Nowadays, Carbon Fiber-Reinforced Polymers (CFRPs) have been widely applied in the aerospace and automotive industries. Secondary adhesive bonding, instead of using rivets or bolts in conventional mechanical fastenings, is promising in joining CFRPs because it is simple and applicable for cured parts, widely applied for repairing structures, and of light weight. However, the mechanical performance of secondary bonding is very sensitive to the treatment of CFRP parts. Besides, another concern arises from the fact that secondary bonded specimen often prematurely fails due to delamination and leads to a catastrophic structural collapse. While enhancing the joint strength and toughness is important, limiting the progression of damage is crucial, to ensure confidence in the design and allow enough time for maintenance and repair. Therefore, it is significant to introduce a crack arrest feature into the joints, to slow down (or even stop) the crack growth and achieve progressive failure. In this thesis, we employ advanced surface preparation strategies to enhance the strength, toughness, and safety of adhesively bonded CFRP joints. Globally uniform surface pretreatments, using conventional mechanical abrasion, peel-ply, and pulsed CO2 laser irradiation, are employed at first to improve the mechanical responses of adhesively bonded CFRP joints. Then, to better understand damage mechanisms and guide the joint design, characterizations of surface chemistry, surface energy, and surface morphology are correlated with obtained strength and toughness. Next, trench patterns, ablated by pulsed CO2 laser irradiation, are applied to CFRP substrate to further analyze the role of surface roughness on increased mode I energy release rate. Finally, a novel surface patterning strategy is proposed to achieve superior toughness enhancement in adhesively bonded CFRP joints to improve the joint safety. Such surface preparation strategy is assessed through 2D numerical models and realized experimentally by patterning of pulsed CO2 laser irradiation, illustrating its potential in toughening the joint and successfully delaying the crack propagation.

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Yes / Osmium nanocrystals can be fabricated by electron (3–50 nm, formed by atom migration), 785–815 nm laser (20–50 nm, in micelle islands), and microwave (ca. 1 nm in arrays, >100 mg scale) irradiation of a polymer-encapsulated OsII carborane; microfocus X-ray absorption studies at the Os LIII-edge show differences between the three preparation methods, suggesting that the electron-beam irradiated materials have a significant support interaction and/or surface oxidation, while the laser and microwave samples are more like metallic osmium. / Royal Society (University Research Fellowship No. UF150295 to NPEB), the Leverhulme Trust (Early Career Fellowship No. ECF-2013-414 to NPEB), the ERC (Grant No. 247450 to PJS), EPSRC (Grant No. EP/F034210/1 to PJS and EP/ J007153/1 to VGS), Diamond Light Source (Beam-time grant number SP11314).

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Abstract Orthodontic tooth movement is a biological response to a mechanical force. One of the challenges in orthodontics is obtaining desired tooth movement during treatment. Accelerating tooth movement and decreasing demands on anchorage can reduce treatment times and overall satisfaction for patient and doctor. Low-level laser therapy (LLLT) is emerging as a technology that may decrease orthodontic treatment time. Many in vitro and in vivo studies have reported the effects of low level lasers at random time points and energy densities. None of the studies have optimized the dose required for osteoblast proliferation and differentiation. The purpose of this study was to find the optimum stimulatory dose of low level laser irradiation (LLLI) on human osteoblast cell proliferation and differentiation and to analyze our findings with reference to the Arndt-Shultz Law of applied energy. In this in vitro study a GaAlAs laser at 830nm, 20 mW with continuous exposure at various doses were used on a human osteoblast cell line. According to the Arndt-Shulz Law weak stimuli initiate vital activity, moderate stimuli enhance the cellular activity with subsequent peak stimulation and greater stimuli (beyond a threshold value) may not have any influence or inhibit the vital activity. The implications of LLLI on human osteoblasts and influencing tooth movement in orthodontics were discussed. Human osteoblasts were cultured in minimum essential medium (MEM) complete medium consisting 10% fetal bovine serum and 1% antibiotics. Cells grown in complete medium were plated onto 96 well plate, allowed to adhere for 4-5 hours and were exposed to GaAlAs lasers at 6 , 12, 18, 24, 30, 36, 45, 60, 75, and 90 seconds. The cells treated with xiii LLLI were