Aural artificial implants are available for patients with moderate
to severe hearing loss. In fact, the FDA has approved several
devices based on pioneering work by the University of Michigan.
Devices already on the market include the Nucleus Freedom from
Cochlear Corp., the HR90k from Advanced Bionics Corp. (a Boston
Scientific company), and the Pulsar CI100 from MED-EL Corp.
Envoy Medical's Envoy implant employs two bio-compatible piezo
transducers. One is a microphone that's attached to the ear's incus
and malleus bones and receives sound from the natural eardrum.
The other, which is attached to the ear's stapes, receives signals
from an implanted processor and stimulates the inner ear.
According to the company, it's the only implantable hearing
device that leverages the natural anatomical function of the ear.
It's powered by a lithium-iodide
battery with a life of three to five
years, and it's currently in the final
phase of testing at the St. Croix
Medical Center.
The Carina hearing implant from Otologics Inc. is also undergoing
final-phase testing before FDA
approval. Its subdermal microphone feeds signals to an implanted processor, which drives a transducer affixed to the incus and
then to the stapes. It operates
from a lithium-ion (Li-ion) battery
that's recharged by the patient
from a belt-worn device, using
transdermal inductive coupling for
power delivery.
Neural Implants Are Next
Neural implants will be key as
researchers learn more about the
nervous system. The neurons that
make up the nervous system act as
pulse-rate-modulated logic elements, forming complex 3D networks that use sensory and physiological functions.
"There is great hope that neural
prostheses will help in overcoming
diseases and ailments like Parkinson's disease, epilepsy, paralysis,
deafness, and blindness," says Kensall Wise, director of the University of Michigan's Engineering Research Center for Wireless Integrated MicroSystems.
Medtronic is working on an
implantable "brain radio" system
to monitor and control nervous disorders. It's part of a broad category
of neural stimulators that send
electrical pulses to the brain to
control ailments like Parkinson's
disease, Alzheimer's disease,
epilepsy, and multiple sclerosis.
Medtronic's engineers tackled key
design issues like noise sensitivity
and very low power dissipation by
developing a chopper-stabilized
amplifier with a noise efficiency factor of 3.6 to 4.5 to handle "popcorn" noise
from silicon digital and mixed-signal circuits,
as well as a 1.6-V battery that delivers 1.5 µA.
Work on a different kind of neural implant,
called "BrainGate," is under way at Brown University. It will enable the mind to control movement—an incredible advantage for the paralyzed. Developed in conjunction with Cyber
Kinetics Neurotechnology Systems (founded
by professor John Donoghue, head of Brown
University's Department of Neuroscience), so
far it's allowed one patient to read e-mails,
play video games, turn lights on and off, and
change and adjust TV controls just by thinking
about these actions ().
Epilepsy patients who must rely on vagus
nerve stimulators (VNSs) or defibrillators
because their seizures don't respond to drugs
can look forward to better treatment options.
The Massachusetts Institute of Technology
(MIT) and the Beth Israel Deaconess Medical Center are creating new software to determine
when best to activate the VNS—in this case, a
model from Cyberonics Inc. They're developing
an implantable detector that measures brain
activity to predict when a seizure is about to
occur, activating the VNS and halting the
seizure before it occurs.
The University of California at Los Angeles
(UCLA) David Giffen School of Medicine is creating an implantable trigeminal nerve stimulator (TNS) with Advanced Bionics Corp. According to the researchers, this unique device
holds several advantages over VNSs, which
only stimulate one side of the brain. A TNS can
stimulate both sides.
And unlike the VNS, the TNS can be tested
externally to gauge its effectiveness before
implantation. Before implanting, the TNS can be
worn on a patient's belt with wires attached to
the stimulator, passed under clothing, and connected to electrodes attached to the face.
An Exciting Future
Many more implants loom on the
horizon. It's come to the point
where designers no longer ask if
they can be developed, but when.
For example, In-Cube Inc. is focusing on tissue engineering. In these
hybrid devices, living cells from the
patient are integrated with traditionally engineered systems. Researchers there believe this will
lead to artificial kidneys, pancreases, lungs, and colons.
In-Cube is pursuing an implantable
kidney dialysis system that incorporates implantable polymers and electronics. The patient's own cells perform the dialysis. According to Mir
Imran, founder of In-Cube, the
implantable kidney is a complex project that's in the bench-testing phase.
The IntelliDrug project for the European Commission's 6th Framework Programme sheds
some light on the growing excitement surrounding biomedical
implants. The program's aim is to
develop electronically controlled
intra-oral drug-delivery systems.
These remote-controlled systems
with replaceable reservoirs would
become alternative sources of
treatment for addictions and
chronic diseases.
Furthermore, nanoparticle
implants will monitor the growth
and treatment of cancer tumors.
Such is the charge of researchers
at MIT. They are building
implantable nano-particles that can
detect specific molecules or analytes like glucose and oxygen, which
are associated with tumor growth.
The implants are encased in silicone, allowing them to remain in a
patient's body for an extended period. They detect tumor growth, show
how much of the drug has reached
the tumor, and reveal the drug's
effectiveness.