Novel biomimetic scaffolds for small diameter vascular tissue engineering

Cardiovascular diseases (CVD) remain the leading cause of mortality, and account for 15% of the total health expenditure in the United States. Tissue-engineered vascular grafts show many advantages, and provide a promising treatment option. Scaffolds play an important role in vascular tissue engineering by supporting cell adhesion, migration, differentiation and proliferation. Understanding of the relationships between scaffolds and cell responses will provide critical guidance in scaffold design for vascular tissue engineering. This doctoral dissertation aimed to explore some innovative approaches in scaffold design by mimicking the native ECM of vascular tissues. Firstly, multifunctional nanofibers were achieved by incorporating various bioactive molecules into electrospun polycaprolactone (PCL) fibers. The release profiles of BSA (as a model growth factor) with various loading concentrations in PCL nanofibers were studied. The biological activity of functionalized fibers was proven by culturing human dermal fibroblasts on fibronectin-containing nanofibers, showing preferred cell attachment. Furthermore, a novel bottom-up layer-by-layer cell assembly approach was proposed to create a multilayered cell-nanofiber constructs towards vascular tissue formation. A series of studies have demonstrated several advantages of this approach over conventional methods in terms of well-controlled distribution of various cells and accelerated formation of layered tissues. To fabricate biomimetic nanofibers for vascular smooth muscle cells (MOVAS) and endothelial cells (MS-1), blends of PCL and collagen containing either elastin or matrigel were electrospun into nanofiber meshes and their properties were characterized. Matrigel-containing nanofibers favored the adhesion and proliferation of MS-1 cells and promoted the gene expression for CD31, vWF, integrin-beta 3 and NOS. Elastin-containing nanofibers supported the growth of MOVAS and significantly upregulated the expression of SMHC. 3D assembly of MOVAS with elastin-containing nanofibers followed by one layer MS-1 with matrigel-containing nanofibers led to the rapid formation of vascular patch-like constructs. Taken together, the biomimetic approach presented in this dissertation represents a new avenue to maximally recapitulate the native vascular tissue environment and allow the possible formation of vascular grafts with similar mechanical properties and cellular responses close to native counterparts. The layer-by-layer approach proves to be effective in rapid formation of multilayered cell-nanofiber constructs with well-controlled cell distribution, important to vascular tissue engineering.