Lung surfactant-particles at fluid interfaces for toxicity assessments

Experiments and modelling of pulmonary surfactant disruption by aerosolised compounds

Within the deep lung, pulmonary surfactant coats the air-liquid interface at the surface of the alveoli. This complex mixture of amphiphilic molecules and proteins modifies the surface tension and mechanical properties of this interface to assist with breathing. In this study, we examine the effects on pulmonary surfactant function by two industrially used compounds composing surfactants and polymers. Using an experimental method previously developed to imitate the in vivo exposure in the alveoli, we quantify the change in the dilational rheology of the pulmonary surfactant due to the introduction of two widely used chemicals; Benzalkonium Chloride (BAC) and Polyhexamethylene Biguanide (PHMB). We observe that these chemicals alter the dilational rheology of the surfactant monolayer. Using a mechanistic theory, we are able to semi-quantitatively model the changes induced by the introduction of these compounds to the pulmonary surfactant.

Validation of a high-performance liquid chromatography method for determining lysophosphatidylcholine content in bovine pulmonary surfactant medication

Pulmonary surfactant replacement therapy is a promising improvement in neonatal care for infants with respiratory distress syndrome. Lysophosphatidylcholine (LPC) is an undesirable component that can hinder surfactant proteins from enhancing the adsorption of surfactant lipids to balance surface tensions by creating a saturated coating on the interior of the lungs. A novel normal-phase liquid chromatography method utilizing UV detection and non-toxic solvents was developed and validated for the first time to analyze LPC in the complex matrix of pulmonary surfactant medication. The analytical method validation included evaluation of system suitability, repeatability, intermediate precision, linearity, accuracy, limit of detection (LOD), limit of quantification (LOQ), stability and robustness. The method yielded detection and quantification limits of 4.4 and 14.5 μg/ml, respectively. The calibration curve was modified linearly within the LOQ to 1.44 mg/ml range, with a determination coefficient of 0.9999 for standards and 0.9997 for sample solutions. Given the lack of reliable published data on LPC analysis in pulmonary surfactant medications, this newly developed method demonstrates promising results and offers advantages of HPLC methodology, including simplicity, accuracy, specificity, sensitivity and an exceptionally low LOD and LOQ. These attributes contribute to considering this achievement as an innovative method.

Structure of graphene oxide-phospholipid monolayers: A grazing incidence X-ray diffraction and neutron and X-ray reflectivity study

HYPOTHESIS

Graphene oxide-based nanotechnology has aroused a great interest due to its applications in the biomedical and optoelectronic fields. The wide use of these materials makes it necessary to study its potential toxicity associated with the inhalation of Graphene Oxide (GO) nanoparticles and its interaction with the lung surfactant. Langmuir monolayers have proven to be an excellent tool for studying the properties of the lung surfactant and the effect of intercalation of nanoparticles on its structure and properties. Therefore, to know the origin of the phospholipids/GO interaction and the structure of the lipid layer with GO, in this work we study the effect of the insertion of GO sheets on a Langmuir film of 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC).

EXPERIMENTS

Surface pressure-area isotherms, Neutron (NR) and X-ray Reflectivity (XRR) and Grazing Incidence X-ray Diffraction (GIXD) measurements of hydrogenated and deuterated DPPC monolayers with and without GO have been carried out.

FINDINGS

The results outline a strong interaction between the GO and the zwitterionic form of DPPC and prove that GO is in three regions of the DPPC monolayer, the aliphatic chains of DPPC, the head groups and water in the subphase. Comparison between results obtained with hydrogenated and deuterated DPPC allows concluding that both, electrostatic attractions, and dispersion forces are responsible of the interaction GO/DPPC. Results also demonstrated that the insertion of GO into the DPPC aliphatic chains does not induce significant changes on unit cell of DPPC.

