Innovative Vascular Prostheses Combining 3D Electrospun Nanofiber Matrices and Bioactive Coatings Prepared by Plasma-Polymerization

There have been considerable efforts in developing prosthetic small-diameter (below 6mm) vascular grafts (VGs) as an alternative to autologous grafts to bypass or replace occluded blood vessels. Primary requirements for functional synthetic small-diameter vascular grafts (SDVGs) or tissue engineered blood vessels are hemocompatibility and favorable compliance. Particularly critical is the formation of a continuous, stable monolayer of endothelial cells (ECs) on the lumen under physiological shear stress. To that purpose, seeding autologous ECs on the lumen side of the graft prior to implantation is commonly done. But its success is limited by low cell retention under flow and by the large pore size of conventional textiles that do not favor the formation of a continuous monolayer. Electrospinning enables one to enhance graft compliance and to mimic the morphology of the extracellular matrix of blood vessels, but EC growth and retention on electrospun mats still remain a problem. In this research, it was shown that random electrospun PET (ePET) nanofiber mat coated by primary-amine rich plasma polymer coating (L-PPE:N) lead to finely controlled structural and surface properties that are required for a confluent EC monolayer on VGs. EC adhesion, -growth, and -retention under shear-induced flow stress were shown to be increased by L-PPE:N coating. However, cell retention is still not ideal. Moreover, this underlying L-PPE:N substrate is thrombogenic. To tackle this problem, chondroitin sulfate (CS) was grafted on LP which is known to prevent platelet adhesion while promoting human umbilical vein endothelial cell (HUVEC) adhesion and growth. It was observed that grafting CS on L-PPE:N coated electrospun mats could significantly enhance HUVEC adhesion, growth and their resistance to detachment. In addition, EC alignment in the direction of blood flow in the natural arteries is known to increase the cell capability to resist detachment under shear stress. This is typically achieved by a long and resource-consuming method involving in vitro fluid flow preconditioning in a bioreactor prior to implantation. Random and aligned electrospun PET mats were fabricated as scaffolds for the luminal layer. It was observed that EC resistance to shear stress was slightly further improved when it was directed by tuning electrospun alignment. On the other hand, the media layer of native vessels contains vascular smooth muscle cells (VSMCs) and circumferentially-aligned collagen fibres, which are essential for contraction, dilation and blood pressure control. In this research, aligned ePET mats were fabricated as scaffolds for the media layer, and three different plasma etching techniques were used to bring their mechanical and surface properties in line with those of natural blood vessels: (i) atmospheric pressure (“HP”) corona discharge in air; (ii) low-pressure radio-frequency plasma (“LP”) and (iii) microwave plasma asher, (ii) and (iii) in pure oxygen (O2), or O2 mixture with Ar or CF4. (iii) gave substantial reduction in Young's modulus after as little as 5 min. treatment in O2, without damage to the fibers. Changes in surface composition and drastic improvement in wettability/wicking were also observed, which resulted in promoting adhesion and growth of smooth muscle cells (SMCs). The aligned mats were then grafted with bioactive coatings, based on L-PPE:N coating, CS with tethered epidermal growth factor (EGF). It was found that a CS-EGF coating promoted the VSMC adhesion, growth, survival and infiltration. Our findings suggest that electrospun mats coated with bioactive coatings provides adequate scaffolds for the luminal and media side of SDVGs, with finely-controlled structural, mechanical and bioactive surface properties required for complete and stable endothelialization. Keywords: electrospinning; nanofibers; poly(ethylene terephthalate); plasma polymerization; plasma-etching; bioactive coatings, morphology, mechanical property; surface chemistry; In vitro cell experiment; endothelialization; vascular graft