Contribution of Particulates to Airborne Disease Transmission and Severity: A Review.

The emergence of coronavirus disease 2019 (COVID-19) has catalyzed great interest in the spread of airborne pathogens. Airborne infectious diseases are classified into viral, bacterial, and fungal infections. Environmental factors can elevate their transmission and lethality. Air pollution has been reported as the leading environmental cause of disease and premature death worldwide. Notably, ambient particulates of various components and sizes are harmful pollutants. There are two prominent health effects of particles in the atmosphere: (1) particulate matter (PM) penetrates the respiratory tract and adversely affects health, such as heart and respiratory diseases; and (2) bioaerosols of particles act as a medium for the spread of pathogens in the air. Particulates contribute to the occurrence of infectious diseases by increasing vulnerability to infection through inhalation and spreading disease through interactions with airborne pathogens. Here, we focus on the synergistic effects of airborne particulates on infectious disease. We outline the concepts and characteristics of bioaerosols, from their generation to transformation and circulation on Earth. Considering that microorganisms coexist with other particulates as bioaerosols, we investigate studies examining respiratory infections associated with airborne PM. Furthermore, we discuss four factors (meteorological, biological, physical, and chemical) that may impact the influence of PM on the survival of contagious pathogens in the atmosphere. Our review highlights the significant role of particulates in supporting the transmission of infectious aerosols and emphasizes the need for further research in this area.

Sodium alginate based artificial biofilms polymerized by electrophoretic deposition for microbial hydrogen generation.

This study developed an artificial biofilm of Rhodospirillum rubrum bacteria immobilized within an alginate matrix using electrophoretic deposition (EPD) on an electrode. The resulting biofilm immobilized bacteria effectively and maintained a high survival rate, facilitating stable and high-efficiency hydrogen generation for longer periods compared to biofilms produced using free bacteria. Hydrogen production efficiency remained constant when the substrate was periodically replaced, indicating that the bacteria could survive within the biofilm for long-term hydrogen production. EPD produced mechanically stable large-scale biofilms economically and rapidly, which effectively overcame operational limitations such as culture medium temperature, pH, and flow rate. Therefore, this proposed method has the potential to accelerate the commercialization of biohydrogen production systems through large-scale biofilm production to facilitate continuous hydrogen generation. The technique can be utilized in various hydrogel-based applications, providing a cost-effective and efficient manufacturing process with customized biological and mechanical properties. The developed biofilms have implications beyond biohydrogen production and could be applied to hydrogel-based medical, cosmetic, and food applications. This study highlights the importance of immobilizing bacteria for stable and efficient hydrogen generation and demonstrates the potential of EPD in fabricating mechanically stable biofilms for large-scale production.

Assessing the cytotoxicity of aerosolized carbon black and benzo[a]pyrene with controlled physical and chemical properties on human lung epithelial cells.

Atmospheric particulate matter (PM) is a complex mixture of hazardous particles containing hundreds of inorganic and organic species. Organic components, such as carbon black (CB) and benzo[a]pyrene (BaP), are known to exhibit diverse genotoxic and carcinogenic effects. The toxicity of CB and polycyclic aromatic hydrocarbons has been well studied, however the combined toxicity is much less understood. A spray-drying system was used to control the size and chemical composition of PMs. PMs were prepared by loading BaP on three different sized CBs (0.1 µm, 2.5 µm, and 10 µm) to obtain BaP-unloaded CB (CB0.1, CB2.5, and CB10) and BaP-loaded CB (CB0.1-BaP, CB2.5-BaP, and CB10-BaP). We analyzed cell viability, levels of oxidative stress, and pro-inflammatory cytokines using human lung cells (A549 epithelial cells). Cell viability decreased when exposed to all PMs (PM0.1, PM2.5, and PM10), regardless of the presence of BaP. The increase in PM size due to BaP-adsorption to CB resulted in insufficient toxic effects on human lung cells compared to CB alone. Smaller CBs reduced cell viability, leading to reactive oxygen species formation, which can cause damage to cellular structures deliver more harmful substances. Additionally, small CBs were predominant in inducing the expression of pro-inflammatory cytokines in A549 epithelial cells. These results indicate that the size of CB is a key factor that immediately affects the inflammation of lung cells, compared to the presence of BaP.

The effect of PhIP precursors on the generation of particulate matter in cooking oil fumes at high cooking temperatures and the inflammation response in human lung cells.

