Artificial Support and Replacement of Human Organs - Biomimetics: Biologically Inspired Technologies - page 462

the recent years, and implants with textured surfaces have been developed in an effort to allow bone
to grow into the implant, this theoretically has the advantage of allowing much stronger biological
cementing. One of the long-term problems after hip replacement is loosening of the components,
which can result in bone loss and pain. This restricts the use of total hip replacement among
younger patients. This happens due to very small plastic particles produced by the wearing of the
cup. Recently metal on metal joints have regained popularity and are particularly suited for the hip
joint replacement in middle age patients since it gives a much longer lasting results compared to the
other hip replacements (Dorr et al., 2000).
Parallel developments allowed the development of total knee replacement. Initial attempts were
to replace the joint cavity with hinges which can cover the joint space to reduce friction. But
problems with loosening and infection frequently occurred. Frank Gunston developed a metal on
plastic knee replacement joint in 1968 (Gunston, 1971). A three component knee-joint prosthesis
was proposed by John Insall in 1972 which covered the femur, tibia, and the patella, and were held
in place using cement (Ranawat et al., 1975). This has resulted in the development of the modern
knee-joint prosthesis. Currently more than 150,000 knee-joint replacements are undertaken in
United States alone (Noble et al., 2005). Similar to the hip prosthesis, attempts have been underway
in recent years to achieve a cementless joint replacement, using biological ability to glue these
components together by allowing new bone growth in the roughened surfaces of these devices,
which then can give strength and eliminate the need for artificial gluing materials that could come
loose.

18.10 BIO-ARTIFICIAL PANCREAS

Long standing diabetes mellitus (types I and II) results due to the inability of the pancreas to secrete
insulin. Therapy has been focused at administering the insulin exogenously to achieve acceptable
blood sugar levels, however, it is often difficult to manage. Transplantation of the isolated islet cells
(which secrete insulin) although promising is limited due to the associated need for immunosup-
pression and limited organ supply.
Devices such as microencapsulated islets (small diameter spherical chamber), and microencap-
sulated islets (including hollow fiber, disk-shaped diffusion chambers and Millipore cellulose
membranes) have been proposed (Lanza et al., 1992; Lim and Sun, 1980; Reach et al., 1981;
Sullivan et al., 1991). Advancements in glucose sensing and insulin sensing technology have
allowed developing automated closed loop insulin delivery systems that can deliver insulin in a
more physiologic way. One such system currently undergoing clinical trials is a diffusion chamber
for a bio-artificial endocrine pancreas (Bio-AEP), which is constructed by placing pancreatic islet
cells, trapped in a scaffold; this is sandwiched between semipermeable membranes, and shielded by
silicone (Hirotani et al., 1999). Although some of the results achieved in animal studies have been
difficult to reproduce in large animal models, this therapy holds promise for the future treatment of
diabetes mellitus.

18.11 VISUAL PROSTHESIS (ARTIFICIAL EYE)

The understanding of the mammalian visual system has given impetus for conceptualizing an
artificial visual prosthesis that can be used in the profoundly blind. The goal of these systems is to
produce a visual perception to allow activities like reading, recognizing shapes and faces, negoti-
ating complex spaces, and giving the perception of light surroundings. This is dealt with in greater
detail in Chapters 11 and 17.