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Event: 1672

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Inhibition of lung surfactant function

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. More help
Inhibition of LS function.
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Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. More help
Level of Biological Organization

Cell term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Organ term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling).  The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor).  Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description.  To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons.  If a desired term does not exist, a new term request may be made via Term Requests.  Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE.Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
AOP Name Role of event in AOP Point of Contact Author Status OECD Status
Lung surfactant function inhibition leading to decreased lung function MolecularInitiatingEvent Jorid Birkelund Sørli (send email) Open for comment. Do not cite Under Development

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help
Term Scientific Term Evidence Link
human Homo sapiens High NCBI
mouse Mus musculus High NCBI

Life Stages

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Life stage Evidence
All life stages High

Sex Applicability

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Term Evidence
Mixed High

Key Event Description

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Airborne substances that penetrate deep into the lungs and reach the alveoli will come into contact with the thin layer of lung surfactant prior to encountering the alveolar epithelial cells. In addition, blood components (such as albumin) that cross the alveolar-capillary membrane and reach the alveolar airspace can interact with the lung surfactant. The nature of this interaction between substances and lung surfactant depends on the origin (intrinsic versus extrinsic) of the substance, its molecular structure, size, and other physicochemical properties such as hydrophobicity, charge, etc. The interaction can be direct, with certain components of the lung surfactant film at the air-liquid interface i.e. by oxidation or cleaving of the phospholipids (Seeds, Grier et al. 2012, Stachowicz-Kusnierz, Cwiklik et al. 2018), or indirect, via competition with the adsorption of lung surfactant. In many cases, the interaction of substances with lung surfactant at the molecular level is responsible for lung surfactant function inhibition.

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help

Measurements of lung surfactant function inhibition

The inhibition of lung surfactant function can be measured in vitro by evaluating the surface activity in dynamic assays that mimic the continuous compression and expansion of the surfactant films at the air-liquid interface in the alveoli during breathing. Values of minimum surface tension, i.e. the lowest value of surface tension reached upon compression of the surfactant film, is a good indicator of the proper functioning of the lung surfactant. Maximum surface tension, i.e. the highest value of surface tension reached upon expansion of the lung surfactant film, reflects the effective re-adsorption of the lung surfactant at the interface. This parameter was shown to be less sensitive than the minimum surface tension to identify inhibitors of lung surfactant function (Valle, Wu et al. 2015, Da Silva, Autilio et al. 2021). These tests can be performed in different setups.

Constrained drop surfactometer

In the constrained drop surfactometer (CDS) a droplet of lung surfactant is deposited on a sharp-edged pedestal, so that a surfactant film is formed at its air-water surface. The adsorbed lung surfactant film is cycled continuously, to mimic breathing (Zuo, Veldhuizen et al. 2008, Valle, Wu et al. 2015, Sørli, Da Silva et al. 2016, Yang, Wu et al. 2018). A camera continuously takes pictures of the droplet before and during exposure to aerosols of the test substance at the air-liquid interface. Alternatively, the lung surfactant and the test substance can be mixed prior to deposition on the pedestal (Sørli, Låg et al. 2020). Surface tension values are obtained by analysis of the drop shape in real-time (Yu, Yang et al. 2016). The main advantages of this method include the accessibility of the air-liquid interface for exposure to airborne substances, flexibility in controlling cycling rates, and ease of determination of the surface tension in real-time while cycling the surfactant film.

Captive bubble surfactometer

In the captive bubble surfactometer (CBS), the lung surfactant film is formed at the air-liquid interface of an air bubble suspended in liquid. The function can be studied by injecting the test substance in the proximity of the surfactant layer at the interface between the air bubble and the surrounding liquid, or by mixing the substance and the surfactant prior to injecting the lung surfactant into the chamber. The captive bubble surfactometer allows study of the rapid initial adsorption of the lung surfactant at the air-liquid interface, post-expansion adsorption, surface activity during dynamic and quasi-static cycles, and stability of the surfactant film to mechanical perturbations (Autilio and Perez-Gil 2019).

Pulsating bubble surfactometer

In the pulsating bubble surfactometer (PBS), an air bubble suspended on a capillary tube is formed in a chamber containing lung surfactant and is periodically compressed and expanded by a piston pulsator (Enhorning 2001, Autilio and Perez-Gil 2019). The method has been used to study the effects of nanoparticles (Schleh, Muhlfeld et al. 2009), bacterial lipopolysaccharides (Kolomaznik, Liskayova et al. 2018), glucocorticoids (Cimato, Facorro et al. 2018), or meconium (Stichtenoth, Jung et al. 2006) on lung surfactant. The pulsating bubble surfactometer was also used to investigate the surface activity of lung surfactant from patients with acute respiratory distress syndrome (Gregory, Longmore et al. 1991, Markart, Ruppert et al. 2007).