Influence of the Type of Biocompatible Polymer in the Shell of Magnetite Nanoparticles on Their Interaction with DPPC in Two-Component Langmuir Monolayers

Magnetite nanoparticles (MNPs) are attractive nanomaterials for applications in magnetic resonance imaging, targeted drug delivery, and anticancer therapy due to their unique properties such as nontoxicity, wide chemical affinity, and intrinsic superparamagnetism. Their functionalization with polymers such as chitosan or poly(vinyl alcohol) (PVA) can not only improve their biocompatibility and biodegradability but it also plays an important role in their interactions with biological cells. In this work, the effect of the functionalization of MNPs with chitosan, PVA, and their blend on model cell membranes formed from 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) using a Langmuir technique was studied. The studies performed showed that the type of biocompatible polymer in the MNP shell plays a crucial role in the effectiveness of its adsorption process into the model cell membrane. Modification of MNPs with chitosan facilitates significantly more effective adsorption than coating them with PVA or with a chitosan and PVA blend. The presence of all the investigated MNPs in the DPPC monolayer at low concentrations does not affect its thermodynamic state, fluidity, or morphology, which is promising in terms of their biocompatibility. On the other hand, their high concentration (molar fraction above ≈0.05) exerts a disruptive effect on the model cell membrane and results in their aggregation, leading probably to the loss of their superparamagnetic properties essential for nanomedicine.

Investigation on the relationship between lipid composition and structure in model membranes composed of extracted natural phospholipids

HYPOTHESIS

Unravelling the structural diversity of cellular membranes is a paramount challenge in life sciences. In particular, lipid composition affects the membrane collective behaviour, and its interactions with other biological molecules.

EXPERIMENTS

Here, the relationship between membrane composition and resultant structural features was investigated by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry on in vitro membrane models of the mammalian plasma and endoplasmic-reticulum-Golgi intermediate compartment membranes in the form of Langmuir monolayers. Natural extracted yeast lipids were used because, unlike synthetic lipids, the acyl chain saturation pattern of yeast and mammalian lipids are similar.

FINDINGS

The structure of the model membranes, orthogonal to the plane of the membrane, as well as their lateral packing, were found to depend strongly on their specific composition, with cholesterol having a major influence on the in-plane morphology, yielding a coexistence of liquid-order and liquid-disorder phases.

Investigating the Effect of Medium Chain Triglycerides on the Elasticity of Pulmonary Surfactant

In recent years, vaping has increased in both popularity and ease of access. This has led to an outbreak of a relatively new condition known as e-cigarette/vaping-associated lung injury (EVALI). This injury can be caused by physical interactions between the pulmonary surfactant (PS) in the lungs and toxins typically found in vaping solutions, such as medium chain triglycerides (MCT). MCT has been largely used as a carrier agent within many cannabis products commercially available on the market. Pulmonary surfactant ensures proper respiration by maintaining low surface tensions and interface stability throughout each respiratory cycle. Therefore, any impediments to this system that negatively affect the efficacy of this function will have a strong hindrance on the individual's quality of life. Herein, neutron spin echo (NSE) and Langmuir trough rheology were used to probe the effects of MCT on the mechanical properties of pulmonary surfactant. Alongside a porcine surfactant extract, two lipid-only mimics of progressing complexity were used to study MCT effects in a range of systems that are representative of endogenous surfactant. MCT was shown to have a greater biophysical effect on bilayer systems compared to monolayers, which may align with biological data to propose a mechanism of surfactant inhibition by MCT oil.

Impact of Natural-Based Viscosity Modifiers of Inhalation Drugs on the Dynamic Surface Properties of the Pulmonary Surfactant

