BIOMATERIAL APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 527

vascular grafts are used to repair weakened vessels or bypass blockages, primarily
in the abdomen and lower extremities. They are also used to obtain vascular
access for hemodialysis treatment of patients with chronic renal failure. Devices
to aid or replace the pumping function of the heart include intra-aortic balloon
pumps, ventricular assist devices, and total implantable artifi cial hearts. Pace-
makers and automatic internal cardiverter defi brillators are used widely to correct
aberrant life-threatining cardiac arrhythmias (Figure 15.1).
Most of these devices either alleviate the health conditions for which they
were implanted or provide otherwise enhanced function and serve well and for
extended periods the patients who receive them. Nevertheless, device failure and/
or other tissue-biomaterials interactions frequently cause clinically observable
complications, reoperation or even death.
15.3.2 Extracorporeal Artifi cial Organs
The term “ extracorporeal artifi cial organs” has been reserved for life support
techniques requiring the online processing of blood outside the patient's body.
The substitution, support, or replacement of organ functions is performed. When
the need is only temporary or intermittent, support may be suffi cient. The oldest
and most widely employed extracorporeal artifi cial organs include kidney substi-
tute, hemodialysis and hemofi ltration for the treatment of chronic renal failure,
fl uid overload, and peritoneal dialysis. The blood treatment process of hemoper-
fusion and apheresis technologies, which include plasma exchange, plasma treat-
ment, and cytapheresis, are used to treat metabolic and immunological diseases
associated with blood. In addition, blood-gas exchangers are used for heart-lung
bypass procedure, and bioartifi cial devices that employ living tissue in an extra-
corporeal circuit mainly involve artifi cial liver devices. Bioartifi cial liver (incorpo-
rated with hepatocyte) (BAL), constituted with extracorporeal blood circuit and
bioreactor, is a developing novel medical technology, still in its pre-clinical stage.
Currently nine bioartifi cial liver support devices are undergoing various stages of
clinical trials, most of which utilize a hollow fi ber technology. A much larger
number of BAL systems in preclinical tests have been suggested to show an
enhanced performance.
15.3.3 Orthopedic Implants
Metallic, ceramic and polymeric biomaterials are used in orthopedic applications.
Metallic materials are normally used as load bearing implants such as pins and
plates and femoral stems, and so on. Ceramics such as alumina and zirconia are
used for wear applications in joint replacements, while hydroxyapatite is used for
bone bonding applications to assist implant integration. Polymers such as ultra-
high molecular weight polyethylene are used as articulating surfaces against
ceramic components in joint replacements. Porous alumina has also been used as
a bone spacer to replace large sections of bone that have had to be removed due
to disease. A summary of prevalent orthopedic biomaterials and their primary