New experiments and models to describe soluble surfactant adsorption above and below the critical micelle concentration.

Hypothesis: Lysopalmitoylphosphatidylcholine (LysoPC) is a soluble single-chain surfactant product of the innate immune system degradation of double-chain phospholipids. LysoPC adsorption to the air-water interface in lung alveoli can be modeled using alveolar-sized bubbles of constant surface area in a capillary pressure microtensiometer to show that adsorption is diffusion limited both below and above the critical micelle concentration (CMC). Above the CMC, a local equilibrium model is proposed in which depletion of the local monomer concentration drives dissociation of micelles in a region near the bubble surface.

Evolution of interfacial mechanics of lung surfactant mimics progression of acute respiratory distress syndrome.

How acute respiratory distress syndrome progresses from underlying disease or trauma is poorly understood, and there are no generally accepted treatments resulting in a 40% mortality rate. However, during the inflammation that accompanies this disease, the phospholipase A concentration increases in the alveolar fluids leading to the hydrolysis of bacterial, viral, and lung surfactant phospholipids into soluble lysolipids. We show that if the lysolipid concentration in the subphase reaches or exceeds its critical micelle concentration, the surface tension, γ, of dipalmitoyl phosphatidylcholine (DPPC) or Curosurf monolayers increases and the dilatational modulus, [Formula: see text], decreases to that of a pure lysolipid interface.

Reply to the 'Comment on "Bilayer aggregate microstructure determines viscoelasticity of lung surfactant suspensions"' by J.-F. Berret, DOI: 10.1039/d2sm00653g.

In their comment, Berret suggests that Curosurf, one of three clinical lung surfactant aqueous suspensions examined in the , 2021, , 5170-51820 is a Newtonian liquid rather than a shear-thinning soft solid with a small, but measurable yield stress. We postulate that these discrepancies may be due to the size of the magnetic wire measurement probe used in their paper (Thai , , 2019, , 337-345) the diameter of which is similar in size to the Curosurf bilayer agregates (1-10 μm). The cone and plate rheometer used by Ciutara and Zasadzinski measures averaged effects over the entire macroscopic sample.

Microtensiometer for Confocal Microscopy Visualization of Dynamic Interfaces.

Adsorption of surface-active molecules to fluid-fluid interfaces is ubiquitous in nature. Characterizing these interfaces requires measuring surfactant adsorption rates, evaluating equilibrium surface tensions as a function of bulk surfactant concentration, and relating how surface tension changes with changes in the interfacial area following equilibration. Simultaneous visualization of the interface using fluorescence imaging with a high-speed confocal microscope allows the direct evaluation of structure-function relationships.

Dilatational and shear rheology of soluble and insoluble monolayers with a Langmuir trough.

Hypothesis: The surface dilatational and shear moduli of surfactant and protein interfacial layers can be derived from surface pressures measured with a Wilhelmy plate parallel, ΔΠ and perpendicular ΔΠ to the barriers in a Langmuir trough.

Experimental: Applying area oscillations, A+ ΔAe, in a rectangular Langmuir trough induces changes in surface pressure, ΔΠ and ΔΠ for monolayers of soluble palmitoyl-lysophosphatidylcholine (LysoPC), insoluble dipalmitoylphosphatidylcholine (DPPC), and the protein β-lactoglobulin to evaluate E+G=AΔΠΔA and E-G=AΔΠΔA. G was independently measured with a double-wall ring apparatus (DWR) and E by area oscillations of hemispherical bubbles in a capillary pressure microtensiometer (CPM) and the results were compared to the trough measurements.

Probing Neuropeptide Volume Transmission In Vivo by Simultaneous Near-Infrared Light-Triggered Release and Optical Sensing.

Neuropeptides are abundant signaling molecules in the central nervous system. Yet remarkably little is known about their spatiotemporal spread and biological activity. Here, we developed an integrated optical approach using Plasmonic nAnovesicles and cell-based neurotransmitter fluorescent engineered reporter (CNiFER), or PACE, to probe neuropeptide signaling in the mouse neocortex.

Liposome-Tethered Gold Nanoparticles Triggered by Pulsed NIR Light for Rapid Liposome Contents Release and Endosome Escape.

Remote triggering of contents release with micron spatial and sub-second temporal resolution has been a long-time goal of medical and technical applications of liposomes. Liposomes can sequester a variety of bioactive water-soluble ions, ligands and enzymes, and oligonucleotides. The bilayer that separates the liposome interior from the exterior solution provides a physical barrier to contents release and degradation.

Spontaneous evolution of equilibrium morphology in phospholipid-cholesterol monolayers.

