Zdrahala R J
PolyMedica Industries, Inc., Woburn, MA 01801, USA.
J Biomater Appl. 1996 Apr;10(4):309-29. doi: 10.1177/088532829601000402.
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.
血管移植物是用于增强功能低效的血管系统的装置，是可植入医疗器械的重要组成部分，在全球范围内超过百万例血管手术中发挥着重要作用。根据本领域公认的定义，小口径移植物是内径（ID）为6毫米或更小的导管；大口径移植物的内径从7毫米开始。虽然利用大隐静脉（SVG）、髂内动脉或乳内动脉的自体移植物仅用于冠状动脉旁路移植术（CABG），并且在许多外周适应症中优先使用，虽然生物源移植物的使用并未广泛普及，但具有可控图案和孔隙率的聚合物基人工移植物是大口径移植物的首选假体。聚酯（PET）纱线被编织或针织成各种多孔图案。聚四氟乙烯管被扩张成多孔导管（ePTFE）。尽管这些技术用于生产内径大于6毫米的移植物，但主要原理也被应用于小口径移植物的开发。聚氨酯也在评估用于小口径应用。通过上述技术生产的移植物（无论内径大小）都是多孔的。这种孔隙率被认为对适当的愈合和移植物的整体通畅至关重要，但会导致血液通过移植物壁或在吻合处通过缝合孔泄漏。壁泄漏和缝合孔出血仍然是相当严重的缺点。目前，胶原蛋白、明胶、白蛋白及其衍生物被用作密封剂。利用各种应用模式和交联程度来控制体内降解和移植物愈合。其他天然和合成水凝胶可以作为密封剂和移植物性能调节剂发挥重要作用。通过应用生物活性涂层可以通过改善初始血液相容性来提高移植物通畅率。肝素化系统似乎在该领域占主导地位，但许多新概念正在研究中。通过介导生物物质实现腔内内皮化可能为合成小口径移植物开辟巨大潜力。此外，多孔可生物降解管可以用作临时支架，以吸引和促进细胞增殖和向内生长，即真正的血管生成。本系列的第一部分讨论小口径移植物的“现状”。以下部分将讨论开发真正通畅的小口径移植物所需的概念，并将报告我们在开发用于血管通路、外周以及可能用于CABG适应症的生物耐用和搏动性移植物方面的进展。