Cooking Oil Fumes (COFs) contain carcinogenic organic substances such as polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs), of which 2-Amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) is known as mainly meat-borne carcinogens. In this work, to identify the mechanisms to induce the inflammation response in human lung cells (A549) exposed to COFs, we investigated the physicochemical and biological characteristics of COFs generated with PhIP precursors (L-phenylalanine, creatinine, and glucose) at high cooking temperatures (300 °C and 600 °C). Interestingly, we found that PhIP was not formed both at 300 °C and 600 °C, while a large number of carbon nanoparticles were generated from soybean oil containing the PhIP precursors at 600 °C. From the biological analysis, COFs generated with the PhIP precursors at 600 °C induced the most significant pro-inflammatory cytokine (IL-6). This result indicates that the particulate matter in COFs generated with the PhIP precursors above the smoke temperature is the primary factor directly affecting the lung inflammatory response rather than PhIP. This study demonstrates for the first time a novel principle of the inflammatory response that the PhIP precursors can aggravate lung injury by affecting the physical properties of COFs depending on cooking temperature. Therefore, our finding is a significant result of overcoming the bias in previous studies focusing only on the chemical toxicity of PhIP in the inflammatory response of COFs.

Schlieren imaging for the visualization of particles entrapped in bubble films.

Bubbles are one of the primary sources of transferring substances from water to air. When bubbles burst, small droplets containing microparticles and microorganisms previously suspended in water disperse. Hence, visualizing small objects in bubble films can provide a new methodology for investigating the material transfer from water to the environment and the dynamic behavior of objects in the films. We used Schlieren imaging of bubbles to visualize small objects such as bacteria and microplastics. Remarkably, black spots (Schlieren spots) appeared when light rays passed parallel to bubbles formed on the water containing microparticles and bacteria. The simulation method of Schlieren imaging of bubbles was developed to clarify the underlying mechanism and experimentally validated with different sizes and concentrations of microparticles. We found that a specific water meniscus is formed around a particle when the bubble film thickness is smaller than the particle diameter, and the meniscus plays an important role in enlarging the Schlieren spots. The Schlieren spots are forty times larger than the bubble film thickness in this work. To understand the magnification rule, we illuminated the correlation between bubble film thickness, particle diameter, and Schlieren spot diameter.

Bioaerosol generation by raindrops on soil.

Aerosolized microorganisms may play an important role in climate change, disease transmission, water and soil contaminants, and geographic migration of microbes. While it is known that bioaerosols are generated when bubbles break on the surface of water containing microbes, it is largely unclear how viable soil-based microbes are transferred to the atmosphere. Here we report a previously unknown mechanism by which rain disperses soil bacteria into the air. Bubbles, tens of micrometres in size, formed inside the raindrops disperse micro-droplets containing soil bacteria during raindrop impingement. A single raindrop can transfer 0.01% of bacteria on the soil surface and the bacteria can survive more than one hour after the aerosol generation process. This work further reveals that bacteria transfer by rain is highly dependent on the regional soil profile and climate conditions.

Antiwetting Fabric Produced by a Combination of Layer-by-Layer Assembly and Electrophoretic Deposition of Hydrophobic Nanoparticles.

This work describes a nanoparticle coating method to produce durable antiwetting polyester fabric. Electrophoretic deposition is used for fast modification of polyester fabric with silica nanoparticles embedded in polymeric networks for high durability coatings. Typically, electrophoretic deposition (EPD) is utilized on electrically conductive substrates due to its dependence on an applied electrical field. EPD on nonconductive materials has been attempted but are limited by weak adhesion, cracks, and other irregularities. To resolve these issues, we coat polyester fabric with thin polymer layers using electrostatic self-assembly (layer-by-layer self-assembly). Next, silica nanoparticles are uniformly dispersed on the polymer layers. Finally, polymerically stabilized silica nanoparticles are deposited by EPD on the fabric, followed by heat treatment. The modified fabric shows high static contact angle and low contact angle hysteresis, while keeping its original color, flexibility, and air permeability. During a skin fiction resistance test, the hydrophobicity of the coating layer was maintained over 500 h. Furthermore, we also show that this approach facilitates patterned regions of wettability by modifying the electric field in EPD.

Antimicrobial behavior of novel surfaces generated by electrophoretic deposition and breakdown anodization.

Biofilms have devastating impacts on many industries such as increased fuel consumption and damage to surfaces in maritime industries. Ideal biofouling management is inhibition of initial bacterial attachment. The attachment of a model marine bacterium (Halomonas pacfica g) was investigated to evaluate the potential of these new novel surfaces to resist initial bacterial adhesion. Novel engineered surfaces were generated via breakdown anodization or electrophoretic deposition, to modify three parameters: hydrophobicity, surface chemistry, and roughness. Mass transfer rates were determined using a parallel plate flow chamber under relevant solution chemistries. The greatest deposition was observed on the superhydrophilic surface, which had micro- and nano-scale hierarchical structures composed of titanium oxide deposited on a titanium plate. Conversely, one of the hydrophobic surfaces with micro-porous films overlaid with polydimethylsiloxane appeared to be most resistant to cell attachment.

Aerosol generation by raindrop impact on soil.

