Generation and characterization of large-particle aerosols using a center flow tangential aerosol generator with a non-human-primate, head-only aerosol chamber

Abstract

Aerosol droplets or particles produced from infected respiratory secretions have the potential to infect another host through inhalation. These respiratory particles can be polydisperse and range from 0.05 to 500 µm in diameter. Animal models of infection are generally established to facilitate the potential licensure of candidate prophylactics and/or therapeutics. Consequently, aerosol-based animal infection models are needed to properly study and counter airborne infections. Ideally, experimental aerosol exposure should reliably result in animal disease that faithfully reproduces the modeled human disease. Few studies have been performed to explore the relationship between exposure particle size and induced disease course for infectious aerosol particles. The center flow tangential aerosol generator (CenTAG™) produces large-particle aerosols capable of safely delivering a variety of infectious aerosols to non-human primates (NHPs) within a Class III Biological Safety Cabinet (BSC) for establishment or refinement of NHP infectious disease models. Here, we report the adaptation of this technology to the Animal Biosafety Level 4 (ABSL-4) environment for the future study of high-consequence viral pathogens and the characterization of CenTAG™-created sham (no animal, no virus) aerosols using a variety of viral growth media and media supplements.

Keywords: ABSL-4; BSL-4; CenTAG; aerobiology; aerosol; large particle.

Figure 1

Principles of operation of the center flow tangential aerosol generator. To create aerosol particles, liquid (pink arrow) is delivered onto the center of the rotating top through an inlet. A stream of dilution air (blue arrows), contained by a conical upper air shroud, is fed around the liquid feed nozzle to direct airflow around the upper edge of the spinning top (≤80,000 rpm). An adjustable height fence (with openings) surrounds the top and continues about 1–1.5 mm below the top. A siphon vacuum (green arrows) pulls the air stream through the fence at various fractions of the inlet flow rate. This airflow is optimized to entrain and remove the smaller satellite particles while permitting the larger particles to continue into the aerosol chamber. Two observation ports are within the plenum and fitted with polycarbonate inserts. rpm = revolutions per minute.

Figure 2

Mass-weighted particle diameter distribution of generated particles calculated with APS software. Experimental parameters: DMEM in 5% glycerol with a top (disk) rotor speed of 11 100 rpm. DMEM = Dulbecco’s Modified Eagle Medium; rpm = revolutions per minute.

Figure 3

The aerosol management platform. Labeled components are defined as follows: A. Biaera system - Controls, monitors, and records relative humidity and chamber pressure. Flow controllers and sensors monitor temperature, input airflow, and exhaust airflow in real time. B. AeroMP dedicated air supply and exhaust - Filters incoming BSC Class III air supply once, and expelled vacuum exhaust twice at laboratory HEPA deck mezzanine. C. Ethernet & power - Connects to sealed Ethernet port and electrical socket in BSC III. All AeroMP system functions are managed with dedicated AeroMP control software running on a personal computer in the laboratory. D. Temperature & humidity sensor - Monitors and displays the temperature and relative humidity within the exposure chamber. E. Pressure sensor - Monitors the pressure of the exposure chamber. The chamber pressure can be positive (outward) or negative (inward) depending on parameters determined by the researcher. F. Exhaust - Draws the particles through the exposure chamber using a HEPA filtered vacuum source, maintaining a balanced and dynamic flow rate. G. Sampler - Collects generated particles to determine the viral titer during the exposure. Utilizes a HEPA-filtered vacuum source to sample particles during the exposure. H. Dilution air - Additional air dilutes air from generator to ensure uniform distribution of air within the chamber. The overall flow rate is determined by the volume of the exposure chamber. I. Generator - Provides airflow to the CenTAG^™. J. CenTAG^™ - Generates large-aerosol particles containing virus from liquid media that is delivered during aerosol exposure. K. HEPA filter - Traps and contains expelled particulates from the exposure chamber’s exhaust ports. L. Head-only exposure chamber - Supports NHP head and contains generated particles within a 16-L chamber. M. NHP ramp - Supports NHP body in supine position throughout aerosol exposure. N. Aerodynamic particle sizer - Provides high-resolution, real-time aerodynamic measurements of particles from 0.5 to 20 μm, which allows the researcher to determine deposition within the respiratory tract. AeroMP = aerosol management platform; BSC = biosafety cabinet; CenTAG = center flow tangential aerosol generator; HEPA = high efficiency particulate air; NHP = nonhuman primate.