Achyut J. Raghavendra

Roll-to-roll production of spray coated N-doped carbon nanotube electrodes for supercapacitors

Although carbon nanomaterials are being increasingly used in energy storage, there has been a lack of inexpensive, continuous, and scalable synthesis methods. Here, we present a scalable roll-to-roll (R2R) spray coating process for synthesizing randomly oriented multi-walled carbon nanotubes electrodes on Al foils. The coin and jellyroll type supercapacitors comprised such electrodes yield high power densities (∼700 mW/cm3) and energy densities (1 mW h/cm3) on par with Li-ion thin film batteries. These devices exhibit excellent cycle stability with no loss in performance over more than a thousand cycles. Our cost analysis shows that the R2R spray coating process can produce supercapacitors with 10 times the energy density of conventional activated carbon devices at ∼17% lower cost.

From the Cover: Disease-Induced Disparities in Formation of the Nanoparticle-Biocorona and the Toxicological Consequences

Nanoparticle (NP) association with macromolecules in a physiological environment forms a biocorona (BC), which alters NP distribution, activity, and toxicity. While BC formation is dependent on NP physicochemical properties, little information exists on the influence of the physiological environment. Obese individuals and those with cardiovascular disease exist with altered serum chemistry, which is expected to influence BC formation and NP toxicity. We hypothesize that a BC formed on NPs following incubation in hyperlipidemic serum will result in altered NP-BC protein content, cellular association, and toxicity compared to normal serum conditions. We utilized Fe3O4 NPs, which are being developed as MRI contrast and tumor targeting agents to test our hypothesis. We used rat aortic endothelial cells (RAECs) within a dynamic flow in vitro exposure system to more accurately depict the in vivo environment. A BC was formed on 20nm PVP-suspended Fe3O4 NPs following incubation in water, 10% normal or hyperlipidemic rat serum. Addition of BCs resulted in increased hydrodynamic size and decreased surface charge. More cholesterol associated with Fe3O4 NPs after incubation in hyperlipidemic as compared with normal serum. Using quantitative proteomics, we identified unique differences in BC protein components between the 2 serum types. Under flow conditions, formation of a BC from both serum types reduced RAECs association of Fe3O4 NPs. Addition of BCs was found to exacerbate RAECs inflammatory gene responses to Fe3O4 NPs (Fe3O4-hyperlipidemic > Fe3O4-normal > Fe3O4) including increased expression of IL-6, TNF-α, Cxcl-2, VCAM-1, and ICAM-1. Overall, these findings demonstrate that disease-induced variations in physiological environments have a significant impact NP-BC formation, cellular association, and cell response.

Defect density in multiwalled carbon nanotubes influences ovalbumin adsorption and promotes macrophage activation and CD4(+) T-cell proliferation.

Carbon nanotubes (CNTs) are of great interest for the development of drugs and vaccines due to their unique physicochemical properties. The high surface area to volume ratio and delocalized pi-electron cloud of CNTs promote binding of proteins to the surface forming a protein corona. This unique feature of CNTs has been recognized for potential delivery of antigens for strong and long-lasting antigen-specific immune responses. Based on an earlier study that demonstrated increased protein binding, we propose that carboxylated multiwalled CNTs (MWCNTs) can function as an improved carrier to deliver antigens such as ovalbumin (OVA). To test this hypothesis, we coated carboxylated MWCNTs with OVA and measured uptake and activation of antigen-presenting cells (macrophages) and their ability to stimulate CD4+ T-cell proliferation. We employed two types of carboxylated MWCNTs with different surface areas and defects (MWCNT-2 and MWCNT-30). MWCNT-2 and MWCNT-30 have surface areas of ~215 m2/g and 94 m2/g, respectively. The ratios of D- to G-band areas (ID/IG) were 0.97 and 1.37 for MWCNT-2 and MWCNT-30, respectively, samples showing that MWCNT-30 contained more defects. The increase in defects in MWCNT-30 led to increased binding of OVA as compared to MWCNT-2 (1,066±182 μg/mL vs 582±41 μg/mL, respectively). Both types of MWCNTs, along with MWCNT–OVA complexes, showed no observable toxicity to bone-marrow-derived macrophages up to 5 days. Surprisingly, we found that MWCNT–OVA complex significantly increased the expression of major histocompatibility complex class II on macrophages and production of pro-inflammatory cytokines (tumor necrosis factor-α and interleukin 6), while MWCNTs without OVA protein corona did not. The coculture of MWCNT–OVA-complex-treated macrophages and OVA-specific CD4+ T-cells isolated from OT-II mice demonstrated robust proliferation of CD4+ T-cells. This study provides strong evidence for a role for defects in carboxylated MWCNTs and their use in the efficient delivery of antigens for the development of next-generation vaccines.

