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Crosslinked, chemically modified hyaluronan (HA) hydrogels preloaded with two cytokine growth factors, vascular endothelial growth factor (VEGF) and Angiopoietin-1 (Ang-1), were employed to elicit new microvessel growth in vivo, in both the presence and absence of heparin in the gels. HA hydrogel film samples were surgically implanted in the ear pinnae of mice, and the ears were harvested at 7 or 14 days post implantation. Analysis of neovascularization showed that each of the treatment groups receiving an implant, except for HA/Hp at day 14, demonstrated significantly more microvessel density than control ears undergoing surgery but receiving no implant (p < 0.015). Treatment groups receiving either Ang-1 alone, or aqueous co-delivery of both Ang-1 and VEGF, were statistically unchanged with time. In contrast, film delivery of both growth factors produced continuing increases in vascularization from day 7 to day 14 in the absence of heparin, but decreases in its presence. However, presentation of both VEGF and Ang-1 in crosslinked HA gels containing heparin generated intact microvessel beds with well defined borders. The HA hydrogels containing Ang-1+VEGF produced the greatest angiogenic response of any treatment group tested at day 14 (NI = 7.44 in the absence of heparin and 4.67 in its presence, where NI is a neovascularization index). Even in the presence of heparin, this was 29% greater vessel density than the next largest treatment group, that receiving HA/Hp+VEGF (NI = 3.61, p = 0.04). New therapeutic approaches for numerous pathologies could be notably enhanced by the localized, sustained angiogenic response produced by release of both VEGF and Ang-1 from crosslinked HA films.

As one important step in the investigation of the mechanical factors that lead to rupture of abdominal aortic aneurysms, flow fields and flow-induced wall stress distributions have been investigated in model aneurysms under pulsatile flow conditions simulating the in vivo aorta at rest. Vortex pattern emergence and evolution were evaluated, and conditions for flow stability were delineated. Systolic flow was found to be forward-directed throughout the bulge in all the models, regardless of size. Vortices appeared in the bulge initially during deceleration from systole, then expanded during the retrograde flow phase. The complexity of the vortex field depended strongly on bulge diameter In every model, the maximum shear stress occurred at peak systole at the distal bulge end, with the greatest shear stress developing in a model corresponding to a 4.3 cm AAA in vivo. Although the smallest models exhibited stable flow throughout the cycle, flow in the larger models became increasingly unstable as bulge size increased, with strong amplification of instability in the distal half of the bulge. These data suggest that larger aneurysms in vivo may be subject to more frequent and intense turbulence than smaller aneurysms. Concomitantly, increased turbulence may contribute significantly to wall stress magnitude and thereby to risk of rupture.