The mechanical properties of the extracellular matrix are dynamic and change during biological processes such as disease progression and wound healing. Most synthetic (or man-made) tissue scaffolds have static properties. Therefore it is necessary to replate cells in order to determine the effects that different matrix mechanical properties have on cells, and virtually impossible to study the effects of a dynamically changing modulus on cell growth. There have been several scaffolds recently developed with tunable mechanical properties, but few exhibit any reversibility which is important for simulating repeated wounding and healing cycles. In this work, we develop a gelatin based hydrogel with azodianiline (ADA) as a secondary crosslinking unit. Upon irradiation with 365 nm light the gel softens as the ADA undergoes a photoisomerization. These changes can be reversed upon exposure to visible light. With applications in mechanobiology in mind, contraction at the cellular scale was measured, as well as the macroscopic changes in the shear elastic modulus and compressive modulus in response to exposure to UV and visible light.

Multilayer polymer systems are a focus of increasing research effort motivated by the possibility to realize compact and flexible energy storage and energy harvesting devices. However, the performance and stability of these polymer systems are highly dependent on temperature. In this study the structure of monolayer ferroelectric polyvinylidene fluoride (PVDF) thin films and the relaxation dynamics as a function of temperature are characterized using XRD, FTIR and second harmonic generation (SHG). Multilayered ferroelectric polyvinylidene fluoride (PVDF) systems are fabricated using enabling technology in co-extrusion for increased energy storage and energy harvesting efficiency as well as increased stability at elevated temperatures. To understand the physics of why these multilayered systems perform better than single layer PVDF characterization techniques using second harmonic generation (SHG), electric field induced second harmonic (EFISH) and Raman laser spectroscopy are developed. Results show that the combination of Raman and SHG is a very sensitive, non-destructive and versatile technique that can be used to study the ferroelectric and structural properties of these systems. The addition of the EFISH technique allows the interrogation of structural and dielectric properties within individual layers and at the interfaces.

Since the development of batteries by Edison and Volta, energy storage has become an integral part of our technology. As the energy storage devices we manufacture, research and develop new energy storage systems has been standardized. This dissertation present three alternative approaches to developing energy storage devices which could completely change the paradigm by which we manufacture and use energy storage. First, I present my work in developing energy storage devices that can be directly integrated into the back of Silicon photovoltaics. This includes initial proof of concept of direct integration of porous Si supercapacitors followed by investigations into high rate faradaic chemical reactions with porous Si and coated porous Si. These faradaic reactions have the possibility of higher energy storage and power matching the performance of silicon photovoltaics. Second, I demonstrate the feasibility of using scrap metals to make high rate batteries that can be paired with photovoltaics by anodizing scrap steel and brass using simple manufacturing methods compatible with do it yourself manufacturing. Third, I will present my work in developing multifunctional structural supercapacitor composites. I demonstrate the ability to measure in-situ the electrochemical response of solid state electrolyte and supercapacitors. I follow this initial work up with the realization of a structural supercapacitor with the mechanical performance approaching that of commercial structural composites and energy storage performance approaching commercial supercapacitors.

Nanomaterials have enabled significant breakthroughs in energy storage capabilities. In particular, the use of nanoscale components in lithium-sulfur and lithium-oxygen batteries have generated energy densities 2-3x greater than todayâs lithium-ion batteries. However, a major roadblock to commercially viable applications of nanomaterials is the ability to cost-effectively manufacture electrode-scale films while still maintaining precise control over the nanoscale morphology. In this regard, electrophoretic deposition (EPD) provides a promising tool for large-scale manufacture of nanomaterial systems using conventional liquid processing techniques. During EPD, the use of electrochemical equilibria to stabilize suspensions of nanomaterials eliminates the need for additives and provides a mechanism to control the placement of individual nanostructures on both 2D and 3D substrates through the application of an electric field. The viability of this process for large scale manufacture is demonstrated by integrating EPD electrode fabrication with nanomaterial synthesis processes on a benchtop roll-to-roll platform. Using this approach, lithium-sulfur and lithium-oxygen electrodes are fabricated that demonstrate enhanced mass-specific performance compared with identical material compositions assembled using conventional techniques. For lithium-oxygen batteries, the role that catalyst assembly plays in dictating the performance of the battery is elucidated and improved through EPD. Likewise, for lithium-sulfur batteries, the coating of an elemental sulfur layer is engineered in conjunction with an all-carbon EPD assembled electrode to produce one of highest capacity and most reversible lithium-sulfur cathodes ever reported. Overall, this thesis demonstrates the role of nanomaterial assembly in determining the energy storage performance of electrode-scale films and presents a method to control this assembly that is amenable to large-scale manufacture.

