Michel M. Maharbiz

A Highly Elastic, Capacitive Strain Gauge Based on Percolating Nanotube Networks

We present a highly elastic strain gauge based on capacitive sensing of parallel, carbon nanotube-based percolation electrodes separated by a dielectric elastomer. The fabrication, relying on vacuum filtration of single-walled carbon nanotubes and hydrophobic patterning of silicone, is both rapid and inexpensive. We demonstrate reliable, linear performance over thousands of cycles at up to 100% strain with less than 3% variability and the highest reported gauge factor for a device of this class (0.99). We further demonstrate use of this sensor in a robotics context to transduce joint angles.

A Minimally Invasive 64-Channel Wireless μECoG Implant

Emerging applications in brain-machine interface systems require high-resolution, chronic multisite cortical recordings, which cannot be obtained with existing technologies due to high power consumption, high invasiveness, or inability to transmit data wirelessly. In this paper, we describe a microsystem based on electrocorticography (ECoG) that overcomes these difficulties, enabling chronic recording and wireless transmission of neural signals from the surface of the cerebral cortex. The device is comprised of a highly flexible, high-density, polymer-based 64-channel electrode array and a flexible antenna, bonded to 2.4 mm × 2.4 mm CMOS integrated circuit (IC) that performs 64-channel acquisition, wireless power and data transmission. The IC digitizes the signal from each electrode at 1 kS/s with 1.2 μV input referred noise, and transmits the serialized data using a 1 Mb/s backscattering modulator. A dual-mode power-receiving rectifier reduces data-dependent supply ripple, enabling the integration of small decoupling capacitors on chip and eliminating the need for external components. Design techniques in the wireless and baseband circuits result in over 16× reduction in die area with a simultaneous 3× improvement in power efficiency over the state of the art. The IC consumes 225 μW and can be powered by an external reader transmitting 12 mW at 300 MHz, which is over 3× lower than IEEE and FCC regulations.

Remote radio control of insect flight

We demonstrated the remote control of insects in free flight via an implantable radio-equipped miniature neural stimulating system. The pronotum mounted system consisted of neural stimulators, muscular stimulators, a radio transceiver-equipped microcontroller and a microbattery. Flight initiation, cessation and elevation control were accomplished through neural stimulus of the brain which elicited, suppressed or modulated wing oscillation. Turns were triggered through the direct muscular stimulus of either of the basalar muscles. We characterized the response times, success rates, and free-flight trajectories elicited by our neural control systems in remotely controlled beetles. We believe this type of technology will open the door to in-flight perturbation and recording of insect flight responses.

A cyborg beetle: Insect flight control through an implantable, tetherless microsystem

We present an implantable flight control microsystem for a cyborg beetle. The system consists of multiple inserted neural and muscular stimulators, a visual stimulator, a polyimide assembly and a microcontroller. The system is powered by two size 5 cochlear microbatteries. The insect platform is Cotinis texana, a 2 cm long, 1-2 gram Green June Beetle. We also provide data on the implantation of silicon neural probes, silicon chips, microfluidic tubes, and LEDs introduced during the pupal stage of the beetle.

A microsystem for sensing and patterning oxidative microgradients during cell culture

We present the design, modeling, fabrication and testing of a microsystem for the electrolytic patterning and sensing of oxidative microgradients within 1 x 1 mm2 area during cell culture. The system employs an array of microfabricated electrodes (3-40 microm in width) embedded in gas-permeable microchannels to generate precise doses of dissolved oxygen (ranging from 10 fmol O2 mm(-2) s(-1) to 100 nmol O2 mm(-2) s(-1)) via electrolysis. The microgradients generated by different microelectrodes in the array can be superimposed to pattern multi-dimensional oxygen profiles not possible with other methods. We demonstrate the patterning, sensing and quantification of dissolved oxygen microgradients in the 0 to 40% dO2 range using this microsystem. Reactive oxygen species generation and dosing is also quantified. Lastly, we demonstrate how the microtechnology enables new types of experiments in three different cell culture models: localized hyperoxia-induced apoptosis in C2C12 myoblasts, dynamic aerotaxis assays of Bacillus subtilis, and studies of calcium release in an ischemia/re-oxygenation myoblast model.

