Abstract
There are many ways in which blood vessels can be damaged, resulting in the need for replacement vessels. Traumatic injury to surrounding tissue, diseases that degrade the elasticity or other features, and life-style choices that lead to blockages are all examples of how damage can occur. Surgical treatment for damage blood vessels typically involves replacing the damaged section. Self-donated vessels guarantee compatibility with the patient, but many patients cannot self-donate. Additionally self-donating requires additional surgeries and results in impaired functionality at the donor site. The creation of multiple wounds increases the risk of infection. Synthetic grafts do exist in clinical use, but they tend to be short term solutions as a result of insufficient biocompatibility. This low biocompatibility can lead to immune rejection and may leading to the graft becoming blocked.
In this research, a potential design and manufacturing basis for tissue engineering blood vessels is explored. A novel combination of meltelectrowriting and fused deposition modelling was used to generate scaffolds via moulds. This allowed for increased scaffold design freedom not attainable with either additive manufacturing technology alone. The primary material used for these scaffolds was polycaprolactone. This is an FDA-approved synthetic polymer well-established to possess excellent compatibility with both biological systems and other materials. This compatibility with other materials allows for both the biological and material properties of scaffolds to be customised for their specific uses.
The moulds used in this study were created using a varied of materials from glass to conductive polylactic acid. This latter material, polylactic acid with graphite added to improve electrical conductivity, was found to be an excellent moulds material in its compatibility with standard fused deposition modelling to make moulds of nearly any shape while still concentrating the
electric field in melt-electrowriting and allowing the scaffolds to be removed from the mould without difficulty or residue.
This study characterised the pure polycaprolactone scaffolds both mechanically and biologically. The biological characterisation consisted of seeding the scaffolds with normal human dermal fibroblasts, similar in size to endothelial cells, and culturing them over the course of a month. This indicated that the manufacturing process did not introduce any factors that negatively impacted cell growth. Further, the mechanical characterisation, in conjunction with simulation, validated previous research and identified potential means for accurate simulation for future scaffold development.
Dynamic mechanical analysis was used to characterise the mechanical properties of the scaffolds, giving both the viscous and elastic properties of the scaffolds. The scaffolds were also physically simulated in different potential pore structures using the finite element method and theoretical values predicted by literature and observed strand sizes. The results showed that the mechanical properties of the scaffolds could be well approximated through three-dimensional Voronoi tessellation. This means that future scaffold designs made with melt-electrowriting may have their mechanical performance predicted without needing to consume materials and even when their geometries would prohibit direct testing.