Capillary surfactometer

In the capillary surfactometer (CS), surfactant is deposited in a capillary tube of uneven diameter that simulate the cylindrical surfaces of the terminal conducting airways a constant airflow is led through the capillary. The percent of time with an open passage is used to assess the functionality of lung surfactant (Enhorning 2001, Larsen, Dallot et al. 2014, Sørli, Da Silva et al. 2016).

Surfactant adsorption test

The surfactant adsorption test is a fluorescence-based method that measures the extent and rate of adsorption of lung surfactant at the air-liquid interface. Lung surfactant is labelled with a fluorescent probe, and injected into the wells of a multi-well plate containing a light-absorbing agent (typically brilliant black). The plates are shaken and the fluorescence (of the lung surfactant sample reaching the surface of the wells) is measured. The fluorescence of the lung surfactant sample in the bulk (not adsorbed at the interface) is quenched by the light-adsorbing agent. This method is high-throughput compared to the biophysical assays described above and it allows to measure the effects of physiologically relevant factors, such as temperature, surfactant concentration, or presence of inhibitors in a high number of samples (Ravasio, Cruz et al. 2008). However, this assay does not measure other biophysical properties like pressure-area isotherms, compressibility etc.

Investigation of the interaction of a substance with lung surfactant

The interaction between a substance (exogenous airborne substances or biological components) and lung surfactant components can be investigated at the molecular level in vitro and estimated in silico. The methods rely on lung surfactant models, ranging from simple monolayers of dipalmitoylphosphatidylcholine (DPPC, the main surface-active component of lung surfactant), to the most complex native surfactant, obtained from broncho-alveolar lavage fluid or minced lung tissue. In most methods, a film of lung surfactant is formed at air-liquid interfaces and exposed to the substance of interest via aerosolisation or deposition. In some cases, the lung surfactant model is mixed directly with the test substance before spreading of the film.

Atomic force microscopy

The topography of surfactant structures formed at respiratory-like air-liquid interfaces upon exposure to test substances can be studied by atomic force microscopy on fixed samples.

Langmuir-Blodgett films

Langmuir-Blodgett films are interfacial films of surfactant transferred from the air-liquid interface onto solid supports. They are used to gain information about the distribution of lipids and proteins within the surfactant film and the effect of the interaction with test substances (Cruz and Perez-Gil 2007). Surfactant films deposited at the air-liquid interface of a trough filled with liquid can be compressed by reducing the surface area of the trough. A sensor plate measures the variation in surface pressure over compression to yield surface pressure – area isotherms. It should be noted that in addition to the traditional Langmuir trough, the Langmuir-Blodgett technique has been adapted in the constrained drop surfactometer to study adsorbed surfactant films (Xu, Yang et al. 2020). The comparison of such isotherms in the presence or absence of the test substance gives insights in the interaction of a substance with lung surfactant at the molecular level. Shifts in the surface pressure-area isotherms are identified most easily using simple models such as DPPC monolayers, but can also be seen using the more complex lung surfactant. Structural changes can be identified during compression of the film when combined with epifluorescence or atomic force microscopy.

Cryogenic transmission electron microscopy

In aqueous dispersions, lung surfactant forms vesicles. Cryogenic transmission electron microscopy allows visualizing morphological and structural changes at the single membrane vesicle level. After incubation with the test substance, the surfactant model is applied onto a carbon grid and vitrified in liquid ethane cooled by liquid nitrogen. Changes in the size, circularity or lamerallity of the vesicles indicate disruption of the three-dimensional surfactant structures.

Differential scanning calorimetry

Differential scanning calorimetry allows the study of phase transitions occurring in lipid membranes (such as lung surfactant) over changes in temperature (Demetzos 2008). It can be used to characterize the thermotropic phase behaviours of phospholipids in the surfactant models in the absence or presence of interacting substances. Associated enthalpy, transition temperature, and cooperativity can be estimated from the thermograms. It is a very sensitive method when working with simple models such as pure DPPC bilayers. The method is much less sensitive when using complex lung surfactant models. This is because several transitions overlap in membranes made of complex mixtures, each occurring at different temperature so it is difficult to identify one specific variation.

