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This thesis focuses on the electrical output of polyaniline films subjected to uniaxial strain in hydrochloric acid solutions. Polyaniline belongs to novel class of materials known as conducting polymers. Alternating single and double bonds in the backbone of conducting polymers allow them to transmit electric charge when they are doped with negatively charged ions. Modifying the degree of doping and other electrical/chemical treatments allow conducting polymers to exhibit conducting, semi-conducting, or insulating electrical properties. Resilient mechanical properties, good processability, and low cost make conducting polymers good candidates for applications traditionally held by metals and semi-conductors. When tensile strain is applied to polyaniline in an electrolyte solution, the material selectively absorbs negatively charged ions. This charge imbalance produces a measurable electrical output. Theoretical models based on Fick’s second law of diffusion were compared against experimental results to determine fundamental material properties such as diffusivity and ion solubility in polyaniline. These properties were used to quantify polyaniline as a sensor material based on characteristics including sensitivity, accuracy, precision, range, linearity, and error. Films were cast from solutions of polyaniline powder (Mn = 65,000) in N-methyl-2-pyrrolidinone solvent, with thicknesses ranging from 2.72 to 158 µm.

Intravascular devices, such as stents, must be rigorously tested before they can be approved by the FDA. This includes bench top in vitro testing to determine biocompatibility, and animal model testing to ensure safety and efficacy. As an intermediate step, a blood vessel mimic (BVM) testing method has been developed that mimics the three dimensional structure of blood vessels using a perfusion bioreactor system, human derived endothelial cells, and a biocompatible polymer scaffold used to support growth of the blood vessel cells. The focus of this thesis was to find an in-house fabrication method capable of making cellular scaffolding for use in the BVM. Research was conducted based on three aims. The first aim was to survey possible fabrication methods to choose a technique most appropriate for producing BVM scaffolding. The second aim was to set up the selected fabrication method (electrospinning) in-house at Cal Poly and gain understanding of the process. The third aim was to evaluate consistency of the technique. The work described in this thesis determined that electrospinning is a viable fabrication technique for producing scaffolding for BVM use. Electrospun scaffolding is highly tailorable, and a structure that mimics the natural organization of nano sized collagen fibers is especially desirable when culturing endothelial cells. An electrospinning apparatus was constructed in house and a series of trial experiments was conducted to better understand the electrospinning process. A consistency study evaluated scaffold reproducibility between different spins and within individual spins while setting a baseline that can be used for comparison in future work aimed at electrospinning.

<p>  </p> <p>The smashing mantis shrimp is a crustacean that uses its dactyl club to defend itself or prey on other animals. This dactyl club is so strong that it can reach accelerations as high as a bullet of a caliber 0.22 gun and impact without breaking. We seek to understand the secrets behind the staggering properties of this club that withstand several high-damage impacts without breaking catastrophically. The dactyl club comprises three parts: the impact region, the periodic region, and the striated region.</p> <p>The first region of interest is the periodic region. This region is made of a helicoidal arrangement of fibers called Bouligand architecture, and in this architecture, cracks only form in the matrix between fibers. The first research project approximates the Bouligand composite with a single helicoidal crack embedded in an isotropic material. The test consists of a disk with a notch under quasistatic biaxial boundary conditions. We found an enhancement of mechanical properties when we increase the pitch angle.</p> <p>In the following section, a coarse-grained model is developed. This model allows multiple crack formation. This approximation tells us that as the initial crack grows, the driving force of crack propagation, the energy release rate, diminishes. The crack stops growing, confining itself, and allowing multiple crack nucleation and delocalization. At the same time, this dissipates more energy as more cracked surfaces appear.</p> <p>Hashin damage model with a cohesive zone model are used under different boundary conditions, geometries, and material properties, to model Bouligand composites. The helicoidal composites outperform the reference ones in peak load and absorbed energy.</p> <p>The next part of this thesis investigates the bicontinuous particles present in the impact surface of the dactyl club. These bicontinuous particles consist of a soft phase (organic) and a hard phase (hydroxyapatite) that can withstand high strain rates. Their stiffness and strength increase with strain rate. On the other hand, preliminary studies suggest that they perform well in cyclic loading.</p> <p>Finally, we proceed to use the helicoidal composites to design structural parts. We introduce a model for simulating the fiber-reinforced composites called LARC05. We verify, validate, and then use models for fiber-reinforced composites.</p>

Damage to our tissues occurs daily and must be repaired by the body in a timely manner in order to prevent infection and restore tissue integrity. Many cell types are involved in the healing process, but it is the cells of the stroma that are largely responsible for rebuilding fibrous tissue, which provides structure and support for all other cell types during healing. This dissertation focuses on stromal tissue repair, the rebuilding of fibrous tissue by fibroblasts following injury. Specifically, I focus on 1) models to study wound healing in vitro, and the specific biological processes of healing that each model captures, 2) the response of engineered stromal microtissues to different methods of injury, namely laceration and laser ablation, and the subsequent clearance and rebuilding of the extracellular matrix by fibroblasts, and 3) how different types of stromal cells and extracellular matrix proteins contribute to tissue repair in vitro.

Chronic wound healing can be seriously impeded by the formation of biofilms, infections, peri-wound edema, hematoma, osteomyelitis, and the formation of reactive oxidative species (ROS). We hypothesize that a scaffold created from Silver-Doped Nanoceria (AgCNP) embedding silk can be beneficial to aid the wound healing process, inhibit inflammation and prevent microorganisms from forming a biofilm over the wound. Current wound healing methods such as intradermal injections are not advantageous to use since they can cause unwanted responses elsewhere in the body other than the wound site. Silk, however, has a positive impact on the wound healing effect and can be used as an alternative delivery method to deliver the drugs to the target site rather than intradermal injections since its degradability is controllable and it is bioresorbable, therefore it can get absorbed by the body and degrade safely without causing bodily harm. AgCNPs are used as they have antimicrobial/antioxidant properties to scavenge harmful ROS species at the wound site and can also modify silk for UV protection. As silk's degradability can be controlled, our experiment will involve collecting data on release studies conducted in vitro to see how long it takes for the silk patch to release the drugs. Our goal is to ensure the drug is not released immediately but rather over a longer controlled time manner to protect the wound while healing.

Coral reefs are an important element of marine ecosystem that are critical to maintain a healthy environment. Unfortunately, in recent years coral reefs are doing poorly and many in parts of the ocean are simply dying. Therefore, study of coral’s structural response to external loads could answer what will happen with their structures, while they exhibit different types of loading. Therefore, the proposition of using in-situ micro-Raman spectroscopy to study skeletons of Acropora cervicornis was used. Coral skeleton samples I subjected to mechanical loading studied their vibrational properties by exciting the material with 532nm visible light. A uniaxial compressive load I applied using a MTS universal testing machine and then using the Raman Spectroscopy to study the vibrational response of coral skeletons. Indentations used Vickers Hardness tester and performed 2D mapping of the coral structure around the indentation. If it’s expected that as a result of the proposed research the better understanding of structural stability of the Acropora Cervicornis coral skeletons will be achieved.

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