Fibrin is a biopolymer that assembles into a network during blood coagulation to become the structural scaffold of a blood clot. The precise mechanics of this network are crucial for a blood clot to properly stem the flow of blood at the site of vascular injury while still remaining pliable enough to avoid dislocation. A hallmark of fibrin's mechanical response is strain-stiffening: at small strains, its response is low and linear; while at high strains, its stiffness increases non-linearly with increasing strain. The physical origins of strain-stiffening have been studied for other biopolymer systems but have remained elusive for biopolymer networks composed of stiff filaments, such as fibrin. To understand the origins of this intriguing behavior, we directly observe and quantify the motion of all of the fibers in the fibrin networks as they undergo shear in 3D using confocal microscopy. We show that the strain-stiffening response of a clot is a result of the full network deformation rather than an intrinsic strain-stiffening response of the individual fibers. We observe a distinct transition from a linear, low-strain regime, where all fibers avoid any internal stretching, to a non-linear, high-strain regime, where an increasing number of fibers become stretched. This transition is characterized by a high degree of non-affine motion. Moreover, we are able to precisely calculate the non-linear stress-strain response of the network by using the strains on each fiber measured directly with confocal microscopy and by assuming the fibers behave like linearly elastic beams. This result confirms that it is the network deformation that causes the strain-stiffening behavior of fibrin clots. These data are consistent with predictions for low-connectivity networks with soft, bending, or floppy modes. Moreover, we show that the addition of small contractile cells, platelets, increases the low-strain stiffness of the network while the high-strain stiffness is independent of the presence of the platelets; this is also consistent with expectations for small contractile elements in a network with low connectivity. Our results elucidate the origins of strain-stiffening in fibrin networks as well as the mechanism underlying platelet-induced clot stiffening. / Physics

Microbeam radiation therapy (MRT) is a potential cancer therapy technique that uses an intense X-ray beam produced by a synchrotron. In MRT, an array of microplanar beams, called a microbeam, is delivered to a tumour. The dose at each centre of planar beams is extremely large (several hundred grays) while dose level in the valley between the peaks is below several tens of gray. Moreover, the width of each planar beam is typically 20 - 50 µm, and the distance from a centre of planar-beam to that of adjacent beam is 200 - 400 µm. For the latter reasons, the fundamental requirements for the dosimetry technique in MRT are (1) a micrometer-scale spatial resolution and (2) detection sensitivity at large doses (5 - 1000 Gy). No existing detectors can satisfy those two requirements together. The objective of the Ph.D. research is to develop a prototype dosimetry technique which fulfils the requirements for measuring the dose profile in the microbeam. The currently used approach relies on the indirect detection of X-rays; in which the X-ray dose is recorded on a detector plate, and then the recorded signals are digitized using a reader. Our proposed approach utilizes Sm3+-doped polycrystallites, glasses, and/or suitable glass-ceramics (though our approach is not limited to the use of Sm ion) for the detector plate, in which a valence reduction of Sm3+, that is the conversion of Sm3+ to Sm2+, takes place upon irradiation of X-rays. The extent of reduction is further read out using confocal fluorescence microscopy via the photoluminescence (PL) signals of Sm3+ and Sm2+. The work carried out throughout the course of the research includes the construction of confocal fluorescence microscopy, synthesis and characterizations of dosimeter materials, as well as application tests of our approach for measuring the dose profile of a microbeam used at synchrotron facilities -- Canadian Light Source (CLS), Saskatoon, Canada, European Synchrotron Radiation Facility (ESRF), Grenoble, France, and SPring-8, Hyogo, Japan. Further, the research has shown that 1 % Sm-doped fluoroaluminate glass is one of the best candidates for the type of dosimetric application. It has the dynamic range of ~1 to over 1000 Gy which covers the dose range used in MRT, excellent signal-to-noise ratio (large extent of Sm3+ → Sm2+ change), and excellent stability of recorded signal over time. The recorded signal in the detector is erasable by heating or exposing to light such as UV. Furthermore, with a use of confocal microscope, it has ability to measure the distribution pattern of dose over the cross-section of microbeam. Therefore, we believe that our approach is one of the most promising techniques available.

The first real-time uorescence confocal microlaparoscope has been de- veloped that provides instant in vivo cellular images, comparable to those provided by histology, through a nondestructive procedure. The device in- cludes an integrated contrast agent delivery mechanism and a computerized depth scan system. The instrument uses a fiber bundle to relay the image plane of a slit-scan confocal microlaparoscope into tissue. The confocal laparoscope was used to image the ovaries of twenty-one patients in vivo using uorescein sodium and acridine orange as the uorescent contrast agents. The results indicate that the device is safe and functions as designed. A Monte Carlo model was developed to characterize the system performance in a scattering media representative of human tissues. The results indicate that a slit aperture has limited ability to image below the surface of tissue. In contrast, the results show that multi-pinhole apertures such as a Nipkow disk or a linear pinhole array can achieve nearly the same depth performance as a single pinhole aperture. The model was used to determine the optimal aperture spacing for the multi-pinhole apertures. The confocal microlaparoscope represents a new type of in vivo imaging device. With its ability to image cellular details in real time, it has the potential to aid in the early diagnosis of cancer. Initially, the device may be used to locate unusual regions for guided biopsies. In the long term, the device may be able to supplant traditional biopsies and allow the surgeon to identify early stage cancer in vivo.