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided).  More help

The applicability domain is restricted to the groups of organisms where the structure and the functioning of the pulmonary system, including the lung surfactant, are conserved and relevant. Lung surfactant is a vital component of the lungs found in all major vertebrate groups, but particularly, to sustain the delicate structure of the mammalian lung. The lung surfactant system has a single point of origin and was a prerequisite for the evolution of air breathing (Sullivan, Daniels et al. 1998). While the composition and function of lung surfactant are conserved in vertebrates, changes in composition among non-vertebrates are noted and likely reflect differences in the structure of the respiratory units (Veldhuizen, Nag et al. 1998). Decreased lung function has been observed after exposure to airborne toxicants in humans of all sexes and ages, and in common experimental animal species, such as mice, rats, and rabbits.


List of the literature that was cited for this KE description. More help

Al-Saiedy, M., L. Gunasekara, F. Green, R. Pratt, A. Chiu, A. Yang, J. Dennis, C. Pieron, C. Bjornson, B. Winston and M. Amrein (2018). "Surfactant Dysfunction in ARDS and Bronchiolitis is Repaired with Cyclodextrins." Mil Med 183(suppl_1): 207-215.

Autilio, C., M. Echaide, A. Cruz, C. Mouton, A. Hidalgo, E. Da Silva, D. De Luca, B. S. Jorid and J. Perez-Gil (2021). "Molecular and biophysical mechanisms behind the enhancement of lung surfactant function during controlled therapeutic hypothermia." Sci Rep 11(1): 728.

Autilio, C. and J. Perez-Gil (2019). "Understanding the principle biophysics concepts of pulmonary surfactant in health and disease." Arch Dis Child Fetal Neonatal Ed 104(4): F443-F451.

Bakshi, M. S., L. Zhao, R. Smith, F. Possmayer and N. O. Petersen (2008). "Metal nanoparticle pollutants interfere with pulmonary surfactant function in vitro." Biophys J 94(3): 855-868.

Cimato, A., G. Facorro and M. Martinez Sarrasague (2018). "Developing an exogenous pulmonary surfactant-glucocorticoids association: Effect of corticoid concentration on the biophysical properties of the surfactant." Respir Physiol Neurobiol 247: 80-86.

Cruz, A. and J. Perez-Gil (2007). "Langmuir films to determine lateral surface pressure on lipid segregation." Methods Mol Biol 400: 439-457.

Da Silva, E., C. Autilio, K. S. Hougaard, A. Baun, A. Cruz, J. Perez-Gil and J. B. Sørli (2021). "Molecular and biophysical basis for the disruption of lung surfactant function by chemicals." Biochim Biophys Acta Biomembr 1863(1): 183499.

Da Silva, E., C. Hickey, G. Ellis, K. S. Hougaard and J. B. Sørli (2021). "In vitro prediction of clinical signs of respiratory toxicity in rats following inhalation exposure." Under review.

Demetzos, C. (2008). "Differential Scanning Calorimetry (DSC): a tool to study the thermal behavior of lipid bilayers and liposomal stability." J Liposome Res 18(3): 159-173.

Enhorning, G. (2001). "Pulmonary surfactant function studied with the pulsating bubble surfactometer (PBS) and the capillary surfactometer (CS)." Comp Biochem Physiol A Mol Integr Physiol 129(1): 221-226.

Fan, Q., Y. E. Wang, X. Zhao, J. S. Loo and Y. Y. Zuo (2011). "Adverse biophysical effects of hydroxyapatite nanoparticles on natural pulmonary surfactant." ACS Nano 5(8): 6410-6416.

Fang, Q., Q. Zhao, X. Chai, Y. Li and S. Tian (2020). "Interaction of industrial smelting soot particles with pulmonary surfactant: Pulmonary toxicity of heavy metal-rich particles." Chemosphere 246: 125702.

Gasser, M., B. Rothen-Rutishauser, H. F. Krug, P. Gehr, M. Nelle, B. Yan and P. Wick (2010). "The adsorption of biomolecules to multi-walled carbon nanotubes is influenced by both pulmonary surfactant lipids and surface chemistry." Journal of Nanobiotechnology 8: 31.

Gomez-Gil, L., D. Schurch, E. Goormaghtigh and J. Perez-Gil (2009). "Pulmonary surfactant protein SP-C counteracts the deleterious effects of cholesterol on the activity of surfactant films under physiologically relevant compression-expansion dynamics." Biophys J 97(10): 2736-2745.

Gregory, T. J., W. J. Longmore, M. A. Moxley, J. A. Whitsett, C. R. Reed, A. A. Fowler, 3rd, L. D. Hudson, R. J. Maunder, C. Crim and T. M. Hyers (1991). "Surfactant chemical composition and biophysical activity in acute respiratory distress syndrome." J Clin Invest 88(6): 1976-1981.