assessed for cell proliferation at 24, 48 and 72 hour intervals. A calorimetric cell proliferation assay (WST-1) assay was performed according to manufacture's instructions. The results indicated that at 24 hours the 6 and 12 seconds doses significantly inhibited proliferation compared to the control. At 48 hours the 30 seconds exposure significantly increased proliferation. At 72 hours time interval, cell proliferation was observed in a dose dependent pattern with a minimum at 6 seconds with peak proliferation at 18 seconds. A gradual decrease in cell viability was observed in the cells treated beyond this dose with a maximum inhibition seen at 60 seconds. At 75 and 90 seconds no difference was observed between the control and experimental group. To establish efficient acquisition of adequate quantities of alkaline phosphatase, cells were grown in 12 well plates in complete medium or osteogenic medium. These cells were exposed to LLLI for 18, 48, and 60 seconds. The activity of early osteogenic differentiation marker alkaline phosphatase (ALP) was investigated 10 days post exposure. Our results demonstrated that alkaline phosphatase activity at 2.4 - 7.3 J/cm2 with 48 - 60 seconds of exposure, and an incident power ranging from 85-269mw significantly increased. The findings suggest that these irradiated cells obeyed the Arndt Shulz Law governing cellular response to applied energy. Further this research indicates the possible role of LLLT to accelerate tooth movement in orthodontics. Complete disclosure of low level laser parameters is essential in order to accurately compare findings of researchers.

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A regeneração dos nervos periféricos é um processo natural, que demanda um período longo para se completar, havendo algumas evidências de que agentes físicos, inclusive o laser, podem acelerá-lo. O objetivo primordial deste estudo foi analisar a influência da irradiação com o laser de baixa potência (AsGaAL) sobre a regeneração nervosa, num modelo de lesão por esmagamento do nervo fibular comum de ratos. O objetivo secundário foi avaliar a concordância entre os índices funcionais do nervo fibular (PFI) e o dos nervos ciático (SFI) e tibial (TFI), segundo os métodos propostos por dois autores diferentes. Foram utilizados 35 ratos Wistar (130 dias de idade, massa corporal média de 240 gramas), divididos em quatro grupos no total, sendo três grupos de dez animais cada, conforme o procedimento realizado (1: esmagamento, sem tratamento; 2: esmagamento e tratamento simulado; 3: esmagamento e tratamento efetivo) e num grupo de cinco animais intactos, para controle. A lesão por esmagamento do nervo fibular comum foi obtida pela aplicação de uma carga de 5 Kgf por dez minutos, com uma pinça especialmente confeccionada para esse fim. A irradiação com o laser foi iniciada no primeiro dia pós-operatório, empregando um equipamento de laser AsGaAL de baixa potência (potência de 100 mW, comprimento de onda de 830 nm, dose de 140 J/cm2) de emissão contínua, pelo método transcutâneo pontual de contato, e continuada por 21 dias consecutivos. Os resultados foram avaliados pela medida da velocidade de marcha do animal e do índice funcional do fibular (PFI, de peroneal functional index). A massa corporal, a velocidade de marcha e o PFI foram medidos antes da operação e no 21º dia pós-operatório, o PFI foi obtido por meio de um programa de computador específico para esse fim, utilizando duas fórmulas diferentes. Os resultados mostraram que a massa corporal aumentou em todos os grupos, sem diferença estatística entre os períodos. A velocidade de marcha diminuiu, com diferença estatística em todos os grupos. O PFI aumentou em todos os grupos e com as duas fórmulas utilizadas na sua medida, mas no Grupo 3, embora sem diferença estatística nos períodos pré e pós-operatórios, evidenciando que a irradiação com o laser interferiu na regeneração do nervo fibular esmagado. Houve uma concordância moderada entre o PFI e o SFI, maior no período pós-operatório, demonstrando que o SFI pode ser empregado para a avaliação do nervo fibular, o que, entretanto, não é recomendável. Concluímos que a irradiação do laser de baixa potência influenciou na regeneração do nervo fibular comum esmagado de ratos, pela medida do índice funcional do fibular. / Peripheral nerve regeneration is a natural process, which requires a long period to complete, with a few evidences that physical agents including laser, can speed it up. The main objective of this investigation was to analyze the influence of low power laser (AsGaAL) irradiation on nerve regeneration, in a model of crush injury of the common fibular nerve of rats. A secondary objective was to evaluate the concordance between the fibular (PFI) and sciatic (SFI) nerves functional indexes, according to the methods proposed by two