Doctor of Philosophy

dissertationImplantable microelectrode arrays are biomedical devices used in-vivo serving as neural interfaces between the nervous system and external systems such as neuroprosthetics. They are designed to be chronically implanted in the central or peripheral nervous system and record or stimulate neural signals. The Utah electrode array (UEA) is a representative example of silicon-based neural interfaces. They are typically encapsulated with the USP Class VI biocompatible material, Parylene-C, on the inactive areas to insulate and encapsulate the electrodes and minimize damage to the neural tissue. In order to record or stimulate neural signals, the active electrode sites must be deinsulated. Tip deinsulation of Parylene-coated UEAs is typically performed by a reactive ion etching (RIE) process using an O2 plasma, and an aluminum foil mask. This technique has limitations due to nonuniform tip exposure lengths contributing to large impedance variations (o > 0.5 MQ), and difficulty in controlling the magnitude of tip exposure, especially for tip exposures less than 40 ^m, which are needed to increase its selectivity in recording or stimulating single or multiple neurons. Moreover, foil masks cannot be used for more complex electrode geometries, such as variable height electrodes. In this work, excimer laser ablation of Parylene from a UEA using a tip metallization of iridium oxide (IrOx) was investigated as an alternative deinsulation technique. A hybrid method of etching Parylene-C using a combination of laser ablation and the O2 RIE was investigated in the efforts to minimize electrode damage and remove carbonaceous residues. The median impedance for fine tip ( 180 °C) temperatures in reducing ambients, resulting in dramatic changes to the structural and electrical properties of the tip metallization. The reduced IrOx material was found to tolerate significantly more laser irradiation than the fully oxidized material. The median impedance, cathodal charge storage capacity (CSCc), and charge injection capacity (CIC) for the reduced electrodes with 40 |im exposure were ~ 25 kQ, ~ 40 mC/cm2, and ~ 0.8 mC/cm2, respectively. These results suggest that a hybrid laser ablation using an excimer laser and RIE is promising for deinsulation of UEAs

Excimer-laser deinsulation of Parylene-C coated Utah electrode array tips

Journal ArticleUtah electrode arrays (UEAs) are highly effective to measure or stimulate neural action potentials from the central or peripheral nervous system. The measured signals can be used for applications including control of prosthetics (recording) and stimulation of proprioceptive percepts. The UEAs are coated with biocompatible Parylene-C, and the electrode tips are deinsulated to expose the active electrode coated with sputtered iridium oxide films (SIROFs) to transduce neural signals. In conventional UEA technology, the electrode tips are deinsulated by poking the electrodes through aluminum foil followed by an oxygen plasma etch of the exposed areas. However, this method suffers from lack of uniformity and repeatability and it is time consuming. We focus on laser tip-deinsulation technology that can provide a repeatable, uniform, and less time consuming tip exposure for UEAs. The laser deinsulated SIROF area is characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscope (AFM), and by measuring the impedance of the exposed sites. The value of impedance and XPS peaks showed that the Parylene was clearly removed. The damage induced by laser irradiation on the SIROF film was also investigated to understand the selectivity of laser deinsulation. Thicker SIROF films showed better resistance to fracture. The results indicate that laser deinsulation is an effective method to etch Parylene films

Single inorganic–organic hybrid nanowires with ambipolar photoresponse

We report for the first time single nanowires (NWs) with ambipolar (positive/negative) photoresponse that changes sign depending on the illumination wavelength. The single NWs were grown by the meniscus-guided method using inorganic (ZnO nanoparticles)–organic (PEDOT:PSS) hybrid materials. The ambipolar photoresponse of the single NWs enabled us to develop an unprecedented spectrum-discriminating NW photodetector array

A Game Theory Based Model of Human Driving with Application to Autonomous and Mixed Driving

In this work, I consider the development of a driver model to better understand human drivers’ various behaviors in the upcoming mixed situation of human drivers and autonomous vehicles. For this, my current effort focuses on modeling the driver’s decisions and corresponding driving behaviors. First, I study an individual driver’s reasoning process through game theoretic investigation. The driver decision model is modeled as the Stackelberg game, which is based on the backward information propagation. In the driver decision model, I focus on the drivers’ insensible desires and corresponding unwanted traffic situations. With the comparison of the model and the field data, it is shown that the model reproduces the relationship between the driver’s inattentiveness and collisions in the real world. Next, the driving behavior control is presented. I propose a human-like predictive perception model of potential collision with an adjacent vehicle. The model is based on hybrid systematic approach. In turn, with the predictive perceptions, a driving safety controller is designed based on model predictive control. The model shows adequate predictive responses against the other vehicles with respect to the driver’s rationality. In sum, I present a driver model that corresponds to and predicts traffic situations according to a human driver’s irrationality factor. This model shows a meaningful similarity to the real-world crashes and predictive behaviors according to the driver’s irrationality

Light propagation in conjugated polymer nanowires decoupled from a substrate

Light-emitting conjugated polymer nanowires are vertically grown and remotely manipulated into a freestanding straight or curved structure in three-dimension. This approach enabled us to eliminate substrate coupling, a critical issue in nanowire photonics in the past decade. We for the first time accomplished characterization of propagation and bending losses of nanowires completely decoupled from a substrate

Enzymatic analysis of the effect of naturally occurring Leu138Pro mutation identified in SHV β-lactamase on hydrolysis of penicillin and ampicillin

<p>Abstract</p> <p>Background</p> <p>The aim of this study was to analyze the significance of leucine to proline substitution at position 138(Leu138Pro) on the hydrolysis of penicillin and ampicillin that we identified in the <it>bla</it>_SHVgene of clinical <it>Escherichia coli </it>swine isolate.</p> <p>Results</p> <p>Kinetic analysis of the mutant proteins showed that <it>K</it>_{<it>m </it>}value of the purified L138P mutant was comparatively higher than SHV-1, SHV-33 and SHV-33(L138P) enzyme for penicillin and ampicillin. Docking simulation of the SHV-1 and SHV-(L138P) enzymes also confirmed that β-lactamases preferred penicillin to ampicillin and the SHV-1 had a higher binding affinity for antibiotics compared to the SHV-(L138P) and other mutants.</p> <p>Conclusions</p> <p>Our result demonstrated that L138P has a reduced role in penicillin and ampicillin hydrolyzing properties of SHV β-lactamases. These naturally occurring mutations rendering reduced function of the existing protein could trigger the emergence or acquisition of more effective alternative mechanisms for β-lactam hydrolysis.</p

Congenital Esophageal Stenosis- Case SNUCH-32 -

This 3-year-old girl was admitted to the Seoul National University Children's Hospital (SNUCH) for the fifth time on July 16, 1990, for a surgical intervention. She was born on September 19, 1987 via normal full term spontaneous delivery with the birth weight of 3.4 kg. The vaccination was done as scheduled The family history was unremarkable except for her maternal grandmother who had diabetes mellitus and grandfather died of stomach cancer. She had been healthy until June, 1988 (9 months of age) when her meal was changed from breast milk and weaning food to solid food. She experienced episodes of regurgitation and vomiting. The vomiting was intermittent and cyclic, and was not projectile or bilious. However, since her general condition was good the parents did not pay much attention for these symptoms On August 21, 1988 (11 months of age) she started to run fever with cough, for which she was brought to a local pediatric Clinic. With the 22impression of pneumonia she was managed With antibiotics. She developed diarrhea at that clinic, and was transferred to SNUCH