Angiogenesis

In Vivo Angiogenesis

Growth factors (GFs) induce neovascularization and microvessel formation in vivo when delivered in Heprasil™ or Extracel-HP™ hydrogel films, which allows intact microvessel beds to form with well-defined borders1,2,3. The thiol-modified heparin in the Extracel-HP™ mimics heparan sulfate proteoglycans normally present in the extracellular matrix. It also regulates the in vivo GF release so that a functional microvessel network can develop. The model used to study in vivo angiogenesis using Heprasil™ or Extracel-HP™ involved making hydrogel films impregnated with GFs and implanting them into the ear pinna of Balb/C mice1,2,3. Heprasil™ and Extracel-HP™ can also be injected subcutaneously as hydrogels.

Growth-Factor Release Rates

Six GFs have been studied for in vitro release from Heprasil™-only and Extracel-HP™ hydrogels:

  • angiopoietin-1 (Ang-1)1
  • vascular endothelial growth factor (VEGF)1,2,3
  • keratinocyte growth factor (KGF)2
  • basic fibroblast growth factor (bFGF)3,4
  • platelet-derived growth factor-AA (PDGF)5
  • transforming growth factor β1 (TGF- β1)5

All six GFs are slowly released over several weeks with varying kinetics. The release rates for bFGF and VEGF have been published3,4. Those for Ang-1, KGF, PDGF and TGF-β1 are summarized in Growth-Factor Release.

Hydrogel Composition

The Extracel-HP™ Hydrogel Kit contains Heprasil™ (thiol-modified hyaluronan with thiol-modified heparin), Gelin-S™ (thiol-modified gelatin, denatured collagen), and Extralink™ (thiol-reactive crosslinking agent). It gels at temperatures from ambient to 37°C at physiological pH, with no low-temperature or low-pH steps in its preparation. The researcher has complete control over gelation time (as short as twenty minutes or as long as several hours), hydrogel stiffness, and hydrogel composition. Extracel-HP™ is tested for bacteria growth, lactate dehydrogenase-elevating virus (LDEV), and endotoxins.

References

  1. C. M. Riley, P. W. Fuegy, M. A. Firpo, X. Z. Shu, G. D. Prestwich, R.A. Peattie, “Stimulation of in vivo angiogenesis using dual growth factor-loaded crosslinking glycosaminoglycan hydrogels,“ Biomaterials, 27, 5935-5943 (2006).
  2. R. A. Peattie, E. Rieke, E. Hewett, R. J. Fisher, X. Z. Shu, and G. D. Prestwich, “Dual growth factor-induced angiogenesis in vivo using hyaluronan hydrogel implants,” Biomaterials, 27, 1868-1875 (2006).
  3. D. B. Pike, S. Cai, K. R. Pomraning, M. A. Firpo, R. J. Fisher, X. Z. Shu, G. D. Prestwich, R. A. Peattie, “Heparin-regulated release of growth factors in vitro and angiogenic response in vivo to implanted hyaluronan hydrogels containing VEGF and bFGF,” Biomaterials, 27, 5242–5251 (2006).
  4. S. Cai, Y. Liu, X. Z. Shu, G. D. Prestwich, “Injectable glycosaminoglycan hydrogels for controlled release of human basic fibroblast growth factor,” Biomaterials, 26, 6054-6067 (2005).
  5. Unpublished data from the Rob Peattie lab (Oregon State University) and S. Cai and B. Yu of the Glenn Prestwich (University of Utah) lab.