The effectiveness of inhalation therapy depends on aerosol size distribution, which determines the penetration and regional deposition of drug in the lungs. As the size of droplets inhaled from medical nebulizers varies depending on the physicochemical properties of the nebulized liquid, it can be adjusted by adding some compounds as viscosity modifiers (VMs) of a liquid drug. Natural polysaccharides have been recently proposed for this purpose and while they are biocompatible and generally recognized as safe (GRAS), their direct influence of the pulmonary structures is unknown. This work studied the direct influence of three natural VMs (sodium hyaluronate, xanthan gum, and agar) on the surface activity of the pulmonary surfactant (PS) measured in vitro using the oscillating drop method. The results allowed for comparing the variations of the dynamic surface tension during breathing-like oscillations of the gas/liquid interface with the PS, and the viscoelastic response of this system, as reflected by the hysteresis of the surface tension. The analysis was done using quantitative parameters, i.e., stability index (SI), normalized hysteresis area (HAn), and loss angle (φ), depending on the oscillation frequency (f). It was also found that, typically, SI is in the range of 0.15-0.3 and increases nonlinearly with f, while φ slightly decreases. The effect of NaCl ions on the interfacial properties of PS was noted, which was usually positive for the size of hysteresis with an HAn value up to 2.5 mN/m. All VMs in general were shown to have only a minor effect on the dynamic interfacial properties of PS, suggesting the potential safety of the tested compounds as functional additives in medical nebulization. The results also demonstrated relationships between the parameters typically used in the analysis of PS dynamics (i.e., HAn and SI) and dilatational rheological properties of the interface, allowing for easier interpretation of such data.

Unravelling the orientation of the inositol-biphosphate ring and its dependence on phosphatidylinositol 4,5-bisphosphate cluster formation in model membranes

HYPOTHESIS

Inositol phospholipids are well known to form clusters in the cytoplasmic leaflet of the plasma membrane that are responsible for the interaction and recruitment of proteins involved in key biological processes like endocytosis, ion channel activation and secondary messenger production. Although their phosphorylated inositol ring headgroup plays an important role in protein binding, its orientation with respect to the plane of the membrane and its lateral packing density has not been previously described experimentally.

EXPERIMENTS

Here, we study phosphatidylinositol 4,5-bisphosphate (PIP2) planar model membranes in the form of Langmuir monolayers by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry to elucidate the relation between lateral (in-plane) and perpendicular (out-of-plane) molecular organization of PIP2.

FINDINGS

Different surface areas were explored through monolayer compression, allowing us to correlate the formation of transient PIP2 clusters with the change in orientation of the inositol-biphosphate headgroup, which was experimentally determined by neutron reflectometry.

Shape-dependent gold nanoparticle interactions with a model cell membrane

Customizable gold nanoparticle platforms are motivating innovations in drug discovery with massive therapeutic potential due to their biocompatibility, stability, and imaging capabilities. Further development requires the understanding of how discrete differences in shape, charge, or surface chemistry affect the drug delivery process of the nanoparticle. The nanoparticle shape can have a significant impact on nanoparticle function as this can, for example, drastically change the surface area available for modifications, such as surface ligand density. In order to investigate the effects of nanoparticle shape on the structure of cell membranes, we directly probed nanoparticle-lipid interactions with an interface sensitive technique termed sum frequency generation (SFG) vibrational spectroscopy. Both gold nanostars and gold nanospheres with positively charged ligands were allowed to interact with a model cell membrane and changes in the membrane structure were directly observed by specific SFG vibrational modes related to molecular bonds within the lipids. The SFG results demonstrate that the +Au nanostars both penetrated and impacted the ordering of the lipids that made up the membrane, while very little structural changes to the model membrane were observed by SFG for the +Au nanospheres interacting with the model membrane. This suggests that the +Au nanostars, compared to the +Au nanospheres, are more disruptive to a cell membrane. Our findings indicate the importance of shape in nanomaterial design and provide strong evidence that shape does play a role in defining nanomaterial-biological interactions.

Current Perspective on the Study of Liquid–Fluid Interfaces: From Fundamentals to Innovative Applications

Liquid–fluid interfaces are ubiquitous systems, having a paramount importance for daily life as well as for academia, providing the basis for the study of different aspects of interest for medicine, biology, and physics [...]

