Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Kibret Mequanint

2nd Supervisor

Elizabeth Gillies

Joint Supervisor

Abstract

The focus of this research was to develop a biomimetic, degradable vascular scaffold that could be considered as part of a tissue-engineered vascular graft strategy. A family of degradable poly(ester amide)s (PEAs) derived from naturally occurring α-amino acids, aliphatic diols and diacids were synthesized to yield PEAs with glass transition temperatures below physiologic temperature ensuring their pliability. Tri-functional amino acids l-lysine or l-aspartic acid were incorporated into the polymer backbone yielding complementary functional handles for subsequent conjugation of growth factors. Higher molecular weight PEAs were obtained using an interfacial polycondensation technique compared with a solution polymerization approach.

Human coronary artery smooth muscle cells (HCASMCs) attached and proliferated on all two-dimensional (2D) PEA films. Well-spread cells were observed on the non-functional and aspartic acid functionalized PEAs up to 7 days, more so than on the corresponding lysine containing PEAs. The HCASMCs formed focal adhesions on all 2D PEA surfaces as illustrated by vinculin immunofluorescence, yet smooth muscle α-actin (SMαA) expression was not abundant, suggesting that the HCASMCs had adopted a synthetic phenotype.

Uniform, nano-scale, fibrous PEA mats ranging in average fiber diameter from 130 to 294 nm were prepared by electrospinning. The increased surface charge attributed to the pendant carboxylic acid groups decreased the average fiber diameter. HCASMCs seeded on the three-dimensional fibrous mat revealed excellent cell attachment and spreading, but limited cell infiltration. In the aspartic acid containing functional PEA, the fibrous structure was lost post-processing due to a plasticizing effect facilitated by the aspartic acid monomer.

The dual effect of topography and TGF-β1 on HCASMC phenotype was investigated by Western blot analysis. While a modest increase in the expression of both smooth SMαA and calponin was observed on all 2D films at four days culture, the 3D topography alone increased both SMαA and calponin expression suggesting the cellular microenvironment can modulate SMC phenotype.

Finally, X-ray photoelectron spectroscopy and immunofluorescence demonstrated the successful conjugation of TGF-β1 to the pendant carboxylic acid groups suggesting that functional PEAs can be used to generate degradable, biomimetic biomaterials for vascular tissue engineering.

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