Abstract:

Objective At present, self-coiling technology is rarely used in the field of blood vessels. Thermally induced self-coiling can make vascular tissue engineering materials self-coil at the corresponding temperature to wrap the injured blood vessels, which has a better fit compared with the existing artificial blood vessels. At the same time, self-coiling is irreversible, and the hardness of tissue engineering materials is enhanced after self-coiling. In orderto solve the problem of vascular endothelialization, gradient modification of growth factors was applied to the surface of the thermally induced self-coiling scaffolds to promote rapid endothelialization of the inner layer of the scaffold. At the same time, the scaffold has a multi-layer microstructure, which simulates the fiber direction of each layer of the blood vessel and has bionic performance.

Method Poly (l-lactic acid) (PLLA) and poly(lactic-co-glycolic acid) (PLGA) were used as raw materials to fabricate thermally induced self-coiling PLLA/PLGA nanofibrous vascular scaffolds by electrospinning technology. The thickness of the scaffolds was measured by a micrometer. The scaffold can self-coil at 37 ℃, and the driving force of self-coil comes from the difference in molecular motion rate between PLLA and PLGA after heating. The surface morphology of PLLA and PLGA nanofibrous membranes was observed by SEM. The gradient growth factor modification of the inner layer of the scaffold was made by electrostatic spraying technology and different mold coverings, and the gradient preparation was observed under fluorescence microscope by replacing vasular endothelial growth factor (VEGF) with rhodamine. The cytocompatibility of scaffolds was tested by CCK-8 assay. The effect of gradient-modified growth factors on rapid endothelialization was examined by seeding cells on both sides of the scaffold and observing them by fluorescent staining after 3 d.

Results The prepared PLLA/PLGA vascular scaffold had a multi-layer oriented nanofiber structure. The microstructures of the inner PLGA and the outer PLLA nanofiber membrane were both oriented fiber structures. The thickness of the scaffold was (6.75 ± 0.4) μm, and it could be self-coiled from a flat structure to a tubular structure at 37 ℃. The CCK-8 experiment showed no significant difference in cell proliferation in each component. The characterization results of gradient modification using rhodamine instead of VEGF showed that the fluorescence intensity gradually increased from both sides to the middle part with the increase of electrostatic spraying time, indicating that more growth factors were modified in the middle part of the inner layer of the scaffold. Gradient of growth factor accelerates the crawling of endothelial cells, and after 3 d into the luminal surface gradient growth factor of cell migration distance are 3.5 times that that of the control group.

Conclusion The preparation of PLLA/PLGA scaffolds has a multilayer orientation nanofiber structure and good biocompatibility. At 37 ℃, the scaffolds can be coiled into a tubular structure. VEGF was in a successful gradient modification on the inner lining to speed up the migration of endothelial cells and promote the fast endothelium of blood vessel lining. However, there are still some problems such as weak adhesion to the vascular stent and gaps after crisping. The adhesion of the scaffold needs to be improved in the future.

Key words: electrospining, vascular scaffold, self-coiling, poly (l-lactic acid), poly(lactic-co-glycolic acid)