High Compliance Vascular Grafts Based on Semi-Interpenetrating Networks

Abstract

Current synthetic vascular grafts have poor patency rates in small diameter applications (<6 mm) due to intimal hyperplasia arising from a compliance mismatch between the graft and native vasculature. Enormous efforts have focused on improving biomechanical properties; however, polymeric grafts are often constrained by an inverse relationship between burst pressure and compliance. We have developed a new, semi-interpenetrating network (semi-IPN) approach to improve compliance without sacrificing burst pressure. The effects of heat treatment on graft morphology, fiber architecture, and resultant biomechanical properties are presented. In addition, biomechanical properties after equilibration at physiological temperature were investigated in relation to polyurethane microstructure to better predict in vivo performance. Compliance values as high as 9.2 ± 2.7 %/mmHg x 10−4 were observed for the semi-IPN graft while also maintaining high burst pressure, 1780 ± 230 mm Hg. The high compliance of these heat-treated poly(carbonate urethane) (PCU) and semi-IPN grafts is expected to improve long-term patency rates beyond even saphenous vein autografts by preventing intimal hyperplasia. The fundamental structure-property relationships gained from this work may also be utilized to advance biomedical device designs based on thermoplastic polyurethanes.

Review of Polymeric Biomimetic Small-Diameter Vascular Grafts to Tackle Intimal Hyperplasia

“…There are several types of AM techniques used in biomedical applications, e.g., selective laser sintering (SLS), direct ink writing (DIW), stereolithography (SLA), fused deposition modeling (FDM) or fused filament fabrication (FFF), and bioprinting technologies. 197 By combining two types of additive manufacturing techniques, Byrne et al 181 proposed a design of a three-layered graft, with the inner layer serving as an impermeable low stiffness matrix (100% modulus: 55.2 kPa) to mimic the role of elastin fabricated by direct ink writing of soft room temperature vulcanized silicone. A fiber reinforcing layer is designed to slack at low pressure and become taut as the mean pressure is increased and incorporated by fused filament fabrication.…”

“…Elastin fibers (elastic modulus: ∼0.6–1 MPa) bear the initial strain imposed by pulsatile pressure. With increasing pressure, the coiled collagen fibers (elastic modulus around ∼1 GPa) straighten up and substantially stiffen to bear the increasing load and protect the vessel from bursting. , The schematic in Figure shows the response of the arterial wall to increasing pulsatile pressure and its effect on compliance.…”

Development of an electrospun biomimetic polyurea scaffold suitable for vascular grafting

“…The difference in the elasticity of the native artery and the vascular graft at the site of suturing is called compliance mismatch. Abnormal proliferation of SMC due to compliance mismatch has been identified as a major cause for the formation of intimal hyperplasia that leads to the formation of occlusion . Hence, a reduction in the proliferation of SMC is a critical step in designing scaffold suitable for vascular grafting.…”

“…Abnormal proliferation of SMC due to compliance mismatch has been identified as a major cause for the formation of intimal hyperplasia that leads to the formation of occlusion. [48][49][50] Hence, a reduction in the proliferation of SMC is a critical step in designing scaffold suitable for vascular grafting.…”

A silicone fiber coating as approach for the reduction of fibroblast growth on implant electrodes

“…[23][24][25] However, through the highly hydrophobic silicone and the microscopic topography of the fibers, we aim to permanently inhibit fibroblast attachment and growth without the release of drugs. To date, only few successful efforts of silicone electrospinning for medical applications have been reported, mostly with silicones being part of a polymer blend, [26][27][28] specially synthesized polymers 29,30 or using the coaxial electrospinning technique together with other polymers. 31,32 To our knowledge, only two groups have published data of successfully electrospinning pure silicone, [33][34][35] but yet without a biomedical application.…”