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

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

Early prediction of molecular remission by monitoring BCR-ABL transcript levels in patients achieving a complete cytogenetic response after imatinib therapy for posttransplantation chronic myelogenous leukemia relapse

Imatinib induces a high complete cytogenetic response (CCR) rate in relapsed chronic myelogenous leukemia. By analyzing minimal residual disease (MRD) under the levels of CCR, we tried to assess the molecular response after imatinib therapy. By using real-time quantitative reverse transcriptase-polymerase chain reaction (Q-RT-PCR), MRD was evaluated in 23 patients (3 in cytogenetic relapse, 6 in chronic phase, 9 in accelerated phase, and 5 in blast crisis) who were treated with standard-dose imatinib for relapsed chronic myelogenous leukemia after allogeneic stem cell transplantation. With a median therapy time of 399 days (range, 35–817 days), 19 (83%) patients achieved a CCR. Meanwhile, 11 (58%) of them achieved a molecular remission (MR), which was associated with improved survival. The Q-RT-PCR data were compared according to the best response (MR, n = 11; CCR, n = 8) in the patients achieving a CCR. The BCR-ABL/ABL ratios were similar in 2 groups at 3 months but were significantly different at 6 months (median, 0.0000012 for MR and 0.00022 for CCR; P = .003). The probability of a subsequent MR was significantly higher in patients with a lower BCR-ABL/ABL ratio at 6 months (100% for <0.0001 versus 33% for ≥0.0001; P = .006) or a greater reduction in the level between 3 and 6 months (log-reduction ≥1.0;, 100%; <1.0, 17%; P = .003). Q-RT-PCR is a reliable method for monitoring MRD: the early trends in the BCR-ABL/ABL ratio may be clinically useful in discriminating patients who will achieve an MR from those who will remain in CCR

The evolution of electrocardiographic changes in patients with Duchenne muscular dystrophies

PurposeMyocardial dysfunction and dysrhythmias are inevitable consequences of Duchenne muscular dystrophy. We aimed to evaluate specific trends of electrocardiographic changes that reflect the progress of cardiomyopathy in patients with Duchenne muscular dystrophy.MethodsFifty electrocardiograms (ECGs) of 30 patients (ages 1 to 27 years) who had not been prescribed medications for heart failure treatment at the time of examination were retrospectively analyzed and compared with 116 ECGs of age-matched healthy 116 controls. Heart rate, leads with fragmented QRS (fQRS), corrected QT, Tpeak-to-Tend, and Tpeak-to-Tend/QT were analyzed.ResultsThe patients with Duchenne muscular dystrophy failed to show a normal age-related decline in heart rate but showed an increasing trend in the prevalence of fQRS, corrected QT, corrected Tpeak-to-Tend, and Tpeak-to-Tend/QT over time. In the ≤10-year-old patient group, a significant difference was found only in the prevalence of fQRS between the patients and the controls. The prevalence of fQRS, heart rate, Tpeak-to-Tend/QT, and corrected Tpeak-to-Tend demonstrated significant differences between the patients and the controls in the middle age group (11 to 15 years old). All the indexes were statistically significantly different in the ≥16-year-old patient group.ConclusionThe prevalence of lead with fQRS representing regional wall motion abnormalities was higher in the young patients than in the young healthy controls, and this might be one of the first signs of myocardial change in the patients. Markers of depolarization and repolarization abnormalities were gradually prominent in the patients aged >10 years. Further studies are needed to confirm these findings