Gross, T., E. Zmora, Y. Levi-Kalisman, O. Regev and A. Berman (2006). "Lung-surfactant-meconium interaction: in vitro study in bulk and at the air-solution interface." Langmuir 22(7): 3243-3250.

Gunasekara, L., S. Schurch, W. M. Schoel, K. Nag, Z. Leonenko, M. Haufs and M. Amrein (2005). "Pulmonary surfactant function is abolished by an elevated proportion of cholesterol." Biochim Biophys Acta 1737(1): 27-35.

Hidalgo, A., F. Salomone, N. Fresno, G. Orellana, A. Cruz and J. Perez-Gil (2017). "Efficient Interfacially Driven Vehiculization of Corticosteroids by Pulmonary Surfactant." Langmuir 33(32): 7929-7939.

Hobi, N., G. Siber, V. Bouzas, A. Ravasio, J. Perez-Gil and T. Haller (2014). "Physiological variables affecting surface film formation by native lamellar body-like pulmonary surfactant particles." Biochim Biophys Acta 1838(7): 1842-1850.

Hu, G., B. Jiao, X. Shi, R. P. Valle, Q. Fan and Y. Y. Zuo (2013). "Physicochemical properties of nanoparticles regulate translocation across pulmonary surfactant monolayer and formation of lipoprotein corona." ACS Nano 7(12): 10525-10533.

Hu, Q., X. Bai, G. Hu and Y. Y. Zuo (2017). "Unveiling the Molecular Structure of Pulmonary Surfactant Corona on Nanoparticles." ACS Nano 11(7): 6832-6842.

Jagalski, V., R. Barker, D. Topgaard, T. Gunther-Pomorski, B. Hamberger and M. Cardenas (2016). "Biophysical study of resin acid effects on phospholipid membrane structure and properties." Biochim Biophys Acta 1858(11): 2827-2838.

Kapralov, A. A., W. H. Feng, A. A. Amoscato, N. Yanamala, K. Balasubramanian, D. E. Winnica, E. R. Kisin, G. P. Kotchey, P. P. Gou, L. J. Sparvero, P. Ray, R. K. Mallampalli, J. Klein-Seetharaman, B. Fadeel, A. Star, A. A. Shvedova and V. E. Kagan (2012). "Adsorption of Surfactant Lipids by Single-Walled Carbon Nanotubes in Mouse Lung upon Pharyngeal Aspiration." Acs Nano 6(5): 4147-4156.

Kolomaznik, M., G. Liskayova, N. Kanjakova, L. Hubcik, D. Uhrikova and A. Calkovska (2018). "The Perturbation of Pulmonary Surfactant by Bacterial Lipopolysaccharide and Its Reversal by Polymyxin B: Function and Structure." Int J Mol Sci 19(7).

Larsen, S. T., E. Da Silva, J. S. Hansen, A. C. O. Jensen, I. K. Koponen and J. B. Sørli (2020). "Acute Inhalation Toxicity After Inhalation of ZnO Nanoparticles: Lung Surfactant Function Inhibition In Vitro Correlates With Reduced Tidal Volume in Mice." Int J Toxicol 39(4): 321-327.

Larsen, S. T., C. Dallot, S. W. Larsen, F. Rose, S. S. Poulsen, A. W. Nørgaard, J. S. Hansen, J. B. Sørli, G. D. Nielsen and C. Foged (2014). "Mechanism of action of lung damage caused by a nanofilm spray product." Toxicol Sci 140(2): 436-444.

Lopez-Rodriguez, E., A. Cruz, R. P. Richter, H. W. Taeusch and J. Perez-Gil (2013). "Transient exposure of pulmonary surfactant to hyaluronan promotes structural and compositional transformations into a highly active state." J Biol Chem 288(41): 29872-29881.

Lopez-Rodriguez, E., M. Echaide, A. Cruz, H. W. Taeusch and J. Perez-Gil (2011). "Meconium impairs pulmonary surfactant by a combined action of cholesterol and bile acids." Biophys J 100(3): 646-655.

Lopez-Rodriguez, E., O. L. Ospina, M. Echaide, H. W. Taeusch and J. Perez-Gil (2012). "Exposure to polymers reverses inhibition of pulmonary surfactant by serum, meconium, or cholesterol in the captive bubble surfactometer." Biophys J 103(7): 1451-1459.

Lugones, Y., O. Blanco, E. Lopez-Rodriguez, M. Echaide, A. Cruz and J. Perez-Gil (2018). "Inhibition and counterinhibition of Surfacen, a clinical lung surfactant of natural origin." PLoS One 13(9): e0204050.

