| There are great challenges to treat the aortic dissection and the aortic arch aneurysm involving its branch vessels. One of those challengeis that it is difficult to design and fabricate a suitable endovascular branched graft. That is because the lesion close to the heart makes the operation more difficult torelease the stent-graft. Meanwhile, the complicated surgical options are easily to lead to unsuccessful surgical operations, resulting in treatment failure. Therefore, the design and preparation of branched graft for simple surgical operation has become the focus and key issues in the field of endovascular graft. It has also become an important branch of the best way to solve the bottlenecks in the clinical application of endovascular graft regarding to the branched vessels.To deal with the existing problems and make a breakthrough of research status in the endovascular grafts with the branched vessels, this paper focuses on the functional design of a suitable endovascular branched graft and its structure molding as well as the their relationship between structure and properties.A hat-like endovascular branched graft model is designed with curved surface, and without metal stent graft,through the results of animal experiments, finite element analysis and computational fluid dynamics. The in vivo measurement of pressure in porcine aortic arch and branched artery have shown that there is a clearly difference in blood pressure before the branched artery was blocked; the value reaches42.78±5.17mmHg. The instantaneous value of the pressure of endovascular branched graft will be far greater than measured in actual release process. Therefore, hat-like endovascular branch graft without metal stent graft can be designed according to the automatic blood pressure difference. The ANSYS simulation software was taken to analyze the stress distribution and displacement of different curve surface by finite element method, and the results showed that the curved arc is optimal. According to the theory of fluid mechanics and the calculation results of energy loss, the parabola curved surface lost the smallest energy. Therefore it is recommended that the hat-like model without metal stents support can be used in the design of endovascular branch graft.The woven polyester (PET) endovascular branch graft was prepared by the compression molding, according to the optimal parabolacurved surface model.The characterization ofcurved shaped endovascular branch graftwas explored.The geometric structure and bursting, tensile strength, elastic recovery and other relationshipsbetween structure and properties were studied. PET multifilament was selected to fabricate two kinds of plain and twill weave fabric with different densities obtained by weaving, desizing and densification process, to form PET endovascular branch graft. Then the PET endovascular branch graft membrane could be obtained after the process of heat-set molded asa hat-like fabric with a parabola curved surface compression mold. After the characterization system of various shaped endovascular branch graft membranes was explored, its geometry compression molding, structure and mechanical properties of aggregation state were tested, as well as the in vitro release of situation. According to the results, the density of hat-like branched vascular membrane samples prepared by molding gradually decreased from the bottom to the crowns, the thickness, weight, degree of crystallinity and bursting strength also show gradient. The density compared with the large twill fabric samples reflected the good mechanical properties. In the in vitro release test of artificial vascular membrane molded under pressures, the resultsshowed the intermediate regions could plunge branched artery and ensure the blood supply to the branch.To further improve the mechanical properties of endovascular branch graft, and to explore the novel molding method and the simulation of the real three-layer structure artery (intima, adventitia, membrane), the porous polycaprolactone (PCL) material was selected for its biocompatibility to form the inner and outer membrane, andthe PET mesh fabric was select as a reinforcing layer in order to improve the mechanical properties of endovascular branch graft. The influences between the concentration, molecular weight and membrane porous structure were conducted by SEM. The results showed the smaller the concentration with the greater the porosity; pore size and porosity of PCL film with a molecular weight of180,000is greater than50000and80000of PCL films. All three-dimensional pore size in the porous membrane is more than10μm. Through the integrated processing technology, using acetic acid as a solvent, choosing180,000molecular weight of PCL for the substrate, the maximum density of the PET mesh knitted fabric as a reinforcing layer to prepare PCL/PET composite film used in endovascular branch graft. A pressure spray and freeze-drying method were used to combine PET knitted fabric mesh as an intermediate layer with PCL membrane. Meanwhile, the specimen geometry, wall microstructure, bursting strength, radial tensile, elastic recovery, strength and other mechanical properties of the suture were conducted to make characterization and analysis of the PCL membrane and PET fabric reinforced composites. Contrast the structure and properties of PCL/PET composite film and pure PCL membranes, the enhancement mechanism of PET fabric mesh was analyzed. The Wall thickness of PCL and PCL/PET endovascular branch graft surrounding the sample area is slightly larger than the central region’s (crowns and caps arc), which is due to occur in trace PCL solution flow under gravity field caused by delay, similar results were found in the PET fabric endovascular branch graft. SEM photographs of PCL/PET composite membrane showed the pore sizewith porouswall is over10μm; the interface compatibility between PCL and PET fiber matrix is good. The water permeability experiment showed that porous membrane is impermeable under the standard pressure, so the leakage will not occur in the in vivo implantation. The result of mechanical properties of the membrane material showed that the bursting strength of PCL/PET composite film branch of artificial blood vessels, radial tensile properties, elastic recovery and suture strength are better than pure PCL membrane materials.The PET fabric mesh showed a significant enhancement to improve the performances. Meanwhile, the mechanical properties of PCL/PET composite endovascular branch graft have also been greatly improved than the monolayer PET film.In summary, the hat-like endovascular branch graftwith stent-less was designed according to the difference of blood pressure between the branch and the aortic arch in the endovascular surgical procedures.The branch graft shape was optimized according to finite element analysis and computational fluid dynamics.Two kinds of endovascular branch graft membrane were prepared and relationship between structure and properties was studied. The hat-like endovascular branch graft can reduce the surgery operational difficulty and provide more choices for clinical surgeon. |
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