Synthetic vascular grafts and materials used in them

Abstract

Synthetic vascular graft used to repair and replace broken blood vessels have persistent chal-lenges although they have been in clinical use for decades. The challenges with synthetic vas-cular grafts are thrombus formation, neointimal hyperplasia, mechanical mismatch, and long-term patency. Small-diameter grafts with diameter under 6 mm are particularly challenging. This thesis is a literature review about synthetic vascular grafts with the aim of determining what kinds of synthetic vascular grafts there are in the research and on the market. In addition, ways to overcome the challenges with the grafts are considered.

Vascular grafts are conventionally made of either expanded polytetrafluoroethylene (ePTFE) or polyethylene terephthalate (PET). Both materials are hydrophobic, highly crystalline, and inert synthetic polymers. Different manufacturing methods are used with these materials. ePTFE grafts are manufactured with extrusion to form uniform tubes whereas PET is manufactured with either knitting or weaving to form a textile structure.

There are two main ways the research is taking to overcome the challenges with synthetic vas-cular grafts. The first is to modify the existing conventional grafts and the second is by re-searching alternative materials for the grafts. With the conventional graft modifications, the fo-cus with PET grafts is coatings and using them as sealants and with ePTFE grafts the focus is wider with embedding materials into the grafts, coatings, and different surface modifications. PET grafts require sealing, because their porous structure can lead to bleeding through the vessel wall, which can be avoided with the sealing. Alternative materials studied for vascular grafts include other synthetic and natural polymers with some of the alternatives being biode-gradable. The main alternative material is polyurethanes which are studied especially for the small diameter grafts.

Currently, ePTFE and PET grafts are sharing the market even though they still have challeng-es. Neither one of them has shown itself to be significantly better than the other. The research has been giving promising results for alternative options and modifications, but the studies are still in early phases.