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We have investigated the surface ordering of a synthetic, asymmetric, fan-shaped dendrimer containing a carboxyl core and perfluorinated tails which was obtained by the esterification of the intermediary. X-ray diffraction patterns and transmission electron microscopy (TEM) images show the molecules self-assemble into a hexagonal, cylindrical mesophase. Surface pressure−area isotherms and Brewster angle microscopy measurements show the molecule forms a stable monolayer at the air−water interface with a single phase transition. As a condensed monolayer, the perfluorinated tails are well-packed with hexagonal symmetry with (10) spacing of ~0.5 nm from molecular-scale atomic force microscopy (AFM) images. Such dense molecular-scale packing has not been observed in other dendritic molecules thus far. Compared to the case of conventional dendritic molecules with alkyl tails, these molecules occupy a much smaller molecular area due to the strong microphase separation between the carboxylic core and perfluorinated tails at the air−water interface. After monolayer collapse, the irregular islands with terrace morphology are observed in contrast with conventional alkyl-terminated self-assembled dendritic molecules where irregular islands do not appear. The interfacial and internal structure of every terrace shows planar columnar morphology from AFM and TEM imaging. From these results, we discuss the stability of perfluorinated, self-assembled dendrimers on water, as well as how to generate planar morphology on a hydrophilic surface.

Monolayer properties such as phase behavior, collapse pressure, and surface viscosity are determined by monolayer composition. Learning how to control these properties through simple additives is important to understanding lung surfactant monolayers and to designing optimal replacement surfactants for treatment of disease. The properties of Infasurf, a replacement lung surfactant derived from calf lung lavage organic extract, can be modified in a controlled fashion by adding hexadecanol (HD). Grazing incidence X-ray diffraction shows that the HD preferentially interacts with dipalmitoylphosphatidylcholine (DPPC), the main phospholipid component of Infasurf, in the same way as in binary mixtures of DPPC and HD. HD intercalates between the DPPC chains, which leads to a tighter packing of the two-dimensional lattice and greater stability of the solid phase. This molecular reorganization triggers changes at the macroscopic scale, leading to a greatly increased solid-phase fraction at a given surface pressure and order of magnitude increases in the surface shear viscosity. However, the collapse pressure decreases, and, hence, the minimum surface tension of the film increases.

We engineer novel structures by “stuffing” the aliphatic regions of self-assembled aggregates with hydrophobic homopolymer. These “stuffed” vesicles and multiple emulsions are formed in a one-step process when we rehydrate stuffed films made of amphiphilic block copolymer and hydrophobic homopolymer. Without such homopolymer, this system forms micelles. With homopolymer, vesicles form; varying vesicle membrane thicknesses show that these structures incorporate different amounts of homopolymer. Multiple emulsions, containing more homopolymer than stuffed vesicles, are also fabricated using this single-amphiphile system. The system's incorporation of homopolymer to modify the properties and morphology of the resultant structures is a convenient strategy for preparing self-assembled macromolecular structures with controllable properties.

Encapsulating small vesicles or colloidal particles within a phospholipid bilayer affords multicompartment structures that are interesting for targeted drug delivery, imaging, or separations. Dioleoylphosphatidylserine (DOPS), an anionic lipid, forms cochleate cylinders, tightly wrapped tubes of concentric bilayers, on addition of millimolar Ca²⁺. Complexation of Ca²⁺ by the subsequent addition of ethylenediaminetetraacetic acid (EDTA) results in the unwrapping of the cochleate cylinders of DOPS sheets and reclosure to form micrometer-sized vesicles, which can entrap smaller vesicles in solution. Polystyrene spheres added to the cochleate cylinders before the EDTA unwrapping can also be enclosed.

The effects of environmental tobacco smoke (ETS) on lung surfactant are difficult to determine from analysis of human and animal lung lavage due to large variations in surfactant recovery, a lack of uniformity of smoke exposure, and the difficulties inherent in analyzing milligram quantities of a multicomponent biological material. An alternative is to examine specific components of lung surfactant in a Langmuir trough with a subphase conditioned by exposure to known quantities of ETS. Pressure−area isotherms and fluorescence microscopy measurements reveal that both the minimum surface tension and respreading of model lung surfactant monolayers and the morphology of the condensed phases at high lateral pressures are changed on subphases exposed to ETS. ETS alters the distribution and fraction of crystalline lipid domains in the monolayer, which are correlated with the minimum surface tension and monolayer viscosity in pristine lung surfactant monolayers. The minimum surface tension of the dominant lipid species in lung surfactant monolayers steadily increases with increased ETS exposure, and surfactant respreading on monolayer expansion is inhibited, which may lead to an increased work of breathing and an altered distribution of alveolar fluids.