Competition between intradomain electrostatic repulsions and interdomain line tension leads to domain shape transitions in phase-separating lipid monolayers. The question remains if these morphologies are energy minima or are kinetically trapped metastable states. We show the reversible evolution of uniform width stripe domains from polydisperse semicircular domains in monolayers of dipalmitoylphosphatidylcholine (DPPC), hexadecanol (HD) or palmitic acid (PA), and dihydrocholesterol (DChol).

Bilayer aggregate microstructure determines viscoelasticity of lung surfactant suspensions.

Neonatal respiratory distress syndrome (NRDS) is treated by intratracheal delivery of suspensions of animal-derived lung surfactant in saline. Lung surfactants are extracted via organic solvents from animal lung lavage, followed by solvent removal and surfactant re-hydration to form multi-bilayer particles suspended in saline. Following intra-tracheal administration, the surfactant suspension spreads throughout the lungs by surface tension gradient induced flow; the spreading rate is limited by suspension viscoelasticity.

Dilatational rheology of water-in-diesel fuel interfaces: effect of surfactant concentration and bulk-to-interface exchange.

Micrometer-sized water droplets dispersed in diesel fuel are stabilized by the fuel's surface-active additives, such as mono-olein and poly(isobutylene)succinimide (PIBSI), making the droplets challenging for coalescing filters to separate. Dynamic material properties found from interfacial rheology are known to influence the behavior of microscale droplets in coalescing filters. In this work, we study the interfacial dilatational properties of water-in-fuel interfaces laden with mono-olein and PIBSI, with a fuel phase of clay-treated ultra-low sulphur diesel (CT ULSD).

Dense nanolipid fluid dispersions comprising ibuprofen: Single step extrusion process and drug properties.

Dense nanolipid fluid (DNLF) dispersions are highly concentrated aqueous dispersions of lipid nanocarriers (LNCs) with more than 10 lipid particles per cubic centimeter. Descriptions of dense nanolipid fluid dispersions in the scientific literature are rare, and they have not been used to encapsulate drugs. In this paper we describe the synthesis of DNLF dispersions comprising ibuprofen using a recently described twin-screw extrusion process.

Inflammation product effects on dilatational mechanics can trigger the Laplace instability and acute respiratory distress syndrome.

In the lungs, the Laplace pressure, ΔP = 2γ/R, would be higher in smaller alveoli than larger alveoli unless the surface tension, γ decreases with alveolar interfacial area, A, such that 2ε > γ in which ε = A(dγ/dA) is the dilatational modulus. In Acute Respiratory Distress Syndrome (ARDS), lipase activity due to the immune response to an underlying trauma or disease causes single chain lysolipid concentrations to increase in the alveolar fluids via hydrolysis of double-chain phospholpids in bacterial, viral, and normal cell membranes. Increasing lysolipid concentrations decrease the dilatational modulus dramatically at breathing frequencies if the soluble lysolipid has sufficient time to diffuse off the interface, causing 2ε < γ, thereby potentially inducing the "Laplace Instability", in which larger alveoli have a lower internal pressure than smaller alveoli.

Near-Infrared Light Triggered-Release in Deep Brain Regions Using Ultra-photosensitive Nanovesicles.

Remote and minimally-invasive modulation of biological systems with light has transformed modern biology and neuroscience. However, light absorption and scattering significantly prevents penetration to deep brain regions. Herein, we describe the use of gold-coated mechanoresponsive nanovesicles, which consist of liposomes made from the artificial phospholipid Rad-PC-Rad as a tool for the delivery of bioactive molecules into brain tissue.

Near Infrared-Triggered Liposome Cages for Rapid, Localized Small Molecule Delivery.

Photolabile chelating cages or protecting groups need complex chemical syntheses and require UV, visible, or two-photon NIR light to trigger release. Different cages have different solubilities, reaction rates,  and energies required for triggering. Here we show that liposomes containing calcium, adenosine triphosphate, or carboxyfluorescein are tethered to plasmon-resonant hollow gold nanoshells (HGN) tuned to absorb light from 650-950 nm.

Interfacial rheology and direct imaging reveal domain-templated network formation in phospholipid monolayers penetrated by fibrinogen.

Phospholipids are found throughout the natural world, including the lung surfactant (LS) layer that reduces pulmonary surface tension and enables breathing. Fibrinogen, a protein involved in the blood clotting process, is implicated in LS inactivation and the progression of disorders such as acute respiratory distress syndrome. However, the interaction between fibrinogen and LS at the air-water interface is poorly understood.

Comparison of Line Tension Measurement Methods for Lipid Monolayers at Liquid-Liquid Coexistence.

Several methods of measuring the line tension between phase-separated liquid-ordered-liquid -disordered domains in phospholipid-cholesterol systems have been proposed. These experimental techniques are typically internally self-consistent, but the measured line tension values vary widely among these techniques. To date, no measurement of line tension has utilized multiple experimental techniques to look at the same monolayer system.

