Nanofibrous vascular grafts
Title Alternative:Nanovlákenné cévní náhrady
Loading...
Date
2015-01-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Technická Univerzita v Liberci
Abstract
V současnosti není v klinické praxi cévní náhrada s vnitřním průměrem pod 6 mm, která by spolehlivě fungovala v dlouhodobém horizontu. Disertační práce se zabývá přípravou maloprůměrových cévních náhrad z biodegradabilních polymerů, které jsou testovány jako potenciálně vhodné materiály pro přípravu tkáňových nosičů pro vaskulární cévní systém. Hlavní myšlenkou tkáňového inženýrství je napodobování přirozeného prostředí - mezibuněčné hmoty. Proto byla ideální cévní náhrada navržena jako dvouvrstvá tubulární struktura s definovanou morfologií vláken. Tato definovaná struktura byla vytvořena elektrostatickým zvlákňováním polykaprolaktonu (PCL). Podobnost morfologie vláken s mezibuněčnou hmotou předpokládá, že po implantaci do organismu proběhne regenerace funkční tkáně. Kromě polymeru polykapronu byl testován polymer ze stejné třídy polyesterů - kopolymer polylatidu a polykaprolaktonu (PLC 70/30). Cévní náhrada připravená z toho polymeru byla tvořena pouze jednou vrstvou.Pro porovnání vlastností polymerů byla provedena charakterizace obou elektrostaticky zvlákněných materiálů. Kopolymer PLC je mírně hydrofilnějšínež polykaprolakton. Termické vlastnosti obou polymerů se značně liší. Zatímco kopolymer PLC je převážně amorfní s teplotou tání okolo 110°C, polykaprolakton je semikrystalický polymer s teplotou tání kolem 57°C. Mechanická pevnost a prodloužení je přibližně desetkrát větší u elektrostaticky zvlákněného kopolymeru PLC než u polykaprolaktonu.Biologické testování elektrostaticky zvlákněných materiálů potvrdilo biokompatibilitu obou testovaných polymerů s fibroblasty i s endotelovými buňkami. Vyšší proliferační stupeň byl pozorován při kultivaci buněk na mírně hydrofilnějším kopolymeru PLC, který zřejmě umožňuje lepší buněčnou adhezi. Vlákenné materiály byly rovněž testovány po interakci s krevními destičkami, které se po inkubaci aktivovaly a agregovaly. Mírnější aktivace byla pozorována po interakci s hladkými foliemi vyrobenými ze stejných materiálů, což dokládá, že na aktivaci destiček má vliv morfologie povrchu. Zvýšená aktivace trombocytů byla naopak pozorována při dynamické inkubaci vlákenných tubulárních vzorků.Vlákenné tkáňové nosiče byly využity jako systém cíleného uvolňování léčiv, konkrétně oxidu dusnatého (NO), který má pozitivní účinky na ardiovaskulární systém. Vlákna polykaprolaktonu byla obohacena o donory NO ze skupiny S-Nitrosothiolů, které umožňují uvolňování NO ve fyziologickém rozmezí po 42 dní v in vitro podmínkách. Po implantaci cévních náhrad jako náhrada břišní části aorty u potkanů bylo zjištěno, že NO inhibuje buněčnou infiltraci do vnitřní a střední vrstvy cévní náhrady. Tento snížený výskyt zánětlivých buněk může bránit vzniku neointimální hyperplazie způsobenou hladkosvalovými buňkami v pozdějších stadiích implantace.