Evaluating the Impact of Hydrophobic Silicon Dioxide in the Interfacial Properties of Lung Surfactant Films

The interaction of hydrophobic silicon dioxide particles (fumed silicon dioxide), as model air pollutants, and Langmuir monolayers of a porcine lung surfactant extract has been studied in order to try to shed light on the physicochemical bases underlying the potential adverse effects associated with pollutant inhalation. The surface pressure-area isotherms of lung surfactant (LS) films including increasing amounts of particles revealed that particle incorporation into LS monolayers modifies the organization of the molecules at the water/vapor interface, which alters the mechanical resistance of the interfacial films, hindering the ability of LS layers for reducing the surface tension, and reestablishing the interface upon compression. This influences the normal physiological function of LS as is inferred from the analysis of the response of the Langmuir films upon the incorporation of particles against harmonic changes of the interfacial area (successive compression-expansion cycles). These experiments evidenced that particles alter the relaxation mechanisms of LS films, which may be correlated to a modification of the transport of material within the interface and between the interface and the adjacent fluid during the respiratory cycle.

Impact of Polymer Nanoparticles on DPPC Monolayer Properties

The application of surface rheology and Brewster angle microscopy on mixed monolayers of DPPC and polymeric nanoparticles (cationic and anionic) showed that the sign of the particle charge affects the dynamic properties of the monolayers less than the nanoparticles’ ability to aggregate. Under almost physiological conditions, the effect of nanoparticles on the elasticity of DPPC monolayer is insignificant. However, the particles prevent the surface tension from decreasing to extremely low values. This effect could affect the functionality of pulmonary surfactants.

Vaping additives negatively impact the stability and lateral film organization of lung surfactant model systems

Aims: Inhalation of vaping additives has recently been shown to impair respiratory function, leading to e-cigarette or vaping product use associated with lung injuries. This work was designed to understand the impact of additives (vitamin E, vitamin E acetate, tetrahydrocannabinol and cannabidiol) on model lung surfactants. Materials & methods: Lipid monofilms at the air-water interface and Brewster angle microscopy were used to assess the impact of vaping additives on model lung surfactant films. Results & conclusion: The addition of 5 mol % of vaping additives, and even more so mixtures of vitamins and cannabinoids, negatively impacts lipid packing and film stability, induces material loss upon cycling and significantly reduces functionally relevant lipid domains. This range of detrimental effects could affect proper lung function.

A broad perspective to particle-laden fluid interfaces systems: from chemically homogeneous particles to active colloids

Particles adsorbed to fluid interfaces are ubiquitous in industry, nature or life. The wide range of properties arising from the assembly of particles at fluid interface has stimulated an intense research activity on shed light to the most fundamental physico-chemical aspects of these systems. These include the mechanisms driving the equilibration of the interfacial layers, trapping energy, specific inter-particle interactions and the response of the particle-laden interface to mechanical perturbations and flows. The understanding of the physico-chemistry of particle-laden interfaces becomes essential for taking advantage of the particle capacity to stabilize interfaces for the preparation of different dispersed systems (emulsions, foams or colloidosomes) and the fabrication of new reconfigurable interface-dominated devices. This review presents a detailed overview of the physico-chemical aspects that determine the behavior of particles trapped at fluid interfaces. This has been combined with some examples of real and potential applications of these systems in technological and industrial fields. It is expected that this information can provide a general perspective of the topic that can be exploited for researchers and technologist non-specialized in the study of particle-laden interfaces, or for experienced researcher seeking new questions to solve.

Characterization of aerosols produced during shampoo use and harmful chemicals in shampoo aerosols

To declare a shampoo toxicologically safe, one should evaluate the hazards posed by the inhalation of aerosols produced during its use. Herein, tap water was sprayed into a shampoo-filled plastic container to investigate the formation of shampoo aerosols and the possibility of their inhalation. The aerosols thus obtained had higher mass concentrations (geometric mean = 5779 μg m^-3 (PM₁₀) and 2249 μg m^-3 (PM_2.5)) than water aerosols (geometric mean = 927 μg m^-3 (PM₁₀) and 476 μg m^-3 (PM_2.5)). In particular, shampoo aerosol particles with an aerodynamic diameter of 2.5 μm, which can penetrate the alveoli when inhaled, had the highest mass concentration (geometric mean = 2000 μg m^-3). The volatile organic compounds contained in shampoo aerosols featured alcohol and ether groups attached to dodecane and tetradecane backbones; these compounds were generated by the thermal decomposition of surfactants (i.e., lauryl and laureth sulfates) during instrumental analysis. The acquired data suggest that inhalation exposure and chronic inhalation toxicity evaluations should be performed for various shampoo usage conditions to ensure inhalation safety.

