Biomedical Engineering Reference
In-Depth Information
evaluating the chemical composition or changes to the elemental distri-
bution on coating surfaces.
Destructive testing of polymeric devices involves microscopy and
chemical analyses. Microscopic examination may be used to find evi-
dence of surface damage or degradation. Inclusions or porosity and
changes in density or crystallinity can be assessed using thin sections
of approximately 5 to 10 microns and optical microscopy using reflected
and transmitted, polarized and nonpolarized light. There is a wide vari-
ety of methods for the material characterization of polymers. Options for
molecular weight of the specimen include gel permeation chromatogra-
phy, osmometry, light scattering, viscometry, and melt index. Density
can be determined from displacement or gradient methods, while
thermal properties are also commonly characterized using differential
scanning calorimetry for glass transition and melt temperatures. The
presence of oxidation or degradation, as well as the chemical composi-
tion, can be analyzed using infrared analysis, Fourier transform infrared
spectroscopy, nuclear magnetic resonance spectroscopy, and electronic
spin resonance.
For retrieved tissues, there may be an interest in understanding if
there are elemental particles contained in the tissue. This can be investi-
gated with the use of chemical analysis tools such as inductively coupled
plasma mass spectrometry (ICP-MS), which helps identify essential
metals, metalloids, or non-metals in the tissue.
In all situations, care must be taken to ensure that any analysis must
be done so as to not destroy any features that may become the subject
of litigation. The choice of tests may be dependent on the reason for
removal of the device, rather than selecting to perform all tests as this
can be an expensive and time-consuming process.
Device evaluations using registries
In addition to establishing a DRA program on an institutional basis,
efforts to collect implants on a regional or national basis require sig-
nificant coordination and planning. Because the cost, complications,
and outcomes of revision surgery are generally worse than in the ini-
tial primary surgery, there is motivation to try to improve the longevity
of implants and to reduce the incidence of complications and the need
for implant removal. As a result, starting in the 1970s, orthopaedic reg-
istries were developed in Scandinavia to track revisions on a national
basis as a function of surgeon, patient, and implant characteristics. Over
the past decade, orthopaedic registries have expanded across Europe,
Canada, Australia, and New Zealand. Efforts to create a national ortho-
paedic registry are still in the early stages in the United States through
the American Joint Replacement Registry. These registries provide addi-
tional resources to better understand the performance of medical devices
in the real world.
A registry is not merely a data repository containing basic clinical,
patient, and implant data regarding the implantation and revision of total
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