In Vitro Water Permeability Of Woven Small Diameter Vascular Grafts

In order to facilitate the endothelialization of artificial vascular grafts,their walls are often designed to be porous structures,which is beneficial to the exchange of substances inside and outside the lumen.Textile based artificial vascular graft is an ideal one which can realize 100% surface connectivity.However,too big pore on its wall will lead to leakage of blood during the operation,resulting in adverse consequences.Therefore,the pre-clotting method is often used in clinic to avoid this problem.However,the patient’s own blood will have to be used,thus adding the surgical procedure,resulting in high risk of infection.On the other hand,the manufacturers often use dense wall structure to prevent blood leakage,so their water permeability tend to be zero,which will greatly weaken the advantages of textile based artificial vascular graft.Therefore,we lack an objective and scientific method to characterize the porous structure of the wall of artificial vascular graft.Pore size and porosity can reflect the characteristics of porous structure in a certain way,but water permeability is more objective and accurate.Therefore,in ISO 7198,water permeability is an index to evaluate the porous structure of the artificial vascular graft.However,the relationship between water permeability and blood permeability has not been established yet.Independent evaluation of water permeability is very limited for directing clinical pre-clotting as well as product development.Therefore,the boundary of pre-coagulating is a key content for the study of water permeability.In this research,we adjust the weaving parameters according to the commercial textile artificial vascular graft.Four kinds of textile artificial vascular materials with different porosities were prepared,and their water,simulated plasma and anticoagulant whole blood permeability were tested at different pressures.The influences of the fabric structure and the testing pressure on the permeability have been analyzed,and the relationships among the water,simulated plasma and anticoagulant whole blood permeability have been discussed and established.The results showed that the vascular graft with a lower porosity has a lower permeability.The permeability decreased over time and increased with the increase of the testing pressure.Under the same testing condition,the water permeability is the highest while the anticoagulant whole blood permeability is the lowest for the same kind of vascular graft.The ratio of the simulated plasma permeability to the water permeability is approximately equal to the ratio of the viscosities of water to simulated plasma.Moreover,for 2# sample,there is an approximate linear relationship between the water and anticoagulant whole blood permeability as well as simulated plasma and anticoagulant whole blood permeability.As for 1#,3# and 4# sample,there is a linear relationship between the water and anticoagulant whole blood permeability as well as simulated plasma and anticoagulant whole blood permeability at low pressure,but have an approximate linear relationship at high pressure.At last,the mechanical properties of the samples were tested.The commercial ePTFE graft was set as control.The results show that the radial tensile strength,retention strength and probe bursting strength of the specimens are better than those of commercial ePTFE graft.That is to say,their mechanical properties have met the application requirements.And the results showed that the endothelial cells were able to permeate from any wall of the four kinds of samples.That is to say,the specimens we made in this research can facilitate endothelialization.In conclusion,this research set a relationship between water permeability,simulated plasma permeability and anticoagulant whole blood permeability of the artificial vascular graft.Therefore,it is possible to predict it’s anticoagulant whole blood permeability through water permeability in vitro.When the blood permeability of anticoagulant blood is low,the artificial vascular graft can still realize endothelialization.This study will provide a basis for further study of establishing the relationship between water permeability and blood permeability in vivo,and lay a foundation for judge the necessity of pre-clotting.