Fluid Films as Models for Understanding the Impact of Inhaled Particles in Lung Surfactant Layers

Pollution is currently a public health problem associated with different cardiovascular and respiratory diseases. These are commonly originated as a result of the pollutant transport to the alveolar cavity after their inhalation. Once pollutants enter the alveolar cavity, they are deposited on the lung surfactant (LS) film, altering their mechanical performance which increases the respiratory work and can induce a premature alveolar collapse. Furthermore, the interactions of pollutants with LS can induce the formation of an LS corona decorating the pollutant surface, favoring their penetration into the bloodstream and distribution along different organs. Therefore, it is necessary to understand the most fundamental aspects of the interaction of particulate pollutants with LS to mitigate their effects, and design therapeutic strategies. However, the use of animal models is often invasive, and requires a careful examination of different bioethics aspects. This makes it necessary to design in vitro models mimicking some physico-chemical aspects with relevance for LS performance, which can be done by exploiting the tools provided by the science and technology of interfaces to shed light on the most fundamental physico-chemical bases governing the interaction between LS and particulate matter. This review provides an updated perspective of the use of fluid films of LS models for shedding light on the potential impact of particulate matter in the performance of LS film. It should be noted that even though the used model systems cannot account for some physiological aspects, it is expected that the information contained in this review can contribute on the understanding of the potential toxicological effects of air pollution.

The Influence of Polysaccharides/TiO2 on the Model Membranes of Dipalmitoylphosphatidylglycerol and Bacterial Lipids

The aim of the study was to determine the bactericidal properties of popular medical, pharmaceutical, and cosmetic ingredients, namely chitosan (Ch), hyaluronic acid (HA), and titanium dioxide (TiO₂). The characteristics presented in this paper are based on the Langmuir monolayer studies of the model biological membranes formed on subphases with these compounds or their mixtures. To prepare the Langmuir film, 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DPPG) phospholipid, which is the component of most bacterial membranes, as well as biological material-lipids isolated from bacteria Escherichia coli and Staphylococcus aureus were used. The analysis of the surface pressure-mean molecular area (π-A) isotherms, compression modulus as a function of surface pressure, C_S^-1 = f(π), relative surface pressure as a function of time, π/π₀ = f(t), hysteresis loops, as well as structure visualized using a Brewster angle microscope (BAM) shows clearly that Ch, HA, and TiO₂ have antibacterial properties. Ch and TiO₂ mostly affect S. aureus monolayer structure during compression. They can enhance the permeability of biological membranes leading to the bacteria cell death. In turn, HA has a greater impact on the thickness of E. coli film.

Physiological fluid interfaces: Functional microenvironments, drug delivery targets, and first line of defense

