Reliability of parylene-based multi-electrode arrays chronically implanted in adult rat brains, and evidence of electrical stimulation on contact impedance.

OBJECTIVE: The goal of this study was to evaluate the long-term behavior of the surface electrode through electrochemical characterization and follow-up of implanted parylene/platinum microelectrodes. APPROACH: To this aim, we designed and manufactured specific planar electrodes for cortical implantation for a rat model. This work was included in the INTENSE® project, one of the goals of which was to prove the feasibility of selective neural recording or stimulation with cuff electrodes around the vagus nerve. MAIN RESULTS: After a 12-week implantation in a rat model, we can report that these microelectrodes have withstood in vivo use. Regarding the biocompatibility of the electrodes (materials and manufacturing process), no adverse effect was reported. Indeed, after the three-month implantation, we characterized limited tissue reaction beneath the electrodes and showed an increase and a stabilization of their impedance. Interestingly, the follow-up of the electrochemical impedance combined with electrical stimulation highlighted a drop in the impedance up to 60% at 1 kHz after ten minutes of electrical stimulation at 110 Hz. SIGNIFICANCE: This study gives evidence of the biocompatibility of the parylene platinum contact array designed for the project and confirms the effect of stimulation on the contact impedance.

Analysis of Al2O3-parylene C bilayer coatings and impact of microelectrode topography on long term stability of implantable neural arrays.

OBJECTIVE: Performance of many dielectric coatings for neural electrodes degrades over time, contributing to loss of neural signals and evoked percepts. Studies using planar test substrates have found that a novel bilayer coating of atomic-layer deposited (ALD) Al2O3 and parylene C is a promising candidate for neural electrode applications, exhibiting superior stability to parylene C alone. However, initial results from bilayer encapsulation testing on non-planar devices have been less positive. Our aim was to evaluate ALD Al2O3-parylene C coatings using novel test paradigms, to rigorously evaluate dielectric coatings for neural electrode applications by incorporating neural electrode topography into test structure design. APPROACH: Five test devices incorporated three distinct topographical features common to neural electrodes, derived from the utah electrode array (UEA). Devices with bilayer (52 nm Al2O3 + 6 µm parylene C) were evaluated against parylene C controls (N ⩾ 6 per device type). Devices were aged in phosphate buffered saline at 67 °C for up to 311 d, and monitored through: (1) leakage current to evaluate encapsulation lifetimes (>1 nA during 5VDC bias indicated failure), and (2) wideband (1-105 Hz) impedance. MAIN RESULTS: Mean-times-to-failure (MTTFs) ranged from 12 to 506 d for bilayer-coated devices, versus 10 to >2310 d for controls. Statistical testing (log-rank test, α = 0.05) of failure rates gave mixed results but favored the control condition. After failure, impedance loss for bilayer devices continued for months and manifested across the entire spectrum, whereas the effect was self-limiting after several days, and restricted to frequencies <100 Hz for controls. These results correlated well with observations of UEAs encapsulated with bilayer and control films. SIGNIFICANCE: We observed encapsulation failure modes and behaviors comparable to neural electrode performance which were undetected in studies with planar test devices. We found the impact of parylene C defects to be exacerbated by ALD Al2O3, and conclude that inferior bilayer performance arises from degradation of ALD Al2O3 when directly exposed to saline. This is an important consideration, given that neural electrodes with bilayer coatings are expected to have ALD Al2O3 exposed at dielectric boundaries that delineate electrode sites. Process improvements and use of different inorganic coatings to decrease dissolution in physiological fluids may improve performance. Testing frameworks which take neural electrode complexities into account will be well suited to reliably evaluate such encapsulation schemes.

Mixture of kerosene and xylene: a contribution to clearing agents / Mezcla de kerosene y xileno: una contribución a agentes de aclaramiento

The aim of this study was to substitute costly and hazardous compound- xylene, used as clearing agent, with less costly compounds (mixture of xylene and kerosene) having less toxicity and without compromising the cellular integrity and staining characteristics of the sections. Tissues (liver and kidney) obtained from a presumable healthy adult Wistar rat, were fixed in 10 percent formol saline, separated in to five groups (A, B, C, D and E) and processed for light microscopic study adopting H & E staining procedure. During the clearing section, groups A, B, C, D and E were respectively cleared in solvent 1 (xylene only), solvent 2 (70ml xylene : 30ml kerosene), solvent 3 (50ml xylene : 50ml kerosene), solvent 4 (30ml xylene : 70ml kerosene) and solvent 5 (kerosene only). Our result revealed that tissues in groups A, B and C were properly cleared without any morphological impairment. The staining characteristics were also observed to be very bright. Groups D and E however presented poor staining intensity with reduced cellular details. Semi-stained transparent patches were also noticed. It is inferred from the present investigation that a mixture of xylene and kerosene could be employed in the clearing of tissues only at the prescribed ratio i.e. solvent 2 and solvent 3 without posing any health risk or compromising the cellular integrity.

