Evaluating toxicological responses of engineered nanomaterials such as silica nanoparticles is critical in assessing health risks and exposure limits. Biological assays can be used to evaluate cytotoxicity of individual materials, but specific nano-bio interactions-which govern its physiological response-cannot currently be predicted from materials characterization and physicochemical properties. Understanding the role of free radical generation from nanomaterial surfaces facilitates understanding of a potential toxicity mechanism and provides insight into how toxic effects can be assessed. Size-matched mesoporous and nonporous silica nanoparticles in aminopropyl-functionalized and native forms were investigated to analyze the effects of porosity and surface functionalization on the observed cytotoxicity. In vitro cell viability data in a murine macrophage cell line (RAW 264.7) provides a model for what might be observed in terms of cellular toxicity upon an environmental or industrial exposure to silica nanoparticles. Electron paramagnetic resonance spectroscopy was implemented to study free radical species generated from the surface of these nanomaterials and the signal intensity was correlated with cellular toxicity. In addition, in vitro assay of intracellular reactive oxygen species (ROS) matched well with both the EPR and cell viability data. Overall, spectroscopic and in vitro studies correlate well and implicate production of ROS from a surface-catalyzed reaction as a predictor of cellular toxicity. The data demonstrate that mesoporous materials are intrinsically less toxic than nonporous materials, and that surface functionalization can mitigate toxicity in nonporous materials by reducing free radical production. The broader implications are in terms of safety by design of nanomaterials, which can only be extracted by mechanistic studies such as the ones reported here.

Zeolites and mesoporous silica nanoparticles are silicate or aluminosilicate nanomaterials with well-defined pore networks.

Understanding complex chemical changes that take place at nano-bio interfaces is of great concern for being able to sustainably implement nanomaterials in key applications such as drug delivery, imaging, and environmental remediation. Typical in vitro assays use cell viability as a proxy to understanding nanotoxicity but often neglect how the nanomaterial surface can be altered by adsorption of solution-phase components in the medium. Protein coronas form on the nanomaterial surface when incubated in proteinaceous solutions. Herein, we apply a broad array of techniques to characterize and quantify protein corona formation on silica nanoparticle surfaces. The porosity and surface chemistry of the silica nanoparticles have been systematically varied. Using spectroscopic tools such as FTIR and circular dichroism, structural changes and kinetic processes involved in protein adsorption were evaluated. Additionally, by implementing thermogravimetric analysis, quantitative protein adsorption measurements allowed for the direct comparison between samples. Taken together, these measurements enabled the extraction of useful chemical information on protein binding onto nanoparticles in solution. Overall, we demonstrate that small alkylamines can increase protein adsorption and that even large polymeric molecules such as poly(ethylene glycol) (PEG) cannot prevent protein adsorption in these systems. The implications of these results as they relate to further understanding nano-bio interactions are discussed.

3D printing is a rapidly growing field that requires the development of yield-stress fluids that can be used in post-printing transformation processes. There are a limited number of yield-stress fluids currently available with the desired rheological properties for building structures with small filaments (≤ l00 μm) with high shape-retention. We present a printingcentric approach for 3D printing particle-free silicone oil-in-water emulsions with a polymer additive, poly (ethylene oxide). This particular material structure and formulation is used to build 3D structure and to pattern at filament diameters below that of any other known material in this class. Increasing the molecular weight of poly (ethylene oxide) drastically increases the extensibility of the material without significantly affecting shear flow properties (shear yield stress and linear viscoelastic moduli). Higher extensibility of the emulsion correlates to the ability of filaments to span relatively large gaps (greater than 6 mm) when extruded at large tip diameters (330 μm) and the ability to extrude filaments at high print rates (20 mm/s). 3D printed structures with these extensible particle-free emulsions undergo post-printing transformation, which converts them into elastomers. These elastomers can buckle and recover from extreme compressive strain with no permanent deformation, a characteristic not native to the emulsion.