Fluid interfaces, i.e. the boundary layer of two liquids or a liquid and a gas, play a vital role in physiological processes as diverse as visual perception, oral health and taste, lipid metabolism, and pulmonary breathing. These fluid interfaces exhibit a complex composition, structure, and rheology tailored to their individual physiological functions. Advances in interfacial thin film techniques have facilitated the analysis of such complex interfaces under physiologically relevant conditions. This allowed new insights on the origin of their physiological functionality, how deviations may cause disease, and has revealed new therapy strategies. Furthermore, the interactions of physiological fluid interfaces with exogenous substances is crucial for understanding certain disorders and exploiting drug delivery routes to or across fluid interfaces. Here, we provide an overview on fluid interfaces with physiological relevance, namely tear films, interfacial aspects of saliva, lipid droplet digestion and storage in the cell, and the functioning of lung surfactant. We elucidate their structure-function relationship, discuss diseases associated with interfacial composition, and describe therapies and drug delivery approaches targeted at fluid interfaces. STATEMENT OF SIGNIFICANCE: Fluid interfaces are inherent to all living organisms and play a vital role in various physiological processes. Examples are the eye tear film, saliva, lipid digestion & storage in cells, and pulmonary breathing. These fluid interfaces exhibit complex interfacial compositions and structures to meet their specific physiological function. We provide an overview on physiological fluid interfaces with a focus on interfacial phenomena. We elucidate their structure-function relationship, discuss diseases associated with interfacial composition, and describe novel therapies and drug delivery approaches targeted at fluid interfaces. This sets the scene for ocular, oral, or pulmonary surface engineering and drug delivery approaches.

Particle-laden fluid/fluid interfaces: physico-chemical foundations

Particle-laden fluid/fluid interfaces are ubiquitous in academia and industry, which has fostered extensive research efforts trying to disentangle the physico-chemical bases underlying the trapping of particles to fluid/fluid interfaces as well as the properties of the obtained layers. The understanding of such aspects is essential for exploiting the ability of particles on the stabilization of fluid/fluid interface for the fabrication of novel interface-dominated devices, ranging from traditional Pickering emulsions to more advanced reconfigurable devices. This review tries to provide a general perspective of the physico-chemical aspects associated with the stabilization of interfaces by colloidal particles, mainly chemical isotropic spherical colloids. Furthermore, some aspects related to the exploitation of particle-laden fluid/fluid interfaces on the stabilization of emulsions and foams will be also highlighted. It is expected that this review can be used for researchers and technologist as an initial approach to the study of particle-laden fluid layers.

Inhaled aerosols: Their role in COVID-19 transmission, including biophysical interactions in the lungs

The high rate of spreading of COVID-19 is attributed to airborne particles exhaled by infected but often asymptomatic individuals. In this review, the role of aerosols in SARS-CoV-2 coronavirus transmission is discussed from the biophysical perspective. The essential properties of the coronavirus virus transported inside aerosol droplets, their successive inhalation, and size-dependent deposition in the respiratory system are highlighted. The importance of face covers (respirators and masks) in the reduction of aerosol spreading is analyzed. Finally, the discussion of the physicochemical phenomena of the coronavirus entering the surface of lung liquids (bronchial mucus and pulmonary surfactant) is presented with a focus on a possible role of interfacial phenomena in pulmonary alveoli. Information given in this review should be important in understanding the essential biophysical conditions of COVID-19 infection via aerosol route as a prerequisite for effective strategies of respiratory tract protection, and possibly, indications for future treatments of the disease.

Exogenous pulmonary surfactant: A review focused on adjunctive therapy for severe acute respiratory syndrome coronavirus 2 including SP-A and SP-D as added clinical marker

Type I and type II pneumocytes are two forms of epithelial cells found lining the alveoli in the lungs. Type II pneumocytes exclusively secrete 'pulmonary surfactants,' a lipoprotein complex made up of 90% lipids (mainly phospholipids) and 10% surfactant proteins (SP-A, SP-B, SP-C, and SP-D). Respiratory diseases such as influenza, severe acute respiratory syndrome coronavirus infection, and severe acute respiratory syndrome coronavirus 2 infection are reported to preferentially attack type II pneumocytes of the lungs. After viral invasion, consequent viral propagation and destruction of type II pneumocytes causes altered surfactant production, resulting in dyspnea and acute respiratory distress syndrome in patients with coronavirus disease 2019. Exogenous animal-derived or synthetic pulmonary surfactant therapy has already shown immense success in the treatment of neonatal respiratory distress syndrome and has the potential to contribute efficiently toward repair of damaged alveoli and preventing severe acute respiratory syndrome coronavirus 2-associated respiratory failure. Furthermore, early detection of surfactant collectins (SP-A and SP-D) in the circulatory system can be a significant clinical marker for disease prognosis in the near future.

