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Engineering
Adhesives for the Assembly of Medical Devices
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Pradhyumna Ingle,
Marketing Manager, Henkel Loctite India |
Introduction
Adhesives have long played
an integral part in the assembly of components for a
wide variety of markets including automotive, general
industrial, electronics, and medical. Anaerobic
sealants, cyanoacrylates, light curing acrylics and
silicones are used in diverse life-saving applications
ranging from automotive air bag sensors to catheters
and blood oxygenators. Each industry has unique
requirements for the selected adhesive ranging from
appearance and bond performance to environmental
resistance. |
Over the
past three decades, the disposable medical market has
undergone a variety of changes including the types of
devices produced, substrates selected, and sterilization
procedures employed. In the early 1970s, device
manufacturers were utilizing materials such as glass,
rubber and metal to assemble syringes, surgical
instruments, and other devices. Such materials were
typically assembled and fastened and /or machined or
molded in the appropriate configuration. In the 1980s, as
medical technology advanced towards intricate and high
performance medical device designs, the need for
engineering plastics became apparent. During this same
period, a shift to single use devices (due to advances in
contagious disease) forced design engineers to evaluate
engineering plastics such as acrylic, polycarbonate, and
PVC.
Types of
Devices
Traditionally, two types of medical devices have been the
focus of adhesive manufacturer’s involvement in the
medical device market: sterile disposables and non-sterile
reusables.
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Sterile
disposables are devices such as syringes, catheters and
oxygenators, which may come in contact with blood or
bodily fluids. Because of such contact, the requirements
for the adhesives used in sterile devices must be
thoroughly tested by the manufacturer and must pass
stringent toxicity testing.
Non-sterile reusables are usually external devices, which
do not come into direct contact with bodily fluids.
Devices such as knee braces, walking aids and hearing aids
would be classified as non-sterile reusables. Typically,
materials conducive to long-term use are selected for the
construction of such devices, and there are no
requirements for toxicity or sterilization resistance. |
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In recent
years, two additional classifications of medical devices
have emerged: sterile reusables and resposables. Sterile
reusable devices have seen a tremendous growth in recent
years due to advances in less invasive surgery. Sterile
reusables include surgical equipment such as endoscopes,
laproscopes, and surgical equipment. Resposables, on the
other hand, are devices that were initially intended for
one time use but are now being considered for reuse.
In all cases, whether the devices undergo single or
multiple sterilization cycles or whether the materials
selected for use are the traditional glass and metal or
thermoplastic resins, medical device designers consider
adhesives among the options for assembly.
Assembly
Methods for Medical Devices
Medical
device manufacturers employ a variety of methods for the
assembly of components including solvent welding,
ultrasonic welding, vibration welding and adhesive
bonding. Each method offers a variety of benefits as well
as limitations.
The use of
solvent welding for device assembly has become both
a mechanical and environmental issue. As environmental
regulations and operator safety become prime issues for
manufacturers throughout the world, the use of solvents in
a production environment has become more problematic. In
addition, solvent welding cannot be used effectively on
thermoset plastics and is more likely to cause stress
cracking of components versus adhesives. Solvent
bonding/welding is also not capable of securing joints
with large induced gaps. Application amount and time are
also critical factors that must be closely monitored when
using solvent bonding to ensure consistency of
performance.
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