Layer-by-layer (LbL) assembly is a versatile and robust technique for fabricating tailored thin films of diverse composition. Herein we report a new method of covalent coupling, click chemistry, to facilitate the LbL assembly of thin films. Linear film growth was observed using both UV-vis and FTIR spectroscopy, and film thicknesses were determined by ellipsometry and atomic force microscopy. The assembled films are shown to be stable in a wide pH range. This technique offers the potential to enable the synthesis of new types of stable and responsive LbL films from a variety of polymers.

Electrowetting is the phenomenon of contact angle decrease under the influence of an external voltage applied across the solid/liquid interface. Electrowetting offers an interesting possibility to enhance the wettability of hydrophobic materials without altering the chemical composition of the system and thus could be incorporated in various microfluidic devices. Electrowetting is fundamentally an electrocapillary effect occurring on an insulated solid electrode (hence the change of the solid/liquid interfacial tension with voltage follows Lippmann's equation). A limiting contact angle value larger than zero is achieved even at very large external voltages. Saturation precludes full wetting of the substrate and restricts the magnitude of the capillary force variation. Contact angle saturation has been given various interpretations (e.g., charge trapping, air ionization) but appears to reflect a natural thermodynamic limit rather than being simply a defective property. The limiting value of the contact angle is given by the Young equation when the value of the solid/liquid interfacial tension reaches zero. The model is in excellent agreement with our own results and often gives an adequate description of published data. It also suggests that the saturation limit is determined by the material properties of the system and electrowetting at voltages exceeding this threshold is essentially a nonequilibrium process.

Atomic force microscopy reveal pit-like structures typically containing three or four, approximately 150 nm in diameter depressions at the apical plasma membrane in live pancreatic acinar cells. Stimulation of secretion causes these depressions to dilate and return to their resting size following completion of the process. Exposure of acinar cells to cytochalasin B results in decreased depression size and a loss in stimulable secretion. It is hypothesized that depressions are the fusion pores, where membrane-bound secretory vesicles dock and fuse to release vesicular contents. Zymogen granules, the membrane-bound secretory vesicles in exocrine pancreas, contain the starch digesting enzyme, amylase. Using amylase-specific immunogold labeling, localization of amylase at depressions following stimulation of secretion is demonstrated. This study confirms depressions to be the fusion pores in pancreatic acinar cells. High-resolution images of the fusion pore in live pancreatic acinar cells reveal the structure in much greater detail than has previously been observed.

Electrowetting (wetting under the influence of an applied electric field) of three fluoropolymer surfaces (amorphous Teflon, DuPont) by electrolyte solutions was studied with the sessile drop method. The electrowetting curve (contact angle/potential) is analogous to the electrocapillary curve (surface tension/ potential) and may be described by a combination of the Young and Lippmann equations. The influence of the electrical double layer at the polymer/solution interface has been neglected in the past because the overall interfacial capacitance is mainly determined by the capacitance of the insulating polymer layer. We demonstrate that for some surfaces a systematic deviation occurs at positive potentials. This departure from the constant capacitance regime is attributed to double layer effects, namely, the adsorption of hydroxide and halide anions. The pH, ionic strength, and polymer composition can all influence electrowetting behavior.

Annexin A5 (AnxA5) is a potent anticoagulant protein that crystallizes over phospholipid bilayers (PLBs), blocking their availability for coagulation reactions. Antiphospholipid antibodies disrupt AnxA5 binding, thereby accelerating coagulation reactions. This disruption may contribute to thrombosis and miscarriages in the antiphospholipid syndrome (APS). We investigated whether the antimalarial drug, hydroxychloroquine (HCQ), might affect this prothrombotic mechanism. Binding of AnxA5 to PLBs was measured with labeled AnxA5 and also imaged with atomic force microscopy. Immunoglobulin G levels, AnxA5, and plasma coagulation times were measured on cultured human umbilical vein endothelial cells and a syncytialized trophoblast cell line. AnxA5 anticoagulant activities of APS patient plasmas were also determined. HCQ reversed the effect of antiphospholipid antibodies on AnxA5 and restored AnxA5 binding to PLBs, an effect corroborated by atomic force microscopy. Similar reversals of antiphospholipid-induced abnormalities were measured on the surfaces of human umbilical vein endothelial cells and syncytialized trophoblast cell lines, wherein HCQ reduced the binding of antiphospholipid antibodies, increased cell-surface AnxA5 concentrations, and prolonged plasma coagulation to control levels. In addition, HCQ increased the AnxA5 anticoagulant activities of APS patient plasmas. In conclusion, HCQ reversed antiphospholipid-mediated disruptions of AnxA5 on PLBs and cultured cells, and in APS patient plasmas. These results support the concept of novel therapeutic approaches that address specific APS disease mechanisms.