Aerosols are investigated because of their significant impact on the environment and human health. To date, windblown dust and sea salt from sea spray through bursting bubbles have been considered the chief mechanisms of environmental aerosol dispersion. Here we investigate aerosol generation from droplets hitting wettable porous surfaces including various classifications of soil. We demonstrate that droplets can release aerosols when they influence porous surfaces, and these aerosols can deliver elements of the porous medium to the environment. Experiments on various porous media including soil and engineering materials reveal that knowledge of the surface properties and impact conditions can be used to predict when frenzied aerosol generation will occur. This study highlights new phenomena associated with droplets on porous media that could have implications for the investigation of aerosol generation in the environment.

Design of capillary flows with functionally graded porous titanium oxide films fabricated by anodization instability.

We have developed an electrochemical fabrication method utilizing breakdown anodization (BDA) to yield capillary flows that can be expressed as functions of capillary height. This method uses anodization instability with high electric potentials and mildly acidic electrolytes that are maintained at low temperature. BDA produces highly porous micro- and nano-structured surfaces composed of amorphous titanium oxide on titanium substrates, resulting in high capillary pressure and capillary diffusivity. With this fabrication technique the capillary flow properties can be controlled by varying the applied electric field and electrolyte temperature. Furthermore, they can be expressed as functions of capillary height when customized electric fields are used in BDA. To predict capillary flows on BDA surfaces, we developed a conceptual model of highly wettable porous films, which are modeled as multiple layers of capillary tubes oriented in the flow direction. From the model, we derived a general capillary flow equation of motion in terms of capillary pressure and capillary diffusivity, both of which can be expressed as functions of capillary height. The theoretical model was verified by comparisons with experimental capillary flows, showing good agreement. From investigation of the surface morphology we found that the surface structures were also functionally graded with respect to the capillary height (i.e. applied electric field). The suggested fabrication method and the theoretical model offer novel design methodologies for microscale liquid transport devices requiring control over propagation speed.

Scaling laws for drop impingement on porous films and papers.

This study investigates drop impingement on highly wetting porous films and papers. Experiments reveal previously unexplored impingement modes on porous surfaces designated as necking, spreading, and jetting. Dimensional analysis yields a nondimensional parameter, denoted the Washburn-Reynolds number, relating droplet kinetic energy and surface energy. The impingement modes correlate with Washburn-Reynolds number variations spanning four orders of magnitude and a corresponding energy conservation analysis for droplet spreading shows good agreement with the experimental results. The simple scaling laws presented will inform the investigation of dynamic interactions between porous surfaces and liquid drops.

A hybrid method employing breakdown anodization and electrophoretic deposition for superhydrophilic surfaces.

A fabrication method is developed for superhydrophilic surfaces with high capillary pressure and fast spreading speed. The fabrication method consists of electrophoretic deposition (EPD) and breakdown anodization (BDA). Nanopores and micropores were produced on titanium plates by EPD and BDA, respectively. In EPD, TiO(2) nanoparticles were used to enhance the surface energy and create nanoporous structures, while BDA was employed to produce microporous structures. Capillary rise measurements (CRM) were utilized to characterize superhydrophilic surfaces in terms of capillary pressure and spreading speed. From CRM, it was revealed that microporous structures play a dominant role in determining transport properties, and nanoporous structures affect local wettability without significantly reducing spreading speed. By combining BDA and EPD into a hybrid method, dual-scale (nano and micro) porous structures were produced on titanium plates. The methods presented offer the potential to vary the transport characteristics of superhydrophilic surfaces by altering the nanoscale and microscale features independently. As an example, surfaces with unconventional capillary flows were produced by the hybrid method. This method provides additional opportunities to investigate wetting phenomena while offering a potentially low cost process for industrial applications.

Electrophoretic deposition of unstable colloidal suspensions for superhydrophobic surfaces.

A novel method to fabricate superhydrophobic surfaces using electrophoretic deposition (EPD) is presented. EPD presents a readily scalable, customizable, and potentially low cost surface manufacturing process. Low surface energy materials with high surface roughness are achieved using EPD of unstable hydrophobic SiO(2) particle suspensions. The effect of suspension stability on surface roughness is quantitatively explored with optical absorbance measurements (to determine suspension stability) and atomic force microscopy (to measure surface roughness). Varying suspension pH modulates suspension stability. Contrary to most applications of EPD, we show that superhydrophobic surfaces favor mildly unstable suspensions since they result in high surface roughness. Particle agglomerates formed in unstable suspensions lead to highly irregular films after EPD. After only 1 min of EPD, we obtain surfaces with low contact angle hysteresis and static contact angles exceeding 160°. We also present a technique to enhance the mechanical durability of the superhydrophobic surfaces by adding a polymeric binder to the suspension prior to EPD.