As electronic and optical devices shrink to the nanoscale, accurate methods for characterizing electromagnetic fields generated by sub-wavelength structures become increasingly important. Absorption in poly(methyl methacrylate) (PMMA) via 4th harmonic generation in metallic nanostructures is a way to characterize complex resonance modes. When exposed with a femptosecond Ti:sapphire oscillator, the damaged PMMA surrounding the nanoparticles can be imaged with an scanning electron microscope, creating an electric near-field intensity profile. This occurs without absorbing the fundamental frequency, and provides an accurate visualization of the resonant fields. Localized surface plasmonic near-fields generated by metallic nanorods have been mapped previously with this technique. In this document, nanorods and bowtie antennas are fabricated and the electric near-field intensity imaged with PMMA mapping. We then analyzed this data to determine more about the technique and about what drives the resonance of plasmonic nanoantennas.

An important aspect of engineering systems for use in extreme environments is understanding the performance of electronic components in radiation environments (e.g., space environments, nuclear reactors, particle accelerators). To accomplish this, experimental and computational modeling approaches are used to understand physical mechanisms that lead to system level failures. When experimentally investigating displacement damage, a common radiation effect, the most important parameter to measure is the particle fluence. An approach that offers benefits over traditional measurement techniques uses the degradation of current gain in silicon bipolar junction transistors as a direct metric for displacement damage in silicon. This thesis covers the bipolar device physics and particle/crystal interactions necessary to understand how displacement damage leads to gain degradation and describes how bipolar devices can be applied as displacement damage sensors to measure particle fluence. The use of bipolar junction transistors as displacement damage sensors in neutron irradiations is demonstrated at lower fluences than previously achieved and first-of-a-kind displacement damage sensor measurements for proton irradiations are provided. The non-ionizing energy loss (NIEL) of each particle is shown to adequately correlate the two particle types, neutrons and protons, across five orders of magnitude of particle fluence using three bipolar junction transistors (2N1486, 2N2484, 2N2222).

Colloidal semiconductor nanocrystals have become one of the most versatile systems for studying the fundamental properties of nanoscale materials and their applications. The ternary I-III-VI2 semiconductors hold particular promise for applications due to their flexible stoichiometry, low toxicity constituent elements, and range of desirable band gap energies (0.5 â 3.5 eV). Furthermore, I-III-VI2 nanocrystals can be isolated in metastable, anisotropic crystal structures not seen in the bulk. This structural anisotropy can be exploited to produce nanostructures with asymmetric morphology and electronic structure, which can enhance their performance in optoelectronic applications. In this dissertation, metastable, anisotropic crystal structures of I-III-VI2 materials are synthesized and their optoelectronic properties are investigated. CuInS2 has been widely explored for use in solar energy capture due to its band gap near the visible spectral region. Here, a direct synthesis to luminescent CuInS2 nanocrystals with the anisotropic wurtzite phase is developed and the mechanism of their formation is identified. A combined experimental and theoretical approach is then used to identify the radiative defect responsible for the luminescence observed. Furthermore, hybrid wurtzite CuInS2-Pt nanocrystals are prepared and their photoelectrical properties characterized to determine the efficacy of this system in photocatalytic applications. The knowledge obtained from the CuInS2 system is then applied to additional I-III-VI2 materials, CuFeS2 and AgFeS2. Wurtzite CuFeS2 is prepared using three distinct synthetic routes and the resultant nanocrystals are compared to each other and the In-containing analogues. Anisotropic, orthorhombic nanocrystals of AgFeS2 are also synthesized and characterized for the first time. The presence of Fe in both these systems leads to the observation of broad multimodal absorbance features at low energy, which can be utilized in thermoelectric and photothermal applications. Experimental measurements and density functional theory calculations indicate that this unique absorbance originates from changes in the composition of the nanocrystals.

