| Vascular stent is a kind of tubular stent made of metal material or polymer.In clinical practice,stent implantation is used to restore the normal blood flow in the damaged vascular area through the narrow occlusive segment of blood vessels or vascular injury.At present,vascular stents have been widely used in the endovascular treatment of intracranial artery,coronary artery,carotid artery,aorta,renal artery and other vascular diseases,and achieved satisfactory results.However,in the aortic arch and other parts,due to the complex anatomical relationship and multi-branch structure of these parts,when lesions occur in these parts(such as aortic dissection,thoracic aortic aneurysm,etc.),traditional straight-tube vascular stents are often difficult to achieve satisfactory clinical effects,because branch vessels are easy to be covered in the process of stent implantation,resulting in various serious complications.Therefore,the ideal vascular stent should be customized branch vascular stent,which can realize personalized customization and conform to the multi-branch physiological structure of complex anatomical sites.3D printing,also known as additive manufacturing,is based on digital modeling files,through computer software and numerical control system,the application of polymer,ceramic,metal powder and medical biological materials and other printing ink,from the bottom up,layer by layer to print out a three-dimensional virtual model to construct a physical model.4D printing adds time as a fourth dimension to 3D printing,and printed structures can be created or changed shape when stimulated.Parameters that vary with time include temperature,water,light,humidity,p H,etc.Therefore,4D printing has attracted more and more attention from researchers and is widely used to manufacture functional responsive materials.Shape memory polymers(SMPs)are also known as stimulation-responsive polymers.This class of functional materials can sense and respond to environmental conditions or stimuli from optical,electrical,magnetomechanical,thermal and chemical signals.These materials are also known as "smart materials" because they can be restored from deformed shape to original shape under external stimuli such as light,heat,magnetism and electricity.Because of its excellent biocompatibility,mechanical properties and deformability,shape memory polymers have great potential applications in vascular stents,drug carriers,surgical instruments,etc.In this study,a polyurethane(PU)was synthesized chemically.PU,DMAEMA and HEMA were mixed in different proportions to produce a thermoresponsive shape memory polymer ink suitable for digital light processing(DLP)printing.By testing the transition temperature,mechanical strength and shape memory properties of polymers at different ratios,it is concluded that the polymer obtained by mixing PU,DMAEMA and HEMA at a mass ratio of 3:5:2 has tensile strength up to 18.1MPa,shape fixation rate of 97.3% and shape recovery rate of 98.7%,which can be used for clinical treatment.To verify the biocompatibility of the polymer,we inoculated and cultured human umbilical vein endothelial cells on the polymer,and performed subcutaneous implantation on the back of Bal/c mice for 12 weeks.The results showed low cytotoxicity and excellent biocompatibility of the polymer,and the antibacterial activity of the polymer was improved due to the presence of DMAEMA.To verify the blood compatibility of the polymer,we performed blood compatibility experiments with fresh blood from healthy volunteers,and the results showed that the polymer prevented platelet aggregation and hemolysis.Finally,the structure of the branch stent was designed by Blender 3D modeling software and a branch stent was printed by DLP printer.Therefore,shape memory branch vascular stents based on 4D printing may be promising for personalized and complete endovascular treatment of aortic dissection,abdominal aortic aneurysm and other diseases. |
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