Air Quality Effects on Human Health and Approaches for Its Assessment through Microfluidic Chips

Abstract

Air quality depends on the various gases and particles present in it. Both natural phenomena and human activities affect the cleanliness of air. In the last decade, many countries experienced an unprecedented industrial growth, resulting in changing air quality values, and correspondingly, affecting our life quality. Air quality can be accessed by employing microchips that qualitatively and quantitatively determine the present gases and dust particles. The so-called particular matter 2.5 (PM2.5) values are of high importance, as such small particles can penetrate the human lung barrier and enter the blood system. There are cancer cases related to many air pollutants, and especially to PM2.5, contributing to exploding costs within the healthcare system. We focus on various current and potential future air pollutants, and propose solutions on how to protect our health against such dangerous substances. Recent developments in the Organ-on-Chip (OoC) technology can be used to study air pollution as well. OoC allows determination of pollutant toxicity and speeds up the development of novel pharmaceutical drugs.

Keywords: PM2.5; air pollution; microchip; organ-on-chip (OoC); particulate matter (PM).

Figure 1

An example of the information provided by air monitoring stations in Beijing, China. Besides the usual temperature, dew, pressure, humidity, and wind values in hourly readings, the information on following pollutants can be seen: particular matter 2.5 (PM2.5), PM10, O₃, NO₂, SO₂, and CO. Here, the unhealthy status is based on current highest PM2.5 values. The figure is reproduced with permission [11].

Figure 2

Different lung-on-a-chip design principles. (A) The cross-sectional view though the microfluidic device shows an early attempt to recreate lung physiology by introducing an air–liquid interface to the cells. Reprinted from [150], with permission from Elsevier; (B) 3D cross-sectional view illustrates the use of an epithelial and endothelial cell line separated by a porous membrane that divides air and a media channel. Reprinted by permission from Macmillan Publishers Ltd: Nature Methods [151], copyright (2015); (C) Building on similar design considerations, the stretchability of the separating membrane is introduced by using vacuum chambers at both sides of the actual compartments for cell growth. From [154], reprinted with permission from AAA; (D) Since breathing introduces 3D multidirectional mechanical stress to the alveoli in human lung, a system was introduced that simulates this stretching more close than unidirectional stretching does. [156]—Published by The Royal Society of Chemistry under creative commons Attribution 3.0 Unported License; (E) Schematic depicting engineered bronchial smooth muscular thin films adopting (i) basal tone, (ii) preconstriction, and (iii) bronchodilator-induced relaxation. Reproduced from [158] with permission from The Royal Society of Chemistry; (F) Shown is a schematic of the microfluidic airway model and photomicrographs of the liquid plug generation. Reprinted from [160], © Springer Science+Business Media LLC 2011, with permission from Springer. PET: Polyethylene

Figure 3

One can visualize how small the air particles are by comparing them to the human hair. The hair cross-section diameter being ~60 µm, about six PM10 particles and 24 PM2.5 particles could extend over the hairs cross-section perimeter. PM2.5 (or fine PM), tend to penetrate into the gas-exchange regions of the lung (alveolus).

Figure 4

The Shanghai University (SHU) iSmart Institute cell culture room for the organ-on-chip (OoC) experiments. The area is isolated, with the high efficiency particulate air (HEPA) filtration, temperature and humidity control. The air pressure inside is kept positive to keep away the outside air. The cell culture room has an area of 30 m² (5 × 6 m) and accommodates the instruments necessary for work: refrigerators, freezers, cell culture incubators, biological safety cabinet, microscope, and chip setup with fluid control.