Nanoporous silica-based protocells at multiple scales for designs of life and nanomedicine.

Various protocell models have been constructed de novo with the bottom-up approach. Here we describe a silica-based protocell composed of a nanoporous amorphous silica core encapsulated within a lipid bilayer built by self-assembly that provides for independent definition of cell interior and the surface membrane. In this review, we will first describe the essential features of this architecture and then summarize the current development of silica-based protocells at both micro- and nanoscale with diverse functionalities. As the structure of the silica is relatively static, silica-core protocells do not have the ability to change shape, but their interior structure provides a highly crowded and, in some cases, authentic scaffold upon which biomolecular components and systems could be reconstituted. In basic research, the larger protocells based on precise silica replicas of cells could be developed into geometrically realistic bioreactor platforms to enable cellular functions like coupled biochemical reactions, while in translational research smaller protocells based on mesoporous silica nanoparticles are being developed for targeted nanomedicine. Ultimately we see two different motivations for protocell research and development: (1) to emulate life in order to understand it; and (2) to use biomimicry to engineer desired cellular interactions

Scalable, biofunctional, ultra-stable nano- bio- composite materials containing living cells

Three-dimensional encapsulation of cells within nanostructured silica gels or matrices enables applications as diverse as biosensors, microbial fuel cells, artificial organs, and vaccines. It also allows study of individual cell behaviors. Recent progress has improved the performance and flexibility of cellular encapsulation, yet there remains a need for robust scalable processes for large format production of cell-encapsulating materials. Here, we detail two novel techniques, that enable the large-scale production of functional Nano-Bio-Composites (NBCs) containing living cells within ordered 3-D lipid/silica nanostructures: 1) thick-casting and 2) spray drying. Furthermore, we detail a third technique for material scaling in which aqueous, silicate-based gel monoliths encapsulate biofunctional yeast or bacteria. Both dry processes are demonstrated to work with multiple cell types and result in dry powders exhibiting a unique combination of properties including: highly ordered 3-D nanostructure, extended lipid fluidity, tunable macro-morphologies and aerodynamic diameters, and unexpectedly high physical strength. Nanoindentation of the encasing nanostructure revealed Young’s modulus and hardness of 13 and 1.4 GPa respectively, which was unexpected considering the low processing conditions. We hypothesized and confirmed that NBC-encapsulated cells would remain viable for extended periods of time under elevated aging conditions. We attribute this due to the high material strength as observed with nanoindentation, which would prevent cell growth and force bacteria into viable but not culturable (VBNC) states. In concordance with the VBNC state, cellular ATP levels remained elevated even over eight months confirming temperature stable, viable cells. However, their ability to undergo resuscitation and enter growth phase greatly decreased with time in the VBNC state. A quantitative method of determining resuscitation frequencies was developed and showed that, after 36 weeks in an NBC-induced VBNC state, less than 1 in 10,000 cells underwent resuscitation. We verify the VBNC phenotype in gel-encapsulated cells by studying cellular RNA expression levels. These latent behaviors are further demonstrated with an in-vivo immunological study in which mice, immunized with NBCs containing the vaccine Bacillus Calmette-Guérin, were observed to be immunized against a latent form of Tuberculosis. This finding is, in our understanding, the first demonstration of a latent disease-specific live cell immunotherapy. The NBC platform production of industrially scalable quantities of VBNC cells is of interest for research in bacterial persistence and screening of drugs targeting such cells. NBC’s may also enable long-term preservation of living cells for applications in cell-based sensing and the packaging and delivery of live-cell vaccines. Moreover, our methodology represents a novel process for preparing formulations of latent cells in-silico, which could find application in basic cellular research and for the development of a latent-specific vaccine

Aerosol-Assisted Synthesis of Monodisperse Single-Crystalline α-Cristobalite Nanospheres

Monodisperse single-crystalline α-cristobalite nanospheres have been synthesized by hydrocarbon-pyrolysis-induced carbon deposition on amorphous silica aerosol nanoparticles, devitrification of the coated silica at high temperature, and subsequent carbon removal by oxidation. The nanosphere size can be well controlled by tuning the size of the colloidal silica precursor. Uniform, high-purity nanocrystalline α-cristobalite is important for catalysis, nanocomposites, advanced polishing, and understanding silica nanotoxicology

