Adsorption of lipid liquid crystalline nanoparticles: effects of particle composition, internal structure, and phase behavior

Controlling the interfacial behavior and properties of lipid liquid crystalline nanoparticles (LCNPs) at surfaces is essential for their application for preparing functional surface coatings as well as understanding some aspects of their properties as drug delivery vehicles. Here we have studied a LCNP system formed by mixing soy phosphatidylcholine (SPC), forming liquid crystalline lamellar structures in excess water, and glycerol dioleate (GDO), forming reversed structures, dispersed into nanoparticle with the surfactant polysorbate 80 (P80) as stabilizer. LCNP particle properties were controlled by using different ratios of the lipid building blocks as well as different concentrations of the surfactant P80. The LCNP size, internal structure, morphology, and charge were characterized by dynamic light scattering (DLS), synchrotron small-ange X-ray scattering (SAXS), cryo-transmission electron microscopy (cryo-TEM), and zeta potential measurements, respectively. With increasing SPC to GDO ratio in the interval from 35:65 to 60:40, the bulk lipid phase structure goes from reversed cubic micellar phase with Fd3m space group to reversed hexagonal phase. Adding P80 results in a successive shift toward more disorganized lamellar type of structures. This is also seen from cryo-TEM images for the LCNPs, where higher P80 ratios results in more extended lamellar layers surrounding the inner, more dense, lipid-rich particle core with nonlamellar structure. When put in contact with a solid silica surface, the LCNPs adsorb to form multilayer structures with a surface excess and thickness values that increase strongly with the content of P80 and decreases with increasing SPC:GDO ratio. This is reflected in both the adsorption rate and steady-state values, indicating that the driving force for adsorption is largely governed by attractive interactions between poly(ethylene oxide) (PEO) units of the P80 stabilizer and the silica surface. On cationic surface, i.e., silica modified with 3-aminopropltriethoxysilane (APTES), the slightly negatively charged LCNPs give rise to a very significant adsorption, which is relatively independent of LCNP composition. Finally, the dynamic thickness measurements indicate that direct adsorption of intact particles occurred on the cationic surface, while a slow buildup of the layer thickness with time is seen for the weakly interacting systems.     

Predicting Resistivity and Permeability of Porous Media Using Minkowski Functionals

Transport in Porous Media - Permeability and formation factor are important properties of a porous medium that only depend on pore space geometry, and it has been proposed that these transport...     

PIV measurements in a liquid–liquid system at volume percentages up to 10% dispersed phase

In this study the effect of the volume percentage dispersed phase on the flow structure in an immiscible liquid–liquid system is investigated. A model system, consisting of two refraction index matched liquids, is presented along with velocity measurements of the continuous phase utilising the particle image velocimetry technique. Velocity fields at three locations have been measured inside a baffled cylindrical tank, stirred with a six-bladed Rushton turbine. The experiments show that this technique is applicable for volume fractions of up to 10% of dispersed phase. The magnitudes of velocity and turbulence are clearly affected by the level of the dispersed volume fraction.     

In-situ ethanol probe based on sample dilution in a double-membrane system

An in-situ probe suitable for monitoring ethanol in fermentors or other bioreactors is described. It is constructed with an ethanol-permeable double membrane covering a solid-state tin(IV) oxide sensor for gas detection. A stream of nitrogen is passed between the two membranes in order to dilute the ethanol vapour from the fermentor that has passed through the first membrane, before it reaches the second membrane covering the detector. A 100-fold dilution was obtained at a flow rate of 30 ml min^?1 of the diluent gas. The delay time was less than 5 min to obtain 80% of maximum response.     

Composition of supported model membranes determined by neutron reflection

We have investigated the formation of supported bilayers by coadsorption of dipalmitoyl phosphatidylcholine (DPPC) with the nonionic surfactant beta-D-dodecyl maltoside. The adsorption of mixed phospholipid-surfactant micelles on hydrophilic silica surfaces at 25 degrees C was followed as a function of bulk concentration by neutron reflection. Using chain-deuterated d(25)-beta-D-dodecyl maltoside and d(62)-DPPC, we demonstrate that it is possible to determine the composition of the bilayers at each stage of a sequential dilution process, which enriches the adsorbed layer in phospholipid and leads to complete elimination of the surfactant. The final supported bilayers have thicknesses of 51 +/- 3 A and are stable to heating to 37 degrees C once all surfactant has been removed, and the structures agree well with other published data on DPPC supported bilayers. The coadsorption of cholesterol in a DPPC-surfactant mixture was also achieved, and the location and volume fraction of cholesterol in the DPPC bilayer was determined. Cholesterol is located in a 18 +/- 1 A thick layer below the lipid headgroup region and leads to an increased bilayer thickness of 58 +/- 2 A at 26 mol % of cholesterol.     

Phosphoryl choline introduces dual activity in biomimetic ionomers

Dual activity of phosphoryl choline (PC) functional poly(trimethylene carbonate) (PTMC) was found which induces the zwitterionic biomimetic PC group to form physical cross-links with ionomers in the bulk, and at the same time enrich at the surface of cast films. The formation of zwitterionic domains from a bifunctional PC-PTMC-PC (ionomer) provided firm films with a low elastic modulus in contrast to the tacky PTMC starting material (Mn approximately 3900 g/mol) with poor mechanical performance. In addition, the ionomer possessed improved hemocompatible properties that was explained by the enrichment of PC at the surface, suggesting a way to tailor the mechanical performance of biodegradable PTMC-based ionomers while providing its bioactivity. Tailored elasticity while maintaining hemocompatibility of a biodegradable ionomer should be of particular interest for a variety of in vivo applications.     

Density functional theory studies on the mechanisms of regioselective allylic and cis-vinylic deprotonation of allyl amides and allylamines

A density functional theory (B3LYP/6-31+G) study was undertaken in an effort to learn more about the mechanisms controlling the regioselective deprotonations of the synthetically versatile N-lithio-N-(tert-butyl)allylamide 1 and N-lithio-N-(trimethylsilyl)allylamine 2 compounds. The calculations suggest that deprotonation of 1 occurs exclusively at the allylic position. This agrees with experimental results. The calculations also suggest that deprotonation of allylamine 2 exclusively at the cis-vinylic position is due to kinetic control.     

Bivalent cholesterol-based coupling of oligonucletides to lipid membrane assemblies

By mimicking Nature's way of utilizing multivalent interactions, we introduce in the present work a novel method to improve the strength of cholesterol-based DNA coupling to lipid membranes. The bivalent coupling of DNA was accomplished by hybridization between a 15-mer DNA and a 30-mer DNA, being modified with cholesterol in the 3' and 5' end, respectively. Compared with DNA modified with one cholesterol moiety only, the binding strength to lipid membranes appears to be significantly stronger and even irreversible over the time scale investigated ( approximately 1 hr). First, this means that the bivalent coupling can be used to precisely control the number of DNA per lipid-membrane area. Second, the strong coupling is demonstrated to facilitate DNA-hybridization kinetics studies. Third, exchange of DNA between differently DNA-modified vesicles was demonstrated to be significantly reduced. The latter condition was verified via site-selective and sequence-specific sorting of differently DNA-modified lipid vesicles on a low-density cDNA array. This means of spatially control the location of different types of lipid vesicles is likely to find important applications in relation to the rapid progress currently made in the protein chip technology and the emerging need for efficient ways to develop membrane protein arrays.