Biomedical Engineering Reference
In-Depth Information
A selection of micromechanical property data based on nanoindentation and tensile
testing of HAp coatings deposited on titanium substrates by the sol-gel method are given
in Table 2.2 along with comparisons to other deposition techniques and other coatings on
different substrates, from a range of literature sources. Also provided for comparative pur-
poses are data for bulk HAp ceramics (dense and porous), human bone, and dentin. There
is a clear difference in the hardness and elastic modulus of bone compared to dentin. The
properties of porous HAp (50% porosity) are similar to bone and the range in data for HAp
coatings indicates that there is plenty of scope for selecting appropriate properties and film
microstructures that can be matched to bone where applicable. It must be emphasized that
there is a degree of compromise involved in any implants or restorations with bioactivity
and in vivo response being critical along with judicious selection of coating properties and
adequate adhesive bonding to the underlying substrate.
FuturePerspective
One of the major disadvantages of current synthetic implants is their failure to adapt to
the local tissue environment. Recently, tissue engineering has been directed toward taking
advantage of the combined use of living cells and three-dimensional ceramic scaffolds to
deliver vital cells to damaged sites in the body.
Stem cells have been incorporated into a range of bioceramics. The use of stem cells in
regenerative medicine has increased the potential to restore a greater range of tissues in a
more sustainable manner and for longer than with conventional tissue-specific differenti-
ated cells. Cultured bone marrow cells derived from adult stem cells can be considered as
mesenchymal precursor cell populations and are similar to stem cells in that they can also
differentiate into different lineages, which are osteoblasts, chondrocytes, adipocytes, and
myocytes. When implanted, these cells can combine with mineralized three-dimensional
scaffolds to form highly vascularized bone tissue.
These nanocoated and nanoscale cultured cell/bioceramic composites can be used to
treat full-thickness gaps in lone bone shafts with excellent integration of the ceramic scaf-
fold with bone and good functional recovery.
Nanostructured materials are associated with a variety of uses within the medical field,
such as nanoparticles in slow drug delivery systems, in diagnostic systems, in devices, and
in regenerative medicine.
Tissue engineers are faced with the challenge of developing scaffolds with diverse func-
tions that must be bioresponsive and evolve in real time to a dynamic host environment.
Nanoscale coatings and surface modification methods are currently being used to produce
body-interactive materials, helping the body to heal, and promoting regeneration of tis-
sues, thus restoring physiological function. This approach is being explored in the devel-
opment of a new generation of nanobioceramics with a widened range of applications in
maxillofacial and orthopedic surgery.
While the impact of nanotechnology is generally considered to be very beneficial, con-
sideration has to be given to the potential risk associated with nanoparticles and nano-
powders. Problems can arise from their unsafe use; for example, in the workplace, while
their long-term health effects in products used by humans (e.g., sunscreens) are still
unknown. A number of research institutions are currently working on the diagnostic
methods and to improve the safe work practices.
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