Ambient-pressure silica aerogel films

Very highly porous (aerogel) silica films with refractive index in the range 1.006--1.05 (equivalent porosity 98.5--88%) were prepared by an ambient-pressure process. It was shown earlier using in situ ellipsometric imaging that the high porosity of these films was mainly attributable to the dilation or `springback` of the film during the final stage of drying. This finding was irrefutably reconfirmed by visually observing a `springback` of >500% using environmental scanning electron microscopy (ESEM). Ellipsometry and ESEM also established the near cent per cent reversibility of aerogel film deformation during solvent intake and drying. Film thickness profile measurements (near the drying line) for the aerogel, xerogel and pure solvent cases are presented from imaging ellipsometry. The thickness of these films (crack-free) were controlled in the range 0.1-3.5 {mu}m independent of refractive index

Nanostructured polyoxometalate arrays with unprecedented properties and functions.

Polyoxometalates (POMs) are ionic (usually anionic) metal -oxo clusters that are both functional entities for a variety of applications, as well as structural units that can be used as building blocks if reacted under appropriate conditions. This is a powerful combination in that functionality can be built into materials, or doped into matrices. Additionally, by assembling functional POMs in ordered materials, new collective behaviors may be realized. Further, the vast variety of POM geometries, compositions and charges that are achievable gives this system a high degree of tunability. Processing conditions to link together POMs to build materials offer another vector of control, thus providing infinite possibilities of materials that can he nano-engineered through POM building blocks. POM applications that can be built into POM-based materials include catalysis, electro-optic and electro-chromic, anti-viral, metal binding, and protein binding. We have begun to explore three approaches in developing this field of functional, nano-engineered POM-based materials; and this report summarizes the work carried out for these approaches to date. The three strategies are: (1) doping POMs into silica matrices using sol-gel science, (2) forming POM-surfactant arrays and metal-POM-surfactant arrays, (3) using aerosol-spray pyrolysis of the POM-surfactant arrays to superimpose hierarchical architecture by self-assembly during aerosol-processing. Doping POMs into silica matrices was successful, but the POMs were partially degraded upon attempts to remove the structure-directing templates. The POM-surfactant and metal-POM-surfactant arrays approach was highly successful and holds much promise as a novel approach to nano-engineering new materials from structural and functional POM building blocks, as well as forming metastable or unusual POM geometries that may not be obtained by other synthetic methods. The aerosol-assisted self assembly approach is in very preliminary state of investigation, but also shows promise in that structured materials were formed; where the structure was altered by aerosol processing. We will be seeking alternative funding to continue investigating the second synthetic strategy that we have begun to develop during this 1-year project

Anomalously high photocurrents in nanostructured electrodes : a new local microchip power source.

An increase in photocurrent has been observed at silicon electrodes coated with nanostructured porous silica films as compared to bare, unmodified silicon. Ultimately, to utilize this effect in devices such as sensors or microchip power supplies, the physical phenomena behind this observation need to be well characterized. To this end, Electrochemical Impedance Spectroscopy (EIS) was used to characterize the effect of surfactant-templated mesoporous silica films deposited onto silicon electrodes on the electrical properties of the electrode space-charge region in an aqueous electrolyte solution, as the electrical properties of this space-charge region are responsible for the photobehavior of semiconductor devices. A significant shift in apparent flat-band potential was observed for electrodes modified with the silica film when compared to bare electrodes; the reliability of this data is suspect, however, due to contributions from surface states to the overall capacitance of the system. To assist in the interpretation of this EIS data, a series of measurements at Pt electrodes was performed with the hope of decoupling electrode and film contributions from the EIS spectra. Surprisingly, the frequency-dependent impedance data for Pt electrodes coated with a surfactant-templated film was nearly identical to that observed for bare Pt electrodes, indicating that the mesoporous film had little effect on the transport of small electrolyte ions to the electrode surface. Pore-blocking agents (tetraalkylammonium salts) were not observed to inhibit this transport process. However, untemplated (non-porous) silica films dramatically increased film resistance, indicating that our EIS data for the Pt electrodes is reliable. Overall, our preliminary conclusion is that a shift in electrical properties in the space-charge region induced by the presence of a porous silica film is responsible for the increase in observed photocurrent

Direct Writing and Actuation of Three-Dimensionally Patterned Hydrogel Pads on Micropillar Supports

Freely swelling, three-dimensionally patterned responsive hydrogels fabricated by multiphoton lithography on the tips of flexible pillars provide unique capabilities for the design of adaptive systems. The resulting materials have tunable actuation direction and angle, sensitive optical response, and precise spatial integration of gels with varying pH and temperature response (see picture; scale bar: 20 μm).Engineering and Applied Science