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Publication Date

2012-11-19

Availability

UM campus only

Embargo Period

2012-11-19

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Biomedical Engineering (Engineering)

Date of Defense

2012-08-02

First Committee Member

Fotios M. Andreopoulos

Second Committee Member

Si M. Pham

Third Committee Member

Jorge E. Bohorquez

Fourth Committee Member

Alicia R. Jackson

Fifth Committee Member

Roberto I. Vazquez-Padron

Abstract

Current therapeutic angiogenesis strategies are focused on the development of biologically responsive scaffolds that can deliver multiple angiogenic cytokines and/or cells in ischemic regions. Herein, we report on a novel electrospinning approach to fabricate cytokine-containing nanofibrous scaffolds with tunable architecture to promote angiogenesis. Fiber diameter and uniformity were controlled by varying the concentration of the polymeric (i.e. gelatin) solution, the feed rate, needle to collector distance, and electric field potential between the collector plate and injection needle. Scaffold fiber orientation (random vs. aligned) was achieved by alternating the polarity of two parallel electrodes placed on the collector plate thus dictating fiber deposition patterns. Basic fibroblast growth factor (bFGF) was physically immobilized within the gelatin scaffolds at variable concentrations and human umbilical vein endothelial cells (HUVEC) were seeded on the top of the scaffolds. Cell proliferation and migration was assessed as a function of growth factor loading and scaffold architecture. HUVECs successfully adhered onto gelatin B scaffolds and cell proliferation was directly proportional to the loading concentrations of the growth factor (0–100 bFGF ng/mL). Fiber orientation had a pronounced effect on cell morphology and orientation. Cells were spread along the fibers of the electrospun scaffolds with the aligned orientation and developed a spindle-like morphology parallel to the scaffold’s fibers. In contrast, cells seeded onto the scaffolds with random fiber orientation, did not demonstrate any directionality and appeared to have a rounder shape. Capillary formation (i.e. sprouts length and number of sprouts per bead), assessed in a 3-D in vitro angiogenesis assay, was a function of bFGF loading concentration (0 ng, 50 ng and 100 ng per scaffold) for both types of electrospun scaffolds (i.e. with aligned or random fiber orientation). In addition, a murine ischemic hind limb model was utilized to assess the reperfusion potential of such scaffolds, both aligned and randomly deposited, and with or without bFGF. Assessment of the treatment groups included LDPI imaging at 5, 7, 10, 14, and 21 days post-surgery, and DiL vessel staining on day 21 visualized with a confocal microscope. Aligned scaffolds achieved 70% reperfusion of the ischemic leg within 21 days and the DiL stained vessel architecture demonstrated significant alignment compared to randomly deposited scaffolds. Hence, this evidence suggest that the herein developed treatment group consisting of aligned bFGF loaded gelatin B electrospun scaffolds successfully enhanced the angiogenic process and had a pronounced effect on the newly formed vessel bed architecture.

Keywords

Electrospinning; Angiogenesis; Scaffolds

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