The Animal Experiment Of Dual Factors Induced Rapid Angiogenesis In Bone Tissue Engineering Scaffold

Objectives To construct the rapid induced angiogenesis experimental model with a prepared coaxial double-layered PLGA scaffold loaded with angiogenic factors VE-GF/PDGF in different layer respectively, and the New Zealand rabbits with femoral arteriovenous bundle dissected and encapsulated in the center of this double-layered scaffold. The concentration gradient of VEGF/PDGF throughout the three dimension-al architectures of the scaffold is hypothesized suitable for the process of angiogenesi-s from central area to its peripheral parts. To investigate the dynamic changing effects of rapid angiogenesis induction and maturation of new formed blood vessels in such a similar anatomical characteristics of axial blood supply as in jaw bones.Method36pairs of inner and outer layer of porous PLGA scaffold were prepared by means of solvent casting and particulate leaching technique. Then the two layers of the coaxial scaffold were telescoped together to assemble the control released ve-hicle for angiogenic inductive factors. The bilateral femoral arteriovenous bundles of18three months old New Zealand rabbits(weighed approximately2-2.5kg)were dis-sected and encapsulated in the scaffold. The animals then were randomly assigned to3groups according to the way the angiogenic factors (VEGF0.5ng, PDGF0.5ng each)composited into the scaffold,(1Experimental group(n=8,16specimens):VEGF in inner layer, while PDGF in outer layer;(2)Experimental control group(n=8,16spe-cimens):VEGF in inner layer, while the outer layer is blank;(3)Empty control group (n=2,4specimens):both the two layers were blank. Each2specimens of group1and2were retrieved at the7,10,14, and21days postoperative time interval respectively. Retrievals of the specimens of group3were performed at7、10days after the operation. The microvascular corrosion casting combined with SEM observation as well as histological study were then performed to compare the morphological charact-eristics of the neo-vascularization system.Result At7days postoperatively, there were conglomerate vascular buds and a la-rge number of endothelial cell imprints on the surface of the casts of the femoral arte-riovenous bundle. The endothelial cell imprints arranged along the major axis of the femoral arteriovenous bundle. There was no obviously changed in the blank control group. At10days postoperatively, completely penetrations of the double layered scaffold by abundant new generated blood vessel sprouts were observed, and density descended gradiently from inside to outside. There was no obviously new blood vessels in the blank control group. At14days postoperatively, new blood vessels in experimental group showed more thickness and layered structure of the wall in exper-imental group, while monolayer endothelial cells in experimental control group. Radially directed branches run from the arteriovenous bundle. There were three dimensional vascular nets around the arteriovenous bundle without obvious classification in these two groups. At21days postoperatively, new blood vessels in experimental group showed more mature characteristics, while less density of blood vessels in experimental control group. There were sporadic blood cells in the pores of the scaffolds.Conclusion The authors constructed a coaxial double-layered PLGA scaffold composited with angiogenic factors in different spatial distribution. This model was proved promoted the angiogenesis process throughout the whole scaffold dramatically. The femoral AV bundle was used in the study as the original stem for neo-angiogene-sis induction in the scaffold to form anastomosis with peripheral tissues. Such rapid vascularization in this PLGA scaffold could improve early blood supply in the internal spatial structure of the tissue engineering scaffold significantly, and improve transport efficiency of oxygen and nutrients.This new scaffold is expected to increase the survival rate of seed cells and early osteogenesis.