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Past Projects
Robert G. Dennis, Ph.D.
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Below is an incomplete
but representative collection of various projects that I have been involved
in. The projects are arranged chronologically from the distant past
(before Al Gore invented the Internet) to the Present. I have only
included projects in which I took a leading or very active role, choosing
to exclude the countless smaller projects in which I have made only an
incidental contribution. Although I am very interested in each of
these areas, and may one day return to working on them, I have decided
to focus my current effort toward the technology related to the development
of functional engineered tissues.
Bob's
Home Page
Current
Research Muscle
Mechanics Lab (U of M) Biomechatronics
Group @ MIT
Antisatellite missile guidance systems:
In 1984 and 1985, while
finishing my B.S. degree in mechanical engineering, I was very involved
in the united states anti satellite missile program. I spent approximately
6 months troubleshooting the targeting and guidance systems for two different
systems. For the first system (MVS-ASAT), I solved several problems
related to the assembly and testing processes for the guidance system of
a kinetic energy weapons system. I also worked on cryogenic sensor
design and device failure analysis. For the second system (HS250),
I designed high reliability mechanisms to protect infra-red targeting optics
and to deploy satellite components in a combat theatre. I also identified
and corrected several critical design flaws, and contributed significantly
to the overall system robustness and reliability.
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Electromechanical components for vehicles:
In 1987 and 1988 I
was employed by an automotive supplier to design, model, and test several
electromechanical and hydraulic components for use in automobiles and light
trucks. I designed test fixturing for variable force solenoids, oil
pressure switches, and other electro-mechanical components.
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Biological Left Ventricular Assist
Device (BLVAD):
In 1990 and 1991 I
was the engineer on a project at the University of Michigan Section of
Thoracic Surgery to develop a biologic left ventricular assist device (BLVAD).
This device was composed of a re-engineered section of skeletal muscle
that was wrapped around the heart to provide additional pumping capacity
for persons awaiting a heart transplant. For the project, I designed
a series of implantable muscle stimulators to re-engineer the latissimus
dorsi muscle to induce fast-to-slow fiber type transformation prior to
the surgery to transpose the muscle. I also modeled the aortic flow
that would result from the additional pumping capacity, designed the instrumentation
and fixturing for the experiments, and analyzed the resulting data.
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Human motor control and learning instrumentation:
From 1988 until 1991,
I designed test instrumentation to measure human motor control in 1, 2,
and 3 dimensional space. I designed and constructed a 3-dimensional
tracking system for hand movements, and instrumentation to measure the
coupling between visual stimuli and motor responses.
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In vivo and in vitro
muscle testing stations (shoe apparatus):
From 1991 until 1996
I designed a series of muscle testing stations. These instruments
are still in use in the Muscle Mechanics Laboratory at the University of
Michigan, and in various departments across campus. The systems involved
computer interfacing, measurement of force and displacement, electrical
stimulation, and maintenance of temperature or positional control of muscle
length or limb position.
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High-speed
sarcomere dynamics of single muscle fibers:
This was essentially my dissertation project.
I developed the initial laser diffraction technology in use in the Muscle
Mechanics Laboratory at the University of Michigan. For
my project, I measured the propagation velocity of longitudinal strain
waves in single permeabilized muscle fibers while relaxed and at low levels
of activation. The most interesting outcome of my research was the
discovery of the source of a very common instrumentation artifact.
This artifact, which manifested itself in apparent "Steps and Pauses" in
the sarcomere length of muscle fibers during steady length changes had
been a source of dismay and controversy among muscle physiologists since
1976,
when it was first reported by Pollack et al. As it turns out, the
"Steps and Pauses" result from the interference of the laser light from
scattering sources near the muscle fiber in solution. The laser light
has a coherence length much longer than the diameter of the fiber, and
light scattered from any source within the coherence length from
the fiber can interfere both constructively and destructively with the
diffracted light, resulting in bright and dark bands which move across
the 1o diffraction peak as the fiber length is changed.
This is best illustrated by a video clip:
Laser
Diffraction Movie
NOTE: (if
the movie opens in Netscape navigator)
To play the following
movie, just left click on the image after it loads.
To return, use
the BACK button on your browser.
To pause or move
frame-by-frame during viewing, right click on image.
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Click on the image to the left to see
a movie of the diffraction pattern generated by passing laser light through
a single muscle fiber. The bright vertical spot to the left is the
0o peak, which is just light transmitted directly through the
muscle fiber. The smaller spot to the right is the 1o
peak of the diffracted light (there is another 1o peak to the
left off screen). As the muscle fiber is manually lengthened and
shortened, the 1o peak moves right and left. Note the
dark bands that move across the 1o peak as the fiber length
is changed. These dark bands result in the so called "Steps and Pauses",
but are simply an instrumentation artifact. |
The persistence of this artifact caused
some investigators, notably Pollack, to insist that our current theories
of muscle contraction at the level of the sarcomere were deeply flawed.
The overwhelming consensus was that the observed "Steps and Pauses" were
an instrumentation artifact, but solid proof of this had been elusive for
over 2 decades. The solution to this artifact turned out to be simple:
operate a diode laser at a voltage at which the coherence length is reduced
to approximately that of the muscle fiber diameter (a few hundred microns
at most). The dark fringes disappear, and so do the steps and pauses.
This is discussed in detail in my doctoral dissertation, Chapter IV.
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General instrumentation design and fabrication:
From 1993 until 1996
I was co-owner and chief engineer at a small instrumentation shop in Dexter
MI. We designed and built test instrumentation for energy, automotive,
health, and education organizations. Most of this instrumentation
involved electro-mechanical, electro-optical, mixed signal, and mechanism
design. Below is a brief list of our projects:
Servo mechanism to
place an intake valve to within +/- 2 mm
in a cylinder head for FORD for flow bench testing.
An optical disdrometer
for measuring the size and velocity of atmospheric precipitants.
A system for the medical
diagnosis of blepharoptosis.
Design of a series
of force transducers for physiological measurements.
An experiment timer
for hydrogen sulfide embrittlement testing.
A system to measure
the muscle power generating capacity of elderly persons, as a predictor
for risks of falls.
All other major projects that I have been
involved with are still current. For additional information, please
visit my Current Projects links
page.
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Mechanics Lab (U of M) Biomechatronics
Group @ MIT