Developing synthetic lung surfactants to replace animal extracts requires a fundamental understanding of the roles of the various lipids and proteins in native lung surfactant. We used Brewster angle microscopy (BAM), atomic force microscopy (AFM), and Langmuir isotherms to study the influence of palmitoyloleoylphosphatidylglycerol (POPG) in monolayers of dipalmitoylphosphatidylcholine and palmitic acid mixtures with or without dSP-B1-25, a peptide dimer based on the first 25 amino acids of surfactant protein B (SP-B). At surface pressures between 30 and 40 mN/m, only monolayers containing POPG and dSP-B1-25 showed plateaus in the isotherm similar to those in Survanta, a bovine extract replacement lung surfactant that contains native SP-B and SP-C proteins. BAM images show distinct morphological changes in the fluid phase during these plateaus, while AFM images of deposited monolayers show that multilayer structures, which we named “nanosilos”, form in the fluid phase at the plateau. These nanosilos are from 50 to 300 nm in diameter and from 5 to 8 nm in height and are similar to those observed in deposited Survanta monolayers. We propose that POPG and SP-B interact to stabilize the monolayer composition by trapping POPG in three-dimensional surface-associated aggregates at high surface pressures, preventing the irreversible loss of POPG and SP-B to the subphase.

Three methods of evaluating vesicle mean radii and polydispersity, quasi-elastic light scattering (QLS), freeze-fracture electron microscopy (FF-TEM), and cryo-transmission electron microscopy (cryo-TEM), were used to determine the size distributions of spontaneous vesicles made from mixtures of cetyltrimethylammonium tosylate (CTAT) and sodium dodecylbenzene sulfonate (SDBS). While QLS is probably the most commonly used method to size vesicles, it is limited to measures of the mean hydrodynamic radius and an estimate of the polydispersity, both of which are heavily weighted toward the largest structures in the solution. Cryo-TEM can provide the entire size distribution of the outer diameters of spherical vesicles, from which the sum of the Helfrich bilayer elastic parameters, K = κ + κ/2 and the spontaneous curvature radius, R0, can be determined. FF-TEM can provide the number-average mean diameter and polydispersity once the influence of the fracture plane has been factored into the distribution, thereby confirming the cryo-TEM size distribution. For 7:3 wt CTAT/SDBS at 1% total surfactant in water, K = κ + κ/2 = 0.15 ± 0.03 kBT and R0 = 55 nm ± 10 nm. For CTAT/SDBS, w/w, at 2% total surfactant, K = 0.54 kT ± 0.05 kBT and R0 = 36 nm ± 1 nm. We find that surfactant mixing is likely the origin of the low bilayer elasticity in catanionic vesicles. However, the lower value of K in the CTAT-rich sample is likely due to the hydrophobic tosylate counterion increasing the area per headgroup.

We have built a magnetic needle viscometer capable of measuring the surface shear viscosity of Langmuir monolayers at constant surface pressure or molecular area. A Langmuir trough with dual symmetrical compression/expansion barriers is positioned between two electromagnetic coils that create a homogeneous magnetic field gradient. The gradient drives a Teflon-encapsulated magnetic needle floating on the monolayer along the surface to a terminal velocity. A channel created by two glass plates centers the needle and minimizes drift. The ratio of monolayer surface shear viscosity at a given composition, temperature, surface pressure, and so forth to a reference surface shear viscosity is determined by taking the appropriate ratio of the limiting velocities of the magnetic needle for a given applied force. The monolayer viscometer was calibrated using thin films of silicone oil of known viscosity. We demonstrate the utility of the viscometer by showing that the shear viscosity of saturated dipalmitoylphosphatidylcholine is strongly dependent on temperature and surface pressure and correlates with the liquid expanded to liquid condensed phase transition.