Fluid Interfaces

Fluid interfaces are promising candidates for the design of new functional materials by confining different types of materials, e.g., polymers, surfactants, colloids, or even small molecules, by direct spreading or self-assembly from solutions. The development of such materials requires a deep understanding of the physico-chemical bases underlying the formation of layers at fluid interfaces, as well as the characterization of the structures and properties of such layers. This is of particular importance, because the constraints associated with the assembly of materials at the interface lead to the emergence of equilibrium and dynamic features in the interfacial systems that are far from those found in traditional 3D materials. These new properties are of importance in many scientific and technological fields, such as food science, cosmetics, biology, oil recovery, electronics, drug delivery, detergency, and tissue engineering. Therefore, the understanding of the theoretical and practical aspects involved in the preparation of these interfacial systems is of paramount importance for improving their usage for designing innovative technological solutions.

Interfacial rheology for the assessment of potential health effects of inhaled carbon nanomaterials at variable breathing conditions

Lung surface is the first line of contact between inhaled carbon nanomaterials, CNMs, and the organism, so this is the place where pulmonary health effects begin. The paper analyzes the influence of several CNMs (single- and multi-walled nanotubes with various surface area: 90-1,280 m²/g and aspect ratio: 8-3,750) on the surface-active properties of the lung surfactant, LS, model (Survanta). Effects of CNM concentration (0.1-1 mg/ml) and surface oscillation rate were determined using the oscillating drop method at simulated breathing conditions (2-10 s per cycle, 37 °C). Based on the values of apparent elasticity and viscosity of the interfacial region, new parameters: S_ε and S_μ were proposed to evaluate potential effect of particles on the LS at various breathing rates. Some of tested CNMs (e.g., COOH- functionalized short nanotubes) significantly influenced the surfactant dynamics, while the other had weaker effects even at high particle concentration. Analysis of changes in S_ε and S_μ provides a new way to evaluate of a possible disturbance of the basic functions of LS. The results show that the expected pulmonary effects caused by inhaled CNMs at variable breathing rate depend not only on particle concentration (inhaled dose) but also on their size, structure and surface properties.

Interaction of Particles with Langmuir Monolayers of 1,2-Dipalmitoyl-Sn-Glycero-3-Phosphocholine: A Matter of Chemistry?

Lipid layers are considered among the first protective barriers of the human body against pollutants, e.g., skin, lung surfactant, or tear film. This makes it necessary to explore the physico-chemical bases underlying the interaction of pollutants and lipid layers. This work evaluates using a pool of surface-sensitive techniques, the impact of carbon black and fumed silica particles on the behavior of Langmuir monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). The results show that the incorporation of particles into the lipid monolayers affects the surface pressure–area isotherm of the DPPC, modifying both the phase behavior and the collapse conditions. This is explained considering that particles occupy a part of the area available for lipid organization, which affects the lateral organization of the lipid molecules, and consequently the cohesion interactions within the monolayer. Furthermore, particles incorporation worsens the mechanical performance of lipid layers, which may impact negatively in different processes presenting biological relevance. The modification induced by the particles has been found to be dependent on their specific chemical nature. This work tries to shed light on some of the most fundamental physico-chemical bases governing the interaction of pollutants with lipid layers, which plays an essential role on the design of strategies for preventing the potential health hazards associated with pollution.

