Structure And Properties Of 3D Printed Small-diameter Vascular Tissue Engineering Scaffold

Cardiovascular disease shows high incidence and mortality.Cardiovascular tissue engineering is considered the best way to reduce the mortality of cardiovascular diseases.However,traditional vascular tissue engineering methods encounter development bottlenecks due to inability to balance thrombosis,restenosis and intimal hyperplasia.3D bio-printing technology is expected to address the limitations in simulating natural vessels to make tubular tissues.3D bioprinting are often used to construct tubular structure:sacrificial layer method has low resolution and is difficult to be used for forming small inner diameter;inner template method has the disadvantages of uneven upper and lower pipe diameter,short printing deposition length and difficult to prepare small diameter support.Coaxial nozzle assisted 3D bioprinting has many limitations on the properties and types of bio-ink.In view of the correlation between the shear stress distribution gradient and the microstructure orientation caused by the printing pressure of the printed hydrogel material in the nozzle,the goal of increasing the printing pressure to change the tubular pore structure and extruding the small diameter hollow tubular structure directly is realized.Meanwhile,this paper achieves 3D printing of small diameter vessels by optimizing printing materials and changing printing parameters.The resulting small-diameter vessels(constructs of cells and gels)and small-diameter vessel scaffolds(lyophilized porous structures after printing)were characterized to reveal the correlation between printing parameters and printing structures.The main research contents are as follows:(1)The stepper motor mechanical extrusion system is combined with the FDM printer to build a small vessel construction platform,in which the fixed frame,multinozzle printing nozzle and related parts of the internal aseptic device of the original FDM printer are designed independently and printed by the original printer.The printing parameters range of the 3D bioprinter after modification meets the requirements of this experiment.The piston driving device is simplified,the printing nozzle has multifunction and the printer runs smoothly as a whole.When the pressure of the stepping motor is transferred to the piston push plate through the screw driven force can be achieve 0-400 kPa and the speed of 3D printer nozzle can achieve 0-180 mm/s.(2)Carrageenan(KC)as the starting material,Modified carrageenan with sodium alginate and water-soluble carbon nanotubes,preparation of carrageenan/alginate(KCSA)and carrageenan/alginate/carbon nanotubes(KC-SA-C)with different blending ratios.The gel diameter of KC-SA-1.0 hydrogel is mainly distributed between 1.0 mm and 1.8 mm,and the KC-SA-C-0.3 gel diameter is mainly distributed between 0.8 mm and 1.2 mm.This indicates that the overall printability of KC-SA-C-0.3 hydrogels is better than that of KC-SA-1.0 hydrogels.To study the rheological and printability of hydrogels with different ratios,the KC-SA-1.0 and KC-SA-C-0.3,can be selected for 3D printing.Specifically,KC-SA blending binary system containing1.0 w/v%sodium alginate and KC-SA-C blending ternary system containing 0.3 w/v%carbon nanotubes.KC-SA-1.0 and KC-SA-C-0.3 component printing results show that the printed small vascular stent forms a pore structure with different cross-linking density due to the shear force of different gradients on the outer wall and center of the tube,and under 35 kPa printing pressure,the hollow structure of small-diameter vessels of KC-SA-C0.3 can be extruded directly.Therefore,the final selection of small-diameter blood vessel 3D printing components for KC-SA-C-0.3 performance characterization.By characterizing the KC-SA-C-0.3 smaller-diameter vessel scaffold structure prepared with different printing pressure,including chemical structure,mechanical properties,swelling properties,hydrophilicity,degradation properties,etc.,it is revealed that the printing pressure affects the corresponding properties through the regulation of the pore structure of the smaller-diameter vessel scaffold and verifies the processing feasibility of the scaffold structure.(4)Introduction of human umbilical vein endothelial cells in KC-SA-C-0.3 hydrogels and printing of bioink with modified 3D bioprinter.Distribution of printed dead HUVEs by means of mean area calculation showed that the cell survival rate of the three regions with different printing pressure decreased in turn,and the difference was about 5%in each region.By characterizing properties of smaller-diameter vessel biocompatibility prepared by different printing pressures,including cell viability,cell proliferation,histocompatibility,blood compatibility,etc.characterization results revealed that the greater the damage to cells with increased print pressure.However,the resulting smaller-diameter vessels with more pronounced orientation microstructure,higher porosity and higher mechanical properties promoted subsequent cell growth and tissue fusion,which verified the biomedical reliability of the bioink.The hemolysis rates of KC-SA-C-15kPa,KC-SA-C-25kPa and KC-SA-C-35kPa were 3.9%,3.7%and 2.8%,respectively,which were lower than 5%.The hemolysis rates of the three materials met the standard of biomedical materials(5%)and the difference was not significant.