Optometry and Vision Sciences - Research Publications
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ItemNo Preview AvailableEnhanced effective diffusion in sub-wavelength, axon-scale microchannels using surface acoustic waves(AIP Publishing, 2023-03)Excitation using surface acoustic waves (SAW) has demonstrated efficacy in improving microscale particle/chemical transport due to its ability to generate microscale wavelengths. However, the effects of acoustic stimulation on transport processes along the length of sub-wavelength microchannels and their underlying mechanisms, essential for long-range transport, have not been examined in detail. In this work, we investigate diffusion along the length of subwavelength microchannels using experimental and simulation approaches, demonstrating enhanced transport under SAW excitation. The microchannel-based enhanced diffusion mechanisms are further studied by investigating the acoustic pressure and streaming fields, finding that the degree of enhancement is a function of applied power, microchannel dimensions, and viscosity. This microchannel-based diffusion enhancement approach is applicable to microfluidic and biomedical microscale transport enhancement, with the findings here being relevant to acoustic-based micro-mixing and neurodegenerative therapies.
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ItemAdvances in Carbon-Based Microfiber Electrodes for Neural Interfacing(FRONTIERS MEDIA SA, 2021-04-12)Neural interfacing devices using penetrating microelectrode arrays have emerged as an important tool in both neuroscience research and medical applications. These implantable microelectrode arrays enable communication between man-made devices and the nervous system by detecting and/or evoking neuronal activities. Recent years have seen rapid development of electrodes fabricated using flexible, ultrathin carbon-based microfibers. Compared to electrodes fabricated using rigid materials and larger cross-sections, these microfiber electrodes have been shown to reduce foreign body responses after implantation, with improved signal-to-noise ratio for neural recording and enhanced resolution for neural stimulation. Here, we review recent progress of carbon-based microfiber electrodes in terms of material composition and fabrication technology. The remaining challenges and future directions for development of these arrays will also be discussed. Overall, these microfiber electrodes are expected to improve the longevity and reliability of neural interfacing devices.
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ItemHigh Fidelity Bidirectional Neural Interfacing with Carbon Fiber Microelectrodes Coated with Boron-Doped Carbon Nanowalls: An Acute Study(WILEY-V C H VERLAG GMBH, 2020-12)Abstract Implantable electrodes that can communicate with a small, selective group of neurons via both neural stimulation and recording are critical for the development of advanced neuroprosthetic devices. Microfiber electrodes with neuron‐scale cross‐sections have the potential to improve the spatial resolution for both stimulation and recording, while minimizing the chronic inflammation response after implantation. In this work, glass insulated microfiber electrodes are fabricated by coating carbon fibers with boron‐doped carbon nanowalls. The coating significantly improves the electrochemical properties of carbon fibers, leading to a charge injection capacity of 7.82 ± 0.35 mC cm−2, while retaining good flexibility, stability and biocompatibility. When used for neural interfacing, the coated microelectrodes successfully elicit localized stimulation responses in explanted retina, and are also able to detect signals from single neurons, in vivo with a signal‐to‐noise ratio as high as 6.7 in an acute study. This is the first report of using carbon nanowall coated carbon fibers for neural interfacing.
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ItemMechanisms and Applications of Neuromodulation Using Surface Acoustic Waves-A Mini-Review(FRONTIERS MEDIA SA, 2021-01-27)The study of neurons is fundamental for basic neuroscience research and treatment of neurological disorders. In recent years ultrasound has been increasingly recognized as a viable method to stimulate neurons. However, traditional ultrasound transducers are limited in the scope of their application by self-heating effects, limited frequency range and cavitation effects during neuromodulation. In contrast, surface acoustic wave (SAW) devices, which are producing wavemodes with increasing application in biomedical devices, generate less self-heating, are smaller and create less cavitation. SAW devices thus have the potential to address some of the drawbacks of traditional ultrasound transducers and could be implemented as miniaturized wearable or implantable devices. In this mini review, we discuss the potential mechanisms of SAW-based neuromodulation, including mechanical displacement, electromagnetic fields, thermal effects, and acoustic streaming. We also review the application of SAW actuation for neuronal stimulation, including growth and neuromodulation. Finally, we propose future directions for SAW-based neuromodulation.
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ItemHybrid diamond/ carbon fiber microelectrodes enable multimodal electrical/chemical neural interfacing(Elsevier, 2020-02-01)Implantable medical devices are now in regular use to treat or ameliorate medical conditions, including movement disorders, chronic pain, cardiac arrhythmias, and hearing or vision loss. Aside from offering alternatives to pharmaceuticals, one major advantage of device therapy is the potential to monitor treatment efficacy, disease progression, and perhaps begin to uncover elusive mechanisms of diseases pathology. In an ideal system, neural stimulation, neural recording, and electrochemical sensing would be conducted by the same electrode in the same anatomical region. Carbon fiber (CF) microelectrodes are the appropriate size to achieve this goal and have shown excellent performance, in vivo. Their electrochemical properties, however, are not suitable for neural stimulation and electrochemical sensing. Here, we present a method to deposit high surface area conducting diamond on CF microelectrodes. This unique hybrid microelectrode is capable of recording single-neuron action potentials, delivering effective electrical stimulation pulses, and exhibits excellent electrochemical dopamine detection. Such electrodes are needed for the next generation of miniaturized, closed-loop implants that can self-tune therapies by monitoring both electrophysiological and biochemical biomarkers.