Showing papers by "Florian Solzbacher published in 2011"

Long term in vitro functional stability and recording longevity of fully integrated wireless neural interfaces based on the Utah Slant Electrode Array.

Abstract: We evaluate the encapsulation and packaging reliability of a fully integrated wireless neural interface based on a Utah Slant Electrode Array/integrated neural interface-recording version 5 (USEA/INI-R5) system by monitoring the long term in vitro functional stability and recording longevity. The INI encapsulated with 6 µm Parylene-C was immersed in phosphate buffered saline (PBS) for a period of over 276 days (with the monitoring of the functional device still ongoing). The full functionality (wireless radio-frequency power, command and signal transmission) and the ability of the electrodes to record artificial neural signals even after 276 days of PBS soaking with little change (within 14%) in signal/noise amplitude constitute a major milestone in long term stability and allow us to study and evaluate the encapsulation reliability, functional stability and its potential usefulness for a wireless neural interface for future chronic implants.

Thermodynamic Analysis of the Selectivity Enhancement Obtained by Using Smart Hydrogels That Are Zwitterionic When Detecting Glucose With Boronic Acid Moieties.

Abstract: Because the boronic acid moiety reversibly binds to sugar molecules and has low cytotoxicity, boronic acid-containing hydrogels are being used in a variety of implantable glucose sensors under development, including sensors based on optical, fluorescence, and swelling pressure measurements. However, some method of glucose selectivity enhancement is often necessary, because isolated boronic acid molecules have a binding constant with glucose that is some 40 times smaller than their binding constant with fructose, the second most abundant sugar in the human body. In many cases, glucose selectivity enhancement is obtained by incorporating pendant tertiary amines into the hydrogel network, thereby giving rise to a hydrogel that is zwitterionic at physiological pH. However, the mechanism by which incorporation of tertiary amines confers selectivity enhancement is poorly understood. In order to clarify this mechanism, we use the osmotic deswelling technique to compare the thermodynamic interactions of glucose and fructose with a zwitterionic smart hydrogel containing boronic acid moieties. We also investigate the change in the structure of the hydrogel that occurs when it binds to glucose or to fructose using the technique of small angle neutron scattering.

Novel isotropic and anisotropic etching of MEMS structures by controlling the dynamics of the etchant

Abstract: In MEMS technology there is an increasing interest in developing high aspect ratio silicon columns having rounded corners, slightly positive tapered shaft, sharp tips, and smooth surface. A precise control of the profile can be used for different applications, such as for molds used in polymer hot embossing processes, micro needles used for drug delivery and blood sampling, and neural probes used for controlling motor or sensory prosthetic devices. The mixture of hydrofluoric acid (HF) and nitric acid (HNO 3 ) is an isotropic etchant and is used in MEMS technology to etch silicon. We present a novel way of isotropically and anisotropically etch MEMS structures using the HF-HNO 3 etchant. The shape and size of the structure is controlled by the dynamics of reactants.

Evaluation of the packaging and encapsulation reliability in fully integrated, fully wireless 100 channel Utah Slant Electrode Array (USEA): Implications for long term functionality

Abstract: We evaluate the encapsulation and packaging reliability in fully integrated, fully wireless 100 channel Utah Slant Electrode Array (USEA)/integrated neural interface-recording version 5 (INI-R5) by monitoring the extended long term in-vitro functional stability and recording longevity. The INI encapsulated with 6-µm Parylene-C was immersed in phosphate buffer saline (PBS) for a period of over 12 months. The full functionality and the ability of the electrodes to record artificial neural signals even after 12 months of PBS soak provides a measure of encapsulation reliability, the functional and recording stability in fully integrated wireless neural interface and potential usefulness for future chronic implants.

Biochemical microsensors on the basis of metabolically sensitive hydrogels

Abstract: With the rapid development of micro systems technology and microelectronics, smart electronic systems are emerging for the continuous surveillance of relevant parameters in the body and even for closed-loop systems with a sensor feedback to drug release systems. With respect to diabetes management, there is a critical societal need for a sensor that can be used to continuously measure a patient's blood glucose concentration twenty four hours a day on a long-term basis. In this work, thin films of "stimuli-responsive" or "smart" hydrogels were combined with microfabricated piezoresistive pressure transducers to obtain "chemomechanical sensors" that can serve as selective and versatile wireless biomedical sensors. The sensitivity of hydrogels with regard to the concentration of glucose in solutions with physiological pH, ionic strength and temperature was investigated in vitro. The response of the glucose-sensitive hydrogel was studied at different regimes of the glucose concentration change and at different temperatures. Sensor response time and accuracy with which a sensor can track gradual changes in glucose was estimated.

Effect of temperature changes on the performance of ionic strength biosensors based on hydrogels and pressure sensors

Abstract: Stimuli responsive hydrogels show a strong ability to change in volume with changes in selected environmental properties. This tendency of these hydrogels to change in volume is captured as pressure-change in confined cavities of pressure sensors. An array of pressure sensors on a single chip may carry hydrogels sensitive to multiple, selected metabolic markers and continuously monitor multiple vital parameters simultaneously. Currently, such sensors are capable of continuously monitoring pH, ionic strength, glucose levels and temperature in the sensor environment. In this paper, we report the effect of temperature changes on the performance of ionic strength sensor. A formulation of hydrogel that renders it sensitive to changes in ionic strength was UV polymerized in situ in piezoresistive pressure sensors with different membrane sizes. The sensor sensitivity, response time and stability are investigated as a function of temperature in vitro. The effect of temperature on these sensor characteristics is discussed.

A novel surface modification method to achieve low impedance neural microelectrode arrays

Abstract: Advances in neuroprostheses are strongly dependent on the development of microelectrodes with an enhanced ability to selectively record or stimulate neural signals. Selectivity for a microelectrode depends on its ability to interact with a small number of neurons and/or nerve fibers. In order to achieve selective electrical transduction, the surface area of active site should be on the order of tens of micrometers. However, as the area of the electrode decreases, the electrode impedance increases, which in turn affects the recording/stimulating characteristics (sensitivity). Thus there is a trade-off between selectivity and sensitivity. One option to overcome this trade-off is by generating a large functional active area without increasing the geometrical surface area (GSA) of the electrodes. This paper for the first time reports a novel method of using a combination of SF 6 and O 2 based reactive ion etching (RIE), to modify the surface of electrodes tip, in order to increase the RSA without increasing the GSA. The study demonstrates that by altering the surface morphology of the electrode tips, the impedance can be lowered significantly. The optimum etching power was 250 W which yielded mechanically robust, high charge storage capacity (CSC), and low electrochemical impedance surface.