Synthesis of biocompatible PEG-Based star polymers with cationic and degradable core for siRNA delivery.

Star polymers with poly(ethylene glycol) (PEG) arms and a degradable cationic core were synthesized by the atom transfer radical copolymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate macromonomer (PEGMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), and a disulfide dimethacrylate (cross-linker, SS) via an "arm-first" approach. The star polymers had a diameter ~15 nm and were degraded under redox conditions by glutathione treatment into individual polymeric chains due to cleavage of the disulfide cross-linker, as confirmed by dynamic light scattering. The star polymers were cultured with mouse calvarial preosteoblast-like cells, embryonic day 1, subclone 4 (MC3T3-E1.4) to determine biocompatibility. Data suggest star polymers were biocompatible, with ≥ 80% cell viability after 48 h of incubation even at high concentration (800 µg/mL). Zeta potential values varied with N/P ratio confirming complexation with siRNA. Successful cellular uptake of the star polymers in MC3T3-E1.4 cells was observed by confocal microscopy and flow cytometry after 24 h of incubation.

Free-standing silica colloidal nanoporous membranes.

We prepared robust free-standing 200 microm-thick colloidal membranes (nanofrits) with a relatively large area and no mechanical defects by sintering silica colloidal films. The silica spheres used to prepare the nanofrits were 338, 300, or 251 nm in diameter, leading to 25, 22.5, and 19 nm nanopore sizes, respectively. The room-temperature diffusional flux through these membranes is of the order of 3.6 x 10(-10) mol s(-1) cm(-2) for a Fe(bpy)32+ ion in acetonitrile test solution in the absence of applied pressure and is in good agreement with the calculated diffusional flux for colloidal crystals of the same thickness. To evaluate the feasibility of nanofrit surface modification, we treated them with 3-aminopropyltriethoxysilane after rehydroxylation. We found, by measuring the surface coverage for dansyl amide on the surface, that the number of the amines on the nanofrit surface is lower as compared to that observed for colloidal films not treated with heat. As a result, the selectivity for the transport of Fe(bpy)3(2+) through the aminated nanofrits in the presence of acid is lower than the selectivity observed for amine-modified colloidal films.

Suspended self-assembled opal membranes.

Suspended self-assembled opal membranes have been prepared from 440- or 170-nm-diameter silica spheres by evaporation of their colloidal solutions over vertically oriented 0.3-mm-thick silicon wafers containing frustum-shaped openings. Robust 0.5 x 0.5 mm(2) membranes with a thickness of ca. 300 mum have been reproducibly prepared using 170 nm silica spheres. The membranes show regular fcc packing with an exposed (111) orientation and are formed in a process that involves drawing silica spheres into the opening with the solvent meniscus.

Photon gated transport at the glass nanopore electrode.

The interior surface of the glass nanopore electrode was modified with spiropyran moieties to impart photochemical control of molecular transport through the pore orifice (15-90 nm radius). In low ionic strength acetonitrile solutions, diffusion of a positively charged species (Fe(bpy)(3)(2+)) is electrostatically blocked with approximately 100% efficiency by UV light-induced conversion of the neutral surface-bound spiropyran to its protonated merocyanine form (MEH+). Transport through the pore orifice is restored by either irradiation of the electrode with visible light to convert MEH+ back to spiropyran or addition of a sufficient quantity of supporting electrolyte to screen the electrostatic field associated with MEH+. The transport of neutral redox species through spiropyran-modified glass nanopores is not affected by light, allowing photoselective transport of redox molecules to the electrode surface based on charge discrimination. The glass nanopore electrode can also be employed as a photochemical trap, by UV light conversion of surface-bound spiropyran to MEH+, preventing Fe(bpy)(3)(2+) initially in the pore from diffusing through the orifice.

pH- and ionic strength-controlled cation permselectivity in amine-modified nanoporous opal films.

The influence of pH and ionic strength on permselective transport in nanoporous opal films prepared from 440 nm silica spheres was investigated by cyclic voltammetry in aqueous and acetonitrile solutions. Three-layer opal films were deposited from a 1.5 wt % colloidal solution of silica spheres onto 25-microm-diameter Pt microdisk electrodes shrouded in glass. The films were chemically modified by immersing them in a dry acetonitrile solution of 3-aminopropyl triethoxysilane. When the surface amino groups of the modified opal films are protonated and there is little or no supporting electrolyte present in solution, the flux of cationic redox species through the opal membrane is blocked because of electrostatic repulsion. The permselectivity is pH-dependent and can be modulated by adjusting the Debye screening length within the nanopores of the opal by changing the ionic strength of the contacting solution.

Chemically modified opals as thin permselective nanoporous membranes.

Thin-film opals comprising three layers of 440 nm diameter SiO2 spheres were assembled on Pt electrodes and modified with amino groups on the silica surface. Diffusion of anionic, cationic, and neutral redox species through the opals was studied by cyclic voltammetry. The chemically modified opal membranes demonstrate high molecular throughput and, at low pH, selectively block transport of a cationic redox species relative to that of anionic and neutral redox species. This permselective behavior is attributed to the electrostatic interactions that are enhanced by the tortuous pathway within the opal and by the high surface area of the chemically modified spheres.