Local and Sustained Gene Delivery in Silica-Collagen Nanocomposites

Local delivery of biomolecules from hydrogels is highly challenging because of their rapid diffusion and degradation. Gene therapy represents an alternative that allows for the prolonged production of proteins by transfected cells. In this study, we have developed nanocomposites consisting of DNA-polyethylenimine-silica nanoparticle complexes coencapsulated with fibroblasts within collagen hydrogels. Through the modulation of the particle size and polyethylenimine molecular weight, it was possible to achieve “in-gel” transfection permitting the sustained production of biomolecules from hydrogels over 1 week. Alternative configurations consisting of particle addition to cellularized gels and cell culture in the presence of complex-containing hydrogels were also investigated. These studies demonstrated that particle encapsulation limits DNA and silica dissemination outside the collagen hydrogels. They also show the key role of cell proliferation within collagen hydrogels on the transfection efficiency. Such nanocomposites therefore constitute promising materials for the development of novel gene delivery systems to promote tissue repair

Mass Transport Properties of Silicified Graphite Felt Electrodes

Mass transport properties of electrodes prepared from graphite felt, as such and after silicification, have been studied using cyclic voltammetry. Within the graphite felt, the mass transport of a probe changes with decreasing scan rate, from a radial diffusion around fibers to a regime that is analogous to “thin-layer” systems. Furthermore, unlike classical “thin-layer” systems, the volume comprised in the felt is macroscopic (resulting in high current densities), while the time required to consume all diffusive species remains in the 1 min range. Silicification of graphite felt does not impact on the mass transport of the negatively charged molecular probe Fe­(CN)₆^3– but significantly slows mass transport of positively charged Ru­(NH₃)₆³⁺. In the latter case, a parallel decrease of peak current intensity reflects limited mobility of the probe due to its strong interaction with the surface of the pore walls. These data provide important information for the optimization of the working conditions of these electrodes for the design of biosensors and biofuel cells

Biochemical Investigation of the Formation of Three-Dimensional Networks from DNA-Grafted Large Silica Particles

DNA is used to rationally build up networks of silica nanoparticles (SiNPs) based on the molecular recognition properties of complementary sequences. Network self-assembly is controlled from DNA covalently grafted at the surface of chemically modified SiNPs. Two strategies are compared, where grafted DNA sequences are designed in a three-strand system using noncomplementary sequences and an extra DNA linker, or in a two-strand approach for direct hybridization. In this paper, both systems are compared in terms of DNA hybridization stability, network size, and three-dimensional organization using a combination of dynamic light scattering and electron microscopy. The observed differences are discussed in terms of hybridization interactions between DNA sequences in particle-free systems through fluorescence, circular dichroism, and UV spectroscopy techniques

Extracellular versus Intracellular Degradation of Nanostructured Silica Particles

Silica nanoparticles appear as promising drug carriers for intracellular delivery. However, the mechanisms by which they are degraded within cells remain largely unknown. In this context, we have prepared three types of PEGylated fluorescent silica nanoparticles with various internal structures (core–shell biocomposite, multilayered, and hollow mesoporous) and studied their degradation in a buffer, in a culture medium, and in contact with human dermal fibroblasts. All particles were prone to dissolve in solution, leading to an increase of porosity and/or the precipitation of new colloids and eventually fragmentation, with a faster rate in the medium compared to that in the buffer. All particles were also uptaken by the cells without significant cytotoxic effect. Their intracellular degradation occurred faster than in suspension, but following almost similar dissolution mechanisms. These results strongly suggest that in these conditions, silica nanoparticles must be primarily considered as hydrolytically degraded and not biodegraded, a point of importance for their future applications in drug delivery

Biochemical Investigation of the Formation of Three-Dimensional Networks from DNA-Grafted Large Silica Particles

DNA is used to rationally build up networks of silica nanoparticles (SiNPs) based on the molecular recognition properties of complementary sequences. Network self-assembly is controlled from DNA covalently grafted at the surface of chemically modified SiNPs. Two strategies are compared, where grafted DNA sequences are designed in a three-strand system using noncomplementary sequences and an extra DNA linker, or in a two-strand approach for direct hybridization. In this paper, both systems are compared in terms of DNA hybridization stability, network size, and three-dimensional organization using a combination of dynamic light scattering and electron microscopy. The observed differences are discussed in terms of hybridization interactions between DNA sequences in particle-free systems through fluorescence, circular dichroism, and UV spectroscopy techniques

Impact of Polyethylenimine Conjugation Mode on the Cell Transfection Efficiency of Silica Nanovectors

The conjugation of polyethylenimine (PEI) to silica nanoparticles has emerged as a useful strategy in gene delivery. Here we investigate the influence of the PEI conjugation mode on the transfection ability of plain silica nanoparticles. Surface functionalization with sulfonate- and chloride-bearing silanes modulates the amount and conformation of PEI and therefore the particles’ affinity for the plasmid, without impacting on cytotoxicity. However, transfection efficiency in both immortalized and primary cells is more directly correlated to the nature and strength of the particle–PEI interactions. It suggests that PEI detachment from the particle surface at the stage of endosomal escape is a key event in the plasmid delivery process. These data should provide fruitful guidelines for the fine tuning of colloidal surfaces intended for intracellular delivery of bioactive molecules

One-Step Introduction of Broad-Band Mesoporosity in Silica Particles Using a Stimuli-Responsive Bioderived Glycolipid

Stimuli-responsive glycolipid biosurfactants belonging to the family of acidic sophorolipids (SL) have been used to introduce a broad range of pore size in the mesoscale regime (2–30 nm) in silica particles using a one-pot co-assembly sol–gel route in water. The pore size distribution is tailored by the sole interaction between an amino-modified silane, aminopropyltriethoxy silane (APTES), and SL. No additional compounds (e.g., block copolymers, polymers, organic solvents, pore-swelling agents) have been used to promote the formation of mesopores larger than 2 nm. Materials morphology and porosity have been characterized by high resolution TEM, SEM, and nitrogen physisorption, while the interaction between the glycolipid and silica is demonstrated by FT-IR and solid-state NMR

DWCNT-Doped Silica Gel Exhibiting Both Ionic and Electronic Conductivities

Silica gels doped with double-walled carbon nanotubes (DWCNTs) were prepared using an aqueous sol–gel route in mild conditions (neutral pH, room temperature). The wet gels exhibited both ionic and electronic conduction. Electrochemical impedance spectroscopy was used to study these two different conduction pathways that prevail at different characteristic time scales. The ionic conduction in the silica network was found to be independent of the DWCNT-doping rate. The electronic conduction through the DWCNT network was found to occur above a critical concentration (0.175 wt %) corresponding to nanotube percolation threshold. The highest content in DWCNTs (0.8 wt %) exhibited a conductivity of 0.05 S/m. Furthermore, the DWCNTs network was found to evolve even after the macroscopic solidification of the gel, suggesting a reorganization of the DWCNTs at the molecular level. This phenomenon could be attributed to the polarization effect of the electrode and was confirmed by Raman spectroscopy studies. Such materials can be useful for the design of sensors incorporating electroactive chemical or biological species