Page 407 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

384 BIOMATERIALS

diminish the oxygen-carrying capacity of the blood. Hemolysis can occur as a reaction to the material
or its degradation products or as a result of shear due to the relative motion between the material
surface and the blood.
Cardiovascular biomaterials are also in contact with other tissues. Another common failure mode
of these devices is excessive growth of the tissues surrounding the device. This can be caused by
reaction to the material (the natural encapsulation reaction to any foreign body), stresses on sur-
rounding tissues caused by the device, or reaction to material degradation products. Vascular grafts
(in particular, smaller-diameter grafts) are subject to anastomotic hyperplasia, which reduces the
diameter of the graft at the anastomosis. A similar hyperplastic response occurs around endovascular
stents used to keep vessels open after angioplasty or as a de novo treatment. Heart valves can fail if
tissue grows into the space occupied by the moving disc. Finally, tissue surrounding a device can die.
As in hemolysis, this can be as a result of reaction with the material or its degradation products or
as a result of continuous micromotion between the device and the tissue. The nonviable tissue can
calcify as well as become a nidus for infection.
Biomaterials that have been used in the cardiovascular system include processed biological sub-
stances, metals, and polymers (see Table 16.1 for typical materials and applications). Materials of
biologic origin include structures such as pericardia, arteries, veins, and heart valves. Devices can
also include biological substances, for example, coatings, such as collagen and heparin.
TABLE 16.1 Cardiovascular Biomaterials

Material Applications
Hydrogels
Hydrocolloids, hydroxyethyl-methacrylate, Slippery coatings for catheters, vascular sealants,
poly(acrylamide), poly(ethylene oxide), antidhesives, thromboresistant coatings,
poly(vinlyalcohol), poly(vinyl-pyrrolidone) endovascular paving, drug delivery coatings
Elastomers
Latex rubber, poly(amide) elast, poly(ester) elast, Central Venus catheters, intraaortic balloon pump
poly(olefin) elast, poly(urethanes, poly(urethanes), balloons (polyurethanes), artificial heart bladders
biostable poly(vinylchloride), silicones, styrene- (polyurethanes), carrier for drug delivery coatings,
butadiene copolymers insulators for pacemaker leads, vascular grafts
(e.g., biostable polyurethanes), heart valve
components (silicones), extracorporeal tubing
Plastics
Acrylics, cyanoacrylates, fluorocarbons, ethylene- Housings for extracorporeal devices (acrylics,
tetrafluoroethylene, ethylene-chloro-tri- poly(carbonates), poly(methylpentane)), catheters,
fluoroethylene, fluorinated ethylene propylene, angioplasty balloons, sutures, vascular grafts
poly(tetrafluoro-ethylene), poly(vinylidene fluoride), (polyester textiles, expanded PTFE), medical tubing,
poly(amides), poly(carbonates), poly(esters), oxygenator, and hemdialysis membranes
poly(methyl pentene), poly(ethylene),
poly(propylene), poly(urethane), poly(vinylchloride)
Engineering plastics and thermosets
Epoxies, Poly(acetals), poly(etherketones), Structural components for bioprosthetic heart valves
poly(imides), poly(methylmethacrylate), poly(olefin) [poly(acetals)], artificial heart housings, catheter
high, crystallinity, poly(sulfones) components, two part systems for adhesives
(e.g., epoxies)
Bioresorbables
Poly(amino acids), poly(anhydrides), Sutures, scaffolds for tissue engineering,
poly(caprolactones), poly(lactic/glycolic) acid nanoparticles for treatment of blood vessels to
copolymers, poly(hydroxybutyrates), prevent restenosis, drug delivery coatings
poly(orthoesters), tyrosine-derived polycarbonates
Biologically derived materials
Bovine vessels, bovine pericardium, human umbilical Vascular grafts, pericardial substitute, heart valves
vein, human heart valves, porcine heart valve