Researchers discovered the existence of non-coding RNA while unraveling the secrets of the human genome. Non-coding RNA molecules are never translated into proteins, yet they are highly abundant and serve critical functions within all cells. Imbalances in one class of regulatory non-coding RNA, known as microRNA (miRNA), lead to diseases such as cancer and cardiovascular disease. MiRNA inhibition is a potent therapeutic strategy because single miRNAs can regulate hundreds of different disease-associated genes. Peptide nucleic acids (PNA) are excellent miRNA inhibitors, yet they have no innate ability to reach miRNA targets in the body. This worksâ central hypothesis is that therapeutic anti-miRNA activity can be improved by engineering nanoparticles to increase PNA blood circulation half-life, cellular uptake, and targeted delivery to the cytoplasm of diseased cells. In this thesis, two highly tunable biomaterials (porous silicon and âsmartâ polymers) are combined to form composite nanoparticles that improve the PNA therapeutic delivery. These nanocomposites are shown to be non-toxic, increase PNA blood-circulation half-life from <1 min to 70 min, and improve PNA delivery to its site of action in target cells. This thesis demonstrates how nanotechnology can aid the clinical translation of a promising new class of therapeutics.

Porous silicon, a nanostructured material formed by electrochemical etching of a silicon substrate, is an ideal candidate for constructing optical biosensors due to its large internal surface area, straightforward fabrication, and tunable optical properties that can be exploited to form numerous photonic structures. A major challenge for porous silicon biosensors is its reactive surface that is highly susceptible to oxidation and corrosion in an aqueous environment. In DNA sensing applications, porous silicon corrosion can mask the DNA binding signal as the dissolution of porous silicon is accelerated by the negative charges on the phosphate backbone of the DNA molecules. This corrosion process can be mitigated through surface passivation of porous silicon and the use of charge neutral peptide nucleic acid molecules as capturing probes for DNA targets. Complete mitigation can be achieved by additionally introducing Mg2+ ions to shield the negative charges on the DNA targets. Another key challenge facing porous silicon biosensors is the inefficient analyte transport through nanopores, which can be as slow as a few molecules per pore per second for molecules whose size approaches that of the pore opening. An open-ended porous silicon membrane is demonstrated to overcome the mass transport challenge by allowing analytes to flow through the pores in microfluidic-based assays. The flow-through approach for biosensing using porous silicon membranes enables a 6-fold improvement in sensor response time compared to closed-ended, flow-over porous silicon sensors when detecting high molecular weight analytes (e.g., streptavidin). For small analytes, little to no sensor performance improvement is observed as the closed-ended porous silicon films do not suffer significant mass transport challenges with these molecules. Experimental results and finite element method simulations also indicate that the flow-through scheme enables more reasonable response times for the detection of dilute analytes and reduces the volume of solution required for analysis. Overall, the improvement of surface stabilization and analyte transport efficiency in porous silicon photonic structures opens the door to a fast and reliable optical biosensing platform.

This research is focused on developing a new type of gamma-ray scintillator and is motivated by the need for more accurate positron emission tomography (PET) imaging. PET scans are used to display regions of high-metabolic activity within the body and can indicate the presence of tumors, so clear images are essential for accurate diagnoses and treatment options. Scintillation detectors currently used for PET scans typically have a time resolution of hundreds of ps that yields images with poorly defined and blurred boundaries. Conversely, ZnO nanowires have a response time that is an order of magnitude faster with the potential for an analogous improvement to spatial resolution. Moreover, initial experiments show ZnO nanowires are radiation hardened with highly transient lattice defects. To optimize overall scintillator efficiency, the emission can be enhanced through a combination of optical-cavity effects (15x enhancement) and plasmon-exciton coupling (3x enhancement), while the low interaction volume of the nanowires can be addressed by adding a high-Z backing layer to attenuate incoming gamma rays. The ability to decouple, and address separately, emission efficiency and gamma-ray interaction provides a unique materials workbench and establishes ZnO nanowires as a highly promising PET scan scintillator material.