 /spl mu/W.

Surface micromachined pressure sensors with integrated CMOS read-out electronics

Abstract In this paper a single chip pressure and tenperature sensor system with on chip electronics is presented. The capacitive pressure sensor is fabricated using a CMOS process with additional surface micromachining steps to form a membranes. The membrane dimensions have been optimized for a pressure range of 2, 3.5, 10 and 35 bars, respectively. The temperature sensor shows a straight linear output signal in a temperature range of 0 to 70 °C. For the signal processing switched capacitor circuits are used. The sensor signals are converted to a pulse width modulated output signal. The silicon chip has an active area of 3.5 mm 2 . Between 0 and 80 °C a temperature dependence of the pressure segnal of less than 200 ppm/°C referring to full scale was found.

Development of a Completely Encapsulated Intraocular Pressure Sensor

A completely encapsulated intraocular pressure (IOP) sensor equipped with telemetric signal and energy transfer is introduced integrated into a silicone disc for implantation into the eye. After implantation into enucleated pig eyes and into rabbit eyes in vivo, the IOP was recorded and compared to established techniques of IOP measurement. Pressure chamber tests showed that the sensor functioned correctly after biocompatible encapsulation in polydimethylsiloxane. In vivo and in vitro tests in rabbit and pig eyes demonstrated that the implanted system worked with the same precision as established techniques for IOP determination. The correlation between the measurements with the implanted device and pneumotonometry in several experiments was between 0.9 and 0.99. This device serves as a functioning model for the realization of a telemetric IOP sensor for integration into an artificial intraocular lens. Such a device will open new perspectives, not only in the management of glaucoma, but also in basic research for mechanisms of glaucoma.

A monolithic sensor array of individually addressable microelectrodes

Abstract A monolithic single-chip sensor array for measuring chemical and biochemical parameters has been developed and fabricated in a modified standard CMOS process. The array can be used for amperometric or potentiometric measurements in order to get a concentration-dependent spatial profile of the detected analyte. In addition to 400 working electrodes and two reference electrodes, the chip contains integrated read-out amplifiers, digital circuits for addressing the individual components and test circuits. The on-chip signal processing allows detection of chemical or biochemical analytes without any interference by the external measurement equipment. High electrode impedances and low power consumption have been achieved by using CMOS technology. Chemical modification of the electrodes is possible by applying an external voltage to the electrodes. In advantage to non-integrated solutions, the system can be used in a wide field of applications, especially for measurements in narrow passages because of the total chip size of only 14×14 mm.

Microfluidic BioLector—Microfluidic Bioprocess Control in Microtiter Plates

In industrial‐scale biotechnological processes, the active control of the pH‐value combined with the controlled feeding of substrate solutions (fed‐batch) is the standard strategy to cultivate both prokaryotic and eukaryotic cells. On the contrary, for small‐scale cultivations, much simpler batch experiments with no process control are performed. This lack of process control often hinders researchers to scale‐up and scale‐down fermentation experiments, because the microbial metabolism and thereby the growth and production kinetics drastically changes depending on the cultivation strategy applied. While small‐scale batches are typically performed highly parallel and in high throughput, large‐scale cultivations demand sophisticated equipment for process control which is in most cases costly and difficult to handle. Currently, there is no technical system on the market that realizes simple process control in high throughput. The novel concept of a microfermentation system described in this work combines a fiber‐optic online‐monitoring device for microtiter plates (MTPs)—the BioLector technology—together with microfluidic control of cultivation processes in volumes below 1 mL. In the microfluidic chip, a micropump is integrated to realize distinct substrate flow rates during fed‐batch cultivation in microscale. Hence, a cultivation system with several distinct advantages could be established: (1) high information output on a microscale; (2) many experiments can be performed in parallel and be automated using MTPs; (3) this system is user‐friendly and can easily be transferred to a disposable single‐use system. This article elucidates this new concept and illustrates applications in fermentations of Escherichia coli under pH‐controlled and fed‐batch conditions in shaken MTPs. Biotechnol. Bioeng. 2010;107: 497–505.

RF-sputtering of iridium oxide to be used as stimulation material in functional medical implants

This paper describes the reactive RF-powered sputter deposition of iridium oxide (IrOx) to be used as the active stimulation layer in functional medical implants. Using an approach based on generic curves, the amount of oxygen gettered by the film is determined for various carrier gas flows and pumping speeds. It is shown that under certain conditions the getter effect peaks in the shape of a plateau when increasing the oxygen supply to the chamber. Films deposited along this curve show strong differences in electrochemical behaviour. At the beginning of the plateau, stable films with high electrochemical activity are deposited, and impedance measurements link the increase in charge delivery to a higher active surface area. On depositing at the far side of the plateau, the maximum deposition rate is recorded; however, unstable films are formed. These films predominantly contain unstable iridium oxide species, with iridium atoms in higher valence states. Protein adsorption, as is known to occur at implanted electrodes, was tested on some samples, and does not deteriorate the IrOx characteristics.

Initial investigations on systems for measuring intraocular pressure

Basic investigations on an intraocular implant system for continuous measurements of the intraocular pressure (IOP) are introduced. The system consists of a pressure sensor connected to transponder components integrated in the haptic of an artificial soft intraocular lens. External transponder components will be integrated in a spectacle and a hand-held unit. The influence of the lens material on the pressure sensor performance will be discussed in detail. Two pre-version of the concept mentioned will be introduced. In the first version, a pressure sensor was connected to a microwire. In a second version, the sensor was connected to transponder components for wireless data and energy transmission. Both versions were encapsulated in standard soft intraocular lens material. Pressure measurements show the same sensitivity before and after encapsulation. In addition, a small offset was observed due to the influence of the silicone coating. The performances of the sensors have the same precision as widely accepted gold standard for the determination of the IOP.

Single chip CMOS imagers and flexible microelectronic stimulators for a retina implant system

We are presenting CMOS image sensors and a microelectronic stimulator for realization of a retina implant system that will provide visual sensations using electrostimulation to patients suffering from photoreceptor degeneration. Four CMOS image sensors implementing different principles, e.g. linear characteristic, logarithmic characteristic, and local brightness adaptation have been developed. These are directly attached to a digital filter and signal processor unit that computes the so-called receptive-field functions for generation of the stimulation data. These external components are wireless linked to an implanted flexible silicon multielectrode microstimulator which generates electrical signals for electrostimulation of the intact ganglion cells. All components including additional hardware for digital signal processing and wireless data and power transmission have been developed for fabrication using our in-house standard CMOS-technology.