Development of hydrogel scaffolds and a bioreactor for vascular tissue engineering
Schmedlen, Rachael Hope
West, Jennifer L.
Doctor of Philosophy
This dissertation determines the feasibility of photopolymerizable hydrogels as novel tissue engineering scaffolds and constructs a pulsatile flow bioreactor for the development of tissue engineered vascular grafts (TEVGs). The large number of small diameter bypass surgeries performed each year coupled with the shortage of suitable, patent vascular grafts has spurred the development of tissue engineered vascular substitutes. This investigation characterizes the mechanical properties of polyvinyl alcohol (PVA) and polyethylene glycol (PEG) hydrogels and evaluates their ability to support cell viability, proliferation, and extracellular matrix protein production for use as a tissue engineering scaffold. The elasticity and tensile strength of PVA and PEG hydrogels may be tailored by changing the polymer concentration, number of crosslinkable groups per PVA chain, PEG molecular weight, or using blends of high and low PEG molecular weights to transmit cyclic strain and still maintain structural integrity in a pulsatile flow bioreactor. At least 75% of cells cultured over two weeks inside PVA hydrogels and for four weeks in PEG hydrogels remained viable, with no differences in viability across the thickness of the hydrogel. Once seeded inside hydrogels, cells continue to function; following two weeks in culture, cells produced hydroxyproline in both PVA and PEG hydrogels. After determining that these hydrogels were suitable materials for scaffolds, a pulsatile flow bioreactor, mimicking transmural strain encountered in vivo, was constructed to culture tubular hydrogel-cell constructs. PEG hydrogels placed in the bioreactor exhibited strains at 2 Hz and between 5.9--15.9%, depending on the material elasticity, with pressures around 70/20 mmHg. Furthermore, smooth muscle cells seeded in PEG hydrogels and cultured in the bioreactor for one week showed similar DNA content to static gels, indicating that the bioreactor does not hinder cell viability. These results suggest that PVA and PEG hydrogels are appropriate materials for TEVG scaffolds and that the bioreactor generates conditions suitable for tissue formation and organization. In the future, this system will require optimization to incorporate the right combination of bioactive molecules, cell types, and bioreactor parameters to achieve a TEVG with composition, organization, and mechanical properties resembling those of native blood vessel.