Markart, P., C. Ruppert, M. Wygrecka, T. Colaris, B. Dahal, D. Walmrath, H. Harbach, J. Wilhelm, W. Seeger, R. Schmidt and A. Guenther (2007). "Patients with ARDS show improvement but not normalisation of alveolar surface activity with surfactant treatment: putative role of neutral lipids." Thorax 62(7): 588-594.

Przybyla, R. J., J. Wright, R. Parthiban, S. Nazemidashtarjandi, S. Kaya and A. M. Farnoud (2017). "Electronic cigarette vapor alters the lateral structure but not tensiometric properties of calf lung surfactant." Respir Res 18(1): 193.

Ravasio, A., A. Cruz, J. Perez-Gil and T. Haller (2008). "High-throughput evaluation of pulmonary surfactant adsorption and surface film formation." J Lipid Res 49(11): 2479-2488.

Roldan, N., J. Perez-Gil, M. R. Morrow and B. Garcia-Alvarez (2017). "Divide & Conquer: Surfactant Protein SP-C and Cholesterol Modulate Phase Segregation in Lung Surfactant." Biophys J 113(4): 847-859.

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Schleh, C., C. Muhlfeld, K. Pulskamp, A. Schmiedl, M. Nassimi, H. D. Lauenstein, A. Braun, N. Krug, V. J. Erpenbeck and J. M. Hohlfeld (2009). "The effect of titanium dioxide nanoparticles on pulmonary surfactant function and ultrastructure." Respir Res 10: 90.

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Stichtenoth, G., P. Jung, G. Walter, J. Johansson, B. Robertson, T. Curstedt and E. Herting (2006). "Polymyxin B/pulmonary surfactant mixtures have increased resistance to inactivation by meconium and reduce growth of gram-negative bacteria in vitro." Pediatr Res 59(3): 407-411.

Sullivan, L. C., C. B. Daniels, I. D. Phillips, S. Orgeig and J. A. Whitsett (1998). "Conservation of surfactant protein A: evidence for a single origin for vertebrate pulmonary surfactant." J Mol Evol 46(2): 131-138.

Sørli, J. B., K. Balogh Sivars, E. Da Silva, K. S. Hougaard, I. K. Koponen, Y. Y. Zuo, I. E. K. Weydahl, P. M. Åberg and R. Fransson (2018). "Bile salt enhancers for inhalation: Correlation between in vitro and in vivo lung effects." Int J Pharm 550(1-2): 114-122.

Sørli, J. B., E. Da Silva, P. Backman, M. Levin, B. L. Thomsen, I. K. Koponen and S. T. Larsen (2016). "A Proposed In Vitro Method to Assess Effects of Inhaled Particles on Lung Surfactant Function." Am J Respir Cell Mol Biol 54(3): 306-311.

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Sørli, J. B., M. Låg, L. Ekeren, J. Perez-Gil, L. S. Haug, E. Da Silva, M. N. Matrod, K. B. Gutzkow and B. Lindeman (2020). "Per- and polyfluoroalkyl substances (PFASs) modify lung surfactant function and pro-inflammatory responses in human bronchial epithelial cells." Toxicol In Vitro 62: 104656.

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Tatur, S. and A. Badia (2012). "Influence of hydrophobic alkylated gold nanoparticles on the phase behavior of monolayers of DPPC and clinical lung surfactant." Langmuir 28(1): 628-639.

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Yu, K., J. Yang and Y. Y. Zuo (2016). "Automated Droplet Manipulation Using Closed-Loop Axisymmetric Drop Shape Analysis." Langmuir 32(19): 4820-4826.

Yuan, Y., X. Liu, T. Liu, W. Liu, Y. Zhu, H. Zhang and C. Zhao (2020). "Molecular dynamics exploring of atmosphere components interacting with lung surfactant phospholipid bilayers." Sci Total Environ 743: 140547.

Zhang, H., Y. E. Wang, C. R. Neal and Y. Y. Zuo (2012). "Differential effects of cholesterol and budesonide on biophysical properties of clinical surfactant." Pediatr Res 71(4 Pt 1): 316-323.

Zhao, Q., Y. Li, X. Chai, L. Xu, L. Zhang, P. Ning, J. Huang and S. Tian (2019). "Interaction of inhalable volatile organic compounds and pulmonary surfactant: Potential hazards of VOCs exposure to lung." J Hazard Mater 369: 512-520.

Zuo, Y. Y., R. A. Veldhuizen, A. W. Neumann, N. O. Petersen and F. Possmayer (2008). "Current perspectives in pulmonary surfactant--inhibition, enhancement and evaluation." Biochim Biophys Acta 1778(10): 1947-1977.