Biomedical Engineering Reference
In-Depth Information
that, when the construct is implanted, there will already be viable cells
present. The cell source has to be carefully considered. Perhaps an ideal
cell source would be bone marrow stem cells from the patient. Bone
marrow stem cells are thought to be those responsible for natural bone
repair, where they differentiate into bone-producing cells (osteoblasts).
Harvesting them from the patient is relatively straightforward compared
to some other cell types, although the numbers that can be obtained are
low. The aim would be to seed them within the scaffold and hope they
attach and proliferate, and that the scaffold stimulates them to become
bone cells rather than another cell type, such a cartilage cell or fibroblast.
Alternatively, blood vessels could be grown inside the scaffold in
the laboratory, with the aim that they will connect up with existing
vasculature. This strategy has been proven to work in mice.
Bone tissue engineering is not in widespread clinical use, unless you
count mixing blood from the patient with a scaffold.
12.8 REGULATORY ISSUES
Once a promising new scaffold material has been developed and tested
in the laboratory with cell culture tests and long-term mechanical tests
as a function of degradation, it is time to translate the work from the
bench to the bedside. This is not a trivial (or inexpensive) process. It
takes considerable time and investment. Difficult decisions also have
to be made. An important early decision is the class of material for
which regulatory approval should be sought. At the time of writing,
regulatory bodies, such as the FDA and the EU, are (quite rightly)
making regulatory approval more difficult to achieve. Although it may
disadvantage new companies with potentially important new products,
safety must be paramount. The regulatory class depends on the claims
made by a company. For example, in the EU, if a company claims
that a scaffold will bond to bone, degrade over time and stimulate
bone regeneration, it will be a Class 3 medical device. If the company
claims a new material will simply do the same as other bone grafts and
fill space, it will be a Class 2 device, but then the marketing or sales
people in the company cannot claim performance superior to current
products. Of course, to obtain regulatory approval of a Class 3 device
takes more investment and may involve lengthy clinical trials. Claiming
pharmaceutical properties of an implant may also mean that approval is
needed from pharmaceutical (rather than device) regulatory bodies such
as the UK Healthcare Products Regulatory Agency (MHRA).
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