Biomedical Engineering Reference
In-Depth Information
the methods and assumptions that a company uses to
test their device should be reasonable and justified.
The methods must be clearly described, including
how the testing mode, environment, sample size, and
other parameters were chosen. Assuming that the
methods were reasonable, then the final task of the
reviewer is to look at the testing results and determine
if they adequately demonstrate that the device is
substantially equivalent to its predicate device (in the
case of a 510(k)), or that it will be reasonably safe
and effective if used properly (for a PMA). This
involves not only the results themselves but also the
acceptance criterion that the manufacturer has
defined for the test. Acceptance criteria are typically
based on values from predicate devices (for 510(k)s)
or physiologic-based values.
Reviewing a new application for a medical device
at the FDA is somewhat like reading a mystery novel
in reverse to see if all the clues add up to the final
solution. The end of the “novel” is always the same:
the author (i.e., manufacturer) always concludes that
their new medical device is reasonably safe and
effective for human use. The interesting and impor-
tant part is seeing how they arrived at that conclusion,
starting with the risk analysis and proceeding through
test methods, results, and acceptance criteria. Rarely
is there one right answer for how a company can
evaluate the safety and effectiveness of a medical
device, and marketplace competition and intellectual
property issues demand that every new device is
different than the ones that came before it. FDA
reviewers are charged with enforcing the laws gov-
erning medical devices by deciding whether
a manufacturer has used valid scientific evidence in
reaching their conclusions about their device's rela-
tive safety and effectiveness.
its final, sterilized form including any important
processing or surface features, making review of
materials an issue that is specific to each individual
device. Recognizing that each device application and
clinical area is different, it is difficult to make blanket
statements about how materials are evaluated.
However, a few basic concepts related to function
and biocompatibility of materials are common
themes in many applications, and we discuss these
concepts below. These statements are based on prior
experience and not intended as official policy or
guidance.
17.8.1 Function
As discussed in the previous section, when an
FDA scientist reviews a device, he or she wants to
make sure whether the device does what it is
supposed to do, that is, the device should function as
intended. The selection of an appropriate device
material is essential in ensuring that a device will
function as intended. The material should be strong
enough so that the device does not fracture under
physiologic loads. The material should have an
appropriate stiffness so that the device can flex and
move (or not move) as intended. If the device
incorporates an articulating joint or bearing surface,
the material should be able to appropriately with-
stand wear, so that the device does not functionally
break down.
The FDA typically recommends testing of
a device be performed to assess the suitability of the
entire device, not just the material, for its intended
function. These tests should be performed on samples
of the device where all materials processing
including any surface treatments, polishing, cleaning,
and sterilizing, if applicable, have been completed so
that, if any of these steps affect the chemistry or
behavior of the material, those effects can be evalu-
ated. While testing the suitability of the overall
device design, the suitability of the device material
for its specific use is also tested. If the device fails to
meet the acceptance criteria of the test (e.g., if it
fractures catastrophically under simulated loading
that is considered to be physiologically relevant) then
the designer has two choices: (1) they can either
bolster the geometry of the device to make it more
robust or (2) they can change to a stronger material to
increase the overall strength of the device.
Another goal of the functionality testing per-
formed on the devices is to ensure that the device will
17.8 Material Considerations
When an FDA scientist reviews a device, consid-
eration of the material is obviously of the utmost
importance. Along with device geometry, materials
will determine the strength and function of a device.
As mentioned previously, it is important to under-
stand that the FDA does not approve materials, but
rather devices with specific intended uses and tech-
nological characteristics. This distinction is impor-
tant to make because choices of materials should be
justified for each device application in which they are
used. In addition, the material should be evaluated in
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