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Poly(L-lactic acid) (PLLA) is of interest in drug delivery applications for its biodegradable and biocompatible properties. Polymer-controlled drug delivery relies on the release of embedded drug molecules from the polymer matrix during its degradation. PLLA degradation exhibits an induction period, during which an insignificant amount of degraded products and embedded drug can be released. Due to this induction period, drug release is initially nonlinear, a complication in drug delivery applications. PLLA degradation is a function of crystallinity, such that control over its crystallinity tailors drug release over time. In this study, the effect of laser-induced PLLA crystallinity reduction on degradation is investigated. Samples having lower surface crystallinity are shown to have higher rates of molecular weight reduction and earlier mass loss than nonlasertreated samples, as observed from gel permeation chromatography and mass change. Wide-angle X-ray diffraction measurements show that crystallinity increases with degradation. A numerical model is implemented from hydrolysis and diffusion mechanisms to investigate the effect of laser irradiation on biodegradation. Controlled laser treatment of PLLA offers a method for constant drug release through the reduction of surface crystallinity.

Laser scribing of multilayer thin films is an important process for producing integrated serial interconnection of minimodules, used to reduce photocurrent and resistance losses in a large-area solar cell. Quality of such scribing contributes to the overall quality and efficiency of the solar cell and therefore predictive capabilities of the process are essential. Limited numerical work has been performed in predicting the thin film laser removal processes. In this study, a sequentially-coupled multilayer thermal and mechanical finite element model is developed to analyze the laser-induced spatio-temporal temperature and thermal stress responsible for SnO 2 :F film removal. A plasma expansion induced pressure model is also investigated to simulate the non-thermal film removal of CdTe due to the micro-explosion process. Corresponding experiments on SnO 2 :F films on glass substrates by 1064nm ns laser irradiation show a similar removal process to that predicted in the simulation. Differences between the model and experimental results are discussed and future model refinements are proposed. Both simulation and experimental results from glass-side laser scribing show clean film removal with minimum thermal effects indicating minimal changes to material electrical properties.

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A laser fusion joining method is investigated for the purpose of through thickness strengthening of fiber pre-forms used in the vacuum infusion fabrication of thick composite structures. Laser joining is achieved without filler materials to replace adhesives, pins or stitches used in conventional composite fabrication.A two step joining process is developed to fuse fibers within a single bundle and between multiple fiber bundles. Finite element analysis is used to investigate the joint strength with respect to joint morphology. Joint strength is found to be a function of the fiber contact angle and packing density at the joint interface. Tensile tests show that laser joined fiber bundles exhibit higher strength than comparable fastening methods. Lessons learned from the axial joining of fiber bundles are applied to joining in the radial and thickness directions of 3d pre-form architectures. Flow induced joint morphology and densification effects observed in the axial direction indicate the need for a two step joining process in the thickness direction. Fiber compaction effects on joint strength in the axial direction motivate the need for high fiber packing fraction at joint interfaces in the thickness direction. INTRODUCTIONComposite pre-preg fabrication involves placing densely packed resin infused tapes of reinforcement fibers in layers (laminates) and then curing to produce thin shell structures. Composite components manufactured from pre-preg processes exhibit high fiber packing fraction and high strength along the fiber directions, but offer little strength perpendicular to the fiber directions. Laminates of pre-preg construction contain no fiber reinforcements aligned in the thickness direction due to the layer by layer assembly process. Thus, pre-preg fabrication is undesirable for making composite parts requiring high through thickness strength and fracture toughness. One method for improving the through thickness strength of pre-preg constructed components is to insert metal pins through layers of pre-preg prior to curing [1,2]. Mechanical pinning increases through thickness strength, relying on matrix load transfer mechanisms between the fibers and pins. The insertion of metal pins into a stack of pre-preg lamina displaces the fibers in the lamina and introduces