Polycarbonate (PC) is among the fastest growing plastics in the medical device and packaging field, largely due to a favorable combination of cost and performance factors. Typical properties of PC that give them an advantage in the healthcare industry include great strength, toughness, rigidity and resistance to rigorous sterilization conditions. The high clarity of PC is also a boon in many medical applications.
PC is not the most widely used plastic in medical products. That distinction belongs to PVC, PE, PP and polystyrene. However, engineering thermoplastics such as PC offers levels of heat and radiation resistance that PVC and other commonly used medical plastics cannot match. The strength and chemical inertness of PC makes it useful for tools used in minimally invasive surgery, a field that is expanding rapidly. PC also costs less than other high-performance engineering plastics used in medicine, such as polysulfone and polyetheretherketone.
The
current market for PC in the medical sector
is about 75,000 tpa. PC is commonly found in
dialysis filter membranes, surgical instrument
handles and the housings of blood oxygenators,
which are used during open-heart surgery. The
manifolds and stopcocks of intravenous connectors
are frequently made of polycarbonates, as are
needle-free injection systems, perfusion equipment
and blood reservoirs. PC is also used in trocars
(long tubes) and retractors employed in endoscopic
surgery.
Blends of PC with other polymers, particularly
ABS and polyester, find wide use in the housings
of many medical instruments. The blends combine
the strength and rigidity of PC with the high-flow
properties of ABS, or the chemical resistance
of polyesters.
Packaging for medical devices is often fabricated
from thermoformed PC film. Such films allow
the package and its contents to be sterilized
together by exposure to radiation.
Emerging applications of PC include inhalers
for the consumer market, ophthalmic products,
orthopedic materials, and "lab-on-a-chip"
devices for determining blood chemistry or analyzing
proteins.
Key properties responsible for usage
of PC in health sector
PC medical products can be sterilized
with ethylene oxide, gamma radiation, electron
beam radiation and steam autoclaves. Polycarbonates
have a high degree of dimensional stability,
which makes them valuable for medical tubing
connectors, where tight fits are essential.
The high transparency of polycarbonates is an
asset in any medical devices where visual monitoring
of blood or other biological fluids is necessary.
High fracture strength and toughness are other
properties of polycarbonates that make them
helpful as delicate probes used in non-invasive
surgical procedures.
PC is generally biocompatible, but device manufacturers
who want to use PC for new tissue or blood contact
applications must conduct biocompatibility tests
in compliance with government regulations. Certain
commercial grades of polycarbonates are certified
to meet specified biocompatibility standards
such as ISO 10993-1. Standard grades of PC for
medical devices can be steam autoclaved at temperatures
up to 121º C. (Temperatures above this
level can warp or distort the devices) But faster
steam autoclaving processes have recently been
developed that require even higher temperatures.
To meet this demand, suppliers have introduced
special PC grades that can be autoclaved at
temperatures as high as 134º C. Multiple
autoclaving of PC devices is not generally recommended,
but some manufacturers now offer PC grades that
are able to be autoclaved more than once.
PC
does not become embrittled when exposed to the
gamma rays and electron beams used in radiation
sterilization. Competing materials such as Teflon,
rubber, PU and PP do not stand up as well to
radiation. However, PC does tend to yellow upon
exposure to radiation. This can be a problem
when clear and transparent windows are required
in a medical device.
To counteract the discoloration problem, polycarbonate
producers have employed additives that absorb
the radiation, thus preventing the cascade of
chemical reactions that lead to polymer degradation.
Another approach has been to market grades of
PC that are inherently radiation stable and
therefore do not require additives.
Fats and oils (lipids) attack polycarbonates,
causing stress cracking. This is a potential
problem because more and more intravenous solutions
contain lipid-based emulsions of drugs. To address
this issue, suppliers have introduced lipid-resistant
PC grades. Intended markets for these recent
entries are mostly IV equipment such as stopcocks
and connectors
High-flow PC grades have recently been unveiled
for the medical market, with the aim of increasing
the output by converters. Standard PC grades
for medical molding have a melt-flow rate (MFR)
in the 5-15 g/10 min. range. The new high-flow
grades have a MFR in the 20-37-g/10 min. area.
The high flow has traditionally been achieved
with the use of additives. Some newer polycarbonates
exhibit enhanced flow without additives, relying
instead on proprietary copolymer formulations.
Also making an appearance in recent years have
been easy mould release PC grades. These products
contain internal mould-release agents that make
it unnecessary to spray release agents into
the mold. Such agents can contaminate the moulded
part and must be regularly cleaned away, which
extends production cycles and adds to costs.
PC for medical applications can be processed
by all the standard techniques: injection moulding,
extrusion, blow moulding and thermoforming.