The design of electronic cigarette (EC) atomizing units has evolved since their introduction over 10 years ago. The purpose of this study was to evaluate atomizer design in ECs sold between 2011-2017. Atomizers from 34 brands representing three generations of ECs were dissected and photographed using a stereoscopic microscope. Five distinct atomizer design categories were identified in first generation products (cig-a-like/cartomizer) and three categories were found in the third generation. Atomizers in most cig-a-like ECs contained a filament, thick wire, wire joints, air-tube, wick, sheath, and fibers, while some later models lacked some of these components. Over time design changes included an increase in atomizer size; removal of solder joints between wires; removal of Polyfil fibers; and removal of the microprocessor from Vuse. In second and third generation ECs, the reservoirs and batteries were larger, and the atomizing units generally lacked a thick wire, fibers, and sheath. These data contribute to an understanding of atomizer design and show that there is no single design for ECs, which are continually evolving. The design of the atomizer is particularly important as it affects the performance of ECs and what transfers into the aerosol.

Background

Since their release in 2004, electronic cigarettes (ECs) and their atomizers have undergone significant evolution.

Objective

The purpose of this study was to evaluate and compare the elemental/metal composition of atomizers in cartomizer and tank style ECs produced over a 5-year period.

Methods

Popular cartomizer and tank models of ECs were dissected and photographed using a stereoscopic microscope, and elemental analysis of EC atomizers was done using scanning electron microscopy coupled with energy dispersive x-ray spectroscopy.

Results

Eight elements/metals were found in most products across and within brands purchased at different times. These included chromium, nickel, copper, silver, tin, silicon, aluminum, and zinc. Iron and lead were found in some but not all products, while manganese, cobalt, molybdenum, titanium, and tungsten were only found in a few of the products. The metals used in various components were often similar in cartomizer and tank models. Filaments were usually chromium and nickel (nichrome), although in some newer products, the filament also contained iron, copper, and manganese. The thick wire in earlier products was usually copper coated with silver, while in some newer products, the thick wire was predominantly nickel. In all products, the wick was silica, and sheaths, when present, were fiberglass (silicon, oxygen, calcium, aluminum, magnesium). Wire-to-wire joints were either brazed or clamped with brass (copper and zinc), and air-tube-to-thick wire joints, when present, were usually soldered with tin. Tank style products generally lacked a thick wire and sheaths.

Conclusion

In general, atomizer components in ECs were remarkably similar over time and between brands. Certain elements/metals were consistently found in most models from all generations, and these should be studied carefully to determine if their transfer to aerosols affects user's health and if their accumulation in trash affects the environment.

OBJECTIVE:To evaluate performance of the I quit original smoking (iQOS) heat-not-burn system as a function of cleaning and puffing topography, investigate the validity of manufacturer's claims that this device does not burn tobacco and determine if the polymer-film filter is potentially harmful. METHODS:iQOS performance was evaluated using five running conditions incorporating two different cleaning protocols. Heatsticks were visually and stereomicroscopically inspected preuse and postuse to determine the extent of tobacco plug charring (from pyrolysis) and polymer-film filter melting, and to elucidate the effects of cleaning on charring. Gas chromatography-mass spectrometry headspace analysis was conducted on unused polymer-film filters to determine if potentially toxic chemicals are emitted from the filter during heating. RESULTS:For all testing protocols, pressure drop decreased as puff number increased. Changes in testing protocols did not affect aerosol density. Charring due to pyrolysis (a form of organic matter thermochemical decomposition) was observed in the tobacco plug after use. When the manufacturer's cleaning instructions were followed, both charring of the tobacco plug and melting of the polymer-film filter increased. Headspace analysis of the polymer-film filter revealed the release of formaldehyde cyanohydrin at 90°C, which is well below the maximum temperature reached during normal usage. DISCUSSION:Device usage limitations may contribute to decreases in interpuff intervals, potentially increasing user's intake of nicotine and other harmful chemicals. This study found that the tobacco plug does char and that charring increases when the device is not cleaned between heatsticks. Release of formaldehyde cyanohydrin is a concern as it is highly toxic at very low concentrations.

Introduction

The purpose of this study was to characterize the performance of disposable button-activated and disposable airflow-activated electronic cigarettes (EC) and electronic hookahs (EH).

Methods

The airflow rate required to produce aerosol, pressure drop, and the aerosol absorbance at 420 nm were measured during smoke-outs of 9 disposable products. Three units of each product were tested in these experiments.

Results

The airflow rates required to produce aerosol and the aerosol absorbances were lower for button-activated models (3 mL/s; 0.41-0.55 absorbance) than for airflow-activated models (7-17 mL/s; 0.48-0.84 absorbance). Pressure drop was also lower across button-activated products (range = 6-12 mm H2O) than airflow-activated products (range = 15-67 mm H20). For 25 of 27 units tested, airflow did not have to be increased during smoke-out to maintain aerosol production, unlike earlier generation models. Two brands had uniform performance characteristics for all parameters, while 3 had at least 1 product that did not function normally. While button-activated models lasted 200 puffs or less and EH airflow-activated models often lasted 400 puffs, none of the models produced as many puffs as advertised. Puff number was limited by battery life, which was shorter in button-activated models.

