Browsing by Subject "Vascular grafts"
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Item Hybrid Polyethylene Glycol Hydrogels for Tissue Engineering Applications(2012-07-11) Munoz Pinto, Dany 1981-Currently, organ transplant procedures are insufficient to address the needs of the number of patients that suffer of organ failure related disease. In the United States alone, only around 19% of the patients are able to get an organ transplant surgery and 25% die while waiting for a suitable donor. Tissue engineering (TE) has emerged as an alternative to organ transplant; thus, the aim of the present study was to validate a poly(ethylene glycol) diacrylate (PEG-DA) hydrogel system as a model for material scaffolding in TE applications. This work explores the influence of scaffold material properties on cell behavior. Specifically, scaffold modulus, mesh size, and biochemical stimuli were characterized and their influence on cell response was analyzed at the biochemical, histological and microenvironmental levels. Three different TE targets were evaluated: vocal fold restoration, vascular grafts and osteochondral applications. Vocal fold fibroblast (VFF) phenotype and extracellular matrix (ECM) production were impacted by initial scaffold mesh size and modulus. The results showed increasing levels of SM-?-actin and collagen production with decreasing initial mesh size/increasing initial modulus, which indicated that VFFs were induced to take an undesirable myofibroblast-like phenotype. In addition, it was possible to preserve VFF phenotype in long-term cultured hydrogels containing high molecular weight hyaluronan (HAHMW). On the other hand, regarding vascular graft applications, smooth muscle cell (SMC) phenotype was enhanced by increasing scaffold mesh size and modulus. Finally, the effect of scaffold inorganic content (siloxane) on rat osteoblasts and mouse mesenchymal stem cells was evaluated. Interestingly, the impact of inorganic content on cell differentiation seemed to be highly dependent on the initial cell state. Specifically, mature osteoblasts underwent transdifferentiation into chondrocyte-like cells with increasing inorganic content. However, Mesenchymal stem cells appeared to be preferentially driven toward osteoblast-like cells with an associated increase in osteocalcin and collagen type I production.Item Modeling and optimization of heparinized collagenous surfaces(Texas Tech University, 1987-08) Chen, Jyh-herngThe primary objective of this research is to determine the optimal conditions of heparin immobilization on collagen powder by varying pretreatment methods, pH of reaction environment and l-ethyl-3(3-dimethylaminopropyl) carbodiimide (i.e., EDC) to heparin weight ratio. This research is part of a series of investigations, of which the ultimate purpose is to develop an implantable small diameter (less than 6 mm diameter) (Parsonnet, 1976) vascular prosthesis which will remain functional while serving as a suitable interposition in the circulatory system.Item Optimization of a dual enzyme system and its effect on collagenous surfaces(Texas Tech University, 1985-12) Lokapur, A. KThe main purpose of this thesis is to co-immobilize heparin and plasmin onto collagenous substrates in an effort to produce a biomaterial possessing both fibrinolytic and thromboresistant properties. The path followed in this research has been to immobilize heparin onto collagenous substrates such as collagen powder, human umbilical vein grafts (HUVG) and chymotrypsin treated goat carotid arteries (GCA), and optimize its activity and stability over a period of time. Several pretreatment procedures have been studied in the case of heparin, which include fibronectin. Endothelial cell growth factor (ECGF),* methanol and hydrazine, hydrogen peroxide, and ammonium hydroxide. The crosslink agent 1-ethy1-3(3-dimethy1-aminopropy1) carbodiimide (EDO has been used to activate the carboxyl groups of the heparin structure. Heparin and plasmin have been co-immobi1ized on collagen powder and the activity of each has been studied in co-bound state. Experiments have shown that heparin in excess of 0.0 1 mg/sq cm can be immobilized on chymotrypsin treated GCA. that would remain stable for more than 3 weeks. In vivo studies have been performed on goats and dogs, the results of which show a patency rate of 807. after 1 week and 707« after 2 weeks, for the 10 samples that have been tested. Of all the pretreatment procedures, ammonium hydroxide appears to produce the most active and stable heparin complex. Co-immobi1ization of heparin and plasmin has shown that bound plasmin activity is increased if collagen powder is preimmobi1ized with heparin. Heparin, however, loses its activity. On the other hand, heparinization of plasmin bound collagen has not been successful. Furthermore, originally bound plasmin loses part of its activity. Experiments have been performed to determine the constants V^g>^ and K^j^ assuming M i chael i s-Menten kinetics for plasmin. The activation energy Eg has also been estimated for plasmin in soluble as well as immobilized form.Item The effects of design and surgical parameters on the anti-platelet and fibrinolytic activities of heparin/plasmin bound collageno-elastic tubes(Texas Tech University, 1988-08) Ho, Chih-huangNot available