Preparation And Biocompatibility Of A Novel PLA-PEG-RPM Biodegradable Vascular Stent

Objective:To Prepare a new type of PLA-PEG-RPM biodegradable vascular stent by using 3D printing technology and to evaluate its biocompatibility,which provides the research basis for subsequent animal experiments and clinical trials of biodegradable stents.Method:The vascular stent was modeled by 3D max software and exported as Stereolithography(STL)format.Different proportions of polylactic acid(PLA),polyethylene glycol(PEG),and Rapamycin(RPM)were extruded and pelletized using a twin-screw extruder.The material particles are drawn by a 3D printing wire drawing machine to obtain a 3D printing material.The stent was printed using Fused Deposition Modeling(FDM).The pressure at the time of fracture of the stent was measured using a pressure pump and a balloon to evaluate the toughness of each group of stents and find the best toughness of stent group.The long-term observation of the degradation of this group of stents,measuring the quality of the degradation of the stent and the p H of the extract.Fourier transform infrared spectroscopy(FITC)was used to identify the structure of the scaffold and analyze the functional groups contained in the scaffold.Differential scanning calorimetry(DSC)was used to analyze the drug rapamycin contained in the stent and to investigate if the melting behavior of the polymer in the stent was changed after 3D printing.Bone marrow stem cells were extracted and differentiated into vascular smooth muscle cells and vascular endothelial cells,and were identified by α-actin(α-smooth muscle actin)and v WF(factor VIII related antigen).The prepared stents were co-cultured with vascular smooth muscle cells and vascular endothelial cells,respectively,and the distribution of cells on the scaffolds was observed.Each group of stents was co-cultured with vascular smooth muscle cells and vascular endothelial cells for 8 days.The amount of viable cells on the stents was analyzed by MTT every other day.The results of each group were then graded according to the toxicity standards specified in the national safety standards.By the cocultivation of stent materials and endothelial cells,the number of cells adhered on the surface of different materials and the number of suspended cells were calculated by cell counting method,and whether or not the stents material was conducive to cell adhesion and growth was evaluated.The hemoglobin release was measured indirectly by measuring the OD value,and the haemolysis rate of each stent was observed to evaluate the blood compatibility of the stent.The platelet-rich plasma was contacted with the material for 30 min to observe the number of platelet adhesions on each group of stents under a scanning electron microscope.Result:1.The mass ratio of PLA-PEG mixture with the best toughness measured is 90%.2.The quality of stents containing PEG drops significantly in the short term.The PLA stent had the fastest degradation rate,followed by the PLA-PEG-RPM scaffold.The slowest was the rapamycin PLA-PEG scaffold.(P〈0.05)3.FITC experiments show that PEG has an effect on the structure and functional groups of PLA.The PLA-PEG-RPM stent retains the intrinsic structure and functional groups of rapamycin.4.DSC analysis showed that the melting temperature of PLA decreased due to the addition of PEG,and PEG improved the thermal stability of polylactic acid.Rapamycin still retains its melting peak after 3D printing.5.Endothelial cells were distributed evenly and densely on PLA scaffold,PLA-PEG scaffold and PLA-PEG-RPM scaffold with good growth state.Cells of smooth muscle cells adhered to the surface of PLA and PLA-PEG scaffolds and adhered to the surface of the stent with even distribution and good growth.The number of smooth muscle cells on the PLA-PEG-RPM scaffold was reduced and the distribution was not uniform.6.After 2,4,6,and 8 days of culture,the cytotoxicity levels of endothelial cells and smooth muscle cells grown in each group of scaffold extracts were between 0.9 and 1.3.7.The number of adherent cells in PLA stent group,PLA-PEG-RPM stent group and control group were(36.675±9.98)×104,(35.25±7.14)×104,(34.00±10.68)×104,respectively.The number of adherent cells was(2.74±0.40)×104,(2.50±2.38)×104,(4.1±1.85)×104,and the cell adhesion rates were 93.05%,93.38%,and 89.24%,respectively.(P〈0.05)8.The hemolysis rate of the PLA-PEG stent group was 4.132%.The hemolysis rate HR of the PLA-PEG-RPM stent group was 2.686%.9.Platelets on PLA-PEG and PLA-PEG-RPM stents were uniformly distributed on the surface,and some platelets accumulated.Conclusion:1.The right amount of PEG can help PLA overcome brittleness.The rapamycin coating can delay the degradation of polylactic acid.The PEG-containing stents degraded rapidly in the short term.After 3D printing,PEG has an effect on the structure and functional groups of the PLA.After 3D printing,rapamycin retains its inherent structure,functional groups and melting peaks.The preparation of PLAPEG-RPM stents by 3D printing technology is feasible.2.The cytotoxicity levels of endothelial cells and smooth muscle cells of the PLA-PEG-RPM stent are within the range allowed by national safety standards.The PLA-PEG-RPM stent had no significant effect on cell adhesion,and the PLA-PEGRPM stent did not affect endothelialization.The platelet adsorption assay demonstrated that the PLA-PEG-RPM scaffold had no significant effect on platelet distribution and aggregation.The PLA-PEG-RPM scaffold has good biocompatibility and can be used for in vivo experiments.