Computer controlled multi-walled carbon nanotube inhalation exposure system

Abstract

Inhalation exposure systems are necessary tools for determining the dose-response relationship of inhaled toxicants under a variety of exposure conditions. The objective of this project was to develop an automated computer controlled system to expose small laboratory animals to precise concentrations of airborne multi-walled carbon nanotubes (MWCNT). An aerosol generator was developed which was capable of suspending a respirable fraction of multi-walled carbon nanotubes from bulk material. The output of the generator was used to expose small laboratory animals to constant aerosol concentrations up to 12 mg/m(3). Particle distribution and morphology of the MWCNT aerosol delivered to the exposure chamber were measured and compared to samples previously taken from air inside a facility that produces MWCNT. The comparison showed the MWCNT generator was producing particles similar in size and shape to those found in a work environment. The inhalation exposure system combined air flow controllers, particle monitors, data acquisition devices, and custom software with automatic feedback control to achieve constant and repeatable exposure chamber temperature, relative humidity, pressure, aerosol concentration, and particle size distribution. The automatic control algorithm was capable of maintaining the mean aerosol concentration to within 0.1 mg/m(3) of the selected target value, and it could reach 95% of the target value in less than 10 minutes during the start-up of an inhalation exposure. One of the major advantages of this system was that once the exposure parameters were selected, a minimum amount of operator intervention was required over the exposure period.

A Computer-Controlled Whole-Body Inhalation Exposure System for the Oil Dispersant COREXIT EC9500A

“…Feedback control may also reduce the rise and fall time periods during an exposure. A modified controller was designed that was based on a system described by McKinney et al (2009). As can be seen from Figure 8, the steady-state value of the particulate concentration was much more stable when feedback control was implemented.…”

“…A PD control algorithm, similar to that described in McKinney et al (2009), was included in the software. The first feedback loop regulated the CE particulate concentration within the exposure chamber.…”

“…In the past, our laboratory has utilized small-animal, whole-body inhalation exposure systems to determine the health effects of liquid aerosols and vapors present in various work-place environments (Hubbs et al 2002;Shvedova et al 2002). Recently, a proportionalderivative (PD) software concentration controller was developed and used in exposures to ozone (McKinney and Frazer 2008) and carbon nanotubes (McKinney et al 2009). The controller has resulted in more tightly regulated concentration control and an automation level that has minimized technician interaction with the system.…”

Computer-automated silica aerosol generator and animal inhalation exposure system

“…The exposure system in the current study differs from that previously described (McKinney et al, 2009) by adding a venturi tube (Intox) as a second stage. In addition to assisting in breaking up agglomerated particles, the venturi acts as a diluter and provides higher total flow rates that are needed for the larger animal exposure chamber.…”

“…As a result, the trans-diaphragm pressure was held constant at an optimal value of +0.1 in H 2 O, thus maximizing the generator's performance. Detailed graphs of cylinder pressure versus generator output, generator air flow versus generator output and generator excitation voltage versus generator output have been previously published on a similarly designed acoustical generator (McKinney et al, 2009). …”