Perfluoroheptane-Loaded Hollow Gold Nanoshells Reduce Nanobubble Threshold Flux.

The threshold flux for nanobubble formation and liposome rupture is reduced by 50-60% by adding a liquid mixture of tetradecanol and perfluoroheptane to the interior cavity of 40 nm diameter hollow gold nanoshells (HGN), and allowing the tetradecanol to solidify to hold the perfluoroheptane in place. On absorption of picosecond pulses of near-infrared light, the perfluoroheptane vaporizes to initiate cavitation-like nanobubbles as the HGN temperature increases. The lower spinodal temperature and heat capacity of perfluoroheptane relative to water causes the threshold flux for nanobubble formation to decrease.

Light-Triggered Genome Editing: Cre Recombinase Mediated Gene Editing with Near-Infrared Light.

A light-activated genome editing platform based on the release of enzymes from a plasmonic nanoparticle carrier when exposed to biocompatible near-infrared light pulses is described. The platform relies on the robust affinity of polyhistidine tags to nitrilotriacetic acid in the presence of copper which is attached to double-stranded nucleic acids self-assembled on the gold nanoparticle surface. A protein fusion of the Cre recombinase containing a TAT internalization peptide sequence to achieve endosomal localization is also employed.

Nonlinear chiral rheology of phospholipid monolayers.

Microbutton rheometry reveals that the chiral morphology of dipalmitoylphosphatidylcholine (DPPC) monolayers imparts a chiral nonlinear rheological response. The nonlinear elastic modulus and yield stress of DPPC monolayers are greater when sheared clockwise (C), against the natural winding direction of DPPC domains, than counter-clockwise (CC). Under strong CC shear strains, domains deform plastically; by contrast, domains appear to fracture under strong C shearing.

Optimizing the NIR Fluence Threshold for Nanobubble Generation by Controlled Synthesis of 10 - 40 nm Hollow Gold Nanoshells.

The laser fluence to trigger nanobubbles around hollow gold nanoshells (HGN) with near infrared light was examined through systematic modification of HGN size, localized surface plasmon resonance (LSPR), HGN concentration, and surface coverage. Improved temperature control during silver template synthesis provided monodisperse, silver templates as small as 9 nm. 10 nm HGN with < 2 nm shell thickness were prepared from these templates with a range of surface plasmon resonances from 600 - 900 nm.

Interfacial curvature effects on the monolayer morphology and dynamics of a clinical lung surfactant.

The morphology of surfactant monolayers is typically studied on the planar surface of a Langmuir trough, even though most physiological interfaces are curved at the micrometer scale. Here, we show that, as the radius of a clinical lung surfactant monolayer-covered bubble decreases to ∼100 µm, the monolayer morphology changes from dispersed circular liquid-condensed (LC) domains in a continuous liquid-expanded (LE) matrix to a continuous LC linear mesh separating discontinuous LE domains. The curvature-associated morphological transition cannot be readily explained by current liquid crystal theories based on isotropic domains.

Light-activated RNA interference in human embryonic stem cells.

We describe a near infrared (NIR) light-activated gene silencing method in undifferentiated human embryonic stem cell (hESC) using a plasmonic hollow gold nanoshell (HGN) as the siRNA carrier. Our modular biotin-streptavidin coupling strategy enables positively charged TAT-peptide to coat oligonucleotides-saturated nanoparticles as a stable colloid formation. TAT-peptide coated nanoparticles with dense siRNA loading show efficient penetration into a wide variety of hESC cell lines.

Monitoring phases and phase transitions in phosphatidylethanolamine monolayers using active interfacial microrheology.

Active interfacial microrheology is a sensitive tool to detect phase transitions and headgroup order in phospholipid monolayers. The re-orientation of a magnetic nickel nanorod is used to explore changes in the surface rheology of 1,2-dilauroyl-sn-glycero-3-phosphoethanolamine (DLPE) and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE), which differ by two CH2 groups in their alkyl chains. Phosphatidylethanolamines such as DLPE and DMPE are a major component of cell membranes in bacteria and in the nervous system.

Inside-outside self-assembly of light-activated fast-release liposomes.

Building additional functionality into both the membrane and the internal compartments of biocompatible liposomes by self-assembly can provide ways of enhancing colloidal stability and spatial and temporal control of contents release. An interdigitation-fusion process is used to encapsulate near infrared light absorbing copper sulfide nanoparticles in the interior compartments of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol liposomes. Once formed, the liposome membrane is modified to include lysolipids and polyethylene glycol lipids by partitioning from lysolipid and PEG-lipid micelles in solution.