Wireless Stimulation of Motor Cortex Through a Collagen Dura Substitute Using an Ultra-Thin Implant Fabricated on Parylene/PDMS.

We present the design, fabrication, and in vivo testing of an ultra-thin (100 µm) wireless and battery-free implant for stimulation of the brain's cortex. The implant is fabricated on a flexible and transparent parylene/PDMS substrate, and it is miniaturized to dimensions of 15.6 × 6.6 mm 2. The frequency and pulse width of the monophasic voltage pulses are determined through On-Off keying (OOK) modulation of a wireless transmission at 2.45 GHz. Furthermore, the implant triggered a motor response in vivo when tested in 6 rodents. Limb response was observed by wireless stimulation of the brain's motor cortex through an FDA-approved collagen dura substitute that was placed on the dura in the craniotomy site, with no direct contact between the implant's electrodes and the brain's cortical surface. Therefore, the wireless stimulation method reported herein enables the concept of an e-dura substitute, where wireless electronics can be integrated onto a conventional dura substitute to augment its therapeutic function and administer any desired stimulation protocol without the need for post-surgical intervention for battery replacement or reprogramming stimulation parameters.

Variable self-powered light detection CMOS chip with real-time adaptive tracking digital output based on a novel on-chip sensor.

This paper provides a solution for a self-powered light direction detection with digitized output. Light direction sensors, energy harvesting photodiodes, real-time adaptive tracking digital output unit and other necessary circuits are integrated on a single chip based on a standard 0.18 µm CMOS process. Light direction sensors proposed have an accuracy of 1.8 degree over a 120 degree range. In order to improve the accuracy, a compensation circuit is presented for photodiodes' forward currents. The actual measurement precision of output is approximately 7 ENOB. Besides that, an adaptive under voltage protection circuit is designed for variable supply power which may undulate with temperature and process.

Design and evaluation of a low cost intracranial pressure monitoring system.

One of the most life-threatening neural conditions is elevated intracranial pressure (ICP); it is associated with ischemia and poor short- and long-term outcomes. Currently, monitoring systems that accurately measure ICP are either highly invasive or inaccurate. This work explores the design and evaluation of an epidural intracranial pressure monitoring system for low-cost, minimally invasive detection. Our goal is to develop a monitoring system that could also be integrated with an electrocorticography (ECoG) system. To this end we created a minimally invasive epidural ICP monitor for use with a 2 mm burr hole craniotomy. A MEMS piezoresistive sensors is used in the system, and its performance is evaluated for intracranial pressure measurements. Our system is calibrated and tested on the benchtop and demonstrated in vivo using an animal model.

CMOS self-powered monolithic light-direction sensor with digitalized output.

We present a novel self-powered chip to detect the direction of incident light. This chip directly provides digitized output without the need of any off-chip power supply or optical or mechanical components. The chip was implemented in a standard 0.5 µm CMOS process. A microscale metal baffle was created by stacking all metal layers, contacts, and vias available in the process to produce on-chip shadowing. N-well/p+ photodiode arrays are located on both sides of the baffle to sense light. The photocurrent generated by a photodiode depends on the size of the photodiode and the shadowing. The shadowed area depends on the incident angle of the light. A current mirror circuit is used to compare the currents generated by the photodiodes on the opposite sides of the baffle and, consequently, provide a digital signal to indicate the incident light angle. Compared with the ideal linear digital light-angle detector with the same resolution, the presented sensor achieved the maximum error of only 2 deg over 110 deg test range.

Real-time feedback control of pH within microfluidics using integrated sensing and actuation.

We demonstrate a microfluidic system which applies engineering feedback principles to control the pH of a solution with a high degree of precision. The system utilizes an extended-gate ion-sensitive field-effect transistor (ISFET) along with an integrated pseudo-reference electrode to monitor pH values within a microfluidic reaction chamber. The monitored reaction chamber has an approximate volume of 90 nL. The pH value is controlled by adjusting the flow through two input channels using a pulse-width modulated signal applied to on-chip integrated valves. We demonstrate real-time control of pH through the feedback-controlled stepping of 0.14 pH increments in both the increasing and decreasing direction. The system converges to the pH setpoint within approximately 20 seconds of a step change. The integration of feedback theory into a microfluidic environment is a necessary step for achieving complete control over the microenvironment.

On-chip sensor for light direction detection.

We present an on-chip optical sensor capable of detecting the direction of incident light. No off-chip optical or mechanical components or modifications--for example, baffles, slit structures, mirrors, etc.--are needed. The sensor was implemented in a standard 0.5 µm complementary metal-oxide semiconductor process. A pair of on-chip photodiodes separated by a metal "wall" (created by stacking all metal layers, contacts, and vias available in the process) is used to detect the direction of the incident light. This metal stack wall creates on-chip shadowing to facilitate detection so that the two photodiodes produce different amounts of photocurrent. A model for this device is presented. The analysis indicts that the ratio of the difference of these two currents to the larger of the two currents has a linear relationship with the angle of the incident light. Moreover, we also demonstrate this ratio is almost independent of the incident light intensity. Test results verify these two conclusions and show good sensitivity to light direction and immunity to light intensity. An accuracy of 1.6 deg over a 100 deg range is achieved by the linear relationship.

CMOS biosensor system for on-chip cell culture with read-out circuitry and microfluidic packaging.

A 1.5 mm × 3 mm CMOS chip with sensors for monitoring on-chip cell cultures has been designed. The chip is designed in a 0.5 µm CMOS process which has 3 metal layers and 2 poly layers and is a 5 volt process. The chip contains ion sensitive field effect transistors (ISFETs), as well as ISFETs with read-out circuitry, for monitoring the pH of solutions placed on top of the chip. Interdigitated electrode structures (IDESs) are made using the top metal of the process to be used for sensing cellular attachment and proliferation via impendence. IDES read-out circuits and IDES test structures are included. The chip also contains test amplifiers, bandgap reference test structures, and connections for post-processing. We designed the chip to accommodate packaging into an environment where it will be directly exposed to a cell culture environment. Specifically we designed the chip to have the incorporated sensors near the center of the chip allowing for connections made around the edge of the chip to be sealed off using an epoxy or similar material to prevent shorting. Preliminary electrical characterization results for our amplifier indicate a gain of 48 dB, a bandwidth of 1.65 kHz, and a common mode rejection ratio (CMRR) of 72 dB. We also present a packaging technique using a flexible pcb substrate.

Hybrid silicon/silicone (polydimethylsiloxane) microsystem for cell culture.

We discuss the design, fabrication and testing of a hybrid microsystem for stand-alone cell culture and incubation. The micro-incubator is engineered through the integration of a silicon CMOS die for the heater and temperature sensor, with multilayer silicone PDMS (polydimethylsiloxane) structures namely, fluidic channels and a 4 mm diameter, 30 microL, culture well. A 25 micron thick PDMS membrane covers the top of the culture well, acting as barrier to contaminants while allowing the cells to exchange gases with the ambient environment. The packaging for the microsystem includes a flexible polyimide electronic ribbon cable and four fluidic ports that provide external interfaces to electrical energy, closed loop sensing and electronic control as well as solid and liquid supplies. The complete structure has a size of (2.5x2.5x0.6 cm3). We have employed the device to successfully culture BHK-21 cells autonomously over a sixty hour period in ambient environment.