Innovative bioactive scaffold technologies for vascular tissue engineering: influences of morphology and composition
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Date
30/11/2020Author
Reid, James Alexander
Metadata
Abstract
Vascular disease is currently the leading cause of mortality worldwide, with coronary heart disease,
peripheral arterial disease and strokes accounting for upwards of 30% of all deaths in Europe. Bypass
grafting is one of the major approaches utilised in the treatment of vascular disease. This technique
involves diverting blood flow around an arterial blockage by grafting in an alternative path. This
surgery is widely used in the treatment of coronary heart disease and peripheral arterial disease. This
is either done with a synthetic material, such as PTFE, or by using an autologous vessel such as the
saphenous vein or the internal thoracic artery. The grafting of autologous vessels is considered the
gold standard for small diameter bypass grafts due to the higher patency rates compared to their
synthetic counterparts. However, there are only a finite amount of vessels that can be harvested and in
many cases the vessels are not of a high enough quality for use in surgery. Therefore, there is an
urgent need for the development of novel biomaterials that can improve patency rates in bypass grafts.
As a push for solutions to this problem, the field has placed a focus on improving the biofunctionality
of materials in vitro as a means of testing the translatability of the material.
This thesis presents four different methods of improving the bioactivity of scaffolds for vascular
tissue engineering through alteration of the morphology and composition of the scaffold: 1) Altering
the fibre diameter of electrospun polycaprolactone (PCL) scaffolds to enhance the morphology for
seeded cells. 2) Native aortic and heart bovine extracellular matrices (ECM) were incorporated into
PCL scaffolds. 3) Cell secretome was bound to the PCL scaffolds to enhance the bioactivity of the
scaffold. 4) Altering the cell’s response through environmental factors such as hydrostatic pressure
and hypoxia.
Scaffolds were either seeded with human umbilical vein endothelial cells (HUVECs) or human
umbilical vein smooth muscle cells (HUVSMCs) and their response to their microenvironments were
analysed. Gene expression analysis and immunohistochemical analysis showed that altering the fibre
diameter of the scaffold had evident effects on cellular response. For example, increasing fibre
diameter had the effect of increasing cellular infiltration for both cell types. HUVECs upregulated key
phenotypic genes when seeded on the largest fibre diameter. On the contrary, the HUVSMCs upregulated key genes when cultured on the smallest fibre diameter. Likewise, the incorporation of
ECMs into the scaffold altered their mechanical properties and changed the biological response of the
seeded cells. Incorporating ECM had the effect of decreasing stiffness and increasing scaffold
elasticity. Furthermore, the incorporation of aortic ECM into the fibres led to higher cell viability for
both cell types. Additionally, the binding of proteins released by cultured cells to the PCL scaffold
was shown to alter gene expression and cell survival.
Each method undertaken altered cellular responses such as gene expression and cell viability,
indicating that these methods provide a viable and translatable platform for vascular tissue
engineering. These scaffold have great potential for vascular tissue engineering and offer
translatability to other tissue types.