This article is the first in the Real World Engineering (RWE) Series
that will be presented on LEGOEngineering.com. The RWE Series will
present NXT design challenges that mirror real-world engineering
problems and solutions. Each article in this series will feature an
engineering design problem being addressed by a real world company. The
remainder of the article will focus on the NXT version of the solution,
and building and programming suggestions for classroom use.
Real World Engineering: OmniSonics & Blood Clots
|OmniSonics Medical Technologies, Inc. is a medical device start-up corporation located in Wilmington, Massachusetts, and was established in 1997. OmniSonics has developed a product that can be used in the treatment of vascular occlusive conditions such as blood clots. Blood clots, also known as "thrombus," can block blood supply to the heart, brain, lungs, or limbs or cause heart attack, stroke or limb pain. Traditionally blood clots are treated with medication or interventional means (i.e. catheter based or surgical procedures). OmniSonics has created a treatment of blood clots that is not highly invasive and does not rely on medication.
OmniSonics' products are based on their patented OmniWave Technology.
OmniWave technology is the first that uses ultrasonic
vibrations along a small wire to treat vascular occlusive
conditions. This is done by inserting a wire, or "waveguide,"
with a small diameter into an affected artery or vein. The other end of
the wire is attached to a hand piece that helps the doctor guide the end
that has been inserted into the vessel. The hand piece contains a piezo-electronic
transducer. The transducer causes the wire to vibrate ultrasonically. The proximal part of the wire (that part that is closest to the hand piece)
vibrates longitudinally (i.e. in the direction of the wire). This motion
is converted to transverse waves (vibration that moves in the direction
normal to the axis of the wire) at the distal end of wire (the part farthest
from the hand piece). This ultrasonic vibration causes the blood clot
to break apart and dissolve, allowing the clot to be carried away with
the blood flow and absorbed into the body.
It is crucial that the wire vibrates at the proper frequency and does not fracture or break while treating the clot. In order to ensure these
criteria, extensive testing must occur. Steve Forcucci, a principal mechanical
engineer at OmniSonics, explains that OmniSonics must follow the Federal Drug
AdministrationÂ’s (FDA) regulations since the product will be used on human beings.
This requires extensive testing to prove product safety and efficacy. OmniSonics
has recently received FDA approval of their Omniwave System for use in periperal
vasculature. The safety benchmark, as determined by the FDA, was met and OmniSonics
will soon begin a small limited market study for use in humans.
Testing both durability and efficacy of the wire before moving to human subjects
is necessary to provide confidence that the wire is strong enough and that it
will not break. To ensure its durability, OmniSonics has developed an endurance
rig (See Figures 1 & 3) to test the wire. The wire is run through a hypo tube
(See Figure 2) and into a fixture that bends the wire at 180 degrees. An automated
device, that contains the transducer, slides the wire into the tube and the results
appear on a computer. This configuration allows the working end of the wire
to follow a curved path to simulate use in a curved vessel. The curvature can be adjusted to study the effects of changing the curve's radius.
The graphical programming language LabVIEW is used to control the automated device that threads the wire into the rig and to acquire and analyze the resulting data. The tests monitor the power, current, voltage, and frequency that are being fed into the hand piece containing the transducer. Electrical sensors monitor the results. The engineers use visual inspection to determine if the wire remains unbroken. If the wire breaks, engineers look for discontinuities in the electrical data collected by LabVIEW to determine when the wire broke. In general, a wire will break due to a combination of static strain (bending of the wire), dynamic strain (vibrating the wire), and material fatigue (wear & tear).
Figure 1: OmniSonics Rig Used to
Simulate a Clogged Artery
Figure 2: Fixture with a 180˚ Bend
Figure 3: Parts of the OmniSonics Testing Rig
Figure 4: LabVIEW Screen Shot of Program that
Regulates the Voltage
via an External Function Generator
"Blood Clot" Removal with the LEGO NXT
The first step in emulating OmniSonics' technology was creating a rig that would allow students to work on this problem and would be cost effective for classrooms. In the NXT version of the OmniSonics' rig, plastic tubing with a 7/8 by 5/8-inch opening is used to replicate the arteries and is attached to a board with holes using plastic zip ties (See Figure 5). A mixture of cornstarch and sand is inserted into the tubing and represents the clot when it hardens.
Figure 5: Testing Rig for NXT
We divided OmniSonics' OmniWave technology into three activities:
1. The assessment and comparison of the properties of different materials such as spaghetti, fishing line, and wire to meet the standard requirements of the testing rig.
2. The design and construction of an NXT hand piece that will perform lateral motion and insert the chosen "wire" into the tubing.
3. The alteration of the hand piece that will simulate ultrasonic motion and rid the wire of the cornstarch solution that acts as the blood clot.
Figure 6: Polyethylene Tubing Attached to the Board
LEGOengineering.com's version of OmniWave technology uses polyethylene tubing (See Figure 6) as the wire. It is fed into the tubing on the rig by the rotation of tires connected to the NXT (See Figure 7). The "wire" is inserted into the tubing and vibrated by the NXT. After a few seconds, the cornstarch mixture begins to erode off the sides of the tube.
Figure 7: NXT Handpiece that Threads the "Wire" through the Tubing
The movement with the NXT-based device is obviously not as precise, but this challenge still allows students to emulate possible real-world engineering solutions. Forcucci says, "The NXT activities closely mirror the mechanical effect of wire and hand piece, having both longitudinal and transverse motion."
Although these activities are simplistic mirrors of the real-world technology, they do provide an authentic engineering activity to give students the opportunity to work through the engineering design process and face some of the same dilemmas and successes as the real-world engineers that are working at OmniSonics.
The write-ups for the activities include lesson plans for students and background information for teachers that include a materials list, building and programming instructions for the rig and device, and information about coronary vascular occlusive conditions. This activity has been tested in a lab, but not the classroom. We are eager to hear feedback regarding this activity. Please direct comments and suggestions regarding this activity to
Vascular occlusive condition is a general medical term for a blood vessel blockage.
Frequency is the number of occurrences of a specific even within a given period of time.
Ultrasonic vibrations are vibrations at a frequency higher than what the human ear can hear (e.g. greater than 20 kHz).
Piezoelectricity, converse piezolelectric effect ) occurs when an electrical field is applied to a body thus causing a strain (on the wire) causing it to oscillate and create the ultrasonic vibration.
Strain is when a body is deformed by being stretched or pulled beyond its usual form.