Conclusion

The performance of disposable products was differentiated mainly by the way the aerosol was produced (button vs airflow-activated) rather than by product type (EC vs EH). Users needed to take harder drags on airflow-activated models. Performance varied within models, and battery life limited the number of puffs. Data suggest quality control in manufacturing varies among brands.

Our purpose was to examine the effect of model, puffing topography (voltage, air-flow, puff interval), and method of collection on 19 elements/metals in aerosols from six tank-style electronic cigarettes (EC). Aerosols were collected from six brands using a cold trap or impinger and various puffing topographies. 19 elements were quantified using inductively coupled plasma optical emission spectroscopy. 16 elements/metals were present and quantified in the aerosols. The total concentrations of elements/metals ranged from 43 to 3,138 µg/L with the impinger method of collection and 226 to 6,767 µg/L with the cold trap method. The concentrations of individual elements were often similar across brands and across topographies. Some elements (e.g., zinc) were present in most aerosols, while others (e.g., cadmium, titanium, vanadium) were rarely found. Concentrations of some elements (e.g., lead) increased in aerosols as voltage/power increased. The model with fewest metal parts in the atomizer had the fewest metals in its aerosols. Most elements/metals in the aerosols have been found previously in the atomizers of EC. All tank-style aerosols had elements/metals that appeared to originate in the atomizers, and concentrations increased with increasing power. Concentrations of some elements were high enough to be a health concern.

Introduction

Electronic cigarettes or e-cigarettes are marketed as tobacco-free nicotine delivery devices that have received little laboratory evaluation. In this study, the smoking properties of conventional and e-cigarettes were compared by examining the vacuum required to produce smoke (conventional cigarettes) or aerosol (e-cigarettes) and the density of the smoke/aerosol over time.

Methods

Vacuum was measured using a manometer coupled to a smoking machine. The density of aerosol or smoke was measured spectrophotometrically. E-cigarettes were subjected to smoke-out experiments in which vacuum and aerosol density were measured until each cartridge was exhausted.

Results

The vacuum required to smoke conventional cigarettes varied among the eight brands tested. Lights and ultra-light brands required stronger vacuums to smoke than unfiltered and regular filtered brands. Except for one brand, higher vacuums were required to smoke e-cigarettes than conventional brands. Smoke/aerosol density was stable for conventional brands and for e-cigarettes over the first 10 puffs; however, aerosol density of e-cigarettes dropped during subsequent smoking, and higher vacuums were required to produce aerosol as the puff number increased. While conventional cigarettes were uniform in their smoking behavior within brands, vacuum and density varied within brands of e-cigarettes.

Discussion

Generally, e-cigarettes required stronger vacuums (suction) to smoke than conventional brands, and the effects of this on human health could be adverse. The amount of aerosol produced by e-cigarettes decreased during smoking, which necessitated increasing puff strength to produce aerosol. The decreased efficiency of aerosol production during e-cigarette smoking makes dosing nonuniform over time and calls into question their usefulness as nicotine delivery devices.

Introduction

Chemical elements and their toxicity were evaluated in electronic cigarette (EC) solvents, fluids, and aerosols.

Aims and methods

Element identification and quantification in propylene glycol (PG), glycerin (G), refill fluids before and after use, and aerosols was done using inductively coupled plasma optical emission spectrometry. Cytotoxicity and oxidative stress were evaluated using in vitro assays.

Results

Seven elements were present in PG, G, and popular refill fluids, and they transferred to aerosols made with ECs. Selenium was in all products (0.125-0.292 mg/L), while arsenic, aluminum, and tin were frequently in solvent and refill fluid samples at lower concentrations. Iron, chromium, copper, nickel, zinc, and lead were only detected in fluid after EC use, indicating they came from heated atomizers. Elements transferred most efficiently to aerosols made with second-/third-generation ECs. Of the elements in fluid, selenium and arsenic were the most cytotoxic to human bronchial epithelial cells (BEAS-2B) and pulmonary fibroblasts in the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide assay. Selenium increased superoxide production in mitochondria and nucleoli and elevated selenoprotein H in nucleoli of BEAS-2B cells at concentrations found in EC aerosols (10 nM or 0.002 mg/L).

Conclusions

Elements in EC aerosols came from both e-fluids and atomizing units. Within second-/third-generation products, transfer became more efficient as power increased. In vitro responses occurred at concentrations of selenium found in some EC aerosols. Human exposure to chemical elements in ECs could be reduced by regulating (decreasing) allowable EC power and by improving the purity of PG and G.

Implications

PG, G, refill fluids, and e-fluids contained potentially toxic chemical elements that transferred to aerosols. Transfer was more efficient in second- and third-generation EC products and increased as power increased. Selenium and arsenic were the most cytotoxic of the elements tested in the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide assay. Selenium tetrachloride-induced oxidative stress in BEAS-2B cells, but not in human pulmonary fibroblasts. All fluids contained selenium above the concentration that induced oxidative stress in human bronchial epithelial cells. Selenium increased superoxide in mitochondria and nucleoli and increased selenoprotein H, a redox responsive DNA-binding protein that is upregulated by superoxide and an indicator of nucleolar stress. EC users are exposed to elements in aerosols, which may with chronic exposure contribute to diseases associated with oxidative stress.