Biomedical Engineering Reference
In-Depth Information
promising tunable properties for neural implants such as electrical, nanoscale
structure and organization, and surface energy characteristics.
Neural prostheses are used for monitoring and applying electrical signals to
neural tissue.
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Nanomaterials with exceptional electrical properties are good
candidates to transmit and receive electrical signals. In addition, nanomaterials
that support and enhance nerve cell neurite/axon extension due to their excel-
lent conductivity and biocompatibility properties are promising candidates.
During neural implantation, a cellular process called gliotic response separates
the implant from surrounding tissue through scar formation which is caused by
the activity of astrocytes and meningeal cells. This scar formation is believed
to interfere with the long-term efficacy of neural prostheses. Thus, the design
of materials that will enhance nerve cell interactions while deterring astrocyte
formation of scar tissue is crucial for neural implants.
Implantable probes are required for the continuous monitoring, diagnosis,
and treatment of neural tissue.
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However, such neural probes that are usually
composed of silicon become encapsulated with nonconductive glial scar tissue.
The same encapsulation with soft fibrous tissue usually happens to orthopedic
implants such as titanium and/or titanium alloys as well instead of hard bony
tissue. They have shown that functions of cells that contribute to glial scar tis-
sue formation for neural prostheses (astrocytes) and fibrous tissue encapsulation
events for bone implants (fibroblasts) decreased on PU composites containing
CNFs.
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Studies on the use of biomaterials to improve the function of injured nervous
system tissue have provided promising results
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but not without significant hur-
dles, such as delayed or incomplete tissue regeneration. Because of the need for
better nervous system biomaterials, recent approaches for the next generation of
tissue engineering scaffolds have incorporated nanoscale surface feature dimen-
sions that mimic natural neural tissue. Nanomaterials have enhanced desirable
neural cell activity while suppressing unwanted cell activity like reactive astro-
cyte activity in the central nervous system. To create an environment for tissue
regeneration that is superior to inert scaffolds, a combination of stimulatory
cues may be used to incorporate nanoscale topographical and chemical and/
or electrical cues in the same scaffold.
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Electrically active nanomaterials are
currently being used in the fabrication of composite materials with nanoscale,
piezoelectric zinc oxide particles embedded into a polymer matrix. Zinc oxide
can theoretically provide an electrical stimulus that is a known stimulatory cue
for neural tissue regeneration. Further studies involving the combination of
nanoscale surface dimensions and electrical activity that may provide enhanced
neural tissue regeneration environment deserve further attention.
6.4 PROSTHESIS
Prosthesis is an artificial device that replaces a missing body part. It is typically
used to replace parts of the body that are lost by injury (traumatic) or missing
