Harish Manohara

INTERNALIZATION OF MWCNTS BY MICROGLIA: POSSIBLE APPLICATION IN IMMUNOTHERAPY OF BRAIN TUMORS

There is a pressing need for new therapeutic, diagnostic, and drug delivery approaches for treating brain cancers. Nanotechnology offers a new method for targeted brain cancer therapy and could play a major role in gene and drug delivery. The goals of our study were to visualize in vitro ingestion, cytotoxicity, and loading capacity of Multi-Walled Carbon Nanotubes (MWCNTs) in microglia. Furthermore, we investigated internalization differences between microglia and glioma cells. BV2 microglia and GL261 glioma cells were incubated with MWCNTs, which were synthesized through catalytic chemical vapor deposition technique. Real-time RT-PCR, cell proliferation analysis, siRNA and DNA loading, electron microscopy, and flow cytometry were performed. We demonstrated that MWCNTs do not result in proliferative or cytokine changes in vitro, are capable of carrying DNA and siRNA and are internalized at higher levels in phagocytic cells as compared to tumor cells. This study suggests MWCNTs could be used as a novel, non-toxic, and biodegradable nano-vehicles for targeted therapy in brain cancers. Further studies are needed to demonstrate the full capacity of MWCNTs as nanovectors.

High-current-density field emitters based on arrays of carbon nanotube bundles

We have developed high-current density field emission sources using arrays of multiwalled carbon nanotube bundles. The field emission behavior of a variety of lithographically patterned array geometries was investigated and the arrays of 1-μm and 2-μm-diameter nanotube bundles spaced 5μm apart (edge-to-edge spacing) were identified as the most optimum combination, routinely producing 1.5–1.8A∕cm2 at low electric fields of approximately 4V∕μm, rising to >6A∕cm2 at 20V∕μm over a ∼100-μm-diameter area. We have found that the field emission performance depends strongly on the bundle diameter and interbundle spacing and such arrays perform significantly better in field emission than ordered arrays of isolated nanotubes or dense, continuous mats of nanotubes previously reported in literature.

Field emission testing of carbon nanotubes for THz frequency vacuum microtube sources

A carbon nanotube-based high current density electron field emission source is under development at Jet Propulsion Laboratory (JPL) for submillimeter-wave power generation (300 GHz to 3 THz). This source is the basis for a novel vacuum microtube component: the nanoklystron. The nanoklystron is a monolithically fabricated reflex klystron with dimensions in the micrometer range. The goal is to operate this device at much lower voltages than would be required with hot-electron sources and at much higher frequencies than have ever been demonstrated. Both single-walled (SWNTs) as well as multi-walled nanotubes (MWNTs) are being tested as potential field-emission sources. This paper presents initial results and observations of these field emission tests. SWNTs and MWNTs were fabricated using standard CVD techniques. The tube density was higher in the case of MWNT samples. As previously reported, high-density samples suffered from enhanced screening effect thus decreasing their total electron emission. The highest emission currents were measured from disordered, less dense MWNTs and were found to be ~0.63 mA @ 3.6 V/μm (sample 1) and ~3.55 mA @ 6.25 V/μm (sample 2). The high density vertically aligned MWNTs showed low field emission as predicted: 0.31 mA @ 4.7 V/μm.

Selective uptake of multi-walled carbon nanotubes by tumor macrophages in a murine glioma model

Carbon nantotubes (CNTs) are emerging as a new family of nanovectors for drug and gene delivery into biological systems. To evaluate potential application of this technology for brain tumor therapy, we studied uptake and toxicity of multi-walled CNTs (MWCNTs) in the GL261 murine intracranial glioma model. Within 24 h of a single intratumoral injection of labeled MWCNTs (5 microg), nearly 10-20% of total cells demonstrated CNT internalization. Most CNT uptake, however, occurred by tumor-associated macrophages (MP), which accounted for most (75%) MWCNT-positive cells. Within 24 h of injection, nearly 30% of tumor MP became MWCNT-positive. Despite a transient increase in inflammatory cell infiltration into both normal and tumor-bearing brains following MWCNT injection, no significant toxicity was noted in mice, and minor changes in tumor cytokine expression were observed. This study suggests that MWCNTs could potentially be used as a novel and non-toxic vehicle for targeting MP in brain tumors.

