Interaction force-distance profiles between substrate-supported membranes composed of equimolar ternary mixtures of unsaturated phosphotidylcholine (PC) lipid, saturated PC lipid, and cholesterol were determined using the surface force apparatus. Both double and single unsaturated PC lipids were studied. In all cases, the membranes were slightly negatively charged, resulting in a weak, long-range electrostatic repulsion. Corroborative atomic force microscopy, zeta potential, and fluorescence microscopy measurements were used to establish that a small level of charged lipid impurities (∼1/400 lipid molecules) were responsible for the repulsive electrostatic interaction between the membranes. At contact, the membranes were adhesive. The magnitude of the adhesion was greater than the van der Waals interaction between pure PC membranes without cholesterol. The enhanced adhesion was primarily attributed to hydrophobic attraction due to the presence of nanoscopic membrane defects which exposed the underlying membrane leaflet. The interaction force-distance profiles also demonstrated that the nanoscopic defects enabled membrane restructuring in the contact region.

Dendrimers have shown great potential in drug delivery because of their enhancement of drug solubility in aqueous media, leading to an increase in in vivo circulation and efficacy to targets. The structure of drug-dendrimer complexes however, is not well-known owing to the difficulties associated with visualizing individual drug molecules attached to dendrimers. Scanning tunneling microscopy (STM) enables visualization of dendrimer intramolecular structures using our approach of metal ion tagging. This work extends the approach to reveal the hierarchical structure of indomethacin-loaded poly(amidoamine) hydroxyl-terminated dendrimers. STM imaging provides structural information such as their height, lateral dimensions, and volume. High-resolution STM images enable the identification and count of individual indomethacin molecules bound to the anterior of dendrimers. Removal of drug molecules by the STM tip allows the calculation of individual drug-dendrimer binding energy, which is consistent with 1-3 hydrogen bonds. These investigations provide new insight into the hierarchical structure and nature of indomethacin-dendrimer interactions and deepen our understanding of the stability and pharmacokinetic behavior of dendrimer-based drug delivery vehicles.

A one-step pattern transfer process was developed to produce arrays of hierarchical micro- and nanostructures of organosilanes. The method is based on vapor deposition through polydimethylsiloxane stamps coated with close-packed nanospheres and, as such, creating hierarchical microscale and nanoscale templates, respectively. This method offers intrinsic advantages of simplicity to be used in any laboratory environment and high throughput, that is, a 1 in. wafer can be covered in 6 h. In addition, the size and geometry can be controlled via knowledge of microcontact printing and particle lithography. Finally, the approach is generic in nature and may be utilized to produce designed functionalities.

Oligothiophene thin films have been considered as promising material for molecular electronics due to their desirable electronic properties and high structural stability under ambient conditions. To ensure performance in devices the functional structures, such as individual ordered domains, must be stable under practical and operational conditions or environments including exposure to various media. This work investigates the structure of oligothiophene Langmuir− Blodgett (LB) films upon exposure to liquid media such as water, ethanol (EtOH), and mixed tetrahydrofuran (THF)/EtOH solutions. The LB films form islands ranging from 500 nm up to 1 μm consisting of densely packed oligothiophene molecules. These islands are surrounded by bare substrate and loosely packed adsorbates. In situ and time-dependent AFM images were acquired to reveal the structural evolution, from which degradation pathways and kinetics are extracted. Degradation of these LB films initiates and propagates from intraisland defect sites, such as cracks and pin holes, whereas the edges of islands remain intact on the surface. The observations appear to be in contrast to the known degradation mechanism among self-assembled monolayers, such as alkanethiols on gold, which initiates and progresses at domain boundaries. Rationale for the observed degradation processes will also be discussed.