Neovascularization of poly(ether ester) block-copolymer scaffolds in vivo: long-term investigations using intravital...

Poly(ether ester) block-copolymer scaffolds of different pore size were implanted into the dorsal skinfold chamber of balb/c mice. Using intravital fluorescent microscopy, the temporal course of neovascularization into these scaffolds was quantitatively analyzed. Three scaffold groups (diameter, 5 mm; 220-260 thickness, microm; n = 30) were implanted. Different pore sizes were evaluated: small (20-75 microm), medium (75-212 microm) and large pores (250-300 microm). Measurements were performed on days 8, 12, 16, and 20 in the surrounding normal tissue, in the border zone, and in the center of the scaffold. Standard microcirculatory parameters were assessed (plasma leakage, vessel diameter, red blood cell velocity, and functional vessel density). The large-pored scaffolds showed significantly higher functional vessel density in the border zone and in the center (days 8 and 12) compared with the scaffold with the small and medium-sized pores. These data correlated with a larger vessel diameter and a higher red blood cell velocity in the large-pored scaffold group. Interestingly, during the evaluation period the microcirculatory parameters on the edge of the scaffolds returned to values similar to those found in the surrounding tissue. In the center of the scaffold, however, neovascularization was still active 20 days after implantation. Plasma leakage and vessel diameter were higher in the center of the scaffold. Red blood cell velocity and functional vessel density were 50% lower than in the surrounding tissue. In conclusion, the dorsal skinfold chamber model in mice allows long-term study of blood vessel growth and remodeling in porous biomedical materials. The rate of vessel ingrowth into poly(ether ester) block-copolymer scaffolds is influenced by pore size and was highest in the scaffold with the largest pores. The data generated with this model contribute to knowledge about the development of functional vessels and tissue ingrowth into biomaterials.