Biomolecular Interactions and Biological Responses of Emerging Two-Dimensional Materials and Aromatic Amino Acid Complexes

The present work experimentally investigates the interaction of aromatic amino acids viz., tyrosine, tryptophan, and phenylalnine with novel two-dimensional (2D) materials including graphene, graphene oxide (GO), and boron nitride (BN). Photoluminescence, micro-Raman spectroscopy, and cyclic voltammetry were employed to investigate the nature of interactions and possible charge transfer between 2D materials and amino acids. Graphene and GO were found to interact strongly with aromatic amino acids through π-π stacking, charge transfer, and H-bonding. Particularly, it was observed that both physi and chemisorption are prominent in the interactions of GO/graphene with phenylalanine and tryptophan while tyrosine exhibited strong chemisorption on graphene and GO. In contrast, BN exhibited little or no interactions, which could be attributed to localized π-electron clouds around N atoms in BN lattice. Lastly, the adsorption of amino acids on 2D materials was observed to considerably change their biological response in terms of reactive oxygen species generation. More importantly, these changes in the biological response followed the same trends observed in the physi and chemisorption measurements.

Variations in biocorona formation related to defects in the structure of single walled carbon nanotubes and the hyperlipidemic disease state

Ball-milling utilizes mechanical stress to modify properties of carbon nanotubes (CNTs) including size, capping, and functionalization. Ball-milling, however, may introduce structural defects resulting in altered CNT-biomolecule interactions. Nanomaterial-biomolecule interactions result in the formation of the biocorona (BC), which alters nanomaterial properties, function, and biological responses. The formation of the BC is governed by the nanomaterial physicochemical properties and the physiological environment. Underlying disease states such as cardiovascular disease can alter the biological milieu possibly leading to unique BC identities. In this ex vivo study, we evaluated variations in the formation of the BC on single-walled CNTs (SWCNTs) due to physicochemical alterations in structure resulting from ball-milling and variations in the environment due to the high-cholesterol disease state. Increased ball-milling time of SWCNTs resulted in enhanced structural defects. Following incubation in normal mouse serum, label-free quantitative proteomics identified differences in the biomolecular content of the BC due to the ball-milling process. Further, incubation in cholesterol-rich mouse serum resulted in the formation of unique BCs compared to SWCNTs incubated in normal serum. Our study demonstrates that the BC is modified due to physicochemical modifications such as defects induced by ball-milling and physiological disease conditions, which may result in variable biological responses.

Contribution of engineered nanomaterials physicochemical properties to mast cell degranulation

The rapid development of engineered nanomaterials (ENMs) has grown dramatically in the last decade, with increased use in consumer products, industrial materials, and nanomedicines. However, due to increased manufacturing, there is concern that human and environmental exposures may lead to adverse immune outcomes. Mast cells, central to the innate immune response, are one of the earliest sensors of environmental insult and have been shown to play a role in ENM-mediated immune responses. Our laboratory previously determined that mast cells are activated via a non-FcεRI mediated response following silver nanoparticle (Ag NP) exposure, which was dependent upon key physicochemical properties. Using bone marrow-derived mast cells (BMMCs), we tested the hypothesis that ENM physicochemical properties influence mast cell degranulation. Exposure to 13 physicochemically distinct ENMs caused a range of mast degranulation responses, with smaller sized Ag NPs (5 nm and 20 nm) causing the most dramatic response. Mast cell responses were dependent on ENMs physicochemical properties such as size, apparent surface area, and zeta potential. Surprisingly, minimal ENM cellular association by mast cells was not correlated with mast cell degranulation. This study suggests that a subset of ENMs may elicit an allergic response and contribute to the exacerbation of allergic diseases.