No description available.

Serotonin (5-HT)-containing neuroepithelial cells (NECs) of the gill filament are believed to be the primary O2 chemosensors in fish. In the mammalian carotid body (CB), 5-HT is one of many neurotransmitters believed to play a role in transduction of hypoxic stimuli, with acetylcholine (ACh) being the primary fast-acting excitatory neurotransmitter. Immunohistochemistry and confocal microscopy was used to observe the presence of the vesicular acetylcholine transporter (VAChT), a marker for the presence of ACh, and its associated innervation in the gills of zebrafish. VAChT-positive cells were observed primarily along the afferent side of the filament, with some cells receiving extrabranchial innervation. No VAChT-positive cells were observed in the gills of goldfish; however, certain key morphological differences in the innervation of goldfish gills was observed, as compared to zebrafish. In addition, in zebrafish NECs, whole-cell current is dominated by an O2-sensitive background K+ current; however, this is just one of several currents observed in the mammalian CB. In zebrafish NECs and the CB, membrane depolarization in response to hypoxia, mediated by inhibition of the background K+ (KB) channels, is believed to lead to activation of voltage-gated Ca2+ (CaV) channels and Ca2+-dependent neurosecretion. Using patch-clamp electrophysiology, I discovered several ion channel types not previously observed in the gill chemosensors, including Ca2+-activated K+ (KCa), voltage-dependent K+ (KV), and voltage-activated Ca2+ (CaV) channels. Under whole-cell patch-clamp conditions, the goldfish NECs did not respond to hypoxia (PO2 ~ 11 mmHg). Employing ratiometric calcium imaging and an activity-dependent fluorescent vital dye, I observed that intact goldfish NECs respond to hypoxia (PO2 ~ 11 mmHg) with an increase in intracellular Ca2+ ([Ca2+]i) and increased synaptic vesicle activity. The results of these experiments demonstrate that (1) ACh appears to play a role in the zebrafish, but not goldfish gill, (2) goldfish NECs likely signal hypoxic stimuli primarily via the central nervous system (CNS), (3) goldfish NECs express a broad range of ion channels as compared to the NECs of zebrafish, and (4) goldfish NECs rely on some cytosolic factor(s) when responding to hypoxia (PO2 ~ 11 mmHg). This thesis represents a further step in the study of neurochemical and physiological adaptations to tolerance of extreme hypoxia.

Polyphenol oxidases (PPOs) are ubiquitous enzymes that oxidize phenols to quinones in the presence of molecular oxygen, often leading to tissue discolouration. They are sometimes considered as defense proteins but other functions, for example in phenolic compound biosynthesis, have also been found. In this thesis, bioinformatic searches were conducted to identify putative PPO genes from available genomes representing five Viridiplantae lineages: chlorophytes, bryophytes, lycophytes, monocotyledonous anthophytes and eudicotyledonous anthophytes. Duplicated PPO genes were found in most land plant genomes. A detailed investigation of the poplar (Populus trichocarpa) PPO gene family found nine genes that exhibit differential expression profiles during development and following stress, of which PtrPPO1 was the only significant wound-inducible PPO gene. A phylogenetic reconstruction of the poplar PPOs identified PtrPPO13 to be an unusual PPO homolog and it was studied in detail. Experimental evidence indicated that PtrPPO13 is expressed in most organs, and unlike most PPOs, is localized to the vacuole. Together, the phylogeny, gene expression and subcellular localization studies suggest that PPOs are likely to have variable physiological functions in plants and that PtrPPO13 is distinct from most typical PPOs. / Graduate / 0309

This project has provided a better understanding of the human conjunctiva, the glistening tissue covering the white of the eye, at the cellular level. The observations of this study may serve as a useful marker against which changes in conjunctival tissue due to disease, surgery, drug therapy or contact lens wear can be assessed. Laser scanning confocal microscopy was used to observe and measure characteristics the conjunctiva of healthy human volunteer subjects. It was concluded that this technique is a powerful tool for studying the human conjunctiva and assessing key aspects of the structure of this tissue. The effects of contact lens wear on the conjunctiva can be investigated effectively at a cellular level using this technology.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 132-142).

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Texas at Austin, 1997. / Vita. Includes bibliographical references (leaves 188-199). Available also in a digital version from Dissertation Abstracts.