El objetivo de este estudio fue el de sustituir el costoso y peligroso compuesto xileno, utilizado como agente de aclaramiento, por un compuesto menos costoso (mezcla de kerosene y xileno), con menor toxicidad y sin comprometer la integridad celular ni las características de tinción de las secciones. Los tejidos (hígado y riñon) fueron obtenidos a partir de una rata Wistar adulta presumiblemente sana, los que fueron fijados en solución de formalina salina al 10 por ciento, y separadas en cinco grupos (A, B, C, D y E) y tratadas para estudio con microscópico de luz, con tinción H & E. Durante el aclaramiento de las secciones histológicas, los grupos A, B, C, D y E, fueron, respectivamente, aclarados con el disolvente 1 (sólo xileno), solvente 2 (70ml de xileno: 30ml Kerosene), solvente 3 (50ml de xileno: 50ml Kerosene), solvente 4 (30ml xileno: 70ml kerosene) y solvente 5 (sólo el kerosene). Los resultados revelaron que los tejidos de los grupos A, B y C fueron aclarados correctamente sin alteraciones morfológicas. En la tinción también se observó como característica, ser muy brillante. Los grupos D y E, sin embargo presentaron una tinción de pobre intensidad con la reducción de los detalles celulares. Zonas con manchas semitransparentes también fueron observadas. Se infiere que una mezcla de xileno y kerosene podría ser empleado en el aclaramiento de los tejidos, sólo prescrito en la proporción del solvente 2 y 3, sin suponer ningún riesgo para la salud o comprometer la integridad celular.

Were volatile organic compounds the inducing factors for subjective symptoms of employees working in newly constructed hospitals?

This study demonstrated possible relationships between environmental, personal, and occupational factors and changes in the subjective health symptoms of 214 employees after the relocation of a hospital in a region of Japan. Eight indoor volatile organic compounds (VOCs) were detected in at least one of the 19 rooms investigated, and total VOC (TVOC) concentrations in 8 rooms exceeded the advisable value (400 microg/m(3)) established by the Ministry of Health, Labour and Welfare of Japan. Formaldehyde was detected in all the investigated rooms, but none of the results exceeded the guideline value (100 microg/m(3)). Multiple logistic regression analysis was applied to select variables significantly associated with the subjective symptoms that can be induced by sick building syndrome. The results showed that subjective symptoms of deterioration in the skin, eye, ear, throat, chest, central nervous system, autonomic system, musculoskeletal system, and digestive system among employees were associated mainly with gender difference and high TVOC concentrations (>1200 microg/m(3)). Long work hours (>50 h per week) in females and smoking in males were to be blamed for the deterioration of their symptoms. The present findings suggest that to protect employees from indoor environment-related adverse health effects, it is necessary to reduce the concentration of indoor chemicals in new buildings, to decrease work hours, and to forbid smoking.

Phenylacetylene as a new surrogate standard for the determination of BTEX by GC/FID.

Benzene, toluene, ethylbenzene, xylene (short form: BTEX) and other monoaromatic compounds are environmental contaminants which are often analyzed by GC/FID. For the calculation of BTEX concentrations in water samples normally external quantification with defined BTEX solutions is sufficient. However, for accurate quantification of BTEX in complex matrices it is necessary to use internal standards, e.g. 1-chlorohexane. Isotopes of BTEX are usually the best alternative but they are only applicable to GC/MS, because their retention times are similar to the original BTEX. 1-Chlorohexane and phenylacetylene were compared with respect to their quality as internal standards. Good results were obtained with the monoaromatic phenylacetylene as a surrogate standard. The physical properties of phenylacetylene are very similar to BTEX species and it normally does not occur in environmental samples. 1-Chlorohexane was more strongly adsorbed on the used soil than BTEX during sample preparation. This fact suggests that the single aromatic rings of BTEX and phenylacetylene are mainly responsible for the adsorption behavior.

A membrane filter technique for testing disinfectants.

A membrane filter was used for assessing the surface disinfecting activity of phenolic disinfectants and a chloroxylenol disinfectant. The influence of the type of organism, inoculum size, and hardness of water was investigated. Pseudomonas aeruginosa was chosen for the standardized test. Disinfectant solutions were prepared in water of 300 ppm hardness and applied for two and a half minutes and eight minutes to the bacteria deposited from filtration of 1 ml of a suspension containing 10-6 bacteria. The membrane filter test has certain advantages over many tests, eg, all organisms surviving after treatment can be counted and residual disinfectant is easily removed.