Implants of fibrillar type I collagen support neovascularization and allow for in vivo quantitation of angiogenesis.

The angiogenesis assay relies on the upward invasion of newly forming blood vessels from the CAM into the collagen implant where they are microscopically scored. (A) Schematic illustrates type I collagen polymerized around 2 layers of nylon mesh to form a grid-embedded implant. The implant is then placed on the CAM, from which new blood vessels arise and grow up into the collagen and through the grids of the mesh. (B) Stereomicroscopic view of a collagen implant placed on the CAM of a 10-day chick embryo developing ex ovo. In the photomicrographs shown (C,D), the collagen in the implant had been copolymerized with buffer alone (C) or with bFGF/VEGF (D). The collagen implants were then incubated on the CAM for 65 hours. Blood vessels in representative implants were photographed in vivo through a stereomicroscope. New vessels that grow up into the implants are visualized within the grid boxes of the nylon mesh and scored as positive. Arrowheads indicate only some of these scored vessels. The preexisting, underlying CAM vessels are out of focus (○) and are never scored in the assay. The presence of bFGF and VEGF in the implants (D) clearly enhances the angiogenesis score over the control implants (C). Bar in panels C and D is 300 μm.