Nanoparticle translocation across the lung surfactant film regulated by grafting polymers

Nanoparticle-based pulmonary drug delivery has gained significant attention due to its ease of administration, increased bioavailability, and reduced side effects caused by a high systemic dosage. After being delivered into the deep lung, the inhaled nanoparticles first interact with the lung surfactant lining layer composed of phospholipids and surfactant proteins and then potentially cause the dysfunction of the lung surfactant. Conditioning the surface properties of nanoparticles with grafting polymers to avoid these side effects is of crucial importance to the efficiency and safety of pulmonary drug delivery. Herein, we perform coarse-grained molecular simulations to decipher the involved mechanism responsible for the translocation of the polymer-grafted Au nanoparticles across the lung surfactant film. The simulations illustrate that conditioning of the grafting polymers, including their length, terminal charge, and grafting density, can result in different translocation processes. Based on the energy analysis, we find that these discrepancies in translocation stem from the affinity of the nanoparticles with the lipid tails and heads and their contact with the proteins, which can be tuned by the surface polarity and surface charge of the nanoparticles. We further demonstrate that the interaction between the nanoparticles and the lung surfactant is related to the depletion of the lipids and proteins during translocation, which affects the surface tension of the surfactant film. The change in the surface tension in turn affects the nanoparticle translocation and the collapse of the surfactant film. These results can help understand the adverse effects of the nanoparticles on the lung surfactant film and provide guidance to the design of inhaled nanomedicines for improved permeability and targeting.

Impact of Engineered Carbon Nanodiamonds on the Collapse Mechanism of Model Lung Surfactant Monolayers at the Air-Water Interface

Understanding interactions between inhaled nanoparticles and lung surfactants (LS) present at the air-water interface in the lung, is critical to assessing the toxicity of these nanoparticles. Specifically, in this work, we assess the impact of engineered carbon nanoparticles (ECN) on the ability of healthy LS to undergo reversible collapse, which is essential for proper functioning of LS. Using a Langmuir trough, multiple compression-expansion cycles are performed to assess changes in the surface pressure vs. area isotherms with time and continuous cyclic compression-expansion. Further, theoretical analysis of the isotherms is used to calculate the ability of these lipid systems to retain material during monolayer collapse, due to interactions with ECNs. These results are complemented with fluorescence images of alterations in collapse mechanisms in these monolayer films. Four different model phospholipid systems, that mimic the major compositions of LS, are used in this study. Together, our results show that the ECN does not impact the mechanism of collapse. However, the ability to retain material at the interface during monolayer collapse, as well as re-incorporation of material after a compression-expansion cycle is altered to varying extent by ECNs and depends on the composition of the lipid mixtures.

Influence of Carbon Nanosheets on the Behavior of 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine Langmuir Monolayers

Carbon nanomaterials are widespread in the atmospheric aerosol as a result of the combustion processes and their extensive industrial use. This has raised many question about the potential toxicity associated with the inhalation of such nanoparticles, and its incorporation into the lung surfactant layer. In order to shed light on the main physical bases underlying the incorporation of carbon nanomaterials into lung surfactant layers, this work has studied the interaction at the water/vapor interface of carbon nanosheets (CN) with Langmuir monolayers of 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), with this lipid being the main component of lung surfactant layers and responsible of some of the most relevant features of such film. The incorporation of CN into DPPC Langmuir monolayers modifies the lateral organization of the DPPC at the interface, which is explained on the basis of two different effects: (i) particles occupy part of the interfacial area, and (ii) impoverishment of the lipid composition of the interface due to lipid adsorption onto the CN surface. This results in a worsening of the mechanical performance of the monolayers which may present a negative impact in the physiological performance of lung surfactant. It would be expected that the results obtained here can be useful as a step toward the understanding of the most fundamental physico-chemical bases associated with the effect of inhaled particles in the respiratory cycle.

Colloids at Fluid Interfaces

Over the last two decades, understanding of the attachment of colloids to fluid interfaces has attracted the interest of researchers from different fields. This is explained by considering the ubiquity of colloidal and interfacial systems in nature and technology. However, to date, the control and tuning of the assembly of colloids at fluid interfaces remain a challenge. This review discusses some of the most fundamental aspects governing the organization of colloidal objects at fluid interfaces, paying special attention to spherical particles. This requires a description of different physicochemical aspects, from the driving force involved in the assembly to its thermodynamic description, and from the interactions involved in the assembly to the dynamics and rheological behavior of particle-laden interfaces.