Deciphering and Controlling Structural and Functional Parameters of the Shells in Vesicle-Templated Polymer Nanocapsules.

Vesicle-templated nanocapsules are prepared by polymerization of hydrophobic acrylic monomers and cross-linkers in the hydrophobic interior of self-assembled bilayers. Understanding the mechanism of capsule formation and the influence of synthetic parameters on the structural features and functional performance of nanocapsules is critical for the rational design of functional nanodevices, an emerging trend of application of the nanocapsule platform. This study investigated the relationship between basic parameters of the formulation and synthesis of nanocapsules and structural and functional characteristics of the resulting structures. Variations in the monomer/surfactant ratio, temperature of polymerization, and the molar fraction of the free-radical initiators were investigated with a multipronged approach, including shell thickness measurements using small-angle neutron scattering, evaluation of the structural integrity of nanocapsules with scanning electron microscopy, and determination of the retention of entrapped molecules using absorbance and fluorescence spectroscopy. Surprisingly, the thickness of the shells did not correlate with the monomer/surfactant ratio, supporting the hypothesis of substantial stabilization of the surfactant bilayer with loaded monomers. Decreasing the temperature of polymerization had no effect on the spherical structure of nanocapsules but resulted in progressively lower retention of entrapped molecules, suggesting that a spherical skeleton of nanocapsule forms rapidly, followed by filling the gaps to create the structure without pinholes. Lower content of initiators resulted in slower reactions, outlining the baseline conditions for practical synthetic protocols. Taken together, these findings provide insights into the formation of nanocapsules and offer methods for controlling the properties of nanocapsules in viable synthetic methods.

Childhood body mass index is associated with early dental development and eruption in a longitudinal sample from the Iowa Facial Growth Study.

INTRODUCTION: Children with high body mass index (BMI) values have been demonstrated to have precocious dental development. Research has largely focused on cross-sectional data sets, leaving an incomplete understanding of the longitudinal relationship between BMI and dental maturation. METHODS: We used a pure longitudinal growth series to examine the relationship between dental development and childhood BMI. Periapical radiographs from 77 children from the Iowa Growth Study were used to estimate dental development for those with high BMI values. RESULTS: We confirmed prior studies in finding that children with higher BMI values were more likely to have advanced dental development for their ages (P <0.001). BMI at age 4 years was predictive for the timing of dental development at age 12 (P = 0.052). The precocity of the rate of dental development accelerated across growth. Overall dental development scores also correlated with the age of dental eruption for the mandibular canines and first premolars (P <0.001). CONCLUSIONS: High BMI values at young ages predict advanced dental development at later times, suggesting a long-term effect of BMI on dental maturation and implying the need for earlier orthodontic interventions in obese children. These results corroborate those of previous studies, building further evidence that relatively early dental eruption is another consequence of childhood obesity.

Unraveling the Single-Nanometer Thickness of Shells of Vesicle-Templated Polymer Nanocapsules.

Vesicle-templated nanocapsules have emerged as a viable platform for diverse applications. Shell thickness is a critical structural parameter of nanocapsules, where the shell plays a crucial role providing mechanical stability and control of permeability. Here we used small-angle neutron scattering (SANS) to determine the thickness of freestanding and surfactant-stabilized nanocapsules. Despite being at the edge of detectability, we were able to show the polymer shell thickness to be typically 1.0 ± 0.1 nm, which places vesicle-templated nanocapsules among the thinnest materials ever created. The extreme thinness of the shells has implications for several areas: mass-transport through nanopores is relatively unimpeded; pore-forming molecules are not limited to those spanning the entire bilayer; the internal volume of the capsules is maximized; and insight has been gained on how polymerization occurs in the confined geometry of a bilayer scaffold, being predominantly located at the phase-separated layer of monomers and cross-linkers between the surfactant leaflets.

Tuning Optical Properties of Encapsulated Clusters of Gold Nanoparticles through Stimuli-Triggered Controlled Aggregation.

Gold nanoparticles entrapped in the hollow polymer nanocapsules undergo pH-mediated controlled aggregation. Encapsulated clusters of nanoparticles show absorbance at higher wavelengths compared with individual nanoparticles. The size of the aggregates is controlled by the number of nanoparticles entrapped in individual nanocapsules. Such controlled aggregation may permit small biocompatible nanoparticles exhibit desirable properties for biomedical applications that are typically characteristic of large nanoparticles.

