Biomedical Engineering Reference
In-Depth Information
Besides the studies of undoped and doped a-C and a-C:H, polymer-, nanoparticle-
incorporated a-C:H, another interesting study is on plasma-modified a-C:H [148]. The
a-C:H treated with oxygen plasma exhibits superhydrophilicity with a contact angle of
~ 0°. Although there is a drastic change to the film surface energy, the level of bacteri-
cidal activity of
S. aureus
,
E. coli
,
Pseudomonas aeruginosa
, and
Salmonella typhimurium
is not
affected significantly.
BiomedicalApplications
Biocompatible implants allow the human body to reestablish biological and mechanical
functions and thus increase the quality of life. Depending on the biomedical application,
the implant has to withstand dynamic mechanical loads while performing a desirable
long-term biological interaction with surrounding biological tissue. Bulk properties of the
implant are mainly responsible for the load-bearing capabilities, whereas the interaction
with the surrounding tissue is governed by the implant's surface. The surface influences
the interaction and adsorption of different proteins, which, in turn, control the cell adhe-
sion and behavior. However, the overall reaction of the body on an implant is a system
property that includes many different aspects, such as surface chemistry and texture, im-
plant movement, biodegradation, and surgical aspects. The highly corrosive environment
and the low tolerance of the body to some dissolution products restrict the materials to be
used for implants. As we already know from the previous sections, amorphous carbon is
bio- and hemocompatible. Furthermore, the material can prevent the detrimental effects
caused by the released metal ions from conventional metallic implants. Therefore, there
is a growing interest in modifying implants' surface with amorphous carbon. In addition,
amorphous carbon, due to its amorphous nature, is able to incorporate a certain amount of
additional elements and even compounds into its matrix and still maintain its amorphous
state. By this technique, several properties, including tribological properties, electrical
conductivity, surface energy, and biological reactions of cells in contact with the surface,
can be altered to suit specific applications. There are mainly two fields of biological appli-
cations of amorphous carbon: the application of amorphous carbon in blood-contacting
implants, such as heart valves and stents, and the use of amorphous carbon to reduce
wear in load-bearing joint implants. Amorphous carbon-coated heart valves and stents
are already commercially available. But the situation for amorphous carbon-coated load-
bearing implants is contradicting.
There are extensive reviews on amorphous carbon coatings for biological and biomedical
applications [149-156]. In this section, some of the applications will be discussed. Some of
these are readily available commercial coatings, while others are still under development.
Orthopedic Implants
Total hip replacement is one of the most challenging types of human implants from
the materials science's point of view. The techniques developed for improving the hip
implants can naturally be applied to other articulated or immovable implants. Since the
human body is at the same time both a very hostile and sensitive environment for foreign
objects, the lifespan of a hip implant is limited. The practical lifetime of the current artifi-
cial total hip replacements can be as low as 5-15 years because mechanical wear and stress,
