Solvent-free peroxide-initiated polymer modifications are widely used to improve the physical and/or chemical properties of commodity plastics and elastomers. Although the reactions that underlie polymer grafting are known, our understanding of H-atom transfer reactions in this context is incomplete. Fundamental questions remain unanswered, such as the difference in reactivity between different polymers (polyethylene versus polypropylene and polyisobutylene) and differences in the regiochemical outcomes of grafting reactions upon them. Herein, experimental data pertaining to the H-atom transfers involved in polyolefin graft modifications were obtained to improve our fundamental understanding of these reactions by using radical-trapping techniques and quantum chemical calculations. In this project, experimental measurements of the efficiency of H-atom abstraction by t-butoxyl radicals from polyolefins, and suitable model compounds such as pentane, 2,4-dimethylpentane and 2,2,4,4-tetramethylpentane were determined. Insight is gained from alkyl-trapping experiments to quantify the relative reactivities of the primary, secondary and tertiary positions of the model compounds. Experimental data were compared to quantum chemical calculations, which revealed that entropic effects dictate the regioselectivity and preclude abstraction at the secondary position in favour of the less enthalpically-favourable primary abstraction site. MP2 and CBS-QB3 level calculations were able to reproduce experimental trends in model compound reactivity, while the highly common B3LYP density functional, used in other investigations on the subject, could not. / Thesis (Master, Chemical Engineering) -- Queen's University, 2011-10-20 16:48:38.083

No description available.

Objective: The purpose of this study was to compare the accuracy of cone beam CT (CBCT) imaging with digital orthopantomograms for determining bone quantity in the mandibular ramus. Methods: Twenty-nine cadaveric mandibles marked bilaterally with three fiducial markers were imaged using both CBCT and digital orthopantomography. After sectioning, four cross sectional measurements were made on the specimens and on the CBCT images. Two corresponding linear measurements were made on the orthopantomograms. Statistical analysis was used to compare the CBCT and orthopantomogram measurements with measurements from the anatomic specimens. Results: CBCT measurements were found to significantly differ from those made on the anatomic specimens (P<0.05). Linear measurements from the orthopantomograms varied by 15.9 percent compared to the anatomic specimens. Conclusion: CBCT and orthopantomogram measurements were significantly different from those of the anatomic specimens suggesting inaccuracies in the radiographic technology or a lack of precision in landmark identification.

No description available.

No description available.

Despite advances in bone grafting technology for musculoskeletal injury, re-injury or incomplete healing persists. Efforts to modify bone allografts sing proteins and growth factors show improvement in wound healing outcomes. We use FTY720, an agonist of S1P receptors 1 and 3, to improve bone graft integration through bone regeneration and vascularization. Four methods of delivering FTY720 into a bone defect are described: 1) FTY720 loaded onto a PLAGA-coated bone allograft and implanted in a critical size rat cranial defect; 2) FTY720 loaded onto a PLAGA-coated bone allograft and implanted in a rat tibial defect; 3) FTY720 loaded into a Matrigel plug and injected into a mouse tibial fracture; and 4) FTY720 directly adsorbed to human bone xenografts and implanted in a critical size rat cranial defect. In each of these models, FTY720 release was characterized, and bone regeneration and vascularization was monitored within the defect. Additionally, local tissue composition and immune response was evaluated. The results presented here indicate that FTY720 released locally into the bone defect improved new bone formation and vascularization, promoting improved graft integration.

The aim of this study was to test the application of an in situ–formed synthetic polyethylene glycol (PEG) as a biodegradable membrane with a variety of graft materials and hyperbaric oxygen (HBO) for enhanced bone regeneration. Critical-sized rabbit calvarial defects were created in bilateral parietal bones. Group 1 served as a control with unfilled defects, Group 2 had defects filled with morcelized autogenous bone, and Group 3 had defects filled with biphasic calcium phosphate. One defect was protected PEG membrane and half the animals were subjected to HBOT treatment. The unsupported membrane didn’t produce the desired bone regeneration in the unfilled and bone grafted groups. HBO didn't ameliorate the bone grafted or ceramic filled defects over the 6-week time period. Caution is recommended with the membrane over unsupported defects. Future assessments with HBO should be completed at the 12-week time point.

In this dissertation, small and large NaCl particle-derived surfaces (Ra > 40 microns) were generated on 2D Zn materials, and the surfaces were carefully studied concerning topography, corrosion behavior, and bone cell compatibility. Increases in surface roughness accelerated the corrosion rate, and cell viability was maintained. This method was then extended to 3D porous scaffolds prepared by a hybrid AM/casting technique. The scaffolds displayed a near-net shape, an interconnected pore structure, increasing porosity paralleled to an increased corrosion rate, an ability to support cell growth, and powerful antibacterial properties. Lastly, nano/micro (Rz 0.02–1 microns) topographies were generated on 2D Zn materials, and the materials were comprehensively studied with special attention devoted to corrosion behavior, biocompatibility, osteogenic differentiation, immune cell response, hemocompatibility, and antibacterial performance. For the first time, the textured nonhemolytic surfaces on Zn were shown to direct cell fate, and the micro-textures promoted bone cell differentiation and directed immune cells away from an inflammatory phenotype.

Thesis (M.S.)--Ohio University, November, 1985. / Title from PDF t.p.

Thesis (Ph. D.)--Cornell University, May, 2007. / Vita. Includes bibliographical references (leaves 134-143).