Facile directed assembly of hollow polymer nanocapsules within spontaneously formed catanionic surfactant vesicles.

Surfactant vesicles containing monomers in the interior of the bilayer were used to template hollow polymer nanocapsules. This study investigated the formation of surfactant/monomer assemblies by two loading methods, concurrent loading and diffusion loading. The assembly process and the resulting aggregates were investigated with dynamic light scattering, small angle neutron scattering, and small-angle X-ray scattering. Acrylic monomers formed vesicles with a mixture of cationic and anionic surfactants in a broad range of surfactant ratios. Regions with predominant formation of vesicles were broader for compositions containing acrylic monomers compared with blank surfactants. This observation supports the stabilization of the vesicular structure by acrylic monomers. Diffusion loading produced monomer-loaded vesicles unless vesicles were composed from surfactants at the ratios close to the boundary of a vesicular phase region on a phase diagram. Both concurrent-loaded and diffusion-loaded surfactant/monomer vesicles produced hollow polymer nanocapsules upon the polymerization of monomers in the bilayer followed by removal of surfactant scaffolds.

Synergistic self-assembly of scaffolds and building blocks for directed synthesis of organic nanomaterials.

Surfactants and hydrophobic monomers spontaneously assemble into vesicles containing monomers within the bilayer. The joint action of monomers and surfactants is essential in this synergistic self-assembly. Polymerization in the bilayer formed hollow polymer nanocapsules.

Using in situ X-ray reflectivity to study protein adsorption on hydrophilic and hydrophobic surfaces: benefits and limitations.

We have employed in situ X-ray reflectivity (IXRR) to study the adsorption of a variety of proteins (lysozyme, cytochrome c, myoglobin, hemoglobin, serum albumin, and immunoglobulin G) on model hydrophilic (silicon oxide) and hydrophobic surfaces (octadecyltrichlorosilane self-assembled monolayers), evaluating this recently developed technique for its applicability in the area of biomolecular studies. We report herein the highest resolution depiction of adsorbed protein films, greatly improving on the precision of previous neutron reflectivity (NR) results and previous IXRR studies. We were able to perform complete scans in 5 min or less with the maximum momentum transfer of at least 0.52 Å(-1), allowing for some time-resolved information about the evolution of the protein film structure. The three smallest proteins (lysozyme, cytochrome c, and myoglobin) were seen to deposit as fully hydrated, nondenatured molecules onto hydrophilic surfaces, with indications of particular preferential orientations. Time evolution was observed for both lysozyme and myoglobin films. The larger proteins were not observed to deposit on the hydrophilic substrates, perhaps because of contrast limitations. On hydrophobic surfaces, all proteins were seen to denature extensively in a qualitatively similar way but with a rough trend that the larger proteins resulted in lower coverage. We have generated high-resolution electron density profiles of these denatured films, including capturing the growth of a lysozyme film. Because the solution interface of these denatured films is diffuse, IXRR cannot unambiguously determine the film extent and coverage, a drawback compared to NR. X-ray radiation damage was systematically evaluated, including the controlled exposure of protein films to high-intensity X-rays and exposure of the hydrophobic surface to X-rays before adsorption. Our analysis showed that standard measuring procedures used for XRR studies may lead to altered protein films; therefore, we used modified procedures to limit the influence of X-ray damage.

Scattering studies of hydrophobic monomers in liposomal bilayers: an expanding shell model of monomer distribution.

Hydrophobic monomers partially phase separate from saturated lipids when loaded into lipid bilayers in amounts exceeding a 1:1 monomer/lipid molar ratio. This conclusion is based on the agreement between two independent methods of examining the structure of monomer-loaded bilayers. Complete phase separation of monomers from lipids would result in an increase in bilayer thickness and a slight increase in the diameter of liposomes. A homogeneous distribution of monomers within the bilayer would not change the bilayer thickness and would lead to an increase in the liposome diameter. The increase in bilayer thickness, measured by the combination of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS), was approximately half of what was predicted for complete phase separation. The increase in liposome diameter, measured by dynamic light scattering (DLS), was intermediate between values predicted for a homogeneous distribution and complete phase separation. Combined SANS, SAXS, and DLS data suggest that at a 1.2 monomer/lipid ratio approximately half of the monomers are located in an interstitial layer sandwiched between lipid sheets. These results expand our understanding of using self-assembled bilayers as scaffolds for the directed covalent assembly of organic nanomaterials. In particular, the partial phase separation of monomers from lipids corroborates the successful creation of nanothin polymer materials with uniform imprinted nanopores. Pore-forming templates do not need to span the lipid bilayer to create a pore in the bilayer-templated films.

