Ultrashort-pulsed laser ablation of poly-L-lactide (PLLA) for cell and tissue engineering applications

El contenido de los capítulos 3 y 4 están sujetos a confidencialidad 167 p.La tecnología de ablación láser es una herramienta bien establecida para la modificación superficial de materiales de distinta naturaleza (metales, polímeros, cerámicas, vidrio¿). La ablación de material mediante láseres de pulso ultracorto (menor que 10 picosegundos) es capaz de generar motivos topográficos micrométricos con una alta precisión debido a un proceso de ablación ¿frío¿ minimizando los efectos térmicos en el material sin producir cambios químicos en el mismo. Es por tanto una tecnología versátil para la fabricación de superficies microestructuradas en un proceso directo y sin contacto y aplicable a una gran variedad de materiales para generar motivos con distintas geometrías sobre superficies no planas. En este trabajo de tesis se aplica la tecnología de ablación mediante láser pulsado de picosegundos para la creación de micro-patrones topográficos en planchas de ácido poli-L-láctico (PLLA), para investigar el mecanismo de ablación del mismo y el efecto de los micro-patrones en el comportamiento de varios tipos de células mediante ensayos in vitro, con el objetivo final de elucidar el alcance de la influencia de estos micro-patrones en el comportamiento celular y evaluar la tecnología como método de fabricación de soportes en la ingeniería de tejidos

Advances in test and measurement of the interface adhesion and bond strengths in coating-substrate systems, emphasising blister and bulk techniques

In this paper, recent advances in the minimum-destructive testing of the adhesion of coating-substrate systems are reviewed, focusing on key techniques such as micro- and nano-scale levels of indentation, scratching, laser-induced wave shock, as well as the blister and buckle approach. Along with adhesion failure tests, the latest and most extensive applications of the adhesion test methods in nano-, micro- and bulk-coating technology and the associated techniques to determine the minimum damage defects left on the coatings are discussed and their use reviewed

Menhaden distribution as mediated by feeding (filter-feeding, phytoplankton)

Distribution patterns of the Atlantic menhaden Brevoortia tyrannus) have been evaluated in respect to the feeding ecology of the species. Feeding experiments, functional morphology, and field distribution studies with young postmetamorphic fish were conducted to differentiate the feeding dynamics of different size menhaden, and to define the relationship between feeding and distribution. Feeding experiments were conducted with 138 mm fork length menhaden to determine their particle size-specific feeding abilities. The minimum size of particles filtered, the minimum size threshold, was 7 to 9 (mu)m. Phytoplankton larger than the minimum size threshold and smaller than 20 (mu)m upper limit for nanoplankton, were filtered at efficiencies averaging 21% (n = 24). Prey particles exceeding the size limits of nanoplankton, were filtered at average efficiencies ranging from 22% to 84%. The mean filtration efficiency for Artemia sp. nauplii of 36% (n = 7) was lower than for smaller phytoplankton prey. as menhaden grown, their feeding repertoire shifts to larger planktonic organism. Surface ultrastructure, epithelial organization, and gross morphology of the branchial basket in menhaden were analyzed with respect to food particle capture, transport of food from the point of capture to point of ingestion, and potential gustatory reception. Branchiospinules, sites of small particle capture, lacked mucous cells, suggesting that food is captured primarily by mechanical sieving. Taste buds on the glossohyal are thought to be mechanoreceptors, whereas taste buds on the crest of the fifth branchial arch are thought to be chemoreceptors. Concurrent synoptic observation of the relative abundance of menhaden and parameters relevant to characterizing primary production along transects in estuarine creek ecosystems have been used to interpret the factors governing the fishes\u27 local distribution. The strongest associations were between catch and chlorophyll-a, catch and microflagellates, and catch and diatoms. Fish often distributed with a gradient of one phytoplankton taxa over another based on selectivity for large phytoplankton cell size. Menhaden are optimal foragers displaying kinesis selecting for areas of optimally sized prey, chemosensory preference for plant versus detrital particles, and possibly taxa specific avoidance. Comparison of latitudinal distribution patterns of menhaden with the latitudinal trends in plankton community size frequency suggest that fish stratify by size at latitude to maximize the efficiency with which they filter-feed

