Therapeutic angiogenesis is a promising technique to treat ischemia by creating new blood vessels. The aim of this thesis was to develop and characterize biodegradable elastomers for localized delivery of growth factors and to investigate the ability of released growth factors to induce angiogenesis. An osmotic delivery mechanism using photo-cross-linked elastomers based on trimethylene carbonate (TMC) was used to deliver vascular endothelial growth factor (VEGF165) and hepatocyte growth factor (HGF) alone or in combination at two different doses. It was hypothesized that elastomers made of TMC can provide an effective osmotic release using trehalose as a main osmotigen and that the use of TMC would eliminate the microenvironmental pH drop implicated in denaturing acid sensitive growth factors. To obtain an insight into the degrading zone in which growth factors will be released, the in vivo degradation mechanism and tissue response were investigated. The in vivo degradation of D,L-lactide/ε-caprolactone (DLLACL) elastomers that degrade by hydrolysis was investigated for comparison. Cross-link-density played a significant role in the degradation pattern of DLLACL elastomers. TMC and TMCCL elastomers degraded by surface erosion and oxidation played a significant role in their in vivo degradation. To obtain an efficient release, the mechanical properties of TMC elastomers were tailored by copolymerizing TMC with CL and DLLA and/or by controlling the cross-link density. The delivery device was able to provide a sustained release of growth factors for longer than two weeks with no initial burst. Cell based bioactivity assays indicated that released growth factors were highly bioactive over the entire release period. Microenvironmental pH studies using FITC-BSA indicated no significant drop in pH in TMC elastomers that contained small amounts of DLLA. Using 125I-VEGF165, it was found that the osmotic delivery can provide a direct in vivo-in vitro release correlation. Released growth factors were able to induce angiogenesis in rats when tested by subcutaneous implantation. Angiogenesis was dose dependent for both VEGF165 and HGF. Combined release of VEGF and HGF achieved the best results. The formed blood vessels were stable during the active release period, and they were normal looking and connected to the surrounding vasculature. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2009-09-03 14:54:28.709

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Myocardial infarction (MI) is a leading cause of death in the United States, claiming the lives of approximately 500,000 people each year. The infarcted heart undergoes a compensatory process called cardiac remodeling, which adversely changes left ventricular (LV) size and function and eventually may lead to heart failure. To date, the only clinical treatments for this condition include surgical restoration of blood flow to the ischemic region (e.g., angioplasty), or pharmacological treatments (e.g., angiotensin converting enzyme inhibitors) which indirectly manage the symptoms of cardiac remodeling. Reperfusion of ischemic heart tissue significantly limits myocardial damage after an MI; however, many MI patients are not candidates for traditional reperfusion surgery. Recently, there has been much interest in non-surgical myocardial reperfusion via pro-angiogenic compounds, specifically vascular endothelial growth factor (VEGF). Although animal studies using therapeutic VEGF have shown promising results, these results have failed to translate into successful clinical trials. This may be due to the short half-life of VEGF in circulation. Increasing the dose of VEGF may increase its availability to the target tissue, but harmful side-effects remain a concert. Encapsulating VEGF and selectively targeting it to the MI border zone may improve vascularization, cardiac function, reduce adverse remodeling associated with MI, and may avoid harmful side effects associated with systemic delivery. Anti-P-selectin conjugated immunoliposomes containing VEGF were developed to target the P-selectin ligand overexpressed in the infarct border zone in a rat MI model. Serial echocardiography and Doppler imaging were used to characterize evolutionary changes in LV geometry and function over a period of four weeks after MI. At four weeks, hearts were excised and stained to measure vascularization and collagen deposition. Targeted VEGF treatment resulted in significant improvements in fractional shortening at four weeks post-infarction (32.9 ± 2.2% for targeted VEGF treated vs. 16.9 ± 1.4% for untreated MI). Functional improvements in treated MI hearts were accompanied by a 74% increase in perfused vessels in the MI border zone, compared to untreated MI hearts. Left ventricular filling dynamics were significantly improved in the targeted VEGF treated group, which resulted in a decrease in LV end diastolic pressure in VEGF treated hearts (23.4 ± 2.9 mm Hg), compared to untreated MIs (81.8 ± 31.8 mm Hg). At four weeks after infarction, hearts treated with targeted VEGF therapy exhibited a 37% reduction in collagen deposition, compared to untreated MI hearts. Targeted VEGF therapy significantly improves vascularization, cardiac function, and moderates adverse cardiac remodeling after an infarction. / Mechanical Engineering

The aim of this thesis is to determine the feasibility of an injectable delivery system based on 5-ethylene ketal ε-caprolactone for localized delivery of vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) for treating critical limb ischemia. HGF and VEGF were chosen because of their ability to simultaneously stimulate the proliferation and migration of endothelial cells, to initiate the formation of blood vessels and the recruitment of pericytes to stabilize the blood vessels. Homopolymer of 5-ethylene ketal ε-caprolactone and its copolymer with D,L-Lactide were synthesized by ring opening polymerization using hydrophobic initiator (octan-1-ol) or an hydrophilic initiator (MPEG), and stannous octanoate as a co-initiator/catalyst. The resulting polymers were amorphous and viscous liquids at room temperature. The viscosity, biodegradation rate, and release rate were varied by copolymerizing with D,L-lactide and/or initiating with MPEG or octan-1-ol. In vitro, the polymers degraded with surface erosion characterized by a nearly linear mass loss with time with no significant change in number average molecular weight and glass transition temperature. The ratio of EKC to DLLA in the copolymer remained the same throughout the degradation studies. A similar degradation mechanism was observed in vivo when the copolymer initiated with octan-1-ol was implanted subcutaneously in rats. In vivo, the polymer exhibited a moderate chronic inflammatory response, characterized by the presence of neutrophils, macrophages, fibroblasts and fibrous capsule formation. The inflammatory response decreased with time but was still on going after 18 weeks of subcutaneous implantation. Protein release from the polymer was transported by convection through the hydrated polymer region, at a rate determined by the osmotic pressure generated and the hydraulic conductivity of the polymer. Highly bioactive VEGF and HGF were released in a sustained manner, without burst effect for over 41 days when delivered simultaneously, using the osmotic release mechanism. VEGF was released at the rate of 36 ± 7 ng/day for 41 days, while HGF was released at the rate of 16 ± 2 ng/day for 70 days. Factors that influenced release of proteins were their solubility in the concentrated trehalose solution and hydraulic permeability of the polymer. This delivery system can serve as a potential vehicle for controlled release of VEGF and HGF for treating critical limb ischemia or the controlled release of other proteins for other clinical applications. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2012-05-23 10:18:48.307