Bioactive Polymer Surf ace Modif ications for Artificial Blood Vessels and Intraocular Lenses
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d for intraocular lenses. Mem branes of regenerated cellulose were the most widely used hemodialysis mem branes, but in the recent decades, several attempts were made to replace cellulose with alternative polymers in order to improve blood compatibility—particularly polyacrylonitrile, polycarbonate, PMMA, and polysulfone. However, today there remain problems of both biocompatibility and biofunction ality. Clinically, the main problems emerge from interactions between mate rials and the local tissue environment, as summarized in Table I.1 To ensure a maximum of biocompatibility and functionality, the material in vivo should not evoke any of the reactions outlined in Table I. Today, none of the classical mate rials fulfills this high demand. Generally, the biomaterials display structures and properties quite different from the body tissue itself. One possible approach is to search for new artificial materials that are closer to an optimum than the current materials are. However, the inflammatory/reparative-tissue re sponse after implantation of foreign bodies is a complex process involving resident cells (e.g., fibroblasts), invading inflammatory cells (e.g., macrophages), extracellular matrix components (e.g., fibrinogen and fibronectin), and inflam
matory mediators (e.g., cytokines and growth factors). Since this complex interactive process is not understood in detail, it appears to be more feasible to modify materials that already exist and have been physicochemically characterized. The polymers mentioned here can be combined with biological molecules. The artificial material can serve as a constructive component, determining the physical properties, while the biological component builds up the surface, mimicking the local tissue environment. In this article, we will discuss some strategies for this concept using two examples: artificial blood vessels and intraocular lenses.
Artificial Blood Vessels As a result of our inability to control factors involved in the pathogenesis of arteriosclerosis, vascular surgical procedures become necessary, especially in the advanced stage of this disease. Motivated by the urgency of the expansion and imminent rupturing typical of ab dominal aortic aneurysms, Blakemore and Voorhees2 were the first to report the successful replacement of arterial defects with a synthetic prosthesis. Most of the currently used vascu lar prostheses are made of expanded poly(tetrafluoroethylene) (ePTFE, or Teflon) or woven polyester (e.g., Dacron). The use of these materials in grafts for replacing blood vessels that have high flow and low resistance characteristics (e.g., the lower abdominal aorta, where the aorta branches into the large pelvic arteries—the site where large aortic aneu rysms most frequently occur) has proven to be clinically acceptable. Ca 1 low 3 reported a high graft patency rate (i.e., functional, nonoccluded blood-vessel prostheses) of 99% after implantation in the lower abdominal aorta. The clinical outcome of smaller grafts implanted in more peripheral arterial locat
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