On Development of 100-Gram-Class Spacecraft for Swarm Applications

A novel space system architecture is proposed, which would enable 100-g-class spacecraft to be flown as swarms (100 s-1000 s) in low Earth orbit. Swarms of Silicon Wafer Integrated Femtosatellites (SWIFT) present a paradigm-shifting approach to distributed spacecraft development, missions, and applications. Potential applications of SWIFT swarms include sparse aperture arrays and distributed sensor networks. New swarm array configurations are introduced and shown to achieve the effective sparse aperture driven from optical performance metrics. A system cost analysis based on this comparison justifies deploying a large number of femtosatellites for sparse aperture applications. Moreover, this paper discusses promising guidance, control, and navigation methods for swarms of femtosatellites equipped with modest sensing and control capabilities.

Thin films with ultra-low thermal expansion.

Ultra-low coefficient of thermal expansion (CTE) is an elusive property, and narrow temperature ranges of operation and poor mechanical properties limit the use of conventional materials with low CTE. We structured a periodic micro-array of bi-metallic cells to demonstrate ultra-low effective CTE with a wide temperature range. These engineered tunable CTE thin film can be applied to minimize thermal fatigue and failure of optics, semiconductors, biomedical sensors, and solar energy applications.

Multi-walled carbon nanotube (MWCNT) synthesis, preparation, labeling, and functionalization.

Nanomedicine is a growing field with a great potential for introducing new generation of targeted and personalized drug. Amongst new generation of nano-vectors are carbon nanotubes (CNTs), which can be produced as single or multi-walled. Multi-walled carbon nanotubes (MWCNTs) can be fabricated as biocompatible nanostructures (cylindrical bulky tubes). These structures are currently under investigation for their application in nanomedicine as viable and safe nanovectors for gene and drug delivery. In this chapter, we will provide you with the necessary information to understand the synthesis of MWCNTs, functionalization, PKH26 labeling, RNAi, and DNA loading for in vitro experimentation and in vivo implantation of labeled MWCNT in mice as well as materials used in this experimentation. We used this technique to manipulate microglia as part of a novel application for the brain cancer immunotherapy. Our published data show this is a promising technique for labeling, and gene and drug delivery into microglia.

Growth of carbon nanotube bundle arrays on silicon surfaces

The growth on silicon substrates of arrayed bundles of multiwalled carbon nanotubes (CNTs) by metal catalyzed chemical vapor deposition of carbon from ethylene has been characterized and optimized. We find that, while CNTs can grow on bare Si substrates, the growth is substantially more reproducible if a thin (∼3nm) barrier layer of aluminum oxide is used between the Si surface and iron catalyst. Optimum Fe thickness and growth temperature are 3.0 nm and 650 °C, respectively. We find that the CNT length increases linearly with time at a rate of 3–4μm∕min for up to 2 h of CNT growth, after which the growth ceases. The length of the resulting CNT can thus be controlled up to a maximum length of ∼500μm. Such control over CNT bundle length will be crucial in the incorporation of these bundle arrays into high-intensity electron field emission devices.

Millimeter-wave wireless power transfer technology for space applications

Technologies enabling the development of compact systems for wireless transfer of power through radio frequency waves (RF) continue to be important for future space based systems. For example, for lunar surface operation, wireless power transfer technology enables rapid on-demand transmission of power to loads (robotic systems, habitats, and others) and eliminates the need for establishing a traditional power grid. A typical wireless power receiver consists of an array of rectenna elements. Each rectenna element consists of an antenna together with a high speed diode and a storage capacitor configured in a highly tuned narrowband circuit for this purpose. The conversion of the microwave energy into DC in this fashion is almost instantaneous. Using a high power rectenna array in concert with a fast charging high performance battery can enable charging of the battery at very short time with a large power burst and discharge of it at a lower rate for an extended operation time for remote electronic assets. We have designed and fabricated a novel T-Slot antenna coupled rectenna array at 94 GHz for demonstrating efficient wireless power transfer in this frequency band. Assembly and testing of these devices are under progress now, and are showing great promise.

A multiple electron beam array for a 220 GHz amplifier

An electron beamlet array is being developed for use with power-combined, micro-machined folded waveguide circuits for a 50W, 220 GHz submillimeter RF device.