Limitations of polyester in medical use

Polyester in medical use has undoubtedly improved the quality of life for an aging patient population. However, all implantable devices are prone to three major complications: surface thrombus formation, post-surgical/wound bleeding, and incomplete/non-specific cellular healing.

Surface thrombus formation is the result of the interaction of blood with the relatively thrombogenic biomaterial surface. This problem is evident in medium/small-diameter vascular grafts as well as stents and catheters, which can fail early after implantation due to occlusive thrombus formation within the blood-contacting surface of the device.

A complication of all implantable biomaterials is incompatibility between flowing blood and the biomaterial surface. Thrombin, a pivotal enzyme in the blood coagulation cascade, has been implicated as the primary agent responsible for thrombus formation. The initial interaction of blood and the foreign surface results in a myriad of responses: platelet activation and adhesion [85], activation of the intrinsic pathway of the coagulation cascade resulting in formation of active thrombin [86], leukocyte activation [85], and the release of complement and kallikrein [87]. If unregulated, these responses lead to mural thrombus formation with subsequent occlusive thrombosis and failure of the implanted biomaterial.

Uncontrolled post-surgical/wound bleeding is directly related to the limited interaction of blood with the foreign surface as well as the physical construct (i.e., porosity, weave design) of the material. For hernia repair mesh and wound dressings, the problem arises in that the overall time to create surface thrombus is extensive, thereby delaying hemostasis and compromising the patient.

Lastly, incomplete/non-specific cellular healing affects various medical devices. Since biomaterials are composed offoreign polymeric materials, cellular components normally present within native tissue are not available for the reparative process. These complications are evident in medical devices such as vascular grafts, hernia repair mesh, wound dressings, and catheter cuffs [88-90].

Common to these complications is that currently available biomaterials do not emulate the multitude of dynamic biologic and reparative processes that occur in normal tissue. Thus, development of a novel biomaterial that would emulate some of the normal healing processes of native tissue would improve patient morbidity and mortality upon implantation of various medical devices. Exhaustive studies have been aimed at creating a novel biomaterial surface by either non-specific binding of a biologically active agent, covalent linkage of an agent with abroad spectrum of activity, or altering the biomaterial surface. Thus far, none of these technologies have resulted in a clinically used biomaterial surface.

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