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Abstract: In recent years, great advances have been made in the use of islet transplantation as a treatment for type I diabetes. Indeed, it is possible that stimulation of local neovascularization upon transplantation could improve functional graft outcomes. In the present study, we investigate the use of multilayered alginate microbeads to provide a sustained delivery of FGF-1, and whether this results in increased neovascularization in vivo. Multilayered alginate microbeads, loaded with either 150ng or 600ng of FGF-1 in the outer layer, were surgically implanted into rats using an omentum pouch model and compared to empty microbead implants. Rats were sacrificed at 4days, 1week, and 6weeks. Staining for CD31 showed that both conditions of FGF-1 loaded microbeads resulted in a significantly higher vessel density at all time points studied. Moreover, at 6weeks, alginate microbeads containing 600ng FGF-1 provided a greater vascular density compared to both the control group and the microbeads loaded with 150ng FGF-1. Omenta analyzed via staining for smooth muscle alpha actin showed no variation in mural cell density at either 4days or 1week. At 6weeks, however, omenta exposed to microbeads loaded with 600ng FGF-1 showed an increase in mural cell staining compared to controls. These results suggest that the sustained delivery of FGF-1 from multilayered alginate microbeads results in a rapid and persistent vascular response. An increase in the local blood supply could reduce the number of islets required for transplantation in order to achieve clinical efficacy. [Copyright &y& Elsevier]

Abstract: Microvascular network formation is required for the success of many therapies in regenerative medicine. The process of vessel assembly is fundamentally altered, however, in many people within the potential patient population, including the elderly and people with diabetes. Significant research has been performed to determine how cellular dysfunction contributes to this inadequate neovascularization, but alterations in the extracellular matrix (ECM) may also influence this process. Glycation of ECM proteins, specifically type I collagen, increases as people age and is accelerated due to uncontrolled diabetes. This glycation results in increased ECM stiffness and resistance to degradation. The goal of this research is to determine whether collagen glycation consistent with changes in aged (defined as people older than 80 years old) and diabetic individuals influences neovascularization. Collagen gels that were incubated in glucose-6-phopshate (G6P) for varying times exhibited cross-linking (26.2±8.1% and 31.3±5.6% for incubation in 375 mM G6P for 5 and 8 days, respectively), autofluorescence, and advanced glycation end product levels (666±481 and 2122±501 pmol/mg protein for 5 and 8 days of 375 mM G6P, respectively) consistent with aged and diabetic populations. Three-dimensional culture models showed that sprouting angiogenesis was delayed in collagen gels with high levels of glycation. When implanted in vivo, glycated gels were degraded (44.4±4.2% and 49.5±11.7% nondegraded gel remaining for gels incubated for 5 and 8 days in 375 mM G6P, respectively) and vascularized (75.5±32.0 and 73.7±23.6 vessels/mm2) more slowly than controls (22.3±9.9% gel remaining and 133.3±31.0 vessels/mm2). These results suggest that glycation of collagen can alter neovascularization and may contribute to alterations in vessel assembly observed as people age and due to diabetes. [Copyright &y& Elsevier]

Abstract: Engineered vascularized adipose tissue could serve as an alternative to traditional tissue reconstruction procedures. Adipose formation occurs in a coordinated fashion with neovascularization. Previous studies have shown that extracellular matrix-based materials supplemented with factors that stimulate neovascularization promote adipogenesis in a number of animal models. The present study examines the ability of fibroblast growth factor (FGF-1) delivered from alginate microbeads to induce neovascularization and adipogenesis in type I collagen gels in a vascular pedicle model of adipose tissue engineering. FGF-1 loaded microbeads stimulated greater vascular network formation in an in vitro 3D co-culture model than a single bolus of FGF-1. In in vivo studies, FGF-1 loaded beads suspended in collagen and implanted in a chamber surrounding the exposed femoral pedicle of a rat resulted in a significant increase in vascular density at 1 and 6 weeks in comparison to bolus administration of FGF-1. Staining for smooth muscle actin showed that over 48% of vessels had associated mural cells. While an increase in neovascularization was achieved, there was less than 3% adipose under any condition. These results show that delivery of FGF-1 from alginate beads stimulated a more persistent neovascularization response than bolus FGF-1 both in vitro and in vivo. However, unlike previous studies, this increased neovascularization did not result in adipogenesis. Future studies need to provide a better understanding of the relationship between neovascularization and adipogenesis in order to design advanced tissue engineering therapies. [Copyright &y& Elsevier]

Abstract: The use of growth factors for the therapeutic stimulation of neovascularization in regenerative medicine has been extensively investigated, but the inability to control their temporal delivery may limit clinical success. A strategy that delivers continuous therapeutic concentrations of growth factors may increase the protein''s efficacy. The present study investigates the ability of sustained delivery of fibroblast growth factor-1 (FGF-1), to induce neovascularization in vivo. Alginate microbeads were synthesized to release active FGF-1 for three weeks. Microbeads loaded with FGF-1 (total amount 150 ng) were implanted into a surgically created omentum pouch in rats and were compared to control empty microbead implants and a single bolus injection of 150 ng of FGF-1 with empty microbead implant. Animals were sacrificed at either 3 or 6 weeks post implantation and omenta were analyzed for vascular density and mural cell interactions. Vascular area for bolus FGF-1 and FGF-1 loaded microbeads was higher than control at 3 weeks. At 6 weeks, vascular density in the group with FGF-1 loaded microbeads was significantly higher than the group with bolus administration of FGF-1, primarily due to an increase in the number of vessels less than 20 µm in diameter. Vascular density in omenta of the group receiving the bolus FGF-1 returned to control levels by 6 weeks. Staining for smooth muscle actin showed that 50% of vessels had associated mural cells. There was a trend of increased mural cell staining at 6 weeks for the FGF-1 loaded beads compared to bolus FGF-1 and control levels. Results in these studies suggest that sustained release of FGF-1 increases the duration of the vascular response in contrast to a bolus injection of FGF-1. [Copyright &y& Elsevier]