Recent Developments in the Remote Radio Control of Insect Flight

The continuing miniaturization of digital circuits and the development of low power radio systems coupled with continuing studies into the neurophysiology and dynamics of insect flight are enabling a new class of implantable interfaces capable of controlling insects in free flight for extended periods. We provide context for these developments, review the state-of-the-art and discuss future directions in this field.

Galvanotactic control of collective cell migration in epithelial monolayers

Many normal and pathological biological processes involve the migration of epithelial cell sheets. This arises from complex emergent behaviour resulting from the interplay between cellular signalling networks and the forces that physically couple the cells. Here, we demonstrate that collective migration of an epithelium can be interactively guided by applying electric fields that bias the underlying signalling networks. We show that complex, spatiotemporal cues are locally interpreted by the epithelium, resulting in rapid, coordinated responses such as a collective U-turn, divergent migration, and unchecked migration against an obstacle. We observed that the degree of external control depends on the size and shape of the cell population, and on the existence of physical coupling between cells. Together, our results offer design and engineering principles for the rational manipulation of the collective behaviour and material properties of a tissue.

Model validation of untethered, ultrasonic neural dust motes for cortical recording

A major hurdle in brain-machine interfaces (BMI) is the lack of an implantable neural interface system that remains viable for a substantial fraction of the users lifetime. Recently, sub-mm implantable, wireless electromagnetic (EM) neural interfaces have been demonstrated in an effort to extend system longevity. However, EM systems do not scale down in size well due to the severe inefficiency of coupling radio-waves at those scales within tissue. This paper explores fundamental system design trade-offs as well as size, power, and bandwidth scaling limits of neural recording systems built from low-power electronics coupled with ultrasonic power delivery and backscatter communication. Such systems will require two fundamental technology innovations: (1) 10-100 μm scale, free-floating, independent sensor nodes, or neural dust, that detect and report local extracellular electrophysiological data via ultrasonic backscattering and (2) a sub-cranial ultrasonic interrogator that establishes power and communication links with the neural dust. We provide experimental verification that the predicted scaling effects follow theory; (127 μm)(3) neural dust motes immersed in water 3 cm from the interrogator couple with 0.002064% power transfer efficiency and 0.04246 ppm backscatter, resulting in a maximum received power of ∼0.5 μW with ∼1 nW of change in backscatter power with neural activity. The high efficiency of ultrasonic transmission can enable the scaling of the sensing nodes down to 10s of micrometer. We conclude with a brief discussion of the application of neural dust for both central and peripheral nervous system recordings, and perspectives on future research directions.

Microrelays for batch transfer integration in RF systems

This paper presents the first implementation of batch-transferred microrelays for a broad range of RF applications and substrates. The transferred relays include a variety of electrostatic pull-down type structures, as well as see-saw type structures. The batch-transfer methodology allows integration of optimized MEMS in RF systems on substrates such as sapphire, GaAs, and even CMOS. Gold-to-gold contact series microrelays with insertion loss of <0.15 dB, and isolation better than 36 dB at frequencies from 45 MHz to 40.0 GHz are demonstrated, as well as shunt switches with >40 dB of isolation and <0.12 dB insertion loss in that frequency range. A novel device structure which combines the benefits of see-saw operation and both shunt and series switching was shown to improve isolation of a single switch by /spl sim/8 dB while maintaining low insertion loss.

A microfabricated electrochemical oxygen generator for high-density cell culture arrays

We present a silicon microfabricated electrolytic oxygen generator for use in high-density miniature cell culture arrays. The generator consists of Ti/Pt electrodes patterned at the narrow end of conical hydrophilic silicone microchannels filled with electrolyte. Surface tension forces arising from the conical microchannel geometry push generated gas bubbles away from the electrodes and down the microchannel where the bubbles exhaust into the cell culture. This bubble motion draws fresh electrolyte from an adjacent reservoir onto the electrodes. The oxygen dosage can be precisely controlled in each generator by pulse width modulation of the electrode potential. We demonstrate devices capable of continuously providing for a wide range of oxygen demands (0-10 /spl mu/mol O/sub 2//hr) and operating for days. Lifetime-limiting corrosion of hydrogen-absorbing noble metal electrodes during low-frequency electrolysis can be avoided by using relays to control the electrode potential. Precure silicone additives are also presented as an alternative to plasma surface modification to obtain hydrophilic silicone surfaces.