(536b) A New Injectable Tissue Engineered Scaffold Induces Angiogenesis

Introduction: Tissue engineering is designed to regenerate natural tissues or to create biological substitutes for defective or lost organs by making use of cells. Considering the usage of cells in the body, it is no doubt that a sufficient supply of nutrients and oxygen to the transplanted cells is vital for their survival and functional maintenance. Without a sufficient supply, only a small number of cells pre-seeded in the scaffold or migrated into the scaffold from the surrounding tissue would survive. It is recognized that basic fibroblast growth factor (bFGF) function to promote such an angiogenesis process. However, one cannot always expect the sustained angiogenesis activity when these proteins are only injected in the solution form probably because of their rapid diffusional excretion from the injected site. One possible way for enhancing the in vivo efficacy is to achieve its controlled release over an extended time period by incorporating the growth factor in a polymer carrier. The objective of the present study is to fabricate the 3-D networks of nanofibers by mixing bFGF suspension with aqueous solution of peptide amphiphile and used it for feasibility of prevascularization by the bFGF release from the 3-D networks of nanofibers in improving efficiency of tissue regeneration.

Materials and Method: Peptide-amphiphile (PA) was synthesized by standard solid phase chemistry that ends with the alkylation of the NH2 terminus of the peptide. The sequence of arginine-glycine-aspartic acid (RGD) was included in peptide design as well. A 3-D network of nanofibers was formed by mixing bFGF suspensions with dilute aqueous solutions of PA. Scanning electron microscopy (SEM) observation revealed the formation of fibrous assemblies with an extremely high aspect ratio and high surface areas with mean diameter of 20 nm. In vitro release profile of bFGF from 3-D network of nanofibers was investigated while angiogenesis induced by the released bFGF was assessed. For the evaluation of angiogenesis induced with these injectable scaffolds, 50 ?Ýl of four doses of bFGF solutions (2, 10, 30, and 50 ?Ýg) and 50 ?Ýl of PA solutions were subcutaneously injected at the same time into the back of rats. At 1, 3, 7, 10, 14, 21, and 28 days post-treatment, the rats were sacrificed by an overdose injection of anesthetic and the skin including the injected site (2 °Ñ 2 cm2) was carefully taken off for the subsequent biological examinations. The angiogenesis of bFGF was estimated by determining the amount of tissue hemoglobin as a marker of angiogenesis. Results and Discussion: A transparent gel was formed immediately after injection of bFGF with PA. When bFGF was injected together with PA solution, capillaries were newly formed at the injected site. bFGF injection alone did not contribute to vascularization, and the tissue appearance was similar to that of PA injection alone. The injection of bFGF solution did not increase the amount of hemoglobin at the injection site over the time range studied and the amount of tissue hemoglobin was similar to that of PA solution alone or untreated, normal mice. However, the injection of bFGF together with PA solution induced significant angiogenesis. The amount of tissue hemoglobin notably increased within 1 day of injection and the significantly increased level was retained over 28 days, and thereafter returned to the initial level of tissue hemoglobin. These results strongly suggest that the angiogenesis in advance induced by the controlled release of bFGF from bFGF-incorporated PA is suitable for the survival and activity of transplanted cells for further applications in tissue regeneration.