Self-Limiting Robust Surface-Grafted Organic Nanofilms.

Robust surface-bound insulating polymer films with controlled thickness in <5 nm range are important for technological advances in diverse disciplines such as electrochemical sensors, molecular electronics, separations and anti-corrosive coatings. Creating these films by simple methods from readily available materials has been a significant challenge. Here we report a newly synthesized molecule combining a styrene and thiol moieties, joined via a short linker, that binds to the gold surface, polymerizes and crosslinks polymer chains to form robust films with uniform and controlled thickness and complete surface coverage. Additional layers can be deposited. These films that bridge two- and three-dimensional materials show excellent stability and insulating properties.

Time-resolved loading of monomers into bilayers with different curvature.

Directed assembly of nanostructures within temporary and recyclable self-assembled scaffolds is emerging as an attractive method for the synthesis of nanomaterials with programmed properties. Understanding interactions of building blocks with amphiphilic scaffolds is critical for rational design of new nanostructures and nanodevices. Here we examine loading of hydrophobic monomers into bilayers with different curvatures. Time-resolved loading was studied by high performance liquid chromatography and dynamic light scattering. Despite differences in initial bilayer geometry, loading rates and maximum bilayer capacity are the same for liposomes with radii ranging from 25 to 100 nm. When using divinylbenzene (DVB) and dimyristoylphosphatidylcholine (DMPC), monomer/lipid loading ratio of 1.2 was achieved within 12 h. While accommodation of a large amount of monomers is likely to be accompanied with significant changes in bilayer structure, all liposomes in this study including those with smallest size and higher bilayer curvature retain encapsulated content and show no evidence of fusion during monomer loading. These results contribute to our understanding of interactions between hydrophobic molecules and lipid bilayers and expand the scope of the directed assembly method.

Controlled loading of building blocks into temporary self-assembled scaffolds for directed assembly of organic nanostructures.

Using temporary self-assembled scaffolds to preorganize building blocks is a potentially powerful method for the synthesis of organic nanostructures with programmed shapes. We examined the underlying phenomena governing the loading of hydrophobic monomers into lipid bilayer interior and demonstrated successful control of the amount and ratio of loaded monomers. When excess styrene derivatives or acrylates were added to the aqueous solution of unilamellar liposomes made from saturated phospholipids, most loading occurs within the first few hours. Dynamic light scattering and transmission electron microscopy revealed no evidence of aggregation caused by monomers. Bilayers appeared to have a certain capacity for accommodating monomers. The total volume of loaded monomers is independent of monomer structure. X-ray scattering showed the increase in bilayer thickness consistent with loading monomers into bilayer interior. Loading kinetics is inversely proportional to the hydrophobicity and size of monomers. Loading and extraction kinetic data suggest that crossing the polar heads region is the rate limiting step. Consideration of loading kinetics and multiple equilibria are important for achieving reproducible monomer loading. The total amount of monomers loaded into the bilayer can be controlled by the loading time or length of hydrophobic lipid tails. The ratio of loaded monomers can be varied by changing the ratio of monomers used for loading or by the time-controlled replacement of a preloaded monomer. Understanding and controlling the loading of monomers into bilayers contributes to the directed assembly of organic nanostructures.

Phytoremediation of MTBE with hybrid poplar trees.

This research investigates the fate and transport of methyl tert-butyl ether (MTBE) in phytoremediation, particularly the uptake and volatilization of MTBE in lab-scale hydroponic systems. The research reveals that MTBE was taken up by hybrid poplar cuttings and volatilized to the atmosphere. Volatilization of MTBE occurred through both stems and leaves. The concentration of MTBE in the transpiration stream declined exponentially with height, indicating that the uptake and volatilization along the stems are an important removal mechanism of MTBE in phytoremediation. Volatilization, via diffusion from the stems, has not been directly measured previously. No volatile MTBE metabolites were detected; however, mass balance closure and metabolite detection were not primary objectives of this study. The greatest amount of MTBE in plant biomass was associated with the woody stems from the previous year's growth, owing in part to the large biomass of stems. MTBE in the plant tissues appears to reach a steady state concentration and there does not appear to be an accumulation process that could lead to highly elevated concentrations relative to the groundwater source.