Theoretical and experimental study of generation mechanisms for laser ultrasound in woven graphite /epoxy composites with translaminar stitching

The aerospace industry is beginning to use advanced composite materials for primary load bearing structures and their failure mechanisms must be better understood to predict their behavior in service. The Combined Loads Tests (COLTS) facility is being constructed at the NASA Langley Research Center to characterize these failure mechanisms. Laser based ultrasonic NDE can monitor the samples during dynamic loading without interfering with the structural tests. However, the constraints of implementing laser ultrasound in a structures laboratory reduces the efficiency of the technique. The system has to be eye-safe because many people will be present during the structural tests. Consequently, laser light has to be delivered through fiber optics and a significant amount of light is lost. Also, the nature of the composite materials makes laser ultrasonic inspection difficult. The composites of interest are formed from woven layers that are stitched through the laminate thickness and bound in a resin matrix. These materials attenuate ultrasound strongly and exhibit a high degree of scattering.;Generation mechanisms in laser based ultrasound must be better understood to improve generation efficiency and consequently improve the signal-to-noise ratio. Although some experimental and theoretical studies have been conducted to characterize generation mechanisms, more extensive work is needed for composite materials. Specifically, we are concerned with generation mechanisms in thick, stitched composite structures. We describe a theoretical and experimental investigation of laser generated ultrasound in complex composite materials. We first develop a mathematical model describing the thermoelastic generation of ultrasound in a general anisotropic material. We then present a wide range of experimental data investigating the effects of laser and material parameters on the generated ultrasound. We specifically consider the relationship between laser pulse width, laser wavelength, and material composition. Finally, we compare this data to our mathematical model

Ultrashort-pulsed laser ablation of poly-L-lactide (PLLA) for cell and tissue engineering applications

El contenido de los capítulos 3 y 4 están sujetos a confidencialidad 167 p.La tecnología de ablación láser es una herramienta bien establecida para la modificación superficial de materiales de distinta naturaleza (metales, polímeros, cerámicas, vidrio¿). La ablación de material mediante láseres de pulso ultracorto (menor que 10 picosegundos) es capaz de generar motivos topográficos micrométricos con una alta precisión debido a un proceso de ablación ¿frío¿ minimizando los efectos térmicos en el material sin producir cambios químicos en el mismo. Es por tanto una tecnología versátil para la fabricación de superficies microestructuradas en un proceso directo y sin contacto y aplicable a una gran variedad de materiales para generar motivos con distintas geometrías sobre superficies no planas. En este trabajo de tesis se aplica la tecnología de ablación mediante láser pulsado de picosegundos para la creación de micro-patrones topográficos en planchas de ácido poli-L-láctico (PLLA), para investigar el mecanismo de ablación del mismo y el efecto de los micro-patrones en el comportamiento de varios tipos de células mediante ensayos in vitro, con el objetivo final de elucidar el alcance de la influencia de estos micro-patrones en el comportamiento celular y evaluar la tecnología como método de fabricación de soportes en la ingeniería de tejidos

The Zoo of Non-Fourier Heat Conduction Models

The Fourier heat conduction model is valid for most macroscopic problems. However, it fails when the wave nature of the heat propagation or time lags become dominant and the memory or/and spatial non-local effects significant -- in ultrafast heating (pulsed laser heating and melting), rapid solidification of liquid metals, processes in glassy polymers near the glass transition temperature, in heat transfer at nanoscale, in heat transfer in a solid state laser medium at the high pump density or under the ultra-short pulse duration, in granular and porous materials including polysilicon, at extremely high values of the heat flux, in heat transfer in biological tissues. In common materials the relaxation time ranges from $10^{-8}$ to $10^{-14}$ sec, however, it could be as high as 1 sec in the degenerate cores of aged stars and its reported values in granular and biological objects varies up to 30 sec. The paper considers numerous non-Fourier heat conduction models that incorporate time non-locality for materials with memory (hereditary materials, including fractional hereditary materials) or/and spatial non-locality, i.e. materials with non-homogeneous inner structure