Novel Engineered Ion Channel Provides Controllable Ion Permeability for Polyelectrolyte Microcapsules Coated with a Lipid Membrane

The development of nanostructured microcapsules based on a biomimetic lipid bilayer membrane (BLM) coating of poly(sodium styrenesulfonate) (PSS)/poly(allylamine hydrochloride) (PAH) polyelectrolyte hollow microcapsules is reported. A novel engineered ion channel, gramicidin (bis‐gA), incorporated into the lipid membrane coating provides a functional capability to control transport across the microcapsule wall. The microcapsules provide transport and permeation for drug‐analog neutral species, as well as positively and negatively charged ionic species. This controlled transport can be tuned for selective release biomimetically by controlling the gating of incorporated bis‐gA ion channels. This system provides a platform for the creation of “smart” biomimetic delivery vessels for the effective and selective therapeutic delivery and targeting of drugs.     

Inside Front Cover: Environmental Optical Sensitivity of Gold Nanodecahedra (Adv. Funct. Mater. 9/2007)

As reported on p. 1443 by Isabel Pastoriza‐Santos and Luis M. Liz‐Marzán, the high sensitivity of localized surface plasmon resonances towards changes in the refractive index of the surrounding medium for regular gold nanodecahedra render them strong candidates for (bio)sensing applications. Whereas a monolayer of decahedra deposited on a glass slide looks pink in air, it turns blue when immersed in isopropanol. The sensitivity of localized surface plasmon resonances with respect to changes in the refractive index of the surrounding medium is measured for small (< 60 nm side length) and large (ca. 150 nm side length) regular gold nanodecahedra (pentagonal bipyramids), and compared to rigorous solutions of Maxwell's equations for bicones based upon the boundary element method (BEM). Small particles are prepared through ultrasound‐induced reduction of HAuCl₄ by N,N‐dimethylformamide (DMF) on presynthesized penta‐twinned Au seeds, whereas large decahedra are grown using smaller ones as seeds. Excellent agreement between experimental and calculated spectra is found for dispersions and monolayers of particles in different solvents, as well as for the effect of uniform silica layers of various thicknesses grown on them. These results are expected to be useful for the development of novel biosensors.     

Inside Front Cover: Thermally Responsive Biomineralization on Biodegradable Substrates (Adv. Funct. Mater. 16/2007)

Biomineralization offers an elegant example of how nature can design complex, hierarchical, and structurally/morphologically controllable materials. João Mano and co‐workers of the University of Minho, Portugal report on p. 3312 that modifying the surface of bioactive substrates, together with the effect of temperature, triggers the formation of apatite upon immersion in simulated body fluid. This “smart” biomineralization concept could be combined with patterning methodologies by controlling the microstructure of the surface. Such a concept could be extended in the biomimetic production of other minerals, being triggered by other kind of stimuli (e.g., pH or ionic strength), in substrates with more complex geometries. Biomineralization offers an elegant example of how nature can design complex, hierarchical, and structurally/morphologically controllable materials. In this work, the surface of bioactive substrates prepared from poly(L ‐lactic acid) and reinforced with Bioglass are modified by the graft polymerization of poly(N‐isopropylacrylamide), (PNIPAAm) after plasma activation. It is found that such treatment, together with temperature, could trigger the formation of apatite on the biodegradable substrate upon immersion in simulated body fluid above the PNIPAAm lower critical solution temperature (LCST); in contrast, no apatite is formed at room temperature. A control experiment on a material that is not subjected to surface treatment does not show any evidence of mineral deposition at the two analyzed temperatures. This “smart” biomineralization concept is combined with patterning methodologies to control the microstructure of the surface onto which PNIPAAm is grafted. In this case, the apatite is formed at 37 °C in the modified regions. We suggest that this concept could be extended in the biomimetic production of other minerals, where it would be triggered by another kind of stimulus (e.g., pH or ionic strength) in substrates with more complex geometries.     

Drug Delivery: Wavelength‐Selective Light‐Induced Release from Plasmon Resonant Liposomes (Adv. Funct. Mater. 6/2011)

Biodegradable, spectrally tunable plasmon resonant nanocapsules are created via the deposition of gold onto the surface of 100 nm diameter thermosensitive liposomes. These nanocapsules exhibit selective release of encapsulated contents upon illumination with light of a wavelength matching their distinct resonance bands. In this study, 760 and 1210 nm laser illumination elicits complete release from gold‐coated liposomes with a corresponding resonance, while causing minimal release from liposomes with an unmatching resonance. Spectrally selective release is accomplished through the use of multiple, low‐intensity laser pulses delivered over a period of minutes, ensuring that illumination affects the gold‐coated liposomes without heating the surrounding media. The use of pulsed illumination to achieve spectral selectivity is validated experimentally and through modeling of the heat equation. The result of this illumination scheme for selective release using multiple wavelengths of light is a biologically safe mechanism for realizing drug delivery, microfluidic, and sensor applications.     

Inside Front Cover: Inkjet Printing of Luminescent CdTe Nanocrystal–Polymer Composites (Adv. Funct. Mater. 1/2007)

Schubert and co‐workers have performed a detailed investigation on ink‐jet printing of well‐defined dots of luminescent CdTe nanocrystals (NCs) embedded in a poly(vinyl alcohol) matrix, as reported on p. 23, and subsequently made studies of their morphology and photoluminescence. The inside cover shows a photograph of an ink‐jet‐printed combinatorial library of differently sized CdTe NCs emitting at different wavelengths, and a 3D profilometer image of an array of printed dots. Inkjet printing is used to produce well‐defined patterns of dots (with diameters of ca. 120 μm) that are composed of luminescent CdTe nanocrystals (NCs) embedded within a poly(vinylalcohol) (PVA) matrix. Addition of ethylene glycol (1–2 vol %) to the aqueous solution of CdTe NCs suppresses the well‐known ring‐formation effect in inkjet printing leading to exceptionally uniform dots. Atomic force microscopy characterization reveals that in the CdTe NC films the particle–particle interaction could be prevented using inert PVA as a matrix. Combinatorial libraries of CdTe NC–PVA composites with variable NC sizes and polymer/NC ratios are prepared using inkjet printing. These libraries are subsequently characterized using a UV/fluorescence plate reader to determine their luminescent properties. Energy transfer from green‐light‐emitting to red‐light‐emitting CdTe NCs in the composite containing green‐ (2.6 nm diameter) and red‐emitting (3.5 nm diameter) NCs are demonstrated.