There is a pressing need to develop vascular graft since no clinically available appropriate prosthesis with inner diameter less than 6 mm works in a long term after implantation. In the thesis, blood vessel substitutes made from biodegradable polymers were created and characterized as potential candidates for such a medical device. The idea of tissue engineering scaffolds is based on mimicking natural environment - extracellular matrix therefore ideal bypass graft was designed as double layered structure with defined morphology of each layer. The proposed structure was created by electrospinning of polycaprolactone (PCL). The morphology of the resulting fibers resembled inner and medial layer of native arteries suggesting that this similarity will help body to regenerate functional tissue after implantation. Besides PCL, novel polymer from the same group of polyester - copolymer polylactide-polycaprolactone (PLC 70/30) was electrospun into a tubular form. Vascular graft made from copolymer PLC created only single layered prosthesis. Further tests were conducted with both presented electrospun materials in order to compare their bulk and surface properties. Copolymer PLC was slightly more hydrophilic than polycaprolactone. Thermal behavior revealed that copolymer is mostly amorphous with melting temperature about 110°C whereas polycaprolactone is semicrystalline polymer with melting temperature about 57°C. Mechanical strength and elongation at break of electrospun copolymer PLC was about ten times higher compared to electrospun polycaprolactone.Biological tests using fibroblast and endothelial cell line prove the biocompatibility of both tested electrospun polymers. Higher proliferation rate was found when cells were cultured on electrospun copolymer PLC suggesting that higher hydrophilicity contributes to favorable cell adhesion. Hemocompatibility testing of produced samples were carried out using platelets. It was found that fibrous layers are more thrombogenic than smooth surface when compared with foils made from the same materials. Platelets became activated and aggregated after incubationwith fibrous materials. The level of activation was increased in dynamic conditions.Electrospun fibers were successfully used as a drug delivery system of nitric oxide (NO) that has many beneficial effects on cardiovascular system. Polycaprolactone fibers were blended with NO donors from the group of S-Nitrosothiols that are capable of long term NO release in physiological levels up to 42 days in vitro. After implantation of such grafts as a replacement of rat abdominal aorta, the NO release was found to strongly inhibit cellular infiltration into the medial and luminal regions of the vascular graft. The reduced presence of inflammatory cells within these regions may confer increased protection against neointimal hyperplasia from smooth muscle cells.
There is a pressing need to develop vascular graft since no clinically available appropriate prosthesis with inner diameter less than 6 mm works in a long term after implantation. In the thesis, blood vessel substitutes made from biodegradable polymers were created and characterized as potential candidates for such a medical device. The idea of tissue engineering scaffolds is based on mimicking natural environment - extracellular matrix therefore ideal bypass graft was designed as double layered structure with defined morphology of each layer. The proposed structure was created by electrospinning of polycaprolactone (PCL). The morphology of the resulting fibers resembled inner and medial layer of native arteries suggesting that this similarity will help body to regenerate functional tissue after implantation. Besides PCL, novel polymer from the same group of polyester - copolymer polylactide-polycaprolactone (PLC 70/30) was electrospun into a tubular form. Vascular graft made from copolymer PLC created only single layered prosthesis. Further tests were conducted with both presented electrospun materials in order to compare their bulk and surface properties. Copolymer PLC was slightly more hydrophilic than polycaprolactone. Thermal behavior revealed that copolymer is mostly amorphous with melting temperature about 110°C whereas polycaprolactone is semicrystalline polymer with melting temperature about 57°C. Mechanical strength and elongation at break of electrospun copolymer PLC was about ten times higher compared to electrospun polycaprolactone.Biological tests using fibroblast and endothelial cell line prove the biocompatibility of both tested electrospun polymers. Higher proliferation rate was found when cells were cultured on electrospun copolymer PLC suggesting that higher hydrophilicity contributes to favorable cell adhesion. Hemocompatibility testing of produced samples were carried out using platelets. It was found that fibrous layers are more thrombogenic than smooth surface when compared with foils made from the same materials. Platelets became activated and aggregated after incubationwith fibrous materials. The level of activation was increased in dynamic conditions.Electrospun fibers were successfully used as a drug delivery system of nitric oxide (NO) that has many beneficial effects on cardiovascular system. Polycaprolactone fibers were blended with NO donors from the group of S-Nitrosothiols that are capable of long term NO release in physiological levels up to 42 days in vitro. After implantation of such grafts as a replacement of rat abdominal aorta, the NO release was found to strongly inhibit cellular infiltration into the medial and luminal regions of the vascular graft. The reduced presence of inflammatory cells within these regions may confer increased protection against neointimal hyperplasia from smooth muscle cells.