Pressure−area isotherms, Brewster angle microscopy, and grazing incidence X-ray diffraction measurements reveal that human lung surfactant protein SP-B1-78 and the dimer of the amino terminus dSP-B1-25 modify the phase behavior of lipid mixtures consisting of dipalmitoylphosphatidylcholine/palmitoyl-oleyl-phosphatidylglycerol/palmitic acid (DPPC/POPG/PA). The addition of SP-B increases the fraction of fluid phase in the liquid-expanded/liquid-condensed two-phase region. Brewster angle microscopy enabled the visualization of a fluid network, which separates the condensed phase domains. This network is stabilized by SP-B adsorption. GIXD measurements show that SP-B also alters the structure of the condensed chain lattice leading to higher tilt and increased area per hydrocarbon chain. The comparison of SP-B1-78 with the shorter peptide dSP-B1-25 exhibits, that the dimer alters the lipid order more drastically. The larger effects found for dSP-B1-25 were explained using a model that assumes a partial incorporation of the peptide into the layer. The specific behavior of the dimer could enhance the activity of the peptide as found in recent animal model studies. This is the first investigation showing a systematic influence of SP-B on the condensed chain lattice of phospholipids, thus verifying that SP-B not only interacts with the expanded phase, but also interactions with the condensed phase lipids have to be taken into account which might be essential for proper peptide function.

Constructing compartments to divide space controllably and spontaneously into subunits at the submicron scale is a significant challenge facing nanotechnology. We have developed a simple method of creating nanocompartments in vitro via the “interdigitated” bilayer phase formed by adding ethanol to a variety of saturated phospholipids. At temperatures below the gel−liquid crystalline transition, Tm, the interdigitated lipid−ethanol sheets are rigid and flat; when the temperature is raised above Tm, the sheets become flexible and close on themselves and the surrounding solution to form closed compartments. During this closure, the sheets can entrap other vesicles, biological macromolecules, or colloidal particles. The result is efficient and spontaneous encapsulation without disruption of even fragile materials to form biomimetic nanoenvironments for possible use in drug delivery, in colloidal stabilization, or as microreactors.

Pressure−area isotherms, Brewster angle microscopy, and grazing incidence X-ray diffraction measurements show that palmitic acid induces systematic changes in the physicochemical parameters and molecular organization of model lung surfactant lipid monolayers. Adding increasing fractions of palmitic acid (PA) to a 77/23 (wt/wt) mixture of dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleyl-phosphatidylglycerol (POPG) increased the solid-phase fraction of the monolayer as shown by pressure−area isotherms and fluorescence and Brewster angle microscopy. Grazing incidence X-ray diffraction showed that the palmitic acid interacted specifically with the DPPC fraction to form a mixed crystalline solid phase with a tilt angle that decreased in proportion to the fraction of palmitic acid. Increasing the PA content is roughly equivalent to increasing the surface pressure or decreasing the temperature of the DPPC/POPG monolayers. These results are important to the rational design of replacement lung surfactants for the treatment of respiratory distress syndrome.

Langmuir monolayers can be characterized at the air−subphase interface with fluorescence microscopy at the micron scale, but must be transferred to solid substrates for higher resolution imaging using atomic force microscopy. To utilize both techniques to characterize the same region of interest or to ensure that the deposition process is artifact-free, we have developed a transfer technique that allows for the continuous optical imaging of surface morphology as the monolayer is transferred from the air−subphase interface to the substrate. The advantages of this deposition technique are that it is simple and inexpensive and can be implemented in almost all Langmuir troughs and that artifacts associated with nonideal transfer can readily be identified. This new transfer technique is ideal for transferring rigid and viscous films that are difficult to deposit using the traditional Langmuir−Blodgett technique. This technique can also be used for transferring monolayers to germanium attenuated total reflection (ATR) crystals for Fourier transform infrared (FTIR)−ATR spectroscopic measurements of protein conformation and lipid orientation while maintaining the desired monolayer morphologies.

This study investigates the influence of weld cavity geometry on metal flow during the extrusion process. The results of physical modeling done with lead billets are presented. A method of weld cavity design that ensures uniform metal flow in extrusion of asymmetric shapes is proposed.