| Polytetrafluoroethylene(PTFE)is a perfluorinated linear thermoplastic polymer.The surface of expanded polytetrafluoroethylene(ePTFE)prepared by stretching is porous,which has good mechanical properties,extremely low surface energy and superhydrophobicity.It has been widely used in biological materials.As a potential vascular graft,ePTFE has been extensively studied and has been proved to have good long-term clinical effects in large and medium caliber arteries(≥ 6mm).However,when it‘s use as small diameter blood vessel(SDBV)(<6mm),its long-term patency are affected due to the issues such as heterogeneous surface and compliance mismatch.Rapid endothelialization and payloads of functional drugs are considered as potential solutions.Unfortunately,due to the chemical inertness of ePTFE,traditional surface modification methods and processes are complex and exhibit poor stability.Therefore,how to regulate the structure of ePTFE surface to promote rapid endothelialization on ePTFE surface,and load functional biomacromoleciles is an effective way to solve the problem.In this study,effective methods were proposed to reconsturct micro-nano structure on ePTFE surface,which included drug loading and release.The effects of surface micro-nano structure and drug loading on cell behavior were studied,providing new candidates for the functional modification of small-caliber artificial vascular grafts.The main research work is as below:1.A synergistic cross-linking network was constructed on the inner and outer surfaces of ePTFE small-diameter artificial vessels through layer-by-layer self-assembly(LBL)method.The inner and outer surfaces were coated with different bioactive molecules.Internal surface: heparin,epigallocatechin gallate(EGCG);External surface: Rapamycin,through which implementation of rapid endothelialization of the inner surface,anticoagulation and anti-inflammation of the external surface were realized simultaneously.The results showed that bioactive molecules were successfully coated on the modified surface,and lamellar fibrous structure was formed.The water contact angle(WAC)of inner surface was reduced to 46° while that of outer surface was reduced to 62°,and the hydrophilicity of both inner and outer layers of vascular grafts was improved to varying degrees.The surface cross-linked network results in sustainable release of heparin and rapamycin with a cycle of 42 days.Biological results showed that the inner surface functionalization promoted the growth and proliferation of human umbilical vein endothelial cells(HUVECs),while the outer surface functionalization effectively inhibited the growth and proliferation of smooth muscle cells(SMCs).After modification,both internal and external surfaces effectively inhibited platelet activation and expression of TNF-α,and upregulated the expression of Arg1 and TGFB-1 anti-inflammatory genes to varying degrees.These results suggest that the construction of the cross-linked network can achieve the expected synergistic effect between the internal and external surfaces of the vascular grafts,resulting in effective improvement in the degree of endothelialization,anticoagulant behavior,and anti-inflammatory activity.2.Based on the heterogeneous epiphytic crystallization mechanism,polyhexanolone(PCL)crystallization was induced on the surface of ePTFE nanofiber,and the "Shish-Kebab" multilayer topology of the D period morphology of biomimetic collagen was constructed.The results show that the size of Kebab structure could be controlled by controlling induction time and solution concentration,and the stable structure with 1～2 μm period and the surface roughness(Ra)increased by 69.5 nm.HUVECs culture showed that Shish-Kebab topology significantly improved ePTFE surface adhesion to endothelial cells,where single cell spread area increased by three orders of magnitude compared with the ones without modification.Moreover,the expression of adhesion related to mRNA(Paxillin and Vinculin)was significantly increased and endothelial surface coverage increased from 10% to 60% in the short term.These results suggest that Shish-Kebab structure significantly promotes endothelial regeneration.Therefore,this physical modification method develops a new way for the construction of micro/nano structure on ePTFE surface.The presence of Shish-Kebab structure transformed the two-dimensional inert surface into a three-dimensional bionic structure,which promoted the endodermis fusion regeneration.Meanwhile,the existence of this topology provided a platform or carrier for further drug loading.3.Three-dimensional Shish-Kebab structure based on PCL lamellar was aminolyzed to improve its activity,and further reacted with EDC to load bioactive molecules on Shish-Kebab structure.In order to test the universality of this method,common clinical drugs(heparin,aspirin and atorvastatin)were loaded and their respective functionalization effects were verified.The results showed that by regulating the degree of ammonolysis,the surface activity could be improved while the stability of Shish-Kebab structure was maintained.The stable existence period of loaded drugs was more than 30 days.Meanwhile,the drug-modified Shish-Kebab structure could significantly inhibit the activation of platelets,thus improving their anticoagulant behavior.In vitro culture of HUVECs,SMCs and mouse mononuclear macrophage leukemia cells(RAW264.7)showed that heparin-loaded surface could further enhance the activity of endothelial cells and promote their functional regeneration.Moreover,aspirin and atorvastatin modified surface could effectively inhibit the growth and proliferation of SMC.The modified surface can effectively inhibit the expression of pro-inflammatory mediators TNF-α and up-regulate the expression of anti-inflammatory genes Arg1 and Fizz1 to a certain extent,respectively.The results demonstrated that the modified method constructed a stable multi-level wiener structure on ePTFE surface containing functional drugs,which provided a new candidate for biomacromolecule loading on ePTFE surface. |
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