different research groups. Thirty-five Wistar rats (130 days of age, 240 g average body mass) were used and divided into four groups in total, be three groups of ten animals each, according to the procedure carried out (1: crush injury, no treatment; 2: crush injury, sham irradiation; 3: crush injury, effective irradiation), and a group of five untouched animals, for normal control. The crush injury was obtained by the application of a 5 kgf load for 10 minutes, using a spring forceps especially built for this purpose. Laser irradiation was started on the first postoperative day and continued for 21 consecutive days, using a commercially available continuous emission equipment (100 mW intensity, 830 nm wave length, 140 J/cm2 dose) and the transcutaneous punctual contact method. The results were appraised for the measure of the speed of the gait of the animal and of the functional index of the fibular (PFI, de peroneal functional index). Body mass, walking speed and the functional indexes were measured before the operation and on the 21st postoperative day, the functional indexes using a specific software especially developed for this purpose and the two different methods mentioned above. The results showed that the body mass increased while speed decreased with time for all groups, but without statistical significance. The PFI increased in all groups according to the two methods of evaluation used and more markedly in Group 3, although without statistical significance, period pre and post-operative. Moderate concordance was showed between PFI and SFI, higher in the post-treatment than in the preoperative evaluation, meaning that, although not recommendable, the SFI can be used to evaluate the fibular nerve. We concludes that low power laser irradiation influence the regeneration of the crush fibular nerve of rats, as measured by the peroneal functional index.

Sub-surface modification using a frequency doubled Ti: Sapphire femtosecond (fs) laser at 1kHz repetition rate, producing 100-fs pulse duration at 400nm, is studied in order to fabricate optical components within non-photosensitised polymethyl methacrylate (PMMA). This thesis explores the feasibility of producing three-dimensional optical devices in bulk polymers and polymer optical fibre (POF) using fs laser direct-writing techniques. For effective and optimal structuring, the laser writing parameters and focusing conditions, such as focusing depth, translation speed, and accumulated fluence are investigated by means of photo-modification thresholds; structural changes in dimensions and morphologies; and the magnitude of the refractive index modulation. The highest refractive index change is 3.2x10^(-3) achieved by using a dry (non-immersion) 0.45-NA objective for a single laser scan. Variations in damage threshold with focusing depths are attributed to a combination of material absorption or surface scattering of light due to contamination or surface imperfections, as well as oxygen diffusion and spherical aberration. Distortion of the laser-induced feature size and shape due to spherical aberrations is controlled and compensated by adjusting the laser power near the damage threshold. Permanent refractive index structures with cross-sectional dimensions of 2μm by 0.9μm and 3μm by 1.4μm are demonstrated at depths of 300μm and 500μm below the surface, resulting in the axial/ lateral ratio of 2.2 and 2.1, respectively. A novel phenomenon relevant to effects of translation speed on the fs laser modification is observed for the first time. As translation speeds reduce from 1.2 to 0.6mm/s, the optical damage threshold power decreases by 6μW, whilst other writing conditions remain constant. However, the damage threshold increases by 74μW with decreasing speeds from 0.6 to 0.35mm/s. This significant increase in threshold power enables inscription of refractive index gratings <5μm below the surface, because irradiation on the surface or near the surface initiates ablation rather than refractive index changes, and this forms a limit for writing useful structures. Compensating for this limit by using appropriate writing parameters highlights the potential of fabricating three-dimensional integrated optical circuits in thin (100μm) polymer substrates. Finally, highly localised fabrication of long period gratings into step-index single mode polymer fibres is demonstrated by removing distortion effects due to the curved surface. The distortion is compensated by sandwiching the fibre with two flat PMMA sheets, between which index-matching oil (n=1.5) is injected. This arrangement enables precise laser micro-structuring with flat interfaces and continuous inner material. The first demonstration of a 250-μm-period fibre grating, resulting in attenuation bands in the visible spectral region at 613, 633, 728, 816, 853, 877 and 900nm, is presented.