BIOMATERIAL APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 531

are all outcomes of biomaterial applications. The biomaterials for each of these
devices are generally composed of PMMA, hydroxyapatite and silicon. Glass and
artifi cial eyes have been made for thousands of years, the fi rst ocular implants
were developed about 100 years ago. These small spheres of glass or gold were
later replaced by plastic or silicone spheres; but until recently, the basic design of
these “ fi rst-generation” implants had changed little over the years. Artifi cial eyes
are usually made of plastic (acrylic) or glass. Custom artifi cial eyes are hand-
crafted by highly skilled ocularists (eye makers) to precisely match the natural
eye. The fi rst ocular implant made of hydroxyapatite was implanted in 1985, after
several years of preliminary research. The eye muscles can be attached directly to
this implant, allowing it to move within the orbit, just like the natural eye.
Bio-eye hydroxyapatite ocular implant has been described as “a dream come
true” by eye care specialists, oculatists, and those familiar with the older, fi rst-
generation ocular implants. A keratoprosthesis made up of Silicone, hydroxyethyl
methacrylate (PHEMA), divinyl glycol (DVG), and methyl methacrylate (MMA),
is a device intended to restore vision to patients with severe bilateral corneal dis-
eases for which corneal transplants are not an option. An extraocular orbital
implant is a nonabsorbable device intended to be implanted during surgery,
in which the eyeball or the contents of it are removed. The search for a well-
tolerated orbital implant which gives an excellent appearance as well as good
mobility has covered the gamut of autogenous and alloplastic materials and
implant designs. Almost every conceivable material known to man has been used
as an orbital implant, including magnets, gold, silver, glass, silicone, cartilage, bone,
fat, cork, titanium mesh, acrylics, wool, rubber, catgut, peat, agar, asbestos, ivory,
cellulose, paraffi n, sponge, polyethylene, and hydroxyapatite.
In addition, a wide variety of implant shapes have been implanted in order to
achieve an acceptable cosmetic result including: sphere; sphere with a truncated
surface; sphere with a truncated surface and small knobs projecting from the
surface; and so on. An ophthalmic tantalum clip is a malleable metallic device,
intended to be permanently or temporarily implanted to bring together the edges
of a wound to aid healing or prevent bleeding from small blood vessels in the eye.
An intraocular lens, commonly called an IOL, is a tiny, lightweight, clear-plastic
disk, which is placed in the eye during cataract surgery to replace the eye's natural
lens. The biomaterial examples of IOL are described in Figure 15.3.
15.3.7 Cochlear Prosthesis
Cochlear prosthesis is being clinically used to restore functional hearing in
patients suffering from profound sensorineural deafness. The device includes one
or more electrodes implanted in or near cochlea to provide necessary electrical
stimulation of the remaining auditory nerve fi bers, thereby bypassing the defec-
tive sensory hair-cells. There are many different designs of these devices in various
stages of testing, development, and availability. The therapeutic benefi t of these
devices depends upon the type of device and individual patients receiving a given
device. Cochlear prostheses have evolved from laboratory experiment to a com-