8, 1998 Design News
SPECIAL MEDICAL ISSUE
Accurate assembly leads to safer syringes
Here's an example of how
the right adhesive, and proper application, can be critical
to improving the quality of our lives
Deana Colucci, Associate Editor
Little Elm, TX-based medical device manufacturer Retractable
Technologies Inc. has developed a product that addresses
a major concern of healthcare workers--accidental "sticks"
with contaminated needles. (see below) The company says
its VanishPointTM is the first disposable
syringe to feature a needle that automatically retracts
after injection, greatly reducing the chance of an accidental
Here's how it works: When a healthcare worker administers
an injection, he or she continues to depress the plunger
after the syringe is empty. This action releases a plug
in the end of the plunger handle, knocking a friction
ring off the spring-loaded needle hub or holder. The
spring then opens, pulling the needle up inside the
syringe barrel and removing it from the patient.
"The VanishPoint looks like and is used like a
standard syringe," says Production Manager Jim
Hoover, "but there is no risk of an accidental
stick because the healthcare worker doesn't even see
the needle after the injection."
To assemble the syringe, a stainless-steel needle,
or cannula, must be bonded to a polypropylene hub. The
appropriate adhesive for this process had to meet several
The ability to deliver a strong bond between the
The company chose Dymax Corp.'s (Torrington, CT) 1-20402
medical Ultra Light-Weld adhesive to meet its needs.
In addition to selecting the appropriate adhesive,
Retractable Technologies recognized the importance of
applying the correct amount of adhesive--every time.
"The ability to regulate, document, and accurately
repeat the amount of adhesive flowing into the hub's
recess is critical," says Hoover.
Underapplication could result in the cannula separating
from the hub during injection or retraction. Overapplication
could result in the build-up of excess adhesive on the
hub, which would prevent the needle from retracting.
During clinical trials, operators applied adhesive
to one syringe at a time using air-powered benchtop
dispensers from EFD Inc. (East Providence, RI). The
dispensers proved accurate and reliable, however, the
syringe manufacturer now needed a system capable of
making ten deposits at once. And while output needed
to be increased, accuracy and process control had to
Retractable turned to EFD to design a semiautomated
system to meet its expanding production needs. EFD recommended
its Model 740V, an adjustable needle valve designed
to make microdeposits of low- to medium-viscosity fluids.
Deposit size, the company explained, could be determined
by a combination of fluid pressure, flow control setting,
tip size, and valve open time.
EFD also recommended pairing each valve with a dedicated,
microprocessor-based VALVEMATETM 7000 controller,
to take full advantage of the 740V's precision dispensing
capabilities. This pairing would ensure the required
process control by allowing each valve's dispense-time
setting to be adjusted in increments as small as 0.001
second--without stopping the production line.
Realizing the benefits the "one valve/one controller"
approach could bring to its dispensing operation, Retractable
Technologies designed a semi-automated tabletop assembly
machine and had it fabricated by a local machine builder.
In the new system, ten valves are fixtured in a rack,
with ten controllers mounted above them. A manifold
at the rear of the machine distributes plant air to
each valve/controller system, while pressurized tank
reservoirs supply the adhesive.
The individual controllers make valve setup and deposit-size
adjustment fast and easy. Once optimal settings are
determined for the first pair, the company simply programs
the remaining nine to produce the same results.
Retractable Technologies' new dispensing method is
fast, efficient, and most important, accurate and repeatable,
says Hoover. After placing a loaded work holder in position,
the system operator simply lowers a bar to cycle the
valves and make 10 identical deposits.
Hoover says the company's decision to go with dedicated
controllers has been a tremendous help in maintaining
process control. "They make it easy for us to set
specific operating parameters for air pressure, fluid
pressure, and dispense time, but still allow the operator
to make minor adjustments within a narrow range of approved
settings," he explains.
"The advantage of this approach," Hoover
continues, "is that if something goes amiss and
you are operating within the documented parameters,
you know you need to look elsewhere to isolate the cause
of the problem. It literally forces you to take the
proper corrective action.
"Plus, with some automated systems, when you shut
down at the end of the day and start up again the next
morning, it's hard to duplicate the results you got
the day before. With EFD valves and controllers, we
never have that problem."
The needle-stick epidemic
The International Health Care Worker Safety Center
(University of Virginia) estimates more than 1 million
accidental needle sticks occur per year. Higher rates
have been reported by the Centers for Disease Control
and medical journals.
Although nearly invisible to the public, this epidemic
of accidental needle sticks is infecting thousands of
American medical workers with potentially lethal diseases.
It has reached a crisis stage, as each day medical workers
suffer some 2,400 accidental sticks.
Most of those sticks could be prevented with safety
needles. Yet only 5 to 10% of the syringes used by medical
workers have the safety features ordered six years ago
by the federal Occupational Safety and Health Administration
(OSHA), OSHA says. The Centers for Disease Control believe
safety needles could cut accidental needle sticks by
Here's a look at how a needle stick can cause infection,
and three major diseases transmitted through needle
sticks. Information has been culled from an April 1998
report by the San Francisco Chronicle:
† HIV (also known as the AIDS virus)
Affected: Up to 60 healthcare
workers a year contract the virus from needle sticks,
according to the International Health Care Worker
† Hepatitis B
Affected: Up to 12,000 workers
every year were contracting the virus in the 1980s
say the Centers for Disease Control (CDC), the Occupational
Safety and Health Administration (OSHA), and medical
researchers. As many as 300 of those died from it
each year say the organizations. Cases have fallen
to 1,000 per year according to the CDC and OSHA,
following widespread availability of a vaccine.
Effects: It attacks the liver,
causing jaundice, fatigue, abdominal and joint pain,
fever, and rashes. Chronic hepatitis can lead to
liver cancer, cirrhosis, coma, and death.
† Hepatitis C
Affected: The virus infects at
least 1,000 healthcare workers per year; however,
because cases have been poorly documented, the actual
number may be significantly higher. Most experts
estimate the numbers to be in the thousands each
More than 20 other infections can also be transmitted
through needle sticks, including: Syphilis, malaria,
tuberculosis, streptococcal and staphylococcal sepsis,
Rocky Mountain Spotted Fever, herpes, hepatitis D and
G, babesiosis, brucellosis, leptospirosis, arboviral
infections, relapsing fever, Creutzfeldt-Jakob disease,
human T-lymphotropic virus Type 1, and viral fevers
caused by Ebola.