Investigating, Characterisation and Development of a Biocompatible Material for Biomedical Graft Applications

Abstract

Cardiovascular disease remains a leading cause of death worldwide and coronary artery bypass grafting is a common surgical treatment for advanced coronary artery disease. Natural conduits such as internal thoracic artery and saphenous vein remain the clinical standard; but their limited availability and quality drive the need for a synthetic small diameter vascular graft. The central obstacle to developing such a graft is compliance mismatch, existing synthetic materials such as ePTFE and Dacron are considerably stiffer than the native coronary artery. This inability to replicate its compliant, nonlinear mechanical response, generate stress concentrations at the anastomosis that lead to graft failure. This thesis investigates a series of solution cast TPU:PDMS:EMA polymer blends as candidates for graft materials, there are nine compositions across three blend ratios (90:10:1, 80:20:1 & 70:30:1) with three casting concentrations (10,15, & 20% w/v). The mechanical properties were determined using standardised ISO 37 type 2 dumbbell specimens alongside stepped specimen geometry designed to investigate the effect of a geometric discontinuity on the mechanical properties and performance. The blends exhibited ultimate tensile strengths of 19.33 to 27.76 MPa and elongations at break exceeding 898%, comfortably surpassing both native coronary artery tissue and autologous vessels, however at the same elongation at break as the natural vessels, the blends exhibited the same tensile stress. All compositions displayed a progressively softening mechanical response with secant modulus declining across the deformation range. This profile is fundamentally more favourable for compliance matching than the near consistent stiffness of conventional synthetic grafts. The stepped specimens demonstrated that geometric transitions dictate the site and mode of failure independently of bulk material properties. The 90:10:1 15% w/v blend emerged as the most mechanically well-rounded composition. These findings establish the TPU:PDMS:EMA system as a promising candidate for continued development toward small diameter vascular graft applications.