Biomedical Engineering Reference
In-Depth Information
unique and much higher stimulation rates required to achieve a therapeutic
effect in neurostimulation. As a result, some INS models use rechargeable
battery technology to extend the life of the device.
Neurostimulation leads consist of multiple conductors, each electrically
insulated using high performance materials such as fluoropolymers. Individual
conductors can be made of MP35N or Pt-Ir alloys, and formed into helical coils
or a braided wire. These conductors are further insulated within an insulating
polymer jacket that may be made from a silicon polymer or a polyether
polyurethane polymer.
4.5
Engineering approaches to solve material
problems
Material scientists and engineers often try to develop new materials or modify
existing materials to meet design requirements for new product development
concepts. In the medical device industry, given the expense associated with the
development, testing, and qualification of new materials for medical applica-
tions, the most common approach is to design new technologies using materials
with a demonstrated history of safe use in particular applications. For medical
devices, especially implantable devices, patient safety and risk mitigation must
always be given the highest priority. However, unexpected problems are always
possible given the demand for increasingly complex medical devices to work in
the complicated milieu of the biological environment, and the fact that in vitro
tests and animal models often used in development are not perfectly predictive.
Importantly, many unmet material needs can be solved by applying fundamental
engineering principles. The success of this approach requires careful attention to
specific device design, functions, manufacturing, and testing efforts.
One example of applying fundamental engineering principles, mentioned
previously, addressed the problem of pacing threshold increases in response to
inflammatory reaction occurring at an electrode±cardiac tissue interface. A
natural response may have been to seek out a new electrode material or surface
treatment that did not trigger an inflammation reaction. After decades of
research, however, a material has yet to be found that does not cause an
inflammatory reaction. A few materials have demonstrated minimal or no
inflammation reactions in certain research laboratories, but there is no record
indicating similar results in a chronic implantation. The use of a simple existing
technology ± a monolithic controlled-release of anti-inflammatory steroid at the
electrode tip ± successfully reduced inflammatory reaction to a level that did not
cause significant increases in pacing thresholds. This approach not only
provided a very effective way to solve the threshold increase problem for pacing
leads, but also suggested a principle to solve problems related to material±
biological interactions by combining devices with biologically active agents.
Today's drug eluting stents, antimicrobial coatings, and rhBMP2-charged,