Amorphous silica nanoparticles (NPs) possess unique material properties that make them ideal for many different applications. However, the impact of these materials on human and environmental health needs to be established. We investigated nonporous silica NPs both bare and modified with amine functional groups (3-aminopropyltriethoxysilane (APTES)) in order to evaluate the effect of surface chemistry on biocompatibility. In vitro data showed there to be little to no cytotoxicity in a human lung cancer epithelial cell line (A549) for neither bare silica NPs nor amine-functionalized NPs using doses based on both mass concentration (below 200 μg/mL) and exposed total surface area (below 14 m2/L). To assess lung inflammation, C57/B16 mice were administered bare and amine-functionalized silica NPs via intra-tracheal instillation. Two doses (0.1 and 0.5 mg NPs/mouse) were tested using the in vivo model. At the higher dose used, bare silica NPs elicited a significantly higher inflammatory response, as evidence by increased neutrophils and total protein in bronchoalveolar (BAL) fluid compared to amine-functionalized NPs. From this study, we conclude that functionalization of nonporous silica NPs with APTES molecules reduces murine lung inflammation and improves the overall biocompatibility of the nanomaterial.

Mesoporous silica materials are undergoing rapid development for numerous environmental and biomedical applications. These materials are commonly functionalized with small organic molecules through a reaction between an organosilane and the surface silanols. Despite widespread use and implementation of these materials, ligands on their surfaces are challenging to characterize, particularly in aqueous environments. Employing traditional physicochemical characterization methods such as adsorption isotherms, X-ray diffraction, and electron microscopy, as well as solution-phase 1H NMR methods including one-dimensional NMR, diffusion ordered spectroscopy (DOSY) and two-dimensional nuclear Overhauser effect spectroscopy (NOESY), the labile nature of several different surface ligands on mesoporous silica nanoparticles is revealed. The data presented indicate a dynamic model of organosilane release from the surface, and adsorption of the released molecules is ultimately dependent on the nature of the binding of the functional group to the particle surface. A new paradigm for understanding chemical changes that take place at the liquid–solid interface is described, which incorporates a model of chemical dynamics in aqueous solution. Covalently functionalized nanomaterials are widely used, and the characterization of the ligands on their surfaces is of paramount importance, particularly when they are implemented in biomedical and environmental applications.

The field of 3D printing is an area of active research, with a substantial focus given to the design and construction of customized tools for applications in technology. There exists a particular need in these developing areas of opportunity for new multi‐functional soft materials that are biologically compatible for the growth and directed culturing of cells. Herein, a composite material consisting of gold nanoparticles with useful plasmonic properties embedded within a highly hydrophilic poly‐2‐hydroxyethylmethacrylate matrix is described and characterized. This composite material serves dual functions as both host framework scaffold for cell lines such as pre‐osteoblasts as well as a plasmonic biosensor for in situ measurements of living cells. The plasmonic properties of this system are characterized as a function of the material properties and related to compositional features of the material through a proposed light‐directed mechanism. This chemistry provides a tunable, 3D printable plasmonic composite material of encapsulated gold nanoparticles in a biologically‐compliant, acrylate‐based hydrogel matrix. Surface‐enhanced Raman scattering studies of 3D‐microcultures supported by the scaffolds are carried out and the strong influence of perm‐selective molecular diffusion in its analytical responses is established. Most notably, specific, largely hydrophilic, cellular metabolites are detected within the supported live cultures.

Commercial smart window technologies for dynamic light and heat management in building and automotive environments traditionally rely on electrochromic (EC) materials powered by an external source. This design complicates building-scale installation requirements and substantially increases costs for applications in retrofit construction. Self-powered photoelectrochromic (PEC) windows are an intuitive alternative wherein a photovoltaic (PV) material is used to power the electrochromic device, which modulates the transmission of the incident solar flux. The PV component in this application must be sufficiently transparent and produce enough power to efficiently modulate the EC device transmission. Here, we propose Si solar microcells (μ-cells) that are i) small enough to be visually transparent to the eye, and ii) thin enough to enable flexible PEC devices. Visual transparency is achieved when Si μ-cells are arranged in high pitch (i.e. low-integration density) form factors while maintaining the advantages of a single-crystalline PV material (i.e., long lifetime and high performance).Additionally, the thin dimensions of these Si μ-cells enable fabrication on flexible substrates to realize these flexible PEC devices. The current work demonstrates this concept using WO 3 as the EC material and V 2 O 5 as the ion storage layer, where each component is fabricated via sol-gel methods that afford improved prospects for scalability and tunability in comparison to thermal evaporation methods. The EC devices display fast switching times, as low as 8 seconds, with a modulation in transmission as high as 33%. Integration with two Si μ-cells in series (affording a 1.12 V output) demonstrates an integrated PEC module design with switching times of less than 3 minutes, and a modulation in transmission of 32% with an unprecedented EC:PV areal ratio.