Because of such characteristics as high strength and long-term biocompatability, aerospace carbonaceous materials may be used as surgical implants to correct pathological conditions in the body resulting from disease or injury. Examples of possible medical uses include bone replacement, implantation splints and circulatory bypass implants

Benson, J.

English

NASA Technical Reports Server

April 1969	 Brief 69-10087 
NASA TECH BRIEF. 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Carbon Offers Advantages as Implant Material in Human Body 
Evidence from several sources indicates that a num-
ber of high-purity, high-strength carbon or graphite 
composites which have been developed for aerospace 
applications are chemically, biologically, and physi-
cally compatible with the fluids and tissues in the 
human body. In addition to their high strength and 
long-term biocompatibility, these materials can be 
readily fabricated into complex configurations and 
are amenable to several of the commonly used sterili-
zation techniques. Because of these characteristics, 
the aerospace carbonaceous materials are proposed as 
surgical implants to correct various pathological con-
ditions in the body resulting from disease or injury. 
An example of the possible medical use of the car-
bonaceous materials would be as cosmetic and pro-
tective bone replacements in the skull, face, and 
hands. In present practice, stainless steel (or other 
metal) replacements are prepared as inlays and se-
cured to the adjacent bone by pins or screws. How-
ever, stainless steel has been found to degrade sub-
stantially with time from chemical and galvanic corro-
sion. This results in reduced strength of the replace-
ment and probable toxic reaction of the host tissues to 
the corrosion products. The carbonaceous materials 
could be advantageously substituted directly for met-
als in this application. Other suggested uses of the 
carbonaceous materials in the body are outlined 
below. 
Implantable Splints. Such splints are generally 
beams or elongated plates attached directly to the 
damaged bone by pins or screws. They extend suf -
ficiently beyond the damaged area to carry the full 
loading from the undamaged area on one side of the 
fracture to the undamaged aea on the other side. 
This arrangement permits the damaged area to repair 
itself without being displaced or disturbed by the body
activity. While it is desirable to leave the splints in 
permanently, the degradation of the metals presently 
used is found to make their eventual removal often 
mandatory. In some cases, it has been found necessary 
to remove them even before healing is completed, 
either because of the toxicity of the corrosion products 
or the decline of structural integrity in the splint. Sub-
stitution of carbonaceous materials for metals prom-
ises to alleviate these problems. 
Myoeleciric Probes. These devices are implanted in 
the desired muscle tissue to pick up (or introduce) the 
small electrical signal (picowatts to nanowatts) by 
which the nervous system instructs the muscle to per-
form. In medical research they are used to study the 
phenomena of motor control and reactions to various 
stimuli. In rehabilitation, attempts are being made to 
utilize the naturally occurring myoelectric signals to 
control externally powered prosthetic devices. The 
apparent galvanic inertness of the carbons indicates 
that they should be very desirable materials for this 
application when implanted to provide a percutaneous 
electrical conductor. Flexibility of the carbon fila-
ments or small-diameter rods would permit normal 
motion of the body member without disturbing the 
implant. 
Epithelial Bone Extensions. The orthopedic concept. 
involved is based on the premise that bone can be in-
duced to grow to an inorganic member designed to 
pick up mechanical loads external to the body and 
transfer them directly into the skeletal structure. 
Materials that have been investigated to date are cor-
rosion-resistant metals and high-strength ceramics. 
Success has been very limited because of corrosion 
problems and rejection of these materials by the body 
tissues. The carbon materials show promising poten-
tial for this application.
(continued overleai( 
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Circulatory B ypass Implants. In hemodialysis and 
other treatments of the bloodstream, it is desirable to 
implant a b y  connection permanently into an 
artery and the corresponding vein so that the blood 
may be circulated through auxiliary equipment out-
side the body and returned to the normal bloodstream 
after treatment. Materials presently used for this 
purpose are stainless steels and various polymers. 
The steels lack long-term biocompatibility, and the 
polymers are not sufficiently durable, so that the 
implants must be replaced more frequently than is 
desirable. The improved biocompatibility expected 
from the substitution of the carbon materials, cou-
pled with their high physical strength, indicates their 
attractiveness for this application. 
Implantable Prosthetics. The preferred materials 
presently used for anatomical joint replacement (e.g., 
for hip joints) are type 316 stainless steel, certain 
titanium alloys, and in some cases, ultrahard ma-
terials, such as stellite. Degradation of these materials 
is principally attributable to low-rate galvanic action 
with the body fluids, which results in surface, inter-
granular, or massive corrosion and consequent loss of 
structural integrity of the metals. In some cases, the 
corrosion products are also toxic to the host organism. 
In almost all cases, mobility of the joint decreases 
because of substantially increased friction. The struc-
tural properties of certain aerospace carbons closely 
approximate those of type 316 stainless steel, and in 
addition these carbons provide self-lubrication on 
bearing Surfaces. These carbons therefore appear to
offer excellent potential as replacements for anatomi-
cal joints. 
Replacement Heart Valves. One of the most widely 
used replacement heart valves is the Starr-Edwards 
design, a simple ball-in-cage check valve. Some recent 
reported failures of this valve, are apparently due to 
deterioration of the ball by a very slow chemical reac-
tion with the bloodstream. Vitreous carbon spheres 
can be produced in a variety of sizes to very precise 
dimensions and with polished surfaces. By making 
them hollow, their normal specific gravity can be 
matched to the bloodstream to provide neutral 
buoyancy, thus reducing inertial effects. This ma-
terial is heat-sterilizable and is apparently unaf-
fected by the conditions encountered in the body. 
Note: 
This information is presented as a concept only. 
Questions may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 358.12 
Reference: B69-10087 
Patent status 
No patent action is contemplated by NASA. 
Source: J. Benson 
of North American Rockwell Corporation 
under contract tO 
Marshall Space Flight Center 
(M FS- l82O4thru 18210)
. 
. 
Brief 69-10087
	 Category 04


Carbon offers advantages as implant material in human body

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