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Insulin pumps improve the lives
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of many of the 415 million people
with diabetes around the world
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by monitoring blood sugar, delivering
insulin,
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and preventing the need for constant
finger-pricking and blood testing.
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These small machines include a pump and
a needle which can sense glucose levels;
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feed back to the pump;
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and then calculate how much insulin
to deliver through the needle.
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But they have a catch: they’re temporary.
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Within a few days, glucose sensors have to
be moved and replaced.
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And it’s not just glucose monitors and
insulin pumps that have this problem,
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but all bodily implants,
at different time scales.
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Plastic prosthetic knees have to be
replaced after about 20 years.
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Other implants, such as those used for
cosmetic reasons,
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can meet the same fate in about 10.
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That isn’t just a nuisance: it
can be expensive and risky.
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This inconvenience happens because of
our bodies’ immune systems.
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Honed by several hundred million
years of evolution,
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these defensive fronts have become
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exceptionally good at identifying
foreign objects.
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Our immune systems boast an impressive
arsenal
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of tools to tackle, intercept, and destroy
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anything they believe shouldn’t be there.
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But the consequence of this constant
surveillance
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is that our bodies treat helpful
implants, like insulin pumps,
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with the same suspicion as they would
a harmful virus or bacteria.
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As soon as the insulin pump has been
implanted in the skin,
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its presence triggers what’s known as a
“foreign body response.”
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This starts with free-floating proteins
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that stick themselves to the surface
of the implant.
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Those proteins include antibodies,
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which attempt to neutralize the new object
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and send out a signal that calls other
immune cells to the site
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to strengthen the attack.
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Early-responding inflammatory cells,
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like neutrophils and macrophages,
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respond to the emergency call.
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Neutrophils release little granules filled
with enzymes
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that try to break down the surface
of the insulin pump’s needle.
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Macrophages secrete enzymes too,
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together with nitric oxide radicals,
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which create a chemical reaction that
degrades the object over time.
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If the macrophages are unable to dispatch
the foreign body rapidly,
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they fuse together, forming a mass of
cells called a “giant cell.”
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At the same time, cells called fibroblasts
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travel to the site and begin to deposit
layers of dense connective tissue.
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Those enclose the needle that the pump
uses to deliver insulin
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and test for glucose levels.
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Over time this scaffolding builds up,
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forming a scar around the implant.
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The scar functions as an almost
impenetrable wall
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that might start to block vital
interactions
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between the body and the implant.
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For example, scarring around pacemakers
can interrupt
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the electrical transmission that’s
crucial for their functioning.
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Synthetic knee joints may give off
particles as they’re worn down,
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causing immune cells to inflame
around these fragments.
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Tragically, the immune system’s attack
can even be life-threatening.
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However, researchers are finding ways
to trick the immune system
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into accepting the new devices we
introduce into our bodily tissues.
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We’ve discovered that coating implants
with certain chemicals and drugs
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can dampen the immune response.
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Those basically make the implants
invisible to the immune system.
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We’re also making more implants
out of natural materials
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and in forms that directly mimic tissues,
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so that the body launches a weaker attack
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than it would if it came across a
completely artificial implant.
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Some medical treatments involve implants
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designed to regenerate lost
or damaged tissues.
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In those cases, we can design the implants
to contain ingredients
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that will release specific signals,
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and carefully tailor our bodies’
immune reactions.
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In the future, this way of working
alongside the immune system
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could help us develop completely
artificial organs,
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totally integrative prostheses,
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and self-healing wound therapies.
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These treatments might one day
revolutionize medicine–
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and transform, forever,
the bodies we live in.