8, 1998 Design News
ENGINEER'S NOTEBOOK Readers describe design successes
Laser beams, T-bones, and mood rings
Charles A. Hansford, Senior Model Maker
Lucy Senter, D.V.M., M.S.
Indigo, a Johnson & Johnson Company
10123 Alliance Rd
Cincinnati, OH 45242
Few engineering challenges are greater than creating
the perfect sales aid or demonstration device. In the
minds of our sales reps, who demonstrate lasers to medical
practitioners, the perfect solution would always be:
Small and compact enough to fit into a coat pocket
Non-breakable, so that it can be used over and
Simple enough for a sales representative to understand
At Indigo, we call this the "SINES" of the
perfect sales demo.
Recently, our sales force asked us to produce such
a device to demonstrate the effect of interstitial laser
coagulation (ILC) on tissue. Used to treat ailments
such as prostate cancer, the ILC works by cauterizing
diseased tissue. But instead of producing a unidirectional
beam of energy from the tip of the laser, as with conventional
lasers, our system disperses the energy radially from
the tip. The result is an olive-shaped area of tissue
necrosis located around the end of the laser fiber.
It is important that our sales people demonstrate this
subtle, yet important difference to physicians, who
are typically more accustomed to conventional lasers.
In the past, a sales rep conducted the demonstration
by inserting the laser into a piece of round steak or
harvested animal tissue and firing it. After completion
of the laser cycle, the rep would incise the tissue
to display the effects of the laser energy.
While satisfactory for a lab setting, the procedure
wasn't exactly practical for field reps travelling around
to hospitals, clinics, conventions, and the like. It
usually meant packing an ice cooler and a quick trip
to the neighborhood butcher to purchase a steak on the
way. Sometimes, harvested tissue might be used, but
either approach was expensive.
The challenge to our engineering staff was to produce
a pocket-size sales device that could withstand a temperature
of 85C, had good heat transfer, simulated the effect
on tissue from radiated laser energy, and did not involve
using animal tissue or human cadavers.
Polypropylene, if molded into a disc, fit most of these
criteria, but we struggled with how to replicate the
effect of laser energy on human tissue. Amazingly enough,
the answer came from the toy industry, where certain
temperature-sensitive pigments are often used to cause
objects (remember mood rings?) to change color.
We tested about 12 different formulations before hitting
upon a 5% pigment color additive (temperature grade
#35) from Matsui International, which causes the polypropylene
to change from an indigo blue to pink in the target
area after firing. This simple color contrast is enough
to demonstrate to a physician the unique, olive-shaped
area of tissue necrosis created by our laser.
The polypropylene disc, or "Blue Chip" as
we call it, has a 3 inch diameter, is 1/4 inch thick,
and is injection-molded. To save cost, we used an aluminum
tool. Each disc has 3 holes, 120 degrees apart, to allow
for multiple firing of the laser.
In practice, we've found little Blue Chip to be nearly
indestructible: it does not break down under the heat
of the laser, nor does it break if dropped or crammed
into a briefcase or back pocket.
Customer acceptance, of course, is the true litmus
test of the success of any engineered product. Our problem?
Our field reps like the Blue Chips so much we can't
keep them supply. Initially, we gave each rep 500 discs,
and within two months they were back for more!
Clearly, this device has proved to be a better alternative
than stuffing a steak in your back pocket.
Readers can contact the author at firstname.lastname@example.org
Develop a cost-effective, reusable device for demonstrating
the effect of laser energy on tissue.
Produce a sales device that would:
Withstand a temperature of 85C without breaking
Blue Chip's Market
Grade: PP1105 E2
Lot #: 78303A
Fast Blue #8
Temperature grade #35