1.A Novel Small-diameter Vascular Graft: In Vivo Behavior Of Biodegradable Three-layered Tubular Scaffolds 2.Schwann Cells Promote The Proliferation And Arterial Differentiation Of Bone Marrow Stromal Cells In Vitro

Objective:Small-diameter vascular grafts are potential substitutes for damaged vessels in patients,but most grafts available now are lack of enough mechanical properties or having poor retention for cell seeding.The present study examined a novel biodegradable tubular scaffold for its biomechanical properties and in vivo behavior.Methods:Burst strength,radial compliance and suture retention strength of the scaffolds were tested in this study.The tubular scaffold(6-mm i.d.,4cm long) has three layers including two porous polylacticglycolic-acid layers and a compact polyurethanes layer in between.Bone marrow stromal cells(bMSCs),were seeded on the scaffold and cultured for 7 days to establish a confluent layer covering it,which were then implanted in canine abdominal aorta.After 1,3,6,12 and 24 weeks,the grafts were removed and evaluated through histological,angiographical,and immunohistochemical analysis.Results:The implanted scaffolds showed wall thickness of 0.295 mm to 0.432mm; radial compliance of 3.80%/100mmHg～0.57%/100mmHg,burst strength of 160 kPa～183kPa,and suture retention strength of 1959 N/cm²ï½ž3228N/cm².The grafts were fully patent without any signs of dilation or obstruction after 3 months' implantation. Scanning electron microscopy revealed a confluence endothelial cell layer spreading on the inner luminal surfaces.Although lumens of 6 months' implantation displayed a mild degree of narrowing,the scaffolds were intact in their gross appearances. Immunohistochemically,all the grafts were positive for CD31 in the intima andαSMA in the media.Conclusion:This novel three-layered scaffold exhibited good mechanical strength, long term patency and confluent endothelialization. Objective:Peripheral nerves play an important role in arteriogenesis.The effect of Schwann cells(SCs) on bone marrow stromal cells(bMSCs) was evaluated.Mehtods:SCs and bMSCs from Sprague-Dawley rats were harvested and were co-cultured in Transwell system.Four groups of co-culture system were investigated. In Group A and B,bMSCs(3×10³ per well) were seeded on the upper chamber of the Transwell plate,while SCs which accounted for 30%ofbMSCs amount were seeded on the lower chamber.There was absence(group A) or presence(group B) of 10μg/ ml VEGFR2(Flk-1)-Fc,a potent vascular endothelial growth factor(VEGF) antagonist.In group C(controls) and D,bMSCs were seeded on both chambers in the Transwell plate.There was absence(group C) or presence(group D) of 10ng/ml VEGF.Cell numbers were measured by ³H-TdR incorporation technique and were expressed by Counts Per Minute(CPM) on the 1^st,3^rd,5^th and 7^th day.Arterial differentiation rate of bMSCs was measured by Flow Cytometer through labeling FITC-conjugated anti-ephrinB2 antibodies on bMSCs.Western blotting was performed to assess the expression of ephrinB2,vascular endothelial growth factor (VEGF) and its receptor,neuropilin-1(NRP-1) in different groups.Co-cultured bMSCs were analyzed by immunohistochemistry using antibodies againstαsmooth muscle actin(αSMA),PECAM,βTubulinâ…¢and S-100.Results:The CPM values of bMSCs in the trial group were significantly higher than that in the control group especially on the 5^th day.The ephrinB2 expression rate of co-cultured bMSCs significantly increased to 49.40%.The proliferation and ephrinB2 expression of co-cultured bMSCs could be blocked by VEGF antagonist.Exogenous VEGF could increase proliferation of bMSCs,however,SCs were more effective on the promotion of ephrinB2 expression of bMSCs than simply adding VEGF. Immunohistochemistry found that co-cultured bMSCs could expressαSMA and PECAM,but notβTubulinâ…¢and S-100.Western blotting showed that VEGF was expressed by SCs,and ephrinB2 expression in bMSCs could be blocked by VEGF antagonist.Conclusion:In short,SCs could increase the bMSCs proliferation and promote the arterial differentiation by secreting neural-related VEGF.