Small Caliber Vascular Grafts. Part I: State of the Art

Abstract

Vascular grafts, devices designed to augment inefficiently functioning vascular systems, represent a significant part of implantable medical devices, with major participation in over a million vascular surgeries performed worldwide. By definition accepted in the art, a small caliber graft is a conduit with internal diameter (ID) of 6 mm or less; large caliber grafts start at ID of 7 mm. While the autologous grafts utilizing saphenous veins (SVG) and internal iliac, or mammary arteries are used exclusively in cardiac artery bypass grafts (CABG) procedures and preferentially in many peripheral indications, and while the use of grafts with biological origin did not proliferate, polymer-based artificial grafts of controlled patterns and porosity are prostheses of choice for the large caliber. The polyester (PET) yarn is knitted or woven into various porous patterns. The PTFE tubes are expanded into porous conduits (ePTFE). Although these technologies are used to produce the grafts with ID larger than 6 mm, the dominant principles are being applied to the development of small caliber graft. Polyurethanes are also evaluated for small caliber application. The grafts (regardless of the ID) produced by the above technologies are porous. This porosity, considered to be critical for proper healing and overall graft patency, causes the blood to leak through the graft wall or at anastomosis through the suture holes. Both the wall leakage and suture hole bleeding remain rather serious drawbacks. Currently, collagen, gelatin, albumin and their derivatives are used as sealants. Various modes of application and degrees of crosslinking are utilized to control in vivo degradation and graft healing. Other hydrogels, both natural and synthetic, could play significant roles as sealants and modifiers of the graft performance. Enhancement of graft patency via improvement of initial hemocompatibility could be achieved by application of bioactive coatings. Heparinized systems seem to dominate in this field, but many new concepts are being investigated. Intraluminal endothelialization via mediating biologicals could open significant potential for synthetic small caliber grafts. Furthermore, porous biodegradable tubes could be used as temporary scaffold to attract and promote cell propagation and ingrowth, the true angiogenesis. Part I of this series discusses the "S.O.T.A" of the small caliber graft. The following parts will discuss concepts needed for development of truly patent small caliber grafts and will report on our progress in the development of biodurable and pulsatile grafts for vascular access, peripheral, and potentially for CABG indications.

Photocurable surgical tissue adhesive glues composed of photoreactive gelatin and poly(ethylene glycol) diacrylate

“…Gelatin, which is nontoxic in nature 22,23 and induces cell adhesion via biospecific interaction, 24 has been extensively used in biomedical applications including hemostatic aid materials, [25][26][27][28][29][30] cell adhesive matrices, 31,32 and drug-releasing matrices. [33][34][35] Gelatin, partially derivatized with photoreactive xanthene dyes, which have been used as coloring ingredients for foods over the years, 36,37 is a core material in our technology.…”

Glycerol-Preserved Arterial Allografts Evaluated in the Infrarenal Rat Aorta

“…However, for small diameter reconstructions, such prosthetic grafts have low cumulative patencies, ranging from 24 to 58% after 3 years [25,26] . These results have stimulated research in alternatives to prosthetic grafts such as preserved vascular allografts and xenografts, and the use of biomaterials to serve as a vascular tissue matrix [27,28] . Extracellular matrix scaffolds can serve as templates for cellular attachment and ingrowth of recipient cells [29,30] .…”

Implantation of Novel Small-Diameter Polyurethane Vascular Prostheses Interposed in Canine Femoral and Carotid Arteries

“…Therefore, different polyurethanes have different physical, biological and chemical characteristics. According to medical usage, different kinds of polyurethanes are needed and studies are taking place in this area [28,29]. Polyurethanes have the advantages of superior thromboresistance, rapid ingrowth of living tissue and reduced hyperplasia, easy cannulation and rapid sealing [19].…”