CIMIT
FORUM AGENDA
October 23, 2007
4:00 – 6:00 PM
Biological
Electronics and Sensors for Medical Applications
Moderator: Jay Schnitzer, MD, PhD, Associate
Professor of Surgery, Harvard Medical School; Visiting Surgeon, Massachusetts
General Hospital; Pediatric Surgeon, Shriners Burns Hospital; CIMIT Site Miner
- MGH; CIMIT Program Leader - Clinical Systems Innovation,
jschnitzer@partners.org
4:00PM Electronic and Ionic Neural Interfaces
Presenter: Luke Theogarajan, PhD, Massachusetts Institute of
Technology, ltheogar@mit.edu
Many scientists
have high hopes for neural prosthetics, devices capable of restoring functions
lost as a result of nerve damage. To
date, cochlear implants, which allow otherwise deaf people to hear, are the
most refined and most widely used neural prosthetic. Researchers are attempting to develop retinal
prosthetics that may someday provide a useful level of vision to patients with
conditions such as age-related macular degeneration or retinitis
pigmentosa. Retinal prosthetics, like
all neural prosthetics, will require a robust interface between the device and
the patient’s neural circuitry.
Preliminary trials suggest that retinal
prosthetics are not an impossible dream.
Researchers led by Luke Theogarajan of MIT implanted chips of four
electrodes beneath the retinas of a few blind volunteers, and upon stimulation,
the blind volunteers perceived phosphenes, or the sensation of “seeing
stars.” The electrode chips were powered
by an external power supply and received image information from an external
sensor.
An electrical biotic-abiotic interface,
however, may not be the best interface for a retinal prosthetic. Because of the current-siphoning effect of
soft tissue and because of certain morphological changes that occur in blind
people, a lot of electrical current is needed to stimulate the eye’s
nerves. It is difficult to provide this
current, and this current could be large enough to damage tissue.
Theogarajan’s group is exploring an
interface based on ions, instead of electricity. Ions are naturally abundant in the body, and
changing the ion gradient across a neuron’s plasma membrane can trigger an
action potential. So far, it seems that
boosting extracellular potassium levels is the most effective way to produce an
action potential. Potassium ions could
be sequestered from the device’s environment and would not need to be
stockpiled in the device. Now,
researchers must figure out how to reliably deliver potassium ions to a
specific area. Theogarajan’s team is
currently investigating an ion-delivery mechanism similar to that found in an
inkjet printer.
Neural prosthetics have the potential to
transform medicine, and although electrical interfaces currently dominate the
field, biocompatible ionic interfaces are a technically feasible alternative
and could provide the way of the future.
5:00PM Electronic
Polymers in Biosensors
Presenter: Timothy M. Swager, PhD, John D.
MacArthur Professor and Department Head, Department of
Chemistry, Massachusetts Institute of Technology, tswager@mit.edu
In many biological assays, detecting the
presence of small molecules is crucial.
Researchers led by Timothy J. Swager of MIT are designing polymers
capable of spectroscopically sensing small metabolites. Electrons in the highly conjugated polymers
occupy either valence orbitals or slightly more energetic conduction
orbitals. Light can excite electrons
from valence orbitals into conduction orbitals, and when these excited
electrons fall back into valence orbitals, they emit usually photons. The polymers can be designed so that if the
excited electrons in the conduction orbitals come near another specific
molecule, known as an analyte, they drop back into valence orbitals without
emitting photons. In this case, the
analyte quenches the polymer’s fluorescence, and this quenching can be observed
by measuring the photons emitted by the polymer.
The polymers may soon provide biologists
with a valuable research tool, and Swager’s group is currently experimenting
with polymer-coated microspheres. At the
center of these microspheres, different fluorescent molecules provide a
baseline that allows investigators to make quantitative measurements of
quenching. The microspheres, however,
have not been perfected. Proteins and
other undesirable macromolecules tend to stick to the microspheres’ surfaces,
preventing analytes from binding.
Swager’s group is attempting to circumvent this problem by encasing the
microspheres in a hydrogel that macromolecules can’t penetrate. In the future, microspheres, or nanospheres,
may become part of new biological assays, and this technology might even lead
to particles that could be introduced into the human body to track down
metabolites associated with tumors and other problems.