A pulsatile bioreactor system for durability testing and compliance estimation of vascular grafts

Cardiovascular disease is the leading cause of death worldwide despite the progress that has been made in established surgical treatments such as the coronary artery bypass surgery and the balloon angioplasty. Tissue engineering (TE) has already offered clinical solutions in the areas of skin and cartilage regeneration and is advancing in several research fields, such as vascular graft replacements. In order for TE constructs to be cultivated and conditioned under a controlled environment, bioreactors systems are used, that can maintain physiological O2 and CO2 concentrations and can apply stresses and strains to promote the proliferation of cells and the production of extracellular matrix proteins. In the case of cardiovascular TE, conditioning under pulsatile pressure is common practice by many groups. In this study a bioreactor system is presented that can apply adjustable pressure pulse profiles to vascular grafts under a controlled environment. In addition, it can perform diameter measurement of the vessels in vitro so that the compliance of the vessel can be calculated. The compliance, which is the relative change of volume of a vessel due to a pressure change, is an excellent measure of its mechanical condition and can be used to monitor the development and maturation of the newly formed tissue. The system uses a centrifugal pump that pumps cell culture medium from a reservoir and supplies a perfusion bioreactor. Medium flows both through and around the vessel and its blood gas values, namely the partial pressures of O2 and CO2 and its pH value are monitored with the respective sensors in another chamber. A linear motor with a piston controlled by a computer applies pulses through a silicone membrane. An application developed in Labview® is used to generate the pulses, record the pressure, the flow and the blood gas values and the diameter of the vessel through an optical micrometer. The system was evaluated with experiments that lasted up to 4 weeks, where TE vessels and native porcine carotid arteries were cultivated and conditioned. The results demonstrated that it can be easily assembled under sterile conditions and run without problems for this time. The blood gases were monitored either with the blood gas chamber or externally, with a blood gas analyser and the compliance could be measured accurately over the cultivation period. The system can also be used for the performance of durability testing according to existing regulations for similar products (heart valves and stents), issued by ISO and FDA, and assist in the procedure for clinical approval of tissue engineered vascular grafts

A pulsatile bioreactor system for durability testing and compliance estimation of vascular grafts

Cardiovascular disease is the leading cause of death worldwide despite the progress that has been made in established surgical treatments such as the coronary artery bypass surgery and the balloon angioplasty. Tissue engineering (TE) has already offered clinical solutions in the areas of skin and cartilage regeneration and is advancing in several research fields, such as vascular graft replacements. In order for TE constructs to be cultivated and conditioned under a controlled environment, bioreactors systems are used, that can maintain physiological O2 and CO2 concentrations and can apply stresses and strains to promote the proliferation of cells and the production of extracellular matrix proteins. In the case of cardiovascular TE, conditioning under pulsatile pressure is common practice by many groups. In this study a bioreactor system is presented that can apply adjustable pressure pulse profiles to vascular grafts under a controlled environment. In addition, it can perform diameter measurement of the vessels in vitro so that the compliance of the vessel can be calculated. The compliance, which is the relative change of volume of a vessel due to a pressure change, is an excellent measure of its mechanical condition and can be used to monitor the development and maturation of the newly formed tissue. The system uses a centrifugal pump that pumps cell culture medium from a reservoir and supplies a perfusion bioreactor. Medium flows both through and around the vessel and its blood gas values, namely the partial pressures of O2 and CO2 and its pH value are monitored with the respective sensors in another chamber. A linear motor with a piston controlled by a computer applies pulses through a silicone membrane. An application developed in Labview® is used to generate the pulses, record the pressure, the flow and the blood gas values and the diameter of the vessel through an optical micrometer. The system was evaluated with experiments that lasted up to 4 weeks, where TE vessels and native porcine carotid arteries were cultivated and conditioned. The results demonstrated that it can be easily assembled under sterile conditions and run without problems for this time. The blood gases were monitored either with the blood gas chamber or externally, with a blood gas analyser and the compliance could be measured accurately over the cultivation period. The system can also be used for the performance of durability testing according to existing regulations for similar products (heart valves and stents), issued by ISO and FDA, and assist in the procedure for clinical approval of tissue engineered vascular grafts

ВЛИЯНИЕ ГРАНУЛОМЕТРИЧЕСКОГО СОСТАВА МАТЕРИАЛА НА ЭФФЕКТИВНОСТЬ БЕСШАРОВОГО ИЗМЕЛЬЧЕНИЯ

Процес грохочення моделюється марковським ланцюгом. Тривалість грохочення визна-чена для випадку, коли просівання домінує над сегрегацією. Використано апарат матричної алгебри.Процес грохочення моделюється марковським ланцюгом. Тривалість грохочення визна-чена для випадку, коли просівання